From patchwork Sun Mar 7 11:30:24 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 395733 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7800C433DB for ; Sun, 7 Mar 2021 11:54:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7190E65100 for ; Sun, 7 Mar 2021 11:54:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230437AbhCGLyZ (ORCPT ); Sun, 7 Mar 2021 06:54:25 -0500 Received: from mout.gmx.net ([212.227.15.15]:33417 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230111AbhCGLxz (ORCPT ); Sun, 7 Mar 2021 06:53:55 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1615117999; bh=0mOFH/whRcxwCCNf1FaCVfPgq3zuoVr5XMs4msmzXEk=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=fP/89F57Uvd6wz+HXrnrALfcyL2tIGkyzmhTNPThCqx+itY8xekbKfuA28nl94+TQ E5HlyuaL6bc6hTgQWg3oBN0itIesNWk+9gUA+8Bl8N5foEjA7HbrrX+LCBZQ1eMIV1 /x1QkIefOuiI/1UK1JssrmXh+Pn6WpbsAbswIJqI= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from localhost.localdomain ([83.52.229.153]) by mail.gmx.net (mrgmx005 [212.227.17.184]) with ESMTPSA (Nemesis) id 1N1fn0-1llM6Y3f1U-0120pu; Sun, 07 Mar 2021 12:53:19 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , Andi Kleen , kernel test robot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v6 1/8] security: Add LSM hook at the point where a task gets a fatal signal Date: Sun, 7 Mar 2021 12:30:24 +0100 Message-Id: <20210307113031.11671-2-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210307113031.11671-1-john.wood@gmx.com> References: <20210307113031.11671-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:gjW1lxsS4O/k5Sf+wMA+VJHoZ1qM11KXQETBYwid34I0oYBNmr2 C/OqkV5z9INlzUtp7FYtQoLqydzU9bhhstzt50l8ENfqMYH+YOzd2coK6Ju4El8FUXOa3jk xoXo4At48nMaIfEd8BXPlo1qQgeF1V41qKMoF/n8RLOOh1DVoHmG7gmpe0GuFxNDdSnwhOf IPMxaFSEsnB5la6LeBgQg== X-UI-Out-Filterresults: notjunk:1; V03:K0:ekdqLgRPggU=:Ry3SJ1lEftaEQFRP1dW004 uegRYmgq1qD2F4CQCDaE7r+J9EhwabNP4PICLFAgl6soYo+l8mXoPmdC9ekLhwasJtBdrvAGY b+e/6RctVObiuiI4ZFxtV1ZdKulXUTfx7HYTSyz3JCom9/bUK8KADSdusoYMeQcEyHCu8na33 Ztv+Ii532DUvsRg+m/90I/m9WjYZyB5oBqQn67wPVvlcG2Na4j6uy9kw55JIu5b+21o2BCMkl jnG2shzC9TKnKrLlLkNeYe2om9jDscUubUB8K5p4PIcGRKoN4n2z1eSJTzDIcJHyrKv2V71oQ b03jo20VqZf1P7BQ/p4af0PK8YtH/Hilxit2mALEEzuqvXZSeGpnv9FANijUJdvtwisKc+zqk 13ni2mxgVi6k20SjoEkm5xC64NAcjjfpty9bTjPGLErpO59llY6SD2MGPbXv1YcTTzxYi186+ 9Wm0kkoJWYYXtwxm9WdHkiY4VkQi6qDCU42rON5ZK9vHPaVv243kxc1CNLfipEVH7BUhUAEJx tvE81noKEfMRsGDCCX5miAuQM2Ic/OhogDViU9idzkMXmu3wct8fmtTjBmaN+kXAkxkRgt/Ck 30nNbmaqPxoyuPDbXVhFR2zEXekxCfNbQtyPddaDuLFr1n1/kUH8pppjEmzd9O1MNK/1RaNzj wjsPh0SUprrbiirIbd1svYdTKGDFgPZ5zNvVaMlslBFmmJHT0NUdrhf8xMKn02NspdFE5Qx0F LNtJWPrMLw3QJVsIcQAbtT3IIS1IgcF3zyfa+dWHjk6xQRGbiUqmgOcqJYZn1RFiEyA7H5Nro QMuBa0NKqhuJpdfukUba3qGp6zdR7ZO9p5mvD6nog76zbwIOx+3dBzUELxh98zNG0AegAMska +x8XVkaPzKh9hILDyJVA== Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Add a security hook that allows a LSM to be notified when a task gets a fatal signal. This patch is a previous step on the way to compute the task crash period by the "brute" LSM (linux security module to detect and mitigate fork brute force attack against vulnerable userspace processes). Signed-off-by: John Wood Reviewed-by: Kees Cook --- include/linux/lsm_hook_defs.h | 1 + include/linux/lsm_hooks.h | 4 ++++ include/linux/security.h | 4 ++++ kernel/signal.c | 1 + security/security.c | 5 +++++ 5 files changed, 15 insertions(+) -- 2.25.1 diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index 477a597db013..0208df0955fa 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -220,6 +220,7 @@ LSM_HOOK(int, -ENOSYS, task_prctl, int option, unsigned long arg2, unsigned long arg3, unsigned long arg4, unsigned long arg5) LSM_HOOK(void, LSM_RET_VOID, task_to_inode, struct task_struct *p, struct inode *inode) +LSM_HOOK(void, LSM_RET_VOID, task_fatal_signal, const kernel_siginfo_t *siginfo) LSM_HOOK(int, 0, ipc_permission, struct kern_ipc_perm *ipcp, short flag) LSM_HOOK(void, LSM_RET_VOID, ipc_getsecid, struct kern_ipc_perm *ipcp, u32 *secid) diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index fb7f3193753d..beedaa6ee745 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -784,6 +784,10 @@ * security attributes, e.g. for /proc/pid inodes. * @p contains the task_struct for the task. * @inode contains the inode structure for the inode. + * @task_fatal_signal: + * This hook allows security modules to be notified when a task gets a + * fatal signal. + * @siginfo contains the signal information. * * Security hooks for Netlink messaging. * diff --git a/include/linux/security.h b/include/linux/security.h index 8aeebd6646dc..e4025a13630f 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -430,6 +430,7 @@ int security_task_kill(struct task_struct *p, struct kernel_siginfo *info, int security_task_prctl(int option, unsigned long arg2, unsigned long arg3, unsigned long arg4, unsigned long arg5); void security_task_to_inode(struct task_struct *p, struct inode *inode); +void security_task_fatal_signal(const kernel_siginfo_t *siginfo); int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag); void security_ipc_getsecid(struct kern_ipc_perm *ipcp, u32 *secid); int security_msg_msg_alloc(struct msg_msg *msg); @@ -1165,6 +1166,9 @@ static inline int security_task_prctl(int option, unsigned long arg2, static inline void security_task_to_inode(struct task_struct *p, struct inode *inode) { } +static inline void security_task_fatal_signal(const kernel_siginfo_t *siginfo) +{ } + static inline int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag) { diff --git a/kernel/signal.c b/kernel/signal.c index ba4d1ef39a9e..d279df338f45 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2750,6 +2750,7 @@ bool get_signal(struct ksignal *ksig) /* * Anything else is fatal, maybe with a core dump. */ + security_task_fatal_signal(&ksig->info); current->flags |= PF_SIGNALED; if (sig_kernel_coredump(signr)) { diff --git a/security/security.c b/security/security.c index 5ac96b16f8fa..d9cf653a4e70 100644 --- a/security/security.c +++ b/security/security.c @@ -1840,6 +1840,11 @@ void security_task_to_inode(struct task_struct *p, struct inode *inode) call_void_hook(task_to_inode, p, inode); } +void security_task_fatal_signal(const kernel_siginfo_t *siginfo) +{ + call_void_hook(task_fatal_signal, siginfo); +} + int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag) { return call_int_hook(ipc_permission, 0, ipcp, flag); From patchwork Sun Mar 7 11:30:25 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 395258 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5004FC433E6 for ; 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Sun, 07 Mar 2021 13:15:02 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , Andi Kleen , kernel test robot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v6 2/8] security/brute: Define a LSM and manage statistical data Date: Sun, 7 Mar 2021 12:30:25 +0100 Message-Id: <20210307113031.11671-3-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210307113031.11671-1-john.wood@gmx.com> References: <20210307113031.11671-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:FAIaqHKd9DFkeVPKuFxziNufcLTrbdDB19dh73Z1IY7KMJVJLxv w+bDRZncVD9Knjg6A5DyP/+Rs2i2YC78YJYisYJCWFndaH79FEEGTssoTdi890yEmwDwzpV jFlTGqNsA2oCvPlIMwMa/FjlL2b23oBggMO2aXR7b+XSLAQ5U8x1Q3TiUBlhdcUl0uHSWrn 3PdpuzznoOawKttsl38Pg== X-UI-Out-Filterresults: notjunk:1; V03:K0:mRU4VFHySEI=:5DtJl+hYwWLLbgz5L07ygH 5rWJhdBrIS7b45E2DWoojd07JOLlquTXs+k/qcDL81J2oLEXs4T0CGNJnD1RYhFDeUYvnXuVS m8mxEruz5tWhlfNX+By1X4wC9Pkx1TH2Og8dW0eEs1B1a61731uagrA5TQflfeHYCwT2i8Pzh JU+nmf/hXkefkHqbYuhkP8dGMm6G2TBhTStfqt0KJ9+k6fuD1cCLPCH8fOHCif5nx+LsUrWoQ +irmDxnkrsWNAq32vO9cT3jSv+9XPUOd3v7ws5Eke7Wn1aLh8y+FH+SNUWSiBToz2kGhzoAjz 9XmpW5W+TkVhPNMsLytN0dhHWJXlIQuRgtOINNIHoFyORmLnjnxm/a1GgFRtOadymDVCkG6oo 2gN7pA+9ju8Tz4J3vjxI3aw1WSMRnEl9lKYFK/6Q2mNwfsjLiVOx2g2lEm6N1+sZi5w6JQL6i 2OilvV1n+g8bMWI4NNztam5q2hrm1SK0Kb8G3Mac6uEbwyCeyb6MnuY1zhFKSfLYiGFchx2eV Z2WAQep6X3r01zytueZiqostH+l5+U0ISTkMitpI7MfAZ11pDS6baBveGYh5o5i7rcyuV2FYq tEaO3Muec04dIleI+y7EXeohWKS1R5N/kAYYcV+f/vXvVlL0BrXn0ef0baa44F5L4edldHvP1 Zb2jJRFzeb8PIvkiAM7zWRtFyXNz71Tn1NQL+ZE4Jf8dovOialjXTMuGPohnfHJHdBqoJw8Ex Ce/6DsAIeZTJbrQCSdSNL2E1iHfN+NBl240hBus5GkKJ4ricx2nTB0o8wUSuUAcdvCLCYRFc+ Kcp/TZbRJaHvXBGtAfqsd6nd/6FG6W6gigGv6AvezkLNa/6nInc3GPsEnMQRTGMoKkuzKU4FU EZpAgibuEtb1auR0KOKA== Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Add a new Kconfig file to define a menu entry under "Security options" to enable the "Fork brute force attack detection and mitigation" feature. For a correct management of a fork brute force attack it is necessary that all the tasks hold statistical data. The same statistical data needs to be shared between all the tasks that hold the same memory contents or in other words, between all the tasks that have been forked without any execve call. So, define a statistical data structure to hold all the necessary information shared by all the fork hierarchy processes. This info is basically the number of crashes, the last crash timestamp and the crash period's moving average. When a forked task calls the execve system call, the memory contents are set with new values. So, in this scenario the parent's statistical data no need to be shared. Instead, a new statistical data structure must be allocated to start a new hierarchy. The statistical data that is shared between all the fork hierarchy processes needs to be freed when this hierarchy disappears. So, based in all the previous information define a LSM with three hooks to manage all the commented cases. These hooks are "task_alloc" to do the fork management, "bprm_committing_creds" to do the execve management and "task_free" to release the resources. Also, add to the task_struct's security blob the pointer to the statistical data. This way, all the tasks will have access to this information. Signed-off-by: John Wood --- security/Kconfig | 11 +- security/Makefile | 4 + security/brute/Kconfig | 12 ++ security/brute/Makefile | 2 + security/brute/brute.c | 257 ++++++++++++++++++++++++++++++++++++++++ 5 files changed, 281 insertions(+), 5 deletions(-) create mode 100644 security/brute/Kconfig create mode 100644 security/brute/Makefile create mode 100644 security/brute/brute.c -- 2.25.1 diff --git a/security/Kconfig b/security/Kconfig index 7561f6f99f1d..204bb311b1f1 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -240,6 +240,7 @@ source "security/safesetid/Kconfig" source "security/lockdown/Kconfig" source "security/integrity/Kconfig" +source "security/brute/Kconfig" choice prompt "First legacy 'major LSM' to be initialized" @@ -277,11 +278,11 @@ endchoice config LSM string "Ordered list of enabled LSMs" - default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK - default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR - default "lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO - default "lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC - default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf" + default "brute,lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK + default "brute,lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR + default "brute,lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO + default "brute,lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC + default "brute,lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf" help A comma-separated list of LSMs, in initialization order. Any LSMs left off this list will be ignored. This can be diff --git a/security/Makefile b/security/Makefile index 3baf435de541..1236864876da 100644 --- a/security/Makefile +++ b/security/Makefile @@ -36,3 +36,7 @@ obj-$(CONFIG_BPF_LSM) += bpf/ # Object integrity file lists subdir-$(CONFIG_INTEGRITY) += integrity obj-$(CONFIG_INTEGRITY) += integrity/ + +# Object brute file lists +subdir-$(CONFIG_SECURITY_FORK_BRUTE) += brute +obj-$(CONFIG_SECURITY_FORK_BRUTE) += brute/ diff --git a/security/brute/Kconfig b/security/brute/Kconfig new file mode 100644 index 000000000000..1bd2df1e2dec --- /dev/null +++ b/security/brute/Kconfig @@ -0,0 +1,12 @@ +# SPDX-License-Identifier: GPL-2.0 +config SECURITY_FORK_BRUTE + bool "Fork brute force attack detection and mitigation" + depends on SECURITY + help + This is an LSM that stops any fork brute force attack against + vulnerable userspace processes. The detection method is based on + the application crash period and as a mitigation procedure all the + offending tasks are killed. Like capabilities, this security module + stacks with other LSMs. + + If you are unsure how to answer this question, answer N. diff --git a/security/brute/Makefile b/security/brute/Makefile new file mode 100644 index 000000000000..d3f233a132a9 --- /dev/null +++ b/security/brute/Makefile @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0 +obj-$(CONFIG_SECURITY_FORK_BRUTE) += brute.o diff --git a/security/brute/brute.c b/security/brute/brute.c new file mode 100644 index 000000000000..99d099e45112 --- /dev/null +++ b/security/brute/brute.c @@ -0,0 +1,257 @@ +// SPDX-License-Identifier: GPL-2.0 + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/** + * struct brute_stats - Fork brute force attack statistics. + * @lock: Lock to protect the brute_stats structure. + * @refc: Reference counter. + * @faults: Number of crashes. + * @jiffies: Last crash timestamp. + * @period: Crash period's moving average. + * + * This structure holds the statistical data shared by all the fork hierarchy + * processes. + */ +struct brute_stats { + spinlock_t lock; + refcount_t refc; + unsigned char faults; + u64 jiffies; + u64 period; +}; + +/* + * brute_blob_sizes - LSM blob sizes. + * + * To share statistical data among all the fork hierarchy processes, define a + * pointer to the brute_stats structure as a part of the task_struct's security + * blob. + */ +static struct lsm_blob_sizes brute_blob_sizes __lsm_ro_after_init = { + .lbs_task = sizeof(struct brute_stats *), +}; + +/** + * brute_stats_ptr() - Get the pointer to the brute_stats structure. + * @task: Task that holds the statistical data. + * + * Return: A pointer to a pointer to the brute_stats structure. + */ +static inline struct brute_stats **brute_stats_ptr(struct task_struct *task) +{ + return task->security + brute_blob_sizes.lbs_task; +} + +/** + * brute_new_stats() - Allocate a new statistics structure. + * + * If the allocation is successful the reference counter is set to one to + * indicate that there will be one task that points to this structure. Also, the + * last crash timestamp is set to now. This way, it is possible to compute the + * application crash period at the first fault. + * + * Return: NULL if the allocation fails. A pointer to the new allocated + * statistics structure if it success. + */ +static struct brute_stats *brute_new_stats(void) +{ + struct brute_stats *stats; + + stats = kmalloc(sizeof(struct brute_stats), GFP_KERNEL); + if (!stats) + return NULL; + + spin_lock_init(&stats->lock); + refcount_set(&stats->refc, 1); + stats->faults = 0; + stats->jiffies = get_jiffies_64(); + stats->period = 0; + + return stats; +} + +/** + * brute_share_stats() - Share the statistical data between processes. + * @src: Source of statistics to be shared. + * @dst: Destination of statistics to be shared. + * + * Copy the src's pointer to the statistical data structure to the dst's pointer + * to the same structure. Since there is a new process that shares the same + * data, increase the reference counter. The src's pointer cannot be NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_alloc hook. + */ +static void brute_share_stats(struct brute_stats *src, + struct brute_stats **dst) +{ + unsigned long flags; + + spin_lock_irqsave(&src->lock, flags); + refcount_inc(&src->refc); + *dst = src; + spin_unlock_irqrestore(&src->lock, flags); +} + +/** + * brute_task_alloc() - Target for the task_alloc hook. + * @task: Task being allocated. + * @clone_flags: Contains the flags indicating what should be shared. + * + * For a correct management of a fork brute force attack it is necessary that + * all the tasks hold statistical data. The same statistical data needs to be + * shared between all the tasks that hold the same memory contents or in other + * words, between all the tasks that have been forked without any execve call. + * + * To ensure this, if the current task doesn't have statistical data when forks, + * it is mandatory to allocate a new statistics structure and share it between + * this task and the new one being allocated. Otherwise, share the statistics + * that the current task already has. + * + * Return: -ENOMEM if the allocation of the new statistics structure fails. Zero + * otherwise. + */ +static int brute_task_alloc(struct task_struct *task, unsigned long clone_flags) +{ + struct brute_stats **stats, **p_stats; + + stats = brute_stats_ptr(task); + p_stats = brute_stats_ptr(current); + + if (likely(*p_stats)) { + brute_share_stats(*p_stats, stats); + return 0; + } + + *stats = brute_new_stats(); + if (!*stats) + return -ENOMEM; + + brute_share_stats(*stats, p_stats); + return 0; +} + +/** + * brute_task_execve() - Target for the bprm_committing_creds hook. + * @bprm: Points to the linux_binprm structure. + * + * When a forked task calls the execve system call, the memory contents are set + * with new values. So, in this scenario the parent's statistical data no need + * to be shared. Instead, a new statistical data structure must be allocated to + * start a new hierarchy. This condition is detected when the statistics + * reference counter holds a value greater than or equal to two (a fork always + * sets the statistics reference counter to a minimum of two since the parent + * and the child task are sharing the same data). + * + * However, if the execve function is called immediately after another execve + * call, althought the memory contents are reset, there is no need to allocate + * a new statistical data structure. This is possible because at this moment + * only one task (the task that calls the execve function) points to the data. + * In this case, the previous allocation is used but the statistics are reset. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the bprm_committing_creds hook. + */ +static void brute_task_execve(struct linux_binprm *bprm) +{ + struct brute_stats **stats; + unsigned long flags; + + stats = brute_stats_ptr(current); + if (WARN(!*stats, "No statistical data\n")) + return; + + spin_lock_irqsave(&(*stats)->lock, flags); + + if (!refcount_dec_not_one(&(*stats)->refc)) { + /* execve call after an execve call */ + (*stats)->faults = 0; + (*stats)->jiffies = get_jiffies_64(); + (*stats)->period = 0; + spin_unlock_irqrestore(&(*stats)->lock, flags); + return; + } + + /* execve call after a fork call */ + spin_unlock_irqrestore(&(*stats)->lock, flags); + *stats = brute_new_stats(); + WARN(!*stats, "Cannot allocate statistical data\n"); +} + +/** + * brute_task_free() - Target for the task_free hook. + * @task: Task about to be freed. + * + * The statistical data that is shared between all the fork hierarchy processes + * needs to be freed when this hierarchy disappears. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_free hook. + */ +static void brute_task_free(struct task_struct *task) +{ + struct brute_stats **stats; + unsigned long flags; + bool refc_is_zero; + + stats = brute_stats_ptr(task); + if (WARN(!*stats, "No statistical data\n")) + return; + + spin_lock_irqsave(&(*stats)->lock, flags); + refc_is_zero = refcount_dec_and_test(&(*stats)->refc); + spin_unlock_irqrestore(&(*stats)->lock, flags); + + if (refc_is_zero) { + kfree(*stats); + *stats = NULL; + } +} + +/* + * brute_hooks - Targets for the LSM's hooks. + */ +static struct security_hook_list brute_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(task_alloc, brute_task_alloc), + LSM_HOOK_INIT(bprm_committing_creds, brute_task_execve), + LSM_HOOK_INIT(task_free, brute_task_free), +}; + +/** + * brute_init() - Initialize the brute LSM. + * + * Return: Always returns zero. + */ +static int __init brute_init(void) +{ + pr_info("Brute initialized\n"); + security_add_hooks(brute_hooks, ARRAY_SIZE(brute_hooks), + KBUILD_MODNAME); + return 0; +} + +DEFINE_LSM(brute) = { + .name = KBUILD_MODNAME, + .init = brute_init, + .blobs = &brute_blob_sizes, +}; From patchwork Sun Mar 7 11:30:26 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 395732 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B2BBC433E0 for ; Sun, 7 Mar 2021 12:38:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C97E965101 for ; Sun, 7 Mar 2021 12:38:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230422AbhCGMhp (ORCPT ); Sun, 7 Mar 2021 07:37:45 -0500 Received: from mout.gmx.net ([212.227.17.22]:57215 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230323AbhCGMhi (ORCPT ); Sun, 7 Mar 2021 07:37:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1615120607; bh=xfp74GhSnHiwLpsi3uHJPLTgd+kXFH6dVoRAtVepyzE=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=ZsrEFJX5ZBAgaqO5IMFee9kYiExoLHwpibZmMr5AaO+8bqYhAIMWpeTUSi/B3i5jD Jhd+E6Ktz9Dx3lB7usOlJ52Nb1oAzWiIsPplOIB9WYZHtw2EfpD0Z/m5tDi/Q0ysxV dsXFpLybyso0YLZk0vd6UnSdcH3BKZL0MlY5CiOQ= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from localhost.localdomain ([83.52.229.153]) by mail.gmx.net (mrgmx105 [212.227.17.174]) with ESMTPSA (Nemesis) id 1MOzSu-1l6j0l0IP6-00PNtZ; Sun, 07 Mar 2021 13:36:47 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , Andi Kleen , kernel test robot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v6 3/8] securtiy/brute: Detect a brute force attack Date: Sun, 7 Mar 2021 12:30:26 +0100 Message-Id: <20210307113031.11671-4-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210307113031.11671-1-john.wood@gmx.com> References: <20210307113031.11671-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:V5wXiWyrt/fTbgQQup/A2xwEulUiqjNwEt+/TggDUsotNXIrQso eGT2ReD3Wtqpo4LrHMv0fvr+4LaBwHO+zSWHBhOqNJLMEZedK3I6237LsJyeKTPd3IXgUNb t21W33F49i+ilfYJQ9d/6GqBYUNfYX876nbUAJma07NI/qi5SdZ2SfX+fXCFLpbep+gyG1s b02a08iBaJu8f7TOivEjw== X-UI-Out-Filterresults: notjunk:1; V03:K0:YD89M5lRYQA=:Q04wP1nyyEZ5klFp0ZY7aH aNSwyXTs9a97VdW1sOF4AkuTe1DH/t6fonubMLNDbu6iRQhj4SkG2x7eknaCzDgY8jeZsU0SH b6XB+EFbyLrUy5zFktvVHTuYpFjoNjvQ2RCfDDj+1+dpf2Bdw9OyQR9Mq/vUCr3NE1veSSRUR RnTWaYR02B4WQCPMgrvjZoTt1t7tdooGCGjYAn7uH+rp6XA17IKBc2TwySTyBEUubcjQp9MAr eKxbEbwOTXdoe85wVaiLUGc0wzW860l3JnoNLYtvHOJZmvCf/Sp/cG9DOalM8gCozirIc7Mvv P0tYVzqeaAcjlX2Y+Q0COc7QBe+EDVSnITp97lVxFUqtj5ozY4qXU5Z0VAQjpnY3Pjnaum9AX 2HQqJzXDOoot+Xx01X8cYENhaG6G0yfpRFnrnObPif7ZFX1H5juSpSpbvbTey4UPWW5Gxxsmd tNE85CFNJWrJmlZO+prsGiFslCct6Y9GiLWo4ykNIZpuWvSWgvOut3g7Wgo+q3Bu+rp9KQ/gW cBWaxUOhOm6Ud4CYQvK2iQ/rN80Mm7t6+V17eJXlYJFLV3j8ol/hmMHpXJ11DIa+PXwdVdjX0 VdoBxNUwd/MGppUibq9TSSdppm7xFTIgQ6xzAz8MOy4XMaAv1BTxHc/XRRiY164ypOqs9mYMM ky3yw9hL9FVHat9PQNU5GP5ElKxXeOZ/R4NzRmiWAYOB+459SPGlQwt9IltUvfeIVYMdY3u+M FOHQmkIsVDYNnD/0n+Ye9kodpSTa4zUg9O6wDUB6h6QsdHn4iFwNX8l37Q9Og2FRd5Fa5AKt3 JiFFdoKW8bucr+99NWgEhf2Hv/UDWWt/lwNRv+/jMzPefPIlp0hgJonJ3SJL7zYrFCHFjYQK4 JAcw8gErvi/XpdAwAmxA== Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org To detect a brute force attack it is necessary that the statistics shared by all the fork hierarchy processes be updated in every fatal crash and the most important data to update is the application crash period. To do so, use the new "task_fatal_signal" LSM hook added in a previous step. The application crash period must be a value that is not prone to change due to spurious data and follows the real crash period. So, to compute it, the exponential moving average (EMA) is used. There are two types of brute force attacks that need to be detected. The first one is an attack that happens through the fork system call and the second one is an attack that happens through the execve system call. The first type uses the statistics shared by all the fork hierarchy processes, but the second type cannot use this statistical data due to these statistics disappear when the involved tasks finished. In this last scenario the attack info should be tracked by the statistics of a higher fork hierarchy (the hierarchy that contains the process that forks before the execve system call). Moreover, these two attack types have two variants. A slow brute force attack that is detected if the maximum number of faults per fork hierarchy is reached and a fast brute force attack that is detected if the application crash period falls below a certain threshold. Also, this patch adds locking to protect the statistics pointer hold by every process. Signed-off-by: John Wood --- security/brute/brute.c | 498 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 479 insertions(+), 19 deletions(-) -- 2.25.1 diff --git a/security/brute/brute.c b/security/brute/brute.c index 99d099e45112..870db55332d4 100644 --- a/security/brute/brute.c +++ b/security/brute/brute.c @@ -11,9 +11,14 @@ #include #include #include +#include #include #include +#include +#include #include +#include +#include #include #include #include @@ -37,6 +42,11 @@ struct brute_stats { u64 period; }; +/* + * brute_stats_ptr_lock - Lock to protect the brute_stats structure pointer. + */ +static DEFINE_RWLOCK(brute_stats_ptr_lock); + /* * brute_blob_sizes - LSM blob sizes. * @@ -74,7 +84,7 @@ static struct brute_stats *brute_new_stats(void) { struct brute_stats *stats; - stats = kmalloc(sizeof(struct brute_stats), GFP_KERNEL); + stats = kmalloc(sizeof(struct brute_stats), GFP_ATOMIC); if (!stats) return NULL; @@ -99,16 +109,17 @@ static struct brute_stats *brute_new_stats(void) * It's mandatory to disable interrupts before acquiring the brute_stats::lock * since the task_free hook can be called from an IRQ context during the * execution of the task_alloc hook. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * held. */ static void brute_share_stats(struct brute_stats *src, struct brute_stats **dst) { - unsigned long flags; - - spin_lock_irqsave(&src->lock, flags); + spin_lock(&src->lock); refcount_inc(&src->refc); *dst = src; - spin_unlock_irqrestore(&src->lock, flags); + spin_unlock(&src->lock); } /** @@ -126,26 +137,36 @@ static void brute_share_stats(struct brute_stats *src, * this task and the new one being allocated. Otherwise, share the statistics * that the current task already has. * + * It's mandatory to disable interrupts before acquiring brute_stats_ptr_lock + * and brute_stats::lock since the task_free hook can be called from an IRQ + * context during the execution of the task_alloc hook. + * * Return: -ENOMEM if the allocation of the new statistics structure fails. Zero * otherwise. */ static int brute_task_alloc(struct task_struct *task, unsigned long clone_flags) { struct brute_stats **stats, **p_stats; + unsigned long flags; stats = brute_stats_ptr(task); p_stats = brute_stats_ptr(current); + write_lock_irqsave(&brute_stats_ptr_lock, flags); if (likely(*p_stats)) { brute_share_stats(*p_stats, stats); + write_unlock_irqrestore(&brute_stats_ptr_lock, flags); return 0; } *stats = brute_new_stats(); - if (!*stats) + if (!*stats) { + write_unlock_irqrestore(&brute_stats_ptr_lock, flags); return -ENOMEM; + } brute_share_stats(*stats, p_stats); + write_unlock_irqrestore(&brute_stats_ptr_lock, flags); return 0; } @@ -167,9 +188,9 @@ static int brute_task_alloc(struct task_struct *task, unsigned long clone_flags) * only one task (the task that calls the execve function) points to the data. * In this case, the previous allocation is used but the statistics are reset. * - * It's mandatory to disable interrupts before acquiring the brute_stats::lock - * since the task_free hook can be called from an IRQ context during the - * execution of the bprm_committing_creds hook. + * It's mandatory to disable interrupts before acquiring brute_stats_ptr_lock + * and brute_stats::lock since the task_free hook can be called from an IRQ + * context during the execution of the bprm_committing_creds hook. */ static void brute_task_execve(struct linux_binprm *bprm) { @@ -177,24 +198,33 @@ static void brute_task_execve(struct linux_binprm *bprm) unsigned long flags; stats = brute_stats_ptr(current); - if (WARN(!*stats, "No statistical data\n")) + read_lock_irqsave(&brute_stats_ptr_lock, flags); + + if (WARN(!*stats, "No statistical data\n")) { + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); return; + } - spin_lock_irqsave(&(*stats)->lock, flags); + spin_lock(&(*stats)->lock); if (!refcount_dec_not_one(&(*stats)->refc)) { /* execve call after an execve call */ (*stats)->faults = 0; (*stats)->jiffies = get_jiffies_64(); (*stats)->period = 0; - spin_unlock_irqrestore(&(*stats)->lock, flags); + spin_unlock(&(*stats)->lock); + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); return; } /* execve call after a fork call */ - spin_unlock_irqrestore(&(*stats)->lock, flags); + spin_unlock(&(*stats)->lock); + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); + + write_lock_irqsave(&brute_stats_ptr_lock, flags); *stats = brute_new_stats(); WARN(!*stats, "Cannot allocate statistical data\n"); + write_unlock_irqrestore(&brute_stats_ptr_lock, flags); } /** @@ -204,9 +234,9 @@ static void brute_task_execve(struct linux_binprm *bprm) * The statistical data that is shared between all the fork hierarchy processes * needs to be freed when this hierarchy disappears. * - * It's mandatory to disable interrupts before acquiring the brute_stats::lock - * since the task_free hook can be called from an IRQ context during the - * execution of the task_free hook. + * It's mandatory to disable interrupts before acquiring brute_stats_ptr_lock + * and brute_stats::lock since the task_free hook can be called from an IRQ + * context during the execution of the task_free hook. */ static void brute_task_free(struct task_struct *task) { @@ -215,17 +245,446 @@ static void brute_task_free(struct task_struct *task) bool refc_is_zero; stats = brute_stats_ptr(task); - if (WARN(!*stats, "No statistical data\n")) + read_lock_irqsave(&brute_stats_ptr_lock, flags); + + if (WARN(!*stats, "No statistical data\n")) { + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); return; + } - spin_lock_irqsave(&(*stats)->lock, flags); + spin_lock(&(*stats)->lock); refc_is_zero = refcount_dec_and_test(&(*stats)->refc); - spin_unlock_irqrestore(&(*stats)->lock, flags); + spin_unlock(&(*stats)->lock); + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); if (refc_is_zero) { + write_lock_irqsave(&brute_stats_ptr_lock, flags); kfree(*stats); *stats = NULL; + write_unlock_irqrestore(&brute_stats_ptr_lock, flags); + } +} + +/* + * BRUTE_EMA_WEIGHT_NUMERATOR - Weight's numerator of EMA. + */ +static const u64 BRUTE_EMA_WEIGHT_NUMERATOR = 7; + +/* + * BRUTE_EMA_WEIGHT_DENOMINATOR - Weight's denominator of EMA. + */ +static const u64 BRUTE_EMA_WEIGHT_DENOMINATOR = 10; + +/** + * brute_mul_by_ema_weight() - Multiply by EMA weight. + * @value: Value to multiply by EMA weight. + * + * Return: The result of the multiplication operation. + */ +static inline u64 brute_mul_by_ema_weight(u64 value) +{ + return mul_u64_u64_div_u64(value, BRUTE_EMA_WEIGHT_NUMERATOR, + BRUTE_EMA_WEIGHT_DENOMINATOR); +} + +/* + * BRUTE_MAX_FAULTS - Maximum number of faults. + * + * If a brute force attack is running slowly for a long time, the application + * crash period's EMA is not suitable for the detection. This type of attack + * must be detected using a maximum number of faults. + */ +static const unsigned char BRUTE_MAX_FAULTS = 200; + +/** + * brute_update_crash_period() - Update the application crash period. + * @stats: Statistics that hold the application crash period to update. + * @now: The current timestamp in jiffies. + * + * The application crash period must be a value that is not prone to change due + * to spurious data and follows the real crash period. So, to compute it, the + * exponential moving average (EMA) is used. + * + * This kind of average defines a weight (between 0 and 1) for the new value to + * add and applies the remainder of the weight to the current average value. + * This way, some spurious data will not excessively modify the average and only + * if the new values are persistent, the moving average will tend towards them. + * + * Mathematically the application crash period's EMA can be expressed as + * follows: + * + * period_ema = period * weight + period_ema * (1 - weight) + * + * If the operations are applied: + * + * period_ema = period * weight + period_ema - period_ema * weight + * + * If the operands are ordered: + * + * period_ema = period_ema - period_ema * weight + period * weight + * + * Finally, this formula can be written as follows: + * + * period_ema -= period_ema * weight; + * period_ema += period * weight; + * + * The statistics that hold the application crash period to update cannot be + * NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * held. + * Return: The last crash timestamp before updating it. + */ +static u64 brute_update_crash_period(struct brute_stats *stats, u64 now) +{ + u64 current_period; + u64 last_crash_timestamp; + + spin_lock(&stats->lock); + current_period = now - stats->jiffies; + last_crash_timestamp = stats->jiffies; + stats->jiffies = now; + + stats->period -= brute_mul_by_ema_weight(stats->period); + stats->period += brute_mul_by_ema_weight(current_period); + + if (stats->faults < BRUTE_MAX_FAULTS) + stats->faults += 1; + + spin_unlock(&stats->lock); + return last_crash_timestamp; +} + +/* + * BRUTE_MIN_FAULTS - Minimum number of faults. + * + * The application crash period's EMA cannot be used until a minimum number of + * data has been applied to it. This constraint allows getting a trend when this + * moving average is used. Moreover, it avoids the scenario where an application + * fails quickly from execve system call due to reasons unrelated to a real + * attack. + */ +static const unsigned char BRUTE_MIN_FAULTS = 5; + +/* + * BRUTE_CRASH_PERIOD_THRESHOLD - Application crash period threshold. + * + * The units are expressed in milliseconds. + * + * A fast brute force attack is detected when the application crash period falls + * below this threshold. + */ +static const u64 BRUTE_CRASH_PERIOD_THRESHOLD = 30000; + +/** + * brute_attack_running() - Test if a brute force attack is happening. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * The decision if a brute force attack is running is based on the statistical + * data shared by all the fork hierarchy processes. This statistics cannot be + * NULL. + * + * There are two types of brute force attacks that can be detected using the + * statistical data. The first one is a slow brute force attack that is detected + * if the maximum number of faults per fork hierarchy is reached. The second + * type is a fast brute force attack that is detected if the application crash + * period falls below a certain threshold. + * + * Moreover, it is important to note that no attacks will be detected until a + * minimum number of faults have occurred. This allows to have a trend in the + * crash period when the EMA is used and also avoids the scenario where an + * application fails quickly from execve system call due to reasons unrelated to + * a real attack. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * held. + * Return: True if a brute force attack is happening. False otherwise. + */ +static bool brute_attack_running(struct brute_stats *stats) +{ + u64 crash_period; + + spin_lock(&stats->lock); + if (stats->faults < BRUTE_MIN_FAULTS) { + spin_unlock(&stats->lock); + return false; + } + + if (stats->faults >= BRUTE_MAX_FAULTS) { + spin_unlock(&stats->lock); + return true; + } + + crash_period = jiffies64_to_msecs(stats->period); + spin_unlock(&stats->lock); + + return crash_period < BRUTE_CRASH_PERIOD_THRESHOLD; +} + +/** + * print_fork_attack_running() - Warn about a fork brute force attack. + */ +static inline void print_fork_attack_running(void) +{ + pr_warn("Fork brute force attack detected [%s]\n", current->comm); +} + +/** + * brute_manage_fork_attack() - Manage a fork brute force attack. + * @stats: Statistical data shared by all the fork hierarchy processes. + * @now: The current timestamp in jiffies. + * + * For a correct management of a fork brute force attack it is only necessary to + * update the statistics and test if an attack is happening based on these data. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * held. + * Return: The last crash timestamp before updating it. + */ +static u64 brute_manage_fork_attack(struct brute_stats *stats, u64 now) +{ + u64 last_fork_crash; + + last_fork_crash = brute_update_crash_period(stats, now); + if (brute_attack_running(stats)) + print_fork_attack_running(); + + return last_fork_crash; +} + +/** + * brute_get_exec_stats() - Get the exec statistics. + * @stats: When this function is called, this parameter must point to the + * current process' statistical data. When this function returns, this + * parameter points to the parent process' statistics of the fork + * hierarchy that hold the current process' statistics. + * + * To manage a brute force attack that happens through the execve system call it + * is not possible to use the statistical data hold by this process due to these + * statistics disappear when this task is finished. In this scenario this data + * should be tracked by the statistics of a higher fork hierarchy (the hierarchy + * that contains the process that forks before the execve system call). + * + * To find these statistics the current fork hierarchy must be traversed up + * until new statistics are found. + * + * Context: Must be called with tasklist_lock and brute_stats_ptr_lock held. + */ +static void brute_get_exec_stats(struct brute_stats **stats) +{ + const struct task_struct *task = current; + struct brute_stats **p_stats; + + do { + if (!task->real_parent) { + *stats = NULL; + return; + } + + p_stats = brute_stats_ptr(task->real_parent); + task = task->real_parent; + } while (*stats == *p_stats); + + *stats = *p_stats; +} + +/** + * brute_update_exec_crash_period() - Update the exec crash period. + * @stats: When this function is called, this parameter must point to the + * current process' statistical data. When this function returns, this + * parameter points to the updated statistics (statistics that track the + * info to manage a brute force attack that happens through the execve + * system call). + * @now: The current timestamp in jiffies. + * @last_fork_crash: The last fork crash timestamp before updating it. + * + * If this is the first update of the statistics used to manage a brute force + * attack that happens through the execve system call, its last crash timestamp + * (the timestamp that shows when the execve was called) cannot be used to + * compute the crash period's EMA. Instead, the last fork crash timestamp should + * be used (the last crash timestamp of the child fork hierarchy before updating + * the crash period). This allows that in a brute force attack that happens + * through the fork system call, the exec and fork statistics are the same. In + * this situation, the mitigation method will act only in the processes that are + * sharing the fork statistics. This way, the process that forked before the + * execve system call will not be involved in the mitigation method. In this + * scenario, the parent is not responsible of the child's behaviour. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and tasklist_lock and + * brute_stats_ptr_lock held. + * Return: -EFAULT if there are no exec statistics. Zero otherwise. + */ +static int brute_update_exec_crash_period(struct brute_stats **stats, + u64 now, u64 last_fork_crash) +{ + brute_get_exec_stats(stats); + if (!*stats) + return -EFAULT; + + spin_lock(&(*stats)->lock); + if (!(*stats)->faults) + (*stats)->jiffies = last_fork_crash; + spin_unlock(&(*stats)->lock); + + brute_update_crash_period(*stats, now); + return 0; +} + +/** + * brute_get_crash_period() - Get the application crash period. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * held. + * Return: The application crash period. + */ +static u64 brute_get_crash_period(struct brute_stats *stats) +{ + u64 crash_period; + + spin_lock(&stats->lock); + crash_period = stats->period; + spin_unlock(&stats->lock); + + return crash_period; +} + +/** + * print_exec_attack_running() - Warn about an exec brute force attack. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * Before showing the process name it is mandatory to find a process that holds + * a pointer to the exec statistics. + * + * Context: Must be called with tasklist_lock and brute_stats_ptr_lock held. + */ +static void print_exec_attack_running(const struct brute_stats *stats) +{ + struct task_struct *p; + struct brute_stats **p_stats; + bool found = false; + + for_each_process(p) { + p_stats = brute_stats_ptr(p); + if (*p_stats == stats) { + found = true; + break; + } + } + + if (WARN(!found, "No exec process\n")) + return; + + pr_warn("Exec brute force attack detected [%s]\n", p->comm); +} + +/** + * brute_manage_exec_attack() - Manage an exec brute force attack. + * @stats: Statistical data shared by all the fork hierarchy processes. + * @now: The current timestamp in jiffies. + * @last_fork_crash: The last fork crash timestamp before updating it. + * + * For a correct management of an exec brute force attack it is only necessary + * to update the exec statistics and test if an attack is happening based on + * these data. + * + * It is important to note that if the fork and exec crash periods are the same, + * the attack test is avoided. This allows that in a brute force attack that + * happens through the fork system call, the mitigation method does not act on + * the parent process of the fork hierarchy. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and tasklist_lock and + * brute_stats_ptr_lock held. + */ +static void brute_manage_exec_attack(struct brute_stats *stats, u64 now, + u64 last_fork_crash) +{ + int ret; + struct brute_stats *exec_stats = stats; + u64 fork_period; + u64 exec_period; + + ret = brute_update_exec_crash_period(&exec_stats, now, last_fork_crash); + if (WARN(ret, "No exec statistical data\n")) + return; + + fork_period = brute_get_crash_period(stats); + exec_period = brute_get_crash_period(exec_stats); + if (fork_period == exec_period) + return; + + if (brute_attack_running(exec_stats)) + print_exec_attack_running(exec_stats); +} + +/** + * brute_task_fatal_signal() - Target for the task_fatal_signal hook. + * @siginfo: Contains the signal information. + * + * To detect a brute force attack is necessary to update the fork and exec + * statistics in every fatal crash and act based on these data. + * + * It's mandatory to disable interrupts before acquiring brute_stats_ptr_lock + * and brute_stats::lock since the task_free hook can be called from an IRQ + * context during the execution of the task_fatal_signal hook. + */ +static void brute_task_fatal_signal(const kernel_siginfo_t *siginfo) +{ + struct brute_stats **stats; + unsigned long flags; + u64 last_fork_crash; + u64 now = get_jiffies_64(); + + stats = brute_stats_ptr(current); + read_lock(&tasklist_lock); + read_lock_irqsave(&brute_stats_ptr_lock, flags); + + if (WARN(!*stats, "No statistical data\n")) { + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); + read_unlock(&tasklist_lock); + return; } + + last_fork_crash = brute_manage_fork_attack(*stats, now); + brute_manage_exec_attack(*stats, now, last_fork_crash); + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); + read_unlock(&tasklist_lock); } /* @@ -235,6 +694,7 @@ static struct security_hook_list brute_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(task_alloc, brute_task_alloc), LSM_HOOK_INIT(bprm_committing_creds, brute_task_execve), LSM_HOOK_INIT(task_free, brute_task_free), + LSM_HOOK_INIT(task_fatal_signal, brute_task_fatal_signal), }; /** From patchwork Sun Mar 7 11:30:27 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 395257 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D7DAC433E9 for ; Sun, 7 Mar 2021 12:59:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0714C650FA for ; Sun, 7 Mar 2021 12:59:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231223AbhCGM7Q (ORCPT ); Sun, 7 Mar 2021 07:59:16 -0500 Received: from mout.gmx.net ([212.227.15.19]:53599 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231221AbhCGM7H (ORCPT ); Sun, 7 Mar 2021 07:59:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1615121911; bh=o7VHPwBgANKV0WhM5kFmSgpXMqdSwPsmXEk9FqGI97s=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=lIDRpKtBNlL5mMhdG9uBSkKPosEsy8QdvaUwVBl310HZSwn0jt7dOGiVvCMKdyGwh f7N+Xqp7lUK8Moult89lUULFdbWa86EwlrGKbl8kXRytNo/GKZnezPPjXc10vHu6MG n/SiRdVv2OPGP7bIM+azATfrUWxFDcuqf3YxMvmI= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from localhost.localdomain ([83.52.229.153]) by mail.gmx.net (mrgmx004 [212.227.17.184]) with ESMTPSA (Nemesis) id 1MMXUD-1l0wKW1x1b-00JZo8; Sun, 07 Mar 2021 13:58:31 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , Andi Kleen , kernel test robot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v6 4/8] security/brute: Fine tuning the attack detection Date: Sun, 7 Mar 2021 12:30:27 +0100 Message-Id: <20210307113031.11671-5-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210307113031.11671-1-john.wood@gmx.com> References: <20210307113031.11671-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:R6eJgnctHL5A7zBhbvyPyPyN0PFAG05TDdhnoGhUUeDLGQmh9M/ 7NnU6MXTHKm1sytKwMC3kGMPc0SLYyxqj+56rQ7JW7rPTWdTsJhx7ZrbaOAGp5nvOMpfWKa ZK1jQ3/AxDEzATfNKnYy4gZ2MFCgfSEPxWKCJL14S8wEgbRFnxEM+AxBJORVpBpJ+V/B7Fm n5y1KeSbOwCLADHQ0+5Jg== X-UI-Out-Filterresults: notjunk:1; V03:K0:Duj+BHYrdcY=:lOpXkpjIOTzCg8SHo7Dq/X NSDbZdM374BCOBluRWmosEjSCVCyyaY1XbBVL4ee+FspAr/+ebGWAcxgTdF33Kb8qb+k+znIT 8uB9e1BnzVwzVBMhHgH5nnDYIfIflaWr+1QUCFf1FQSfVZy4yW8v2FHjbEHCvgAOerXDm3PAc GtllFLk0yG/EDe4TPeTSnk+jbUq/uGbsiCJbqfxRkOk0v5uNH4IpWNSbU+jWvxiVc6CfK9nC+ mW8tEv2hBpN30RZrQU7t09oAARZCNjDZnh5pu7ayyK48bTXt/C9RAk3P58sWlqrWQY+ltgWHk uC4sfWdp9emiOs9C4xYSlyiSNAMwrInSCrbDKcU8kln/qyOqVN8/zWAr4d7qLlm18dvxtw8OH 3hlC8rwIFcWPAc9SQ7g6I9kvZPgmqkNX68ESApcpSDFxmUyOBZSKeQR87mpGkMlR2Ug8sOoIH Khw5cSFqux5zwuDhOSU88IudRjJv9EguD1X7LdhDZeGKs2VP40gPc12l9ZCbsG4FLlDJHU841 aUlBQ6q3ewQsLQK3uuyK/lUXMqtM3CzLEgGpcj+nkRaXIKLpam0xbHfTkf4SxgHCqc8MgDaBt QsQEvf7dRfOQzSOZGtlvj2ePD62kQa8t+rYCc8dp2J1T3NzIde/vk5uwRDgjW2vIJjaexpfhg SIvkw5guw6ggFBB5TvFISnpVvn7Z+1tTl+896zBh0tspEPD5MnjILMJEgCYsaLmQQX5EB2DYW TOQwb5fFO91edgtKLe8OFJO7ARQniu/uoKPP1OH4UDj+VEzgku2D+Uw+bOXAymTG8iBclfExv B8YJ/mnmHfvu78tJuh/LVyTuVd+fSn0vP3SUgoKK3r8m8wuckL65atzLY8yauJ33GtlWf7KiZ zE2iHtwWeAwwnSAPUQFg== Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org To avoid false positives during the attack detection it is necessary to narrow the possible cases. Only the following scenarios are taken into account: 1.- Launching (fork()/exec()) a setuid/setgid process repeatedly until a desirable memory layout is got (e.g. Stack Clash). 2.- Connecting to an exec()ing network daemon (e.g. xinetd) repeatedly until a desirable memory layout is got (e.g. what CTFs do for simple network service). 3.- Launching processes without exec() (e.g. Android Zygote) and exposing state to attack a sibling. 4.- Connecting to a fork()ing network daemon (e.g. apache) repeatedly until the previously shared memory layout of all the other children is exposed (e.g. kind of related to HeartBleed). In each case, a privilege boundary has been crossed: Case 1: setuid/setgid process Case 2: network to local Case 3: privilege changes Case 4: network to local So, this patch checks if any of these privilege boundaries have been crossed before to compute the application crash period. Also, in every fatal crash only the signals delivered by the kernel are taken into account with the exception of the SIGABRT signal since the latter is used by glibc for stack canary, malloc, etc failures, which may indicate that a mitigation has been triggered. Signed-off-by: John Wood --- security/brute/brute.c | 293 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 280 insertions(+), 13 deletions(-) -- 2.25.1 diff --git a/security/brute/brute.c b/security/brute/brute.c index 870db55332d4..38e5e050964a 100644 --- a/security/brute/brute.c +++ b/security/brute/brute.c @@ -3,15 +3,25 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include +#include +#include +#include +#include #include #include +#include +#include #include +#include #include +#include #include #include #include #include #include +#include +#include #include #include #include @@ -19,9 +29,35 @@ #include #include #include +#include +#include #include #include +#include #include +#include + +/** + * struct brute_cred - Saved credentials. + * @uid: Real UID of the task. + * @gid: Real GID of the task. + * @suid: Saved UID of the task. + * @sgid: Saved GID of the task. + * @euid: Effective UID of the task. + * @egid: Effective GID of the task. + * @fsuid: UID for VFS ops. + * @fsgid: GID for VFS ops. + */ +struct brute_cred { + kuid_t uid; + kgid_t gid; + kuid_t suid; + kgid_t sgid; + kuid_t euid; + kgid_t egid; + kuid_t fsuid; + kgid_t fsgid; +}; /** * struct brute_stats - Fork brute force attack statistics. @@ -30,6 +66,9 @@ * @faults: Number of crashes. * @jiffies: Last crash timestamp. * @period: Crash period's moving average. + * @saved_cred: Saved credentials. + * @network: Network activity flag. + * @bounds_crossed: Privilege bounds crossed flag. * * This structure holds the statistical data shared by all the fork hierarchy * processes. @@ -40,6 +79,9 @@ struct brute_stats { unsigned char faults; u64 jiffies; u64 period; + struct brute_cred saved_cred; + unsigned char network : 1; + unsigned char bounds_crossed : 1; }; /* @@ -71,18 +113,25 @@ static inline struct brute_stats **brute_stats_ptr(struct task_struct *task) /** * brute_new_stats() - Allocate a new statistics structure. + * @network_to_local: Network activity followed by a fork or execve system call. + * @is_setid: The executable file has the setid flags set. * * If the allocation is successful the reference counter is set to one to * indicate that there will be one task that points to this structure. Also, the * last crash timestamp is set to now. This way, it is possible to compute the * application crash period at the first fault. * + * Moreover, the credentials of the current task are saved. Also, the network + * and bounds_crossed flags are set based on the network_to_local and is_setid + * parameters. + * * Return: NULL if the allocation fails. A pointer to the new allocated * statistics structure if it success. */ -static struct brute_stats *brute_new_stats(void) +static struct brute_stats *brute_new_stats(bool network_to_local, bool is_setid) { struct brute_stats *stats; + const struct cred *cred = current_cred(); stats = kmalloc(sizeof(struct brute_stats), GFP_ATOMIC); if (!stats) @@ -93,6 +142,16 @@ static struct brute_stats *brute_new_stats(void) stats->faults = 0; stats->jiffies = get_jiffies_64(); stats->period = 0; + stats->saved_cred.uid = cred->uid; + stats->saved_cred.gid = cred->gid; + stats->saved_cred.suid = cred->suid; + stats->saved_cred.sgid = cred->sgid; + stats->saved_cred.euid = cred->euid; + stats->saved_cred.egid = cred->egid; + stats->saved_cred.fsuid = cred->fsuid; + stats->saved_cred.fsgid = cred->fsgid; + stats->network = network_to_local; + stats->bounds_crossed = network_to_local || is_setid; return stats; } @@ -137,6 +196,10 @@ static void brute_share_stats(struct brute_stats *src, * this task and the new one being allocated. Otherwise, share the statistics * that the current task already has. * + * Also, if the shared statistics indicate a previous network activity, the + * bounds_crossed flag must be set to show that a network-to-local privilege + * boundary has been crossed. + * * It's mandatory to disable interrupts before acquiring brute_stats_ptr_lock * and brute_stats::lock since the task_free hook can be called from an IRQ * context during the execution of the task_alloc hook. @@ -155,11 +218,14 @@ static int brute_task_alloc(struct task_struct *task, unsigned long clone_flags) if (likely(*p_stats)) { brute_share_stats(*p_stats, stats); + spin_lock(&(*stats)->lock); + (*stats)->bounds_crossed |= (*stats)->network; + spin_unlock(&(*stats)->lock); write_unlock_irqrestore(&brute_stats_ptr_lock, flags); return 0; } - *stats = brute_new_stats(); + *stats = brute_new_stats(false, false); if (!*stats) { write_unlock_irqrestore(&brute_stats_ptr_lock, flags); return -ENOMEM; @@ -170,6 +236,61 @@ static int brute_task_alloc(struct task_struct *task, unsigned long clone_flags) return 0; } +/** + * brute_is_setid() - Test if the executable file has the setid flags set. + * @bprm: Points to the linux_binprm structure. + * + * Return: True if the executable file has the setid flags set. False otherwise. + */ +static bool brute_is_setid(const struct linux_binprm *bprm) +{ + struct file *file = bprm->file; + struct inode *inode; + umode_t mode; + + if (!file) + return false; + + inode = file->f_path.dentry->d_inode; + mode = inode->i_mode; + + return !!(mode & (S_ISUID | S_ISGID)); +} + +/** + * brute_reset_stats() - Reset the statistical data. + * @stats: Statistics to be reset. + * @is_setid: The executable file has the setid flags set. + * + * Reset the faults and period and set the last crash timestamp to now. This + * way, it is possible to compute the application crash period at the next + * fault. Also, save the credentials of the current task and update the + * bounds_crossed flag based on a previous network activity and the is_setid + * parameter. + * + * The statistics to be reset cannot be NULL. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * and brute_stats::lock held. + */ +static void brute_reset_stats(struct brute_stats *stats, bool is_setid) +{ + const struct cred *cred = current_cred(); + + stats->faults = 0; + stats->jiffies = get_jiffies_64(); + stats->period = 0; + stats->saved_cred.uid = cred->uid; + stats->saved_cred.gid = cred->gid; + stats->saved_cred.suid = cred->suid; + stats->saved_cred.sgid = cred->sgid; + stats->saved_cred.euid = cred->euid; + stats->saved_cred.egid = cred->egid; + stats->saved_cred.fsuid = cred->fsuid; + stats->saved_cred.fsgid = cred->fsgid; + stats->bounds_crossed = stats->network || is_setid; +} + /** * brute_task_execve() - Target for the bprm_committing_creds hook. * @bprm: Points to the linux_binprm structure. @@ -188,6 +309,11 @@ static int brute_task_alloc(struct task_struct *task, unsigned long clone_flags) * only one task (the task that calls the execve function) points to the data. * In this case, the previous allocation is used but the statistics are reset. * + * Also, if the statistics of the process that calls the execve system call + * indicate a previous network activity or the executable file has the setid + * flags set, the bounds_crossed flag must be set to show that a network to + * local privilege boundary or setid boundary has been crossed respectively. + * * It's mandatory to disable interrupts before acquiring brute_stats_ptr_lock * and brute_stats::lock since the task_free hook can be called from an IRQ * context during the execution of the bprm_committing_creds hook. @@ -196,6 +322,8 @@ static void brute_task_execve(struct linux_binprm *bprm) { struct brute_stats **stats; unsigned long flags; + bool network_to_local; + bool is_setid = false; stats = brute_stats_ptr(current); read_lock_irqsave(&brute_stats_ptr_lock, flags); @@ -206,12 +334,18 @@ static void brute_task_execve(struct linux_binprm *bprm) } spin_lock(&(*stats)->lock); + network_to_local = (*stats)->network; + + /* + * A network_to_local flag equal to true will set the bounds_crossed + * flag. So, in this scenario the "is setid" test can be avoided. + */ + if (!network_to_local) + is_setid = brute_is_setid(bprm); if (!refcount_dec_not_one(&(*stats)->refc)) { /* execve call after an execve call */ - (*stats)->faults = 0; - (*stats)->jiffies = get_jiffies_64(); - (*stats)->period = 0; + brute_reset_stats(*stats, is_setid); spin_unlock(&(*stats)->lock); read_unlock_irqrestore(&brute_stats_ptr_lock, flags); return; @@ -222,7 +356,7 @@ static void brute_task_execve(struct linux_binprm *bprm) read_unlock_irqrestore(&brute_stats_ptr_lock, flags); write_lock_irqsave(&brute_stats_ptr_lock, flags); - *stats = brute_new_stats(); + *stats = brute_new_stats(network_to_local, is_setid); WARN(!*stats, "Cannot allocate statistical data\n"); write_unlock_irqrestore(&brute_stats_ptr_lock, flags); } @@ -653,12 +787,103 @@ static void brute_manage_exec_attack(struct brute_stats *stats, u64 now, print_exec_attack_running(exec_stats); } +/** + * brute_priv_have_changed() - Test if the privileges have changed. + * @stats: Statistics that hold the saved credentials. + * + * The privileges have changed if the credentials of the current task are + * different from the credentials saved in the statistics structure. + * + * The statistics that hold the saved credentials cannot be NULL. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * and brute_stats::lock held. + * Return: True if the privileges have changed. False otherwise. + */ +static bool brute_priv_have_changed(struct brute_stats *stats) +{ + const struct cred *cred = current_cred(); + bool priv_have_changed; + + priv_have_changed = !uid_eq(stats->saved_cred.uid, cred->uid) || + !gid_eq(stats->saved_cred.gid, cred->gid) || + !uid_eq(stats->saved_cred.suid, cred->suid) || + !gid_eq(stats->saved_cred.sgid, cred->sgid) || + !uid_eq(stats->saved_cred.euid, cred->euid) || + !gid_eq(stats->saved_cred.egid, cred->egid) || + !uid_eq(stats->saved_cred.fsuid, cred->fsuid) || + !gid_eq(stats->saved_cred.fsgid, cred->fsgid); + + return priv_have_changed; +} + +/** + * brute_threat_model_supported() - Test if the threat model is supported. + * @siginfo: Contains the signal information. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * To avoid false positives during the attack detection it is necessary to + * narrow the possible cases. Only the following scenarios are taken into + * account: + * + * 1.- Launching (fork()/exec()) a setuid/setgid process repeatedly until a + * desirable memory layout is got (e.g. Stack Clash). + * 2.- Connecting to an exec()ing network daemon (e.g. xinetd) repeatedly until + * a desirable memory layout is got (e.g. what CTFs do for simple network + * service). + * 3.- Launching processes without exec() (e.g. Android Zygote) and exposing + * state to attack a sibling. + * 4.- Connecting to a fork()ing network daemon (e.g. apache) repeatedly until + * the previously shared memory layout of all the other children is exposed + * (e.g. kind of related to HeartBleed). + * + * In each case, a privilege boundary has been crossed: + * + * Case 1: setuid/setgid process + * Case 2: network to local + * Case 3: privilege changes + * Case 4: network to local + * + * Also, only the signals delivered by the kernel are taken into account with + * the exception of the SIGABRT signal since the latter is used by glibc for + * stack canary, malloc, etc failures, which may indicate that a mitigation has + * been triggered. + * + * The signal information and the statistical data shared by all the fork + * hierarchy processes cannot be NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * held. + * Return: True if the threat model is supported. False otherwise. + */ +static bool brute_threat_model_supported(const kernel_siginfo_t *siginfo, + struct brute_stats *stats) +{ + bool bounds_crossed; + + if (siginfo->si_signo == SIGKILL && siginfo->si_code != SIGABRT) + return false; + + spin_lock(&stats->lock); + bounds_crossed = stats->bounds_crossed; + bounds_crossed = bounds_crossed || brute_priv_have_changed(stats); + stats->bounds_crossed = bounds_crossed; + spin_unlock(&stats->lock); + + return bounds_crossed; +} + /** * brute_task_fatal_signal() - Target for the task_fatal_signal hook. * @siginfo: Contains the signal information. * - * To detect a brute force attack is necessary to update the fork and exec - * statistics in every fatal crash and act based on these data. + * To detect a brute force attack it is necessary, as a first step, to test in + * every fatal crash if the threat model is supported. If so, update the fork + * and exec statistics and act based on these data. * * It's mandatory to disable interrupts before acquiring brute_stats_ptr_lock * and brute_stats::lock since the task_free hook can be called from an IRQ @@ -675,18 +900,59 @@ static void brute_task_fatal_signal(const kernel_siginfo_t *siginfo) read_lock(&tasklist_lock); read_lock_irqsave(&brute_stats_ptr_lock, flags); - if (WARN(!*stats, "No statistical data\n")) { - read_unlock_irqrestore(&brute_stats_ptr_lock, flags); - read_unlock(&tasklist_lock); - return; - } + if (WARN(!*stats, "No statistical data\n")) + goto unlock; + + if (!brute_threat_model_supported(siginfo, *stats)) + goto unlock; last_fork_crash = brute_manage_fork_attack(*stats, now); brute_manage_exec_attack(*stats, now, last_fork_crash); +unlock: read_unlock_irqrestore(&brute_stats_ptr_lock, flags); read_unlock(&tasklist_lock); } +/** + * brute_network() - Target for the socket_sock_rcv_skb hook. + * @sk: Contains the sock (not socket) associated with the incoming sk_buff. + * @skb: Contains the incoming network data. + * + * A previous step to detect that a network to local boundary has been crossed + * is to detect if there is network activity. To do this, it is only necessary + * to check if there are data packets received from a network device other than + * loopback. + * + * It's mandatory to disable interrupts before acquiring brute_stats_ptr_lock + * and brute_stats::lock since the task_free hook can be called from an IRQ + * context during the execution of the socket_sock_rcv_skb hook. + * + * Return: -EFAULT if the current task doesn't have statistical data. Zero + * otherwise. + */ +static int brute_network(struct sock *sk, struct sk_buff *skb) +{ + struct brute_stats **stats; + unsigned long flags; + + if (!skb->dev || (skb->dev->flags & IFF_LOOPBACK)) + return 0; + + stats = brute_stats_ptr(current); + read_lock_irqsave(&brute_stats_ptr_lock, flags); + + if (!*stats) { + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); + return -EFAULT; + } + + spin_lock(&(*stats)->lock); + (*stats)->network = true; + spin_unlock(&(*stats)->lock); + read_unlock_irqrestore(&brute_stats_ptr_lock, flags); + return 0; +} + /* * brute_hooks - Targets for the LSM's hooks. */ @@ -695,6 +961,7 @@ static struct security_hook_list brute_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(bprm_committing_creds, brute_task_execve), LSM_HOOK_INIT(task_free, brute_task_free), LSM_HOOK_INIT(task_fatal_signal, brute_task_fatal_signal), + LSM_HOOK_INIT(socket_sock_rcv_skb, brute_network), }; /** From patchwork Sun Mar 7 11:30:28 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 395731 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6A341C433DB for ; Sun, 7 Mar 2021 13:21:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4661464F6D for ; Sun, 7 Mar 2021 13:21:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231340AbhCGNVH (ORCPT ); Sun, 7 Mar 2021 08:21:07 -0500 Received: from mout.gmx.net ([212.227.17.22]:53133 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231284AbhCGNU5 (ORCPT ); Sun, 7 Mar 2021 08:20:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1615123217; bh=aP9TI99dMfaQo+gcI1iSEpC7EfKYPJvVFnknEuxuH3M=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=RrEhpFsGx+tgWi6nQd02ItRnQd0+wPeEk8q9AJCJLkcLqobf2ReUlhnefTzEPYD8R RAmFZNrr7ZSqK+lePNAe/qhnV2ygxqsCoueYgNLTAc/ao0z3J8Sd3Z6ruqRNARBHy8 hhoYy4gpSqKfaYjtGiUH3zW8zpGnOFaVYvRj+Y2M= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from localhost.localdomain ([83.52.229.153]) by mail.gmx.net (mrgmx104 [212.227.17.174]) with ESMTPSA (Nemesis) id 1N9dwj-1lmgC41189-015Vg3; Sun, 07 Mar 2021 14:20:17 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , Andi Kleen , kernel test robot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v6 5/8] security/brute: Mitigate a brute force attack Date: Sun, 7 Mar 2021 12:30:28 +0100 Message-Id: <20210307113031.11671-6-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210307113031.11671-1-john.wood@gmx.com> References: <20210307113031.11671-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:a1oAnkCNBKI7ysm6dOe85zYlkyf25P8dwb+DHXdqd4I4Tf7YYXl av22WKf0AmiuqFEbXw+kcpBjDU+HoPL0p/Mp90/Spo/wCOoBtV4NntH4k8kqYlB6IH7q0AJ sZpJ64LK5iLMLESeVtx1XZddXyOOt1uST2kS4tBA7fGlI50mcskUMnh3lQRpisgpbW7lCLK 44zkw+xrElkxGF1VciwpA== X-UI-Out-Filterresults: notjunk:1; V03:K0:ompjBVQHa64=:/+3YhGVOliRn996LDTBC9I VOYsYrr3bqzHhK6v/CYGVHX4NDQfTBafYs8pjMHWbKQT79Lo5Tkc4XZDD2xDq8HThh7WAVnVe dPYLSjdYvIDawWci8/dtz4NNtEp6IGEKE5wTbTTgtZ6v5wIiQaR+++4ftRM6W7q5ANRfql2V6 uEe54C6y1Z1f6vYQGzrX3qrJH1++n3p0ol+luxacssCZnlYXi/b2E/O+7ysEkXY3pqXLqAVPg lenzAZOro33yTG0dt0XyHhlmB4XuSxA58zkKztGyXoBnnirbLiKENXQqQBGv23Khru6BNfmx6 OUb/t71aHaqpTIsDd2fsZnP7ShzApUI/wkp1bj1uSD2849NuZ9JhKiCCde4or1n5i92Lg00Rv yeM3AjPMtgFTL/sbxMWZ/yfefti02j+/ggVEd76pvjEY5osaUIrxnoNVMDS+8/xDwuwgXQYAh K52Wwg9qh6JDaC54DAyND8B3Nl9uoalFkoBCkbFvSAWkQyhxQ7TqztASMYrugL8wwXFXBeD0I dZ5RpdSnU6PJ7M2A+T/Nw/uTyxX3SiXNqya92fb8JlDnLEhGrr4v1DAOP0XZUGr5TZnLamxIO uRwdYAm06bja35l/OuLUIFQonZj2sVxm5/6iWWKiBlN1Yykubd2famnrN0dHYWWWMTJbAWmYh LinsQx0xLUaPoeYJUWxbk7a3x4sJMesGFtLjlBAZmoCgL8VmwFgT8tM8k5T4CtsEvyFIprsXl 9Evw96LLvxhmtx0BSM9NjmlIQF7susoHkrRmyv3c9+EwY+BQ0ZqPqKMn0mOuG/9Cdee8YzIh2 +qZPbyyd19RsYOxD/qZMmrV8NNmW0ec+dHgemxwHg1E0LQXgSRR4sHz5Zt47dXjOusoaxXed5 6Run7n8HiCSpIsU7cLRA== Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org In order to mitigate a brute force attack all the offending tasks involved in the attack must be killed. In other words, it is necessary to kill all the tasks that share the fork and/or exec statistical data related to the attack. Moreover, if the attack happens through the fork system call, the processes that have the same group_leader that the current task (the task that has crashed) must be avoided since they are in the path to be killed. When the SIGKILL signal is sent to the offending tasks, the function "brute_kill_offending_tasks" will be called in a recursive way from the task_fatal_signal LSM hook due to a small crash period. So, to avoid kill again the same tasks due to a recursive call of this function, it is necessary to disable the attack detection for the involved hierarchies. To disable the attack detection, set to zero the last crash timestamp and avoid to compute the application crash period in this case. Signed-off-by: John Wood --- security/brute/brute.c | 141 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 132 insertions(+), 9 deletions(-) -- 2.25.1 diff --git a/security/brute/brute.c b/security/brute/brute.c index 38e5e050964a..36a3286a02dd 100644 --- a/security/brute/brute.c +++ b/security/brute/brute.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include #include @@ -64,7 +65,7 @@ struct brute_cred { * @lock: Lock to protect the brute_stats structure. * @refc: Reference counter. * @faults: Number of crashes. - * @jiffies: Last crash timestamp. + * @jiffies: Last crash timestamp. If zero, the attack detection is disabled. * @period: Crash period's moving average. * @saved_cred: Saved credentials. * @network: Network activity flag. @@ -571,6 +572,125 @@ static inline void print_fork_attack_running(void) pr_warn("Fork brute force attack detected [%s]\n", current->comm); } +/** + * brute_disabled() - Test if the brute force attack detection is disabled. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * The brute force attack detection enabling/disabling is based on the last + * crash timestamp. A zero timestamp indicates that this feature is disabled. A + * timestamp greater than zero indicates that the attack detection is enabled. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * held. + * Return: True if the brute force attack detection is disabled. False + * otherwise. + */ +static bool brute_disabled(struct brute_stats *stats) +{ + bool disabled; + + spin_lock(&stats->lock); + disabled = !stats->jiffies; + spin_unlock(&stats->lock); + + return disabled; +} + +/** + * brute_disable() - Disable the brute force attack detection. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * To disable the brute force attack detection it is only necessary to set the + * last crash timestamp to zero. A zero timestamp indicates that this feature is + * disabled. A timestamp greater than zero indicates that the attack detection + * is enabled. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * and brute_stats::lock held. + */ +static inline void brute_disable(struct brute_stats *stats) +{ + stats->jiffies = 0; +} + +/** + * enum brute_attack_type - Brute force attack type. + * @BRUTE_ATTACK_TYPE_FORK: Attack that happens through the fork system call. + * @BRUTE_ATTACK_TYPE_EXEC: Attack that happens through the execve system call. + */ +enum brute_attack_type { + BRUTE_ATTACK_TYPE_FORK, + BRUTE_ATTACK_TYPE_EXEC, +}; + +/** + * brute_kill_offending_tasks() - Kill the offending tasks. + * @attack_type: Brute force attack type. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * When a brute force attack is detected all the offending tasks involved in the + * attack must be killed. In other words, it is necessary to kill all the tasks + * that share the same statistical data. Moreover, if the attack happens through + * the fork system call, the processes that have the same group_leader that the + * current task must be avoided since they are in the path to be killed. + * + * When the SIGKILL signal is sent to the offending tasks, this function will be + * called again from the task_fatal_signal hook due to a small crash period. So, + * to avoid kill again the same tasks due to a recursive call of this function, + * it is necessary to disable the attack detection for this fork hierarchy. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and tasklist_lock and + * brute_stats_ptr_lock held. + */ +static void brute_kill_offending_tasks(enum brute_attack_type attack_type, + struct brute_stats *stats) +{ + struct task_struct *p; + struct brute_stats **p_stats; + + spin_lock(&stats->lock); + + if (attack_type == BRUTE_ATTACK_TYPE_FORK && + refcount_read(&stats->refc) == 1) { + spin_unlock(&stats->lock); + return; + } + + brute_disable(stats); + spin_unlock(&stats->lock); + + for_each_process(p) { + if (attack_type == BRUTE_ATTACK_TYPE_FORK && + p->group_leader == current->group_leader) + continue; + + p_stats = brute_stats_ptr(p); + if (*p_stats != stats) + continue; + + do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_PID); + pr_warn_ratelimited("Offending process %d [%s] killed\n", + p->pid, p->comm); + } +} + /** * brute_manage_fork_attack() - Manage a fork brute force attack. * @stats: Statistical data shared by all the fork hierarchy processes. @@ -586,8 +706,8 @@ static inline void print_fork_attack_running(void) * since the task_free hook can be called from an IRQ context during the * execution of the task_fatal_signal hook. * - * Context: Must be called with interrupts disabled and brute_stats_ptr_lock - * held. + * Context: Must be called with interrupts disabled and tasklist_lock and + * brute_stats_ptr_lock held. * Return: The last crash timestamp before updating it. */ static u64 brute_manage_fork_attack(struct brute_stats *stats, u64 now) @@ -595,8 +715,10 @@ static u64 brute_manage_fork_attack(struct brute_stats *stats, u64 now) u64 last_fork_crash; last_fork_crash = brute_update_crash_period(stats, now); - if (brute_attack_running(stats)) + if (brute_attack_running(stats)) { print_fork_attack_running(); + brute_kill_offending_tasks(BRUTE_ATTACK_TYPE_FORK, stats); + } return last_fork_crash; } @@ -783,8 +905,10 @@ static void brute_manage_exec_attack(struct brute_stats *stats, u64 now, if (fork_period == exec_period) return; - if (brute_attack_running(exec_stats)) + if (brute_attack_running(exec_stats)) { print_exec_attack_running(exec_stats); + brute_kill_offending_tasks(BRUTE_ATTACK_TYPE_EXEC, exec_stats); + } } /** @@ -900,10 +1024,9 @@ static void brute_task_fatal_signal(const kernel_siginfo_t *siginfo) read_lock(&tasklist_lock); read_lock_irqsave(&brute_stats_ptr_lock, flags); - if (WARN(!*stats, "No statistical data\n")) - goto unlock; - - if (!brute_threat_model_supported(siginfo, *stats)) + if (WARN(!*stats, "No statistical data\n") || + brute_disabled(*stats) || + !brute_threat_model_supported(siginfo, *stats)) goto unlock; last_fork_crash = brute_manage_fork_attack(*stats, now); From patchwork Sun Mar 7 11:30:29 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 395256 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A298FC433E9 for ; Sun, 7 Mar 2021 13:43:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D28465107 for ; Sun, 7 Mar 2021 13:43:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231393AbhCGNnP (ORCPT ); Sun, 7 Mar 2021 08:43:15 -0500 Received: from mout.gmx.net ([212.227.17.21]:48565 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230272AbhCGNm5 (ORCPT ); Sun, 7 Mar 2021 08:42:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1615124521; bh=yBo7hGCSzN1cx8Cw6x+gmnMXafaZYnF6cZpWUcCnFjw=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=e+VGYaPh1V8utWRjSzAaZf7vesjkpi4NR9TeuP1sdttN0YSFAQkir2NPMMX/60t4D hDf+2UujimHyf+ipspGXkl5S6sGB95CBEF9sPblz9ALIYR1E3GtABSRCR51LTp+tLH gYuX+5ddOidCaP2WSSePV1/kpKe0lZK24pvj0VvU= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from localhost.localdomain ([83.52.229.153]) by mail.gmx.net (mrgmx104 [212.227.17.174]) with ESMTPSA (Nemesis) id 1MY6Cb-1lFokG212D-00YNOi; Sun, 07 Mar 2021 14:42:01 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , Andi Kleen , kernel test robot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v6 6/8] selftests/brute: Add tests for the Brute LSM Date: Sun, 7 Mar 2021 12:30:29 +0100 Message-Id: <20210307113031.11671-7-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210307113031.11671-1-john.wood@gmx.com> References: <20210307113031.11671-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:mvsxY7Ykuor4unsAnNlbbu6SaElApBmWwMDgxWVYAVGrNsbkNwB twwjS+0aY/v1rceXHNaW+TVHs5pSECLlSTzG71xBBNgC8cszd9QuVtnhlEYztEKOr8Jv58Y S09yd+BrusjdSJgHyfJ9+adidmb5SWl7nbb9f0THB2MSBH4yTBcY4SHYAt6nMDKQkinXd8v Ojg/ExjwXqTBMQhRwMAMA== X-UI-Out-Filterresults: notjunk:1; V03:K0:0sqsvWMK2H0=:cdWoY0iZPtfGybVenbtWtp 7vg6VPWaMTbFdshKHt0gCwWOlx0alCoMGgqpVufZkWNeJhL9QG5PkC6lCF4AMSIy4Eol8phVE nvqXAYnly6a/QooFeGl5zlmVBBcJrcProYKwjadp/Ie5ybJtCSyM54qYieXCXLcRmgRJV17U6 8kBq4pyyCAyDlCDm6qHo6Cvt8g+BPwHzR/Gkm3QKidZeAOAzOdJQEcA43Ftr6Bb/kS2wugCuv qei/MQDdBcPFh5BGIv3fB5ROYZS4/K1hiy21jG2fNLTONu5yohlCl5rFkKaqtsSZdTPbiamq9 9VaLFCEZYWQrLFhohmrxI8lQIB/qxDwbDCEX7AtoyMxzBZSVK8licraT22KpAtT5r2Dx6w+7c pobaXDv/pBfe+iUt6DT4/jSchMotJT2+I39iPHzPYWcAIaBXRdf5CtA+lTAO/zKPSyC/u25JR mIZndYNWL3kHqVur/ywtQOotUTQKgGbkJo1n9B+GR5ctzM51pD72/ugp/MaFqOZGzGKNspSZI 8LmoCEtqgRQyBmTrdoxvVYjPROrx5Qw8t/Pv66JiNNozD+W2pKvWLtoW7gvK3uQnwQJNzVSr3 KEf8xZ7BUp2zEdblDC+MHdkLJUCBfTp0wPu/8b/Gpb1CluwHKnP+0CW0BHU6FTervjIpxIDHg XLBeE7e9wCZeGsg3ikPs+JJv80tt9nCqo1xQJqhV1Nbqpq9Z7KOzOtjHvPUK5iGMmqeW6xWo2 VJh5GSL9VjSzeewb3/26B80Kakiy2jkf3PJnD2djt6+/m1QbbbCUM6YJxnlwB6RdYkP0zQn2b TzhBEyebj1Y0xOBIjNt6HEETo9JHwfjUpw0mFW8XSV2NsNrCcljceATmeeEMJp6FARGc053gN PjVAnGg9YVQ0ttfUAnqA== Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Add tests to check the brute LSM functionality and cover fork/exec brute force attacks crossing the following privilege boundaries: 1.- setuid process 2.- privilege changes 3.- network to local Also, as a first step check that fork/exec brute force attacks without crossing any privilege boundariy already commented doesn't trigger the detection and mitigation stage. All the fork brute force attacks are carried out via the "exec" app to avoid the triggering of the "brute" LSM over the shell script running the tests. Signed-off-by: John Wood --- tools/testing/selftests/Makefile | 1 + tools/testing/selftests/brute/.gitignore | 2 + tools/testing/selftests/brute/Makefile | 5 + tools/testing/selftests/brute/config | 1 + tools/testing/selftests/brute/exec.c | 44 ++ tools/testing/selftests/brute/test.c | 507 +++++++++++++++++++++++ tools/testing/selftests/brute/test.sh | 226 ++++++++++ 7 files changed, 786 insertions(+) create mode 100644 tools/testing/selftests/brute/.gitignore create mode 100644 tools/testing/selftests/brute/Makefile create mode 100644 tools/testing/selftests/brute/config create mode 100644 tools/testing/selftests/brute/exec.c create mode 100644 tools/testing/selftests/brute/test.c create mode 100755 tools/testing/selftests/brute/test.sh -- 2.25.1 diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile index 6c575cf34a71..d4cf9e1c0a6d 100644 --- a/tools/testing/selftests/Makefile +++ b/tools/testing/selftests/Makefile @@ -2,6 +2,7 @@ TARGETS = arm64 TARGETS += bpf TARGETS += breakpoints +TARGETS += brute TARGETS += capabilities TARGETS += cgroup TARGETS += clone3 diff --git a/tools/testing/selftests/brute/.gitignore b/tools/testing/selftests/brute/.gitignore new file mode 100644 index 000000000000..1ccc45251a1b --- /dev/null +++ b/tools/testing/selftests/brute/.gitignore @@ -0,0 +1,2 @@ +exec +test diff --git a/tools/testing/selftests/brute/Makefile b/tools/testing/selftests/brute/Makefile new file mode 100644 index 000000000000..52662d0b484c --- /dev/null +++ b/tools/testing/selftests/brute/Makefile @@ -0,0 +1,5 @@ +# SPDX-License-Identifier: GPL-2.0 +CFLAGS += -Wall -O2 +TEST_PROGS := test.sh +TEST_GEN_FILES := exec test +include ../lib.mk diff --git a/tools/testing/selftests/brute/config b/tools/testing/selftests/brute/config new file mode 100644 index 000000000000..3587b7bf6c23 --- /dev/null +++ b/tools/testing/selftests/brute/config @@ -0,0 +1 @@ +CONFIG_SECURITY_FORK_BRUTE=y diff --git a/tools/testing/selftests/brute/exec.c b/tools/testing/selftests/brute/exec.c new file mode 100644 index 000000000000..1bbe72f6e4bd --- /dev/null +++ b/tools/testing/selftests/brute/exec.c @@ -0,0 +1,44 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include +#include +#include +#include + +static __attribute__((noreturn)) void error_failure(const char *message) +{ + perror(message); + exit(EXIT_FAILURE); +} + +#define PROG_NAME basename(argv[0]) + +int main(int argc, char **argv) +{ + pid_t pid; + int status; + + if (argc < 2) { + printf("Usage: %s \n", PROG_NAME); + exit(EXIT_FAILURE); + } + + pid = fork(); + if (pid < 0) + error_failure("fork"); + + /* Child process */ + if (!pid) { + execve(argv[1], &argv[1], NULL); + error_failure("execve"); + } + + /* Parent process */ + pid = waitpid(pid, &status, 0); + if (pid < 0) + error_failure("waitpid"); + + return EXIT_SUCCESS; +} diff --git a/tools/testing/selftests/brute/test.c b/tools/testing/selftests/brute/test.c new file mode 100644 index 000000000000..44c32f446dca --- /dev/null +++ b/tools/testing/selftests/brute/test.c @@ -0,0 +1,507 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +static const char *message = "message"; + +enum mode { + MODE_NONE, + MODE_CRASH, + MODE_SERVER_CRASH, + MODE_CLIENT, +}; + +enum crash_after { + CRASH_AFTER_NONE, + CRASH_AFTER_FORK, + CRASH_AFTER_EXEC, +}; + +enum signal_from { + SIGNAL_FROM_NONE, + SIGNAL_FROM_USER, + SIGNAL_FROM_KERNEL, +}; + +struct args { + uint32_t ip; + uint16_t port; + int counter; + long timeout; + enum mode mode; + enum crash_after crash_after; + enum signal_from signal_from; + unsigned char has_counter : 1; + unsigned char has_change_priv : 1; + unsigned char has_ip : 1; + unsigned char has_port : 1; + unsigned char has_timeout : 1; +}; + +#define OPT_STRING "hm:c:s:n:Ca:p:t:" + +static void usage(const char *prog) +{ + printf("Usage: %s \n", prog); + printf("OPTIONS:\n"); + printf(" -h: Show this help and exit. Optional.\n"); + printf(" -m (crash | server_crash | client): Mode. Required.\n"); + printf("Options for crash mode:\n"); + printf(" -c (fork | exec): Crash after. Optional.\n"); + printf(" -s (user | kernel): Signal from. Required.\n"); + printf(" -n counter: Number of crashes.\n"); + printf(" Required if the option -c is used.\n"); + printf(" Not used without the option -c.\n"); + printf(" Range from 1 to INT_MAX.\n"); + printf(" -C: Change privileges before crash. Optional.\n"); + printf("Options for server_crash mode:\n"); + printf(" -a ip: Ip v4 address to accept. Required.\n"); + printf(" -p port: Port number. Required.\n"); + printf(" Range from 1 to UINT16_MAX.\n"); + printf(" -t secs: Accept timeout. Required.\n"); + printf(" Range from 1 to LONG_MAX.\n"); + printf(" -c (fork | exec): Crash after. Required.\n"); + printf(" -s (user | kernel): Signal from. Required.\n"); + printf(" -n counter: Number of crashes. Required.\n"); + printf(" Range from 1 to INT_MAX.\n"); + printf("Options for client mode:\n"); + printf(" -a ip: Ip v4 address to connect. Required.\n"); + printf(" -p port: Port number. Required.\n"); + printf(" Range from 1 to UINT16_MAX.\n"); + printf(" -t secs: Connect timeout. Required.\n"); + printf(" Range from 1 to LONG_MAX.\n"); +} + +static __attribute__((noreturn)) void info_failure(const char *message, + const char *prog) +{ + printf("%s\n", message); + usage(prog); + exit(EXIT_FAILURE); +} + +static enum mode get_mode(const char *text, const char *prog) +{ + if (!strcmp(text, "crash")) + return MODE_CRASH; + + if (!strcmp(text, "server_crash")) + return MODE_SERVER_CRASH; + + if (!strcmp(text, "client")) + return MODE_CLIENT; + + info_failure("Invalid mode option [-m].", prog); +} + +static enum crash_after get_crash_after(const char *text, const char *prog) +{ + if (!strcmp(text, "fork")) + return CRASH_AFTER_FORK; + + if (!strcmp(text, "exec")) + return CRASH_AFTER_EXEC; + + info_failure("Invalid crash after option [-c].", prog); +} + +static enum signal_from get_signal_from(const char *text, const char *prog) +{ + if (!strcmp(text, "user")) + return SIGNAL_FROM_USER; + + if (!strcmp(text, "kernel")) + return SIGNAL_FROM_KERNEL; + + info_failure("Invalid signal from option [-s]", prog); +} + +static int get_counter(const char *text, const char *prog) +{ + int counter; + + counter = atoi(text); + if (counter > 0) + return counter; + + info_failure("Invalid counter option [-n].", prog); +} + +static __attribute__((noreturn)) void error_failure(const char *message) +{ + perror(message); + exit(EXIT_FAILURE); +} + +static uint32_t get_ip(const char *text, const char *prog) +{ + int ret; + uint32_t ip; + + ret = inet_pton(AF_INET, text, &ip); + if (!ret) + info_failure("Invalid ip option [-a].", prog); + else if (ret < 0) + error_failure("inet_pton"); + + return ip; +} + +static uint16_t get_port(const char *text, const char *prog) +{ + long port; + + port = atol(text); + if ((port > 0) && (port <= UINT16_MAX)) + return htons(port); + + info_failure("Invalid port option [-p].", prog); +} + +static long get_timeout(const char *text, const char *prog) +{ + long timeout; + + timeout = atol(text); + if (timeout > 0) + return timeout; + + info_failure("Invalid timeout option [-t].", prog); +} + +static void check_args(const struct args *args, const char *prog) +{ + if (args->mode == MODE_CRASH && args->crash_after != CRASH_AFTER_NONE && + args->signal_from != SIGNAL_FROM_NONE && args->has_counter && + !args->has_ip && !args->has_port && !args->has_timeout) + return; + + if (args->mode == MODE_CRASH && args->signal_from != SIGNAL_FROM_NONE && + args->crash_after == CRASH_AFTER_NONE && !args->has_counter && + !args->has_ip && !args->has_port && !args->has_timeout) + return; + + if (args->mode == MODE_SERVER_CRASH && args->has_ip && args->has_port && + args->has_timeout && args->crash_after != CRASH_AFTER_NONE && + args->signal_from != SIGNAL_FROM_NONE && args->has_counter && + !args->has_change_priv) + return; + + if (args->mode == MODE_CLIENT && args->has_ip && args->has_port && + args->has_timeout && args->crash_after == CRASH_AFTER_NONE && + args->signal_from == SIGNAL_FROM_NONE && !args->has_counter && + !args->has_change_priv) + return; + + info_failure("Invalid use of options.", prog); +} + +static uid_t get_non_root_uid(void) +{ + struct passwd *pwent; + uid_t uid; + + while (true) { + errno = 0; + pwent = getpwent(); + if (!pwent) { + if (errno) { + perror("getpwent"); + endpwent(); + exit(EXIT_FAILURE); + } + break; + } + + if (pwent->pw_uid) { + uid = pwent->pw_uid; + endpwent(); + return uid; + } + } + + endpwent(); + printf("A user different of root is needed.\n"); + exit(EXIT_FAILURE); +} + +static inline void do_sigsegv(void) +{ + int *p = NULL; + *p = 0; +} + +static void do_sigkill(void) +{ + int ret; + + ret = kill(getpid(), SIGKILL); + if (ret) + error_failure("kill"); +} + +static void crash(enum signal_from signal_from, bool change_priv) +{ + int ret; + + if (change_priv) { + ret = setuid(get_non_root_uid()); + if (ret) + error_failure("setuid"); + } + + if (signal_from == SIGNAL_FROM_KERNEL) + do_sigsegv(); + + do_sigkill(); +} + +static void execve_crash(char *const argv[]) +{ + execve(argv[0], argv, NULL); + error_failure("execve"); +} + +static void exec_crash_user(void) +{ + char *const argv[] = { + "./test", "-m", "crash", "-s", "user", NULL, + }; + + execve_crash(argv); +} + +static void exec_crash_user_change_priv(void) +{ + char *const argv[] = { + "./test", "-m", "crash", "-s", "user", "-C", NULL, + }; + + execve_crash(argv); +} + +static void exec_crash_kernel(void) +{ + char *const argv[] = { + "./test", "-m", "crash", "-s", "kernel", NULL, + }; + + execve_crash(argv); +} + +static void exec_crash_kernel_change_priv(void) +{ + char *const argv[] = { + "./test", "-m", "crash", "-s", "kernel", "-C", NULL, + }; + + execve_crash(argv); +} + +static void exec_crash(enum signal_from signal_from, bool change_priv) +{ + if (signal_from == SIGNAL_FROM_USER && !change_priv) + exec_crash_user(); + if (signal_from == SIGNAL_FROM_USER && change_priv) + exec_crash_user_change_priv(); + if (signal_from == SIGNAL_FROM_KERNEL && !change_priv) + exec_crash_kernel(); + if (signal_from == SIGNAL_FROM_KERNEL && change_priv) + exec_crash_kernel_change_priv(); +} + +static void do_crash(enum crash_after crash_after, enum signal_from signal_from, + int counter, bool change_priv) +{ + pid_t pid; + int status; + + if (crash_after == CRASH_AFTER_NONE) + crash(signal_from, change_priv); + + while (counter > 0) { + pid = fork(); + if (pid < 0) + error_failure("fork"); + + /* Child process */ + if (!pid) { + if (crash_after == CRASH_AFTER_FORK) + crash(signal_from, change_priv); + + exec_crash(signal_from, change_priv); + } + + /* Parent process */ + counter -= 1; + pid = waitpid(pid, &status, 0); + if (pid < 0) + error_failure("waitpid"); + } +} + +static __attribute__((noreturn)) void error_close_failure(const char *message, + int fd) +{ + perror(message); + close(fd); + exit(EXIT_FAILURE); +} + +static void do_server(uint32_t ip, uint16_t port, long accept_timeout) +{ + int sockfd; + int ret; + struct sockaddr_in address; + struct timeval timeout; + int newsockfd; + + sockfd = socket(AF_INET, SOCK_STREAM, 0); + if (sockfd < 0) + error_failure("socket"); + + address.sin_family = AF_INET; + address.sin_addr.s_addr = ip; + address.sin_port = port; + + ret = bind(sockfd, (const struct sockaddr *)&address, sizeof(address)); + if (ret) + error_close_failure("bind", sockfd); + + ret = listen(sockfd, 1); + if (ret) + error_close_failure("listen", sockfd); + + timeout.tv_sec = accept_timeout; + timeout.tv_usec = 0; + ret = setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, + (const struct timeval *)&timeout, sizeof(timeout)); + if (ret) + error_close_failure("setsockopt", sockfd); + + newsockfd = accept(sockfd, NULL, NULL); + if (newsockfd < 0) + error_close_failure("accept", sockfd); + + close(sockfd); + close(newsockfd); +} + +static void do_client(uint32_t ip, uint16_t port, long connect_timeout) +{ + int sockfd; + int ret; + struct timeval timeout; + struct sockaddr_in address; + + sockfd = socket(AF_INET, SOCK_STREAM, 0); + if (sockfd < 0) + error_failure("socket"); + + timeout.tv_sec = connect_timeout; + timeout.tv_usec = 0; + ret = setsockopt(sockfd, SOL_SOCKET, SO_SNDTIMEO, + (const struct timeval *)&timeout, sizeof(timeout)); + if (ret) + error_close_failure("setsockopt", sockfd); + + address.sin_family = AF_INET; + address.sin_addr.s_addr = ip; + address.sin_port = port; + + ret = connect(sockfd, (const struct sockaddr *)&address, + sizeof(address)); + if (ret) + error_close_failure("connect", sockfd); + + ret = write(sockfd, message, strlen(message)); + if (ret < 0) + error_close_failure("write", sockfd); + + close(sockfd); +} + +#define PROG_NAME basename(argv[0]) + +int main(int argc, char **argv) +{ + int opt; + struct args args = { + .mode = MODE_NONE, + .crash_after = CRASH_AFTER_NONE, + .signal_from = SIGNAL_FROM_NONE, + .has_counter = false, + .has_change_priv = false, + .has_ip = false, + .has_port = false, + .has_timeout = false, + }; + + while ((opt = getopt(argc, argv, OPT_STRING)) != -1) { + switch (opt) { + case 'h': + usage(PROG_NAME); + return EXIT_SUCCESS; + case 'm': + args.mode = get_mode(optarg, PROG_NAME); + break; + case 'c': + args.crash_after = get_crash_after(optarg, PROG_NAME); + break; + case 's': + args.signal_from = get_signal_from(optarg, PROG_NAME); + break; + case 'n': + args.counter = get_counter(optarg, PROG_NAME); + args.has_counter = true; + break; + case 'C': + args.has_change_priv = true; + break; + case 'a': + args.ip = get_ip(optarg, PROG_NAME); + args.has_ip = true; + break; + case 'p': + args.port = get_port(optarg, PROG_NAME); + args.has_port = true; + break; + case 't': + args.timeout = get_timeout(optarg, PROG_NAME); + args.has_timeout = true; + break; + default: + usage(PROG_NAME); + return EXIT_FAILURE; + } + } + + check_args(&args, PROG_NAME); + + if (args.mode == MODE_CRASH) { + do_crash(args.crash_after, args.signal_from, args.counter, + args.has_change_priv); + } else if (args.mode == MODE_SERVER_CRASH) { + do_server(args.ip, args.port, args.timeout); + do_crash(args.crash_after, args.signal_from, args.counter, + false); + } else if (args.mode == MODE_CLIENT) { + do_client(args.ip, args.port, args.timeout); + } + + return EXIT_SUCCESS; +} diff --git a/tools/testing/selftests/brute/test.sh b/tools/testing/selftests/brute/test.sh new file mode 100755 index 000000000000..f53f26ae5b96 --- /dev/null +++ b/tools/testing/selftests/brute/test.sh @@ -0,0 +1,226 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 + +TCID="test.sh" + +KSFT_PASS=0 +KSFT_FAIL=1 +KSFT_SKIP=4 + +errno=$KSFT_PASS + +check_root() +{ + local uid=$(id -u) + if [ $uid -ne 0 ]; then + echo $TCID: must be run as root >&2 + exit $KSFT_SKIP + fi +} + +count_fork_matches() +{ + dmesg | grep "brute: Fork brute force attack detected" | wc -l +} + +assert_equal() +{ + local val1=$1 + local val2=$2 + + if [ $val1 -eq $val2 ]; then + echo "$TCID: $message [PASS]" + else + echo "$TCID: $message [FAIL]" + errno=$KSFT_FAIL + fi +} + +test_fork_user() +{ + COUNTER=20 + + old_count=$(count_fork_matches) + ./exec test -m crash -c fork -s user -n $COUNTER + new_count=$(count_fork_matches) + + message="Fork attack (user signals, no bounds crossed)" + assert_equal $old_count $new_count +} + +test_fork_kernel() +{ + old_count=$(count_fork_matches) + ./exec test -m crash -c fork -s kernel -n $COUNTER + new_count=$(count_fork_matches) + + message="Fork attack (kernel signals, no bounds crossed)" + assert_equal $old_count $new_count +} + +count_exec_matches() +{ + dmesg | grep "brute: Exec brute force attack detected" | wc -l +} + +test_exec_user() +{ + old_count=$(count_exec_matches) + ./test -m crash -c exec -s user -n $COUNTER + new_count=$(count_exec_matches) + + message="Exec attack (user signals, no bounds crossed)" + assert_equal $old_count $new_count +} + +test_exec_kernel() +{ + old_count=$(count_exec_matches) + ./test -m crash -c exec -s kernel -n $COUNTER + new_count=$(count_exec_matches) + + message="Exec attack (kernel signals, no bounds crossed)" + assert_equal $old_count $new_count +} + +assert_not_equal() +{ + local val1=$1 + local val2=$2 + + if [ $val1 -ne $val2 ]; then + echo $TCID: $message [PASS] + else + echo $TCID: $message [FAIL] + errno=$KSFT_FAIL + fi +} + +test_fork_kernel_setuid() +{ + old_count=$(count_fork_matches) + chmod u+s test + ./exec test -m crash -c fork -s kernel -n $COUNTER + chmod u-s test + new_count=$(count_fork_matches) + + message="Fork attack (kernel signals, setuid binary)" + assert_not_equal $old_count $new_count +} + +test_exec_kernel_setuid() +{ + old_count=$(count_exec_matches) + chmod u+s test + ./test -m crash -c exec -s kernel -n $COUNTER + chmod u-s test + new_count=$(count_exec_matches) + + message="Exec attack (kernel signals, setuid binary)" + assert_not_equal $old_count $new_count +} + +test_fork_kernel_change_priv() +{ + old_count=$(count_fork_matches) + ./exec test -m crash -c fork -s kernel -n $COUNTER -C + new_count=$(count_fork_matches) + + message="Fork attack (kernel signals, change privileges)" + assert_not_equal $old_count $new_count +} + +test_exec_kernel_change_priv() +{ + old_count=$(count_exec_matches) + ./test -m crash -c exec -s kernel -n $COUNTER -C + new_count=$(count_exec_matches) + + message="Exec attack (kernel signals, change privileges)" + assert_not_equal $old_count $new_count +} + +network_ns_setup() +{ + local vnet_name=$1 + local veth_name=$2 + local ip_src=$3 + local ip_dst=$4 + + ip netns add $vnet_name + ip link set $veth_name netns $vnet_name + ip -n $vnet_name addr add $ip_src/24 dev $veth_name + ip -n $vnet_name link set $veth_name up + ip -n $vnet_name route add $ip_dst/24 dev $veth_name +} + +network_setup() +{ + VETH0_NAME=veth0 + VNET0_NAME=vnet0 + VNET0_IP=10.0.1.0 + VETH1_NAME=veth1 + VNET1_NAME=vnet1 + VNET1_IP=10.0.2.0 + + ip link add $VETH0_NAME type veth peer name $VETH1_NAME + network_ns_setup $VNET0_NAME $VETH0_NAME $VNET0_IP $VNET1_IP + network_ns_setup $VNET1_NAME $VETH1_NAME $VNET1_IP $VNET0_IP +} + +test_fork_kernel_network_to_local() +{ + INADDR_ANY=0.0.0.0 + PORT=65535 + TIMEOUT=5 + + old_count=$(count_fork_matches) + ip netns exec $VNET0_NAME ./exec test -m server_crash -a $INADDR_ANY \ + -p $PORT -t $TIMEOUT -c fork -s kernel -n $COUNTER & + sleep 1 + ip netns exec $VNET1_NAME ./test -m client -a $VNET0_IP -p $PORT \ + -t $TIMEOUT + sleep 1 + new_count=$(count_fork_matches) + + message="Fork attack (kernel signals, network to local)" + assert_not_equal $old_count $new_count +} + +test_exec_kernel_network_to_local() +{ + old_count=$(count_exec_matches) + ip netns exec $VNET0_NAME ./test -m server_crash -a $INADDR_ANY \ + -p $PORT -t $TIMEOUT -c exec -s kernel -n $COUNTER & + sleep 1 + ip netns exec $VNET1_NAME ./test -m client -a $VNET0_IP -p $PORT \ + -t $TIMEOUT + sleep 1 + new_count=$(count_exec_matches) + + message="Exec attack (kernel signals, network to local)" + assert_not_equal $old_count $new_count +} + +network_cleanup() +{ + ip netns del $VNET0_NAME >/dev/null 2>&1 + ip netns del $VNET1_NAME >/dev/null 2>&1 + ip link delete $VETH0_NAME >/dev/null 2>&1 + ip link delete $VETH1_NAME >/dev/null 2>&1 +} + +check_root +test_fork_user +test_fork_kernel +test_exec_user +test_exec_kernel +test_fork_kernel_setuid +test_exec_kernel_setuid +test_fork_kernel_change_priv +test_exec_kernel_change_priv +network_setup +test_fork_kernel_network_to_local +test_exec_kernel_network_to_local +network_cleanup +exit $errno From patchwork Sun Mar 7 11:30:30 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 395255 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23BBAC433E9 for ; Sun, 7 Mar 2021 14:05:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0C4665106 for ; Sun, 7 Mar 2021 14:05:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231142AbhCGOEl (ORCPT ); Sun, 7 Mar 2021 09:04:41 -0500 Received: from mout.gmx.net ([212.227.15.19]:59611 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230527AbhCGOE0 (ORCPT ); Sun, 7 Mar 2021 09:04:26 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1615125824; bh=ZIBp+9aRe8HF5cEMqSetXmOc0i2AZOSaXMY65qDAbxs=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=jIEMCpRTqyhIbLKiN0m2sptJrhqeYDIw/dTyIxrwH8hRhU/UEmFKhvkR0jK/TfLWk DHrijEMlCVYT91wWfdUu6oBcajaiF5cEaDFj5b/9NbGjQc8HWVsJTsMKrvQpAfQqrY Twu1XT2vy8GMsWVj5h8GIa+iPXULXfQEFHRqq/Qk= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from localhost.localdomain ([83.52.229.153]) by mail.gmx.net (mrgmx005 [212.227.17.184]) with ESMTPSA (Nemesis) id 1MXGvM-1lG5eg1z6U-00YkJt; Sun, 07 Mar 2021 15:03:44 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , Andi Kleen , kernel test robot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v6 7/8] Documentation: Add documentation for the Brute LSM Date: Sun, 7 Mar 2021 12:30:30 +0100 Message-Id: <20210307113031.11671-8-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210307113031.11671-1-john.wood@gmx.com> References: <20210307113031.11671-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:Rv69WmXGPGbGGixEhsXkQdNWZs6NzqXeNL3lDO5CkV581f5lbhO /vVZkKTML3OCqhTm2qrrpJWNakyQ6t+vx9c3jobNx7ZPSYvH+t0ptH1Z8qCDjonmUZbH/Sw 8m89Szr0eMUGrvBFdyUCBBqxuUw6sM0vsm3ytIT/sk4xbqJ6xv4var7OqeAxH8G7lts9IAQ MmWPPaVEC0Ik5Pybo8b8g== X-UI-Out-Filterresults: notjunk:1; V03:K0:Oy15OVBypTk=:tpQwrLsHZ86zb11XhvfMKp nDWAo90loZqJYTDuf8AHjYJycgLUKQ+WiaVB05ypZg44h58rghVfMF+7b5R38MPJoqH5a93Gm Bc2BUpH8gLWTVUqfC1sryssuQdcT1xBG20sDLTDBkGodLzQsm3a/VSJJJ5dDpS24vkjnu/k+A nvZMOPjO1FnScu1EpG2b/3bF3Hn/dMMs464UK6Nn5YgZ6iYLWNp+sI23AL05Nm3BL4RtWWq1H GkwtuHToq6A45jYZgIGF1710Un2ElEyoAAtnSStoKIN9ktfyT/zPGf5zd938Ao9RBA7+MPvNy KThzIwuOWWCyGriwFuqRP5LoMNF3Id89RPdEW+TU+BuouFU8OkJuIZvUljugmWfOxHM/u6RUs JP5fYgmgbLnAZbfT+uaPyaVuK934vAVd5OvVrvk0DFvfnBr/t7i3jiwDrs0Y5eRzP83Bh8iRk SclpylRtMwI+YgShLcRQ7w8JVEsM4MhhL191N22q8W6jTHrHpFS1iI2FE67RpGALuMxMUJwQb Y7vqIv1MuXo/AwP9Aao/dVbIJKqqdfI0q4uD01niSKEVglN+jaOu/MPDNP0YJz/UIaX5yj8Pp BZYlUyNjQKmKkxMkGHVass3S5KhsdMsK7zaYZVZQpQgyR0hkIEIVsjh+DvnIQ8STjQylaZXRN 3NP+oHTIe1RkEyiqJUdmHgoABEA4zgwH1nDzDAtJ31YGkm6IonTZ01b/AXGPz03QDH8szTvDE Ag5whF/3w+YBS21sVjZjz5jPbq0IX1xPh3RDKEid2UXl5c1zbKjfAi0gueW7320NZMqlY/hlL 8AMNnDPryIuxDyOCxKJptvMxhpp//b9jhD+8SCeYOt4WSq6u7B/M0B/513kugvzWRXGns84fW 7pCFCBCp1TamjJ6rmUwQ== Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Add some info detailing what is the Brute LSM, its motivation, weak points of existing implementations, proposed solutions, enabling, disabling and self-tests. Signed-off-by: John Wood --- Documentation/admin-guide/LSM/Brute.rst | 278 ++++++++++++++++++++++++ Documentation/admin-guide/LSM/index.rst | 1 + security/brute/Kconfig | 3 +- 3 files changed, 281 insertions(+), 1 deletion(-) create mode 100644 Documentation/admin-guide/LSM/Brute.rst -- 2.25.1 diff --git a/Documentation/admin-guide/LSM/Brute.rst b/Documentation/admin-guide/LSM/Brute.rst new file mode 100644 index 000000000000..ca80aef9aa67 --- /dev/null +++ b/Documentation/admin-guide/LSM/Brute.rst @@ -0,0 +1,278 @@ +.. SPDX-License-Identifier: GPL-2.0 +=========================================================== +Brute: Fork brute force attack detection and mitigation LSM +=========================================================== + +Attacks against vulnerable userspace applications with the purpose to break ASLR +or bypass canaries traditionally use some level of brute force with the help of +the fork system call. This is possible since when creating a new process using +fork its memory contents are the same as those of the parent process (the +process that called the fork system call). So, the attacker can test the memory +infinite times to find the correct memory values or the correct memory addresses +without worrying about crashing the application. + +Based on the above scenario it would be nice to have this detected and +mitigated, and this is the goal of this implementation. Specifically the +following attacks are expected to be detected: + +1.- Launching (fork()/exec()) a setuid/setgid process repeatedly until a + desirable memory layout is got (e.g. Stack Clash). +2.- Connecting to an exec()ing network daemon (e.g. xinetd) repeatedly until a + desirable memory layout is got (e.g. what CTFs do for simple network + service). +3.- Launching processes without exec() (e.g. Android Zygote) and exposing state + to attack a sibling. +4.- Connecting to a fork()ing network daemon (e.g. apache) repeatedly until the + previously shared memory layout of all the other children is exposed (e.g. + kind of related to HeartBleed). + +In each case, a privilege boundary has been crossed: + +Case 1: setuid/setgid process +Case 2: network to local +Case 3: privilege changes +Case 4: network to local + +So, what really needs to be detected are fork/exec brute force attacks that +cross any of the commented bounds. + + +Other implementations +===================== + +The public version of grsecurity, as a summary, is based on the idea of delaying +the fork system call if a child died due to some fatal signal (SIGSEGV, SIGBUS, +SIGKILL or SIGILL). This has some issues: + +Bad practices +------------- + +Adding delays to the kernel is, in general, a bad idea. + +Scenarios not detected (false negatives) +---------------------------------------- + +This protection acts only when the fork system call is called after a child has +crashed. So, it would still be possible for an attacker to fork a big amount of +children (in the order of thousands), then probe all of them, and finally wait +the protection time before repeating the steps. + +Moreover, this method is based on the idea that the protection doesn't act if +the parent crashes. So, it would still be possible for an attacker to fork a +process and probe itself. Then, fork the child process and probe itself again. +This way, these steps can be repeated infinite times without any mitigation. + +Scenarios detected (false positives) +------------------------------------ + +Scenarios where an application rarely fails for reasons unrelated to a real +attack. + + +This implementation +=================== + +The main idea behind this implementation is to improve the existing ones +focusing on the weak points annotated before. Basically, the adopted solution is +to detect a fast crash rate instead of only one simple crash and to detect both +the crash of parent and child processes. Also, fine tune the detection focusing +on privilege boundary crossing. And finally, as a mitigation method, kill all +the offending tasks involved in the attack instead of using delays. + +To achieve this goal, and going into more details, this implementation is based +on the use of some statistical data shared across all the processes that can +have the same memory contents. Or in other words, a statistical data shared +between all the fork hierarchy processes after an execve system call. + +The purpose of these statistics is, basically, collect all the necessary info +to compute the application crash period in order to detect an attack. This crash +period is the time between the execve system call and the first fault or the +time between two consecutive faults, but this has a drawback. If an application +crashes twice in a short period of time for some reason unrelated to a real +attack, a false positive will be triggered. To avoid this scenario the +exponential moving average (EMA) is used. This way, the application crash period +will be a value that is not prone to change due to spurious data and follows the +real crash period. + +To detect a brute force attack it is necessary that the statistics shared by all +the fork hierarchy processes be updated in every fatal crash and the most +important data to update is the application crash period. + +These statistics are hold by the brute_stats struct. + +struct brute_cred { + kuid_t uid; + kgid_t gid; + kuid_t suid; + kgid_t sgid; + kuid_t euid; + kgid_t egid; + kuid_t fsuid; + kgid_t fsgid; +}; + +struct brute_stats { + spinlock_t lock; + refcount_t refc; + unsigned char faults; + u64 jiffies; + u64 period; + struct brute_cred saved_cred; + unsigned char network : 1; + unsigned char bounds_crossed : 1; +}; + +This is a fixed sized struct, so the memory usage will be based on the current +number of processes exec()ing. The previous sentence is true since in every fork +system call the parent's statistics are shared with the child process and in +every execve system call a new brute_stats struct is allocated. So, only one +brute_stats struct is used for every fork hierarchy (hierarchy of processes from +the execve system call). + +There are two types of brute force attacks that need to be detected. The first +one is an attack that happens through the fork system call and the second one is +an attack that happens through the execve system call. The first type uses the +statistics shared by all the fork hierarchy processes, but the second type +cannot use this statistical data due to these statistics dissapear when the +involved tasks finished. In this last scenario the attack info should be tracked +by the statistics of a higher fork hierarchy (the hierarchy that contains the +process that forks before the execve system call). + +Moreover, these two attack types have two variants. A slow brute force attack +that is detected if a maximum number of faults per fork hierarchy is reached and +a fast brute force attack that is detected if the application crash period falls +below a certain threshold. + +Once an attack has been detected, this is mitigated killing all the offending +tasks involved. Or in other words, once an attack has been detected, this is +mitigated killing all the processes that share the same statistics (the stats +that show an slow or fast brute force attack). + +Fine tuning the attack detection +-------------------------------- + +To avoid false positives during the attack detection it is necessary to narrow +the possible cases. To do so, and based on the threat scenarios that we want to +detect, this implementation also focuses on the crossing of privilege bounds. + +To be precise, only the following privilege bounds are taken into account: + +1.- setuid/setgid process +2.- network to local +3.- privilege changes + +Moreover, only the fatal signals delivered by the kernel are taken into account +avoiding the fatal signals sent by userspace applications (with the exception of +the SIGABRT user signal since this is used by glibc for stack canary, malloc, +etc. failures, which may indicate that a mitigation has been triggered). + +Exponential moving average (EMA) +-------------------------------- + +This kind of average defines a weight (between 0 and 1) for the new value to add +and applies the remainder of the weight to the current average value. This way, +some spurious data will not excessively modify the average and only if the new +values are persistent, the moving average will tend towards them. + +Mathematically the application crash period's EMA can be expressed as follows: + +period_ema = period * weight + period_ema * (1 - weight) + +Related to the attack detection, the EMA must guarantee that not many crashes +are needed. To demonstrate this, the scenario where an application has been +running without any crashes for a month will be used. + +The period's EMA can be written now as: + +period_ema[i] = period[i] * weight + period_ema[i - 1] * (1 - weight) + +If the new crash periods have insignificant values related to the first crash +period (a month in this case), the formula can be rewritten as: + +period_ema[i] = period_ema[i - 1] * (1 - weight) + +And by extension: + +period_ema[i - 1] = period_ema[i - 2] * (1 - weight) +period_ema[i - 2] = period_ema[i - 3] * (1 - weight) +period_ema[i - 3] = period_ema[i - 4] * (1 - weight) + +So, if the substitution is made: + +period_ema[i] = period_ema[i - 1] * (1 - weight) +period_ema[i] = period_ema[i - 2] * pow((1 - weight) , 2) +period_ema[i] = period_ema[i - 3] * pow((1 - weight) , 3) +period_ema[i] = period_ema[i - 4] * pow((1 - weight) , 4) + +And in a more generic form: + +period_ema[i] = period_ema[i - n] * pow((1 - weight) , n) + +Where n represents the number of iterations to obtain an EMA value. Or in other +words, the number of crashes to detect an attack. + +So, if we isolate the number of crashes: + +period_ema[i] / period_ema[i - n] = pow((1 - weight), n) +log(period_ema[i] / period_ema[i - n]) = log(pow((1 - weight), n)) +log(period_ema[i] / period_ema[i - n]) = n * log(1 - weight) +n = log(period_ema[i] / period_ema[i - n]) / log(1 - weight) + +Then, in the commented scenario (an application has been running without any +crashes for a month), the approximate number of crashes to detect an attack +(using the implementation values for the weight and the crash period threshold) +is: + +weight = 7 / 10 +crash_period_threshold = 30 seconds + +n = log(crash_period_threshold / seconds_per_month) / log(1 - weight) +n = log(30 / (30 * 24 * 3600)) / log(1 - 0.7) +n = 9.44 + +So, with 10 crashes for this scenario an attack will be detected. If these steps +are repeated for different scenarios and the results are collected: + +1 month without any crashes ----> 9.44 crashes to detect an attack +1 year without any crashes -----> 11.50 crashes to detect an attack +10 years without any crashes ---> 13.42 crashes to detect an attack + +However, this computation has a drawback. The first data added to the EMA not +obtains a real average showing a trend. So the solution is simple, the EMA needs +a minimum number of data to be able to be interpreted. This way, the case where +a few first faults are fast enough followed by no crashes is avoided. + +Per system enabling/disabling +----------------------------- + +This feature can be enabled at build time using the CONFIG_SECURITY_FORK_BRUTE +option or using the visual config application under the following menu: + +Security options ---> Fork brute force attack detection and mitigation + +Also, at boot time, this feature can be disable too, by changing the "lsm=" boot +parameter. + +Kernel selftests +---------------- + +To validate all the expectations about this implementation, there is a set of +selftests. This tests cover fork/exec brute force attacks crossing the following +privilege boundaries: + +1.- setuid process +2.- privilege changes +3.- network to local + +Also, there are some tests to check that fork/exec brute force attacks without +crossing any privilege boundariy already commented doesn't trigger the detection +and mitigation stage. + +To build the tests: +make -C tools/testing/selftests/ TARGETS=brute + +To run the tests: +make -C tools/testing/selftests TARGETS=brute run_tests + +To package the tests: +make -C tools/testing/selftests TARGETS=brute gen_tar diff --git a/Documentation/admin-guide/LSM/index.rst b/Documentation/admin-guide/LSM/index.rst index a6ba95fbaa9f..1f68982bb330 100644 --- a/Documentation/admin-guide/LSM/index.rst +++ b/Documentation/admin-guide/LSM/index.rst @@ -41,6 +41,7 @@ subdirectories. :maxdepth: 1 apparmor + Brute LoadPin SELinux Smack diff --git a/security/brute/Kconfig b/security/brute/Kconfig index 1bd2df1e2dec..334d7e88d27f 100644 --- a/security/brute/Kconfig +++ b/security/brute/Kconfig @@ -7,6 +7,7 @@ config SECURITY_FORK_BRUTE vulnerable userspace processes. The detection method is based on the application crash period and as a mitigation procedure all the offending tasks are killed. Like capabilities, this security module - stacks with other LSMs. + stacks with other LSMs. Further information can be found in + Documentation/admin-guide/LSM/Brute.rst. If you are unsure how to answer this question, answer N. From patchwork Sun Mar 7 11:30:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 395730 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C25BC433DB for ; Sun, 7 Mar 2021 14:26:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3CD7D650FC for ; Sun, 7 Mar 2021 14:26:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229950AbhCGO0Z (ORCPT ); Sun, 7 Mar 2021 09:26:25 -0500 Received: from mout.gmx.net ([212.227.17.21]:46477 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229960AbhCGO0A (ORCPT ); Sun, 7 Mar 2021 09:26:00 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1615127129; bh=fQX81Of9P558A+iW5ccipb7QmmQldM7xCcBpY9SL5ME=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=JcV9o1aAX1TZ0UNvRSkCxkJT9+7HBfF8fGe3HXMAoOYz/kVBKmJE7x2Dku7rqIuiP aHF0Wzb8PSPOLCLgvKCNgydozo8kfMi5RTMubetRFHsg/Qp/ghR3FXcJBU7JL5D9QR UJSoaT80+nagP5Z/XjVJ8gvxZOhlRSx6SwN3lrYs= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from localhost.localdomain ([83.52.229.153]) by mail.gmx.net (mrgmx104 [212.227.17.174]) with ESMTPSA (Nemesis) id 1MzQgC-1leiYC2bQ0-00vNTO; Sun, 07 Mar 2021 15:25:28 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , Andi Kleen , kernel test robot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v6 8/8] MAINTAINERS: Add a new entry for the Brute LSM Date: Sun, 7 Mar 2021 12:30:31 +0100 Message-Id: <20210307113031.11671-9-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210307113031.11671-1-john.wood@gmx.com> References: <20210307113031.11671-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:92T2xSso/iqnFhtuivLc6H+ad35shneVfp1UrybbP/Im+3YKN1F Nk/9E7+dJeILbl55LIx2eyEl01qi1fhQmD2HJq7R5CvHTdFbaYKt6no4Q68dQ47GgY4MsdZ 1vXzT7Q98HnOEBuTcvKDHqx8r6NjRjQiK/1PNH51ZVcX4l4MgTF77dJjUs8ffI8uK07kERm R0ld+fw4y0HIy3Kci58Xg== X-UI-Out-Filterresults: notjunk:1; V03:K0:UqIghxRRgYU=:wfvvziITSMY1VJyeBqqnaG G48S/wskeSQe9mTR0rxB/3lmVUp4vSGlgy3jZP0haDRKwz9pcHlYOMmOwI6kXugpcH2U87fGV 17AD3cgcVhug/X23JOw0CU/9BuB7VEgV7uHQ2yr/ZEWhmpt7sPmrqBddN7Veojmc2JnxxMw4X eow7YOm7h/BQSOay4lJesnGNtmsN4rau1MwNK2Y+dX52jElFiR2yVK/qZx43xxx0GlI7Q1AhU Y2ZS5PRXRCnvmYul2dFm8tNwFBk6EwMVvDa5z3xTF5QGsJt9n2TA9eT3hD/EMY1op4pWZ4/IP 4+akzd3sCCOv2ZKyiuC5qv0E9IiWFCGHLVH5c1p/zvLSHsFvVYJ3UQoCpreuTJ4d+Swv2nMeW Pbv/nI6CyyCn/ioZaFXhQogNnJ8x8frpjGee/OJz9CLtsPc6XmdMiY6VEqIAu5IFILs11qR/0 N0S1pnLwHN+7sdrvnX1wk0pkl96BU7CsZCZAMBJeFnT/oNqtKbQ+yArIm04iekky7YRE8ulzO cfVGf74agXwMFmNs0671O2FIAx82CaP8Z99i/CRprRJX/v3xkXOiTWNAALARJxCDxrBdKHFzW 7oG2HYLsL+q5whZjfadMsEfKyTNznb1F5GQoJfHSnwHArMon2q/b8Mf40mRzAcj2PC4SP+2Tg Cu43uOdiiJbD7AA6Mz7bMz17375khYdXty5F2xNryTFZBcgnMow5BSuSJCaAH8SfnymOCqwUm g0rShLIdRG8ZsCEqAIsdzodZE4tOjzOQjMmtXXmCgAxl5D7EXoYrkaDFa5w7/p5NLvewjgp91 owuoARapvVS4G1gPeZi6Ih7i6YnDAzz7LunJSt/8HmjBo7XJe1pj7PmNqsw5GqaJUxvBB/fo3 Pr9b2F2RIr8isgnwPvBw== Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org In order to maintain the code for the Brute LSM add a new entry to the maintainers list. Signed-off-by: John Wood --- MAINTAINERS | 7 +++++++ 1 file changed, 7 insertions(+) -- 2.25.1 diff --git a/MAINTAINERS b/MAINTAINERS index d92f85ca831d..0b88b7a99991 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3764,6 +3764,13 @@ L: netdev@vger.kernel.org S: Supported F: drivers/net/ethernet/brocade/bna/ +BRUTE SECURITY MODULE +M: John Wood +S: Maintained +F: Documentation/admin-guide/LSM/Brute.rst +F: security/brute/ +F: tools/testing/selftests/brute/ + BSG (block layer generic sg v4 driver) M: FUJITA Tomonori L: linux-scsi@vger.kernel.org