From patchwork Mon Nov 29 16:43:00 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexander Mikhalitsyn X-Patchwork-Id: 519102 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 40973C433F5 for ; Mon, 29 Nov 2021 16:45:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237317AbhK2Qse (ORCPT ); Mon, 29 Nov 2021 11:48:34 -0500 Received: from relay.sw.ru ([185.231.240.75]:38796 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345295AbhK2Qqd (ORCPT ); Mon, 29 Nov 2021 11:46:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=virtuozzo.com; s=relay; h=MIME-Version:Message-Id:Date:Subject:From: Content-Type; bh=LqDWsTtAP0lDjhAefW3S4qFTwh7myCXnY0NbTQp1WuY=; b=U4XtHXk9ed5y O1DQZgYnmAQ2cMX/5372YhdImSN7ZKNE37DGo/nUrr2alpHt/4wfNSNCGiifYFsAJ1DTtsDOkRtS0 KEvwpwRP5t6XLFILbb8cHW+WHo04lnmK4RktEk1IbWjHHDy7X/QY82RfqdR36yVlRFKXOcYKZ3rBJ jh9zk=; Received: from [10.94.6.52] (helo=dhcp-172-16-24-175.sw.ru) by relay.sw.ru with esmtp (Exim 4.94.2) (envelope-from ) id 1mrjkF-001mzH-GF; Mon, 29 Nov 2021 19:43:11 +0300 From: Alexander Mikhalitsyn To: gregkh@linuxfoundation.org, stable@vger.kernel.org, manfred@colorfullife.com Cc: Alexander Mikhalitsyn , "Eric W. Biederman" , Davidlohr Bueso , Andrei Vagin , Pavel Tikhomirov , Vasily Averin Subject: [PATCH] shm: extend forced shm destroy to support objects from several IPC nses Date: Mon, 29 Nov 2021 19:43:00 +0300 Message-Id: <20211129164300.789517-1-alexander.mikhalitsyn@virtuozzo.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <163758370064179@kroah.com> References: <163758370064179@kroah.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org For 4.4.y: Upstream commit 85b6d24646e4 ("shm: extend forced shm destroy to support objects from several IPC nses") Currently, the exit_shm() function not designed to work properly when task->sysvshm.shm_clist holds shm objects from different IPC namespaces. This is a real pain when sysctl kernel.shm_rmid_forced = 1, because it leads to use-after-free (reproducer exists). This is an attempt to fix the problem by extending exit_shm mechanism to handle shm's destroy from several IPC ns'es. To achieve that we do several things: 1. add a namespace (non-refcounted) pointer to the struct shmid_kernel 2. during new shm object creation (newseg()/shmget syscall) we initialize this pointer by current task IPC ns 3. exit_shm() fully reworked such that it traverses over all shp's in task->sysvshm.shm_clist and gets IPC namespace not from current task as it was before but from shp's object itself, then call shm_destroy(shp, ns). Note: We need to be really careful here, because as it was said before (1), our pointer to IPC ns non-refcnt'ed. To be on the safe side we using special helper get_ipc_ns_not_zero() which allows to get IPC ns refcounter only if IPC ns not in the "state of destruction". Q/A Q: Why can we access shp->ns memory using non-refcounted pointer? A: Because shp object lifetime is always shorther than IPC namespace lifetime, so, if we get shp object from the task->sysvshm.shm_clist while holding task_lock(task) nobody can steal our namespace. Q: Does this patch change semantics of unshare/setns/clone syscalls? A: No. It's just fixes non-covered case when process may leave IPC namespace without getting task->sysvshm.shm_clist list cleaned up. Link: https://lkml.kernel.org/r/67bb03e5-f79c-1815-e2bf-949c67047418@colorfullife.com Link: https://lkml.kernel.org/r/20211109151501.4921-1-manfred@colorfullife.com Fixes: ab602f79915 ("shm: make exit_shm work proportional to task activity") Co-developed-by: Manfred Spraul Signed-off-by: Manfred Spraul Signed-off-by: Alexander Mikhalitsyn Cc: "Eric W. Biederman" Cc: Davidlohr Bueso Cc: Greg KH Cc: Andrei Vagin Cc: Pavel Tikhomirov Cc: Vasily Averin Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/ipc_namespace.h | 15 +++ include/linux/sched.h | 2 +- include/linux/shm.h | 13 ++- ipc/shm.c | 176 +++++++++++++++++++++++++--------- 4 files changed, 159 insertions(+), 47 deletions(-) diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h index 1eee6bcfcf76..cf1a1c126e89 100644 --- a/include/linux/ipc_namespace.h +++ b/include/linux/ipc_namespace.h @@ -123,6 +123,16 @@ static inline struct ipc_namespace *get_ipc_ns(struct ipc_namespace *ns) return ns; } +static inline struct ipc_namespace *get_ipc_ns_not_zero(struct ipc_namespace *ns) +{ + if (ns) { + if (atomic_inc_not_zero(&ns->count)) + return ns; + } + + return NULL; +} + extern void put_ipc_ns(struct ipc_namespace *ns); #else static inline struct ipc_namespace *copy_ipcs(unsigned long flags, @@ -139,6 +149,11 @@ static inline struct ipc_namespace *get_ipc_ns(struct ipc_namespace *ns) return ns; } +static inline struct ipc_namespace *get_ipc_ns_not_zero(struct ipc_namespace *ns) +{ + return ns; +} + static inline void put_ipc_ns(struct ipc_namespace *ns) { } diff --git a/include/linux/sched.h b/include/linux/sched.h index 8c10e97f94fe..eea75f519421 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2792,7 +2792,7 @@ static inline int thread_group_empty(struct task_struct *p) * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring * subscriptions and synchronises with wait4(). Also used in procfs. Also * pins the final release of task.io_context. Also protects ->cpuset and - * ->cgroup.subsys[]. And ->vfork_done. + * ->cgroup.subsys[]. And ->vfork_done. And ->sysvshm.shm_clist. * * Nests both inside and outside of read_lock(&tasklist_lock). * It must not be nested with write_lock_irq(&tasklist_lock), diff --git a/include/linux/shm.h b/include/linux/shm.h index 6fb801686ad6..fbb74824f0df 100644 --- a/include/linux/shm.h +++ b/include/linux/shm.h @@ -19,9 +19,18 @@ struct shmid_kernel /* private to the kernel */ pid_t shm_lprid; struct user_struct *mlock_user; - /* The task created the shm object. NULL if the task is dead. */ + /* + * The task created the shm object, for + * task_lock(shp->shm_creator) + */ struct task_struct *shm_creator; - struct list_head shm_clist; /* list by creator */ + + /* + * List by creator. task_lock(->shm_creator) required for read/write. + * If list_empty(), then the creator is dead already. + */ + struct list_head shm_clist; + struct ipc_namespace *ns; }; /* shm_mode upper byte flags */ diff --git a/ipc/shm.c b/ipc/shm.c index 32974cfe5947..23d5e090271e 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -90,6 +90,7 @@ static void do_shm_rmid(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp) { struct shmid_kernel *shp; shp = container_of(ipcp, struct shmid_kernel, shm_perm); + WARN_ON(ns != shp->ns); if (shp->shm_nattch) { shp->shm_perm.mode |= SHM_DEST; @@ -180,10 +181,43 @@ static void shm_rcu_free(struct rcu_head *head) ipc_rcu_free(head); } -static inline void shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *s) +/* + * It has to be called with shp locked. + * It must be called before ipc_rmid() + */ +static inline void shm_clist_rm(struct shmid_kernel *shp) { - list_del(&s->shm_clist); - ipc_rmid(&shm_ids(ns), &s->shm_perm); + struct task_struct *creator; + + /* ensure that shm_creator does not disappear */ + rcu_read_lock(); + + /* + * A concurrent exit_shm may do a list_del_init() as well. + * Just do nothing if exit_shm already did the work + */ + if (!list_empty(&shp->shm_clist)) { + /* + * shp->shm_creator is guaranteed to be valid *only* + * if shp->shm_clist is not empty. + */ + creator = shp->shm_creator; + + task_lock(creator); + /* + * list_del_init() is a nop if the entry was already removed + * from the list. + */ + list_del_init(&shp->shm_clist); + task_unlock(creator); + } + rcu_read_unlock(); +} + +static inline void shm_rmid(struct shmid_kernel *s) +{ + shm_clist_rm(s); + ipc_rmid(&shm_ids(s->ns), &s->shm_perm); } @@ -238,7 +272,7 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp) shm_file = shp->shm_file; shp->shm_file = NULL; ns->shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT; - shm_rmid(ns, shp); + shm_rmid(shp); shm_unlock(shp); if (!is_file_hugepages(shm_file)) shmem_lock(shm_file, 0, shp->mlock_user); @@ -259,10 +293,10 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp) * * 2) sysctl kernel.shm_rmid_forced is set to 1. */ -static bool shm_may_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp) +static bool shm_may_destroy(struct shmid_kernel *shp) { return (shp->shm_nattch == 0) && - (ns->shm_rmid_forced || + (shp->ns->shm_rmid_forced || (shp->shm_perm.mode & SHM_DEST)); } @@ -293,7 +327,7 @@ static void shm_close(struct vm_area_struct *vma) shp->shm_lprid = task_tgid_vnr(current); shp->shm_dtim = get_seconds(); shp->shm_nattch--; - if (shm_may_destroy(ns, shp)) + if (shm_may_destroy(shp)) shm_destroy(ns, shp); else shm_unlock(shp); @@ -314,10 +348,10 @@ static int shm_try_destroy_orphaned(int id, void *p, void *data) * * As shp->* are changed under rwsem, it's safe to skip shp locking. */ - if (shp->shm_creator != NULL) + if (!list_empty(&shp->shm_clist)) return 0; - if (shm_may_destroy(ns, shp)) { + if (shm_may_destroy(shp)) { shm_lock_by_ptr(shp); shm_destroy(ns, shp); } @@ -335,48 +369,97 @@ void shm_destroy_orphaned(struct ipc_namespace *ns) /* Locking assumes this will only be called with task == current */ void exit_shm(struct task_struct *task) { - struct ipc_namespace *ns = task->nsproxy->ipc_ns; - struct shmid_kernel *shp, *n; + for (;;) { + struct shmid_kernel *shp; + struct ipc_namespace *ns; - if (list_empty(&task->sysvshm.shm_clist)) - return; + task_lock(task); + + if (list_empty(&task->sysvshm.shm_clist)) { + task_unlock(task); + break; + } + + shp = list_first_entry(&task->sysvshm.shm_clist, struct shmid_kernel, + shm_clist); - /* - * If kernel.shm_rmid_forced is not set then only keep track of - * which shmids are orphaned, so that a later set of the sysctl - * can clean them up. - */ - if (!ns->shm_rmid_forced) { - down_read(&shm_ids(ns).rwsem); - list_for_each_entry(shp, &task->sysvshm.shm_clist, shm_clist) - shp->shm_creator = NULL; /* - * Only under read lock but we are only called on current - * so no entry on the list will be shared. + * 1) Get pointer to the ipc namespace. It is worth to say + * that this pointer is guaranteed to be valid because + * shp lifetime is always shorter than namespace lifetime + * in which shp lives. + * We taken task_lock it means that shp won't be freed. */ - list_del(&task->sysvshm.shm_clist); - up_read(&shm_ids(ns).rwsem); - return; - } + ns = shp->ns; - /* - * Destroy all already created segments, that were not yet mapped, - * and mark any mapped as orphan to cover the sysctl toggling. - * Destroy is skipped if shm_may_destroy() returns false. - */ - down_write(&shm_ids(ns).rwsem); - list_for_each_entry_safe(shp, n, &task->sysvshm.shm_clist, shm_clist) { - shp->shm_creator = NULL; + /* + * 2) If kernel.shm_rmid_forced is not set then only keep track of + * which shmids are orphaned, so that a later set of the sysctl + * can clean them up. + */ + if (!ns->shm_rmid_forced) + goto unlink_continue; - if (shm_may_destroy(ns, shp)) { - shm_lock_by_ptr(shp); - shm_destroy(ns, shp); + /* + * 3) get a reference to the namespace. + * The refcount could be already 0. If it is 0, then + * the shm objects will be free by free_ipc_work(). + */ + ns = get_ipc_ns_not_zero(ns); + if (!ns) { +unlink_continue: + list_del_init(&shp->shm_clist); + task_unlock(task); + continue; } - } - /* Remove the list head from any segments still attached. */ - list_del(&task->sysvshm.shm_clist); - up_write(&shm_ids(ns).rwsem); + /* + * 4) get a reference to shp. + * This cannot fail: shm_clist_rm() is called before + * ipc_rmid(), thus the refcount cannot be 0. + */ + WARN_ON(!ipc_rcu_getref(&shp->shm_perm)); + + /* + * 5) unlink the shm segment from the list of segments + * created by current. + * This must be done last. After unlinking, + * only the refcounts obtained above prevent IPC_RMID + * from destroying the segment or the namespace. + */ + list_del_init(&shp->shm_clist); + + task_unlock(task); + + /* + * 6) we have all references + * Thus lock & if needed destroy shp. + */ + down_write(&shm_ids(ns).rwsem); + shm_lock_by_ptr(shp); + /* + * rcu_read_lock was implicitly taken in shm_lock_by_ptr, it's + * safe to call ipc_rcu_putref here + */ + ipc_rcu_putref(&shp->shm_perm, shm_rcu_free); + + if (ipc_valid_object(&shp->shm_perm)) { + if (shm_may_destroy(shp)) + shm_destroy(ns, shp); + else + shm_unlock(shp); + } else { + /* + * Someone else deleted the shp from namespace + * idr/kht while we have waited. + * Just unlock and continue. + */ + shm_unlock(shp); + } + + up_write(&shm_ids(ns).rwsem); + put_ipc_ns(ns); /* paired with get_ipc_ns_not_zero */ + } } static int shm_fault(struct vm_area_struct *vma, struct vm_fault *vmf) @@ -607,7 +690,11 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params) goto no_id; } + shp->ns = ns; + + task_lock(current); list_add(&shp->shm_clist, ¤t->sysvshm.shm_clist); + task_unlock(current); /* * shmid gets reported as "inode#" in /proc/pid/maps. @@ -1252,7 +1339,8 @@ out_nattch: down_write(&shm_ids(ns).rwsem); shp = shm_lock(ns, shmid); shp->shm_nattch--; - if (shm_may_destroy(ns, shp)) + + if (shm_may_destroy(shp)) shm_destroy(ns, shp); else shm_unlock(shp);