From patchwork Thu Apr 16 16:28:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Luis Chamberlain X-Patchwork-Id: 227505 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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham 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 1F03FC2BB55 for ; Thu, 16 Apr 2020 16:29:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB31F206F9 for ; Thu, 16 Apr 2020 16:29:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587054555; bh=u8St400nMjN0sNyN9NH18PmY671N9qxEJ/lckIsz/i8=; h=From:To:Cc:Subject:Date:List-ID:From; b=qQjB9djvXPecLdvJgQL4Ey25qaRHRNjqEhzKY/qR18idIOIIcijZzeKho8EHsLxPL m/O7rphoC5dIOQNbLmOZRw0G66+BqGeTo0vVOf8rihuteiBtAkOwAsoTBQFHUmU6WP EEIrc+ZJ5Sb/jYTS+iiZ2xmXRy0UUTPuaNXRoXnA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389153AbgDPQ3N (ORCPT ); Thu, 16 Apr 2020 12:29:13 -0400 Received: from mail-pj1-f65.google.com ([209.85.216.65]:35520 "EHLO mail-pj1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733145AbgDPQ3L (ORCPT ); Thu, 16 Apr 2020 12:29:11 -0400 Received: by mail-pj1-f65.google.com with SMTP id ms17so578467pjb.0; Thu, 16 Apr 2020 09:29:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=DDeQhmuGsl8P+DilsgHCEUTImjUmWGBw1IP6hd63Tjk=; b=Crv61j+wqF1+7jHShJqfAnBSaKoLv586kb+csDCIeCpIJnuFXcrCiiXob8iKKnAI1n JfxrokzsnVZ6NHK6vcm8ZrtLzoYXse3V160R3mtatfiAeAJ9a3krYKd4VoHnY1r9uitp 3FXTsRmz7InZ8RIhInwgc0LSkkLM03vPsK5L6zoN2LPUG9LJgO7yHLv9sPVtZ/WJRYkh lAgeDmZw2V+rqjxrNgDuvTzDECt3FO8z9o/uoiBf0fC8OIKROQhxvAoWqLGJb1oFwQQd LobQ4FEyWGhRjGsUatdJzF4/N+/1f0ka/L8ffJFdmbeKDBsytGsTB22MBFpp+kcWA6IN YXsQ== X-Gm-Message-State: AGi0PuYrS5FDvo3nww/EegfO25Q0XH0IFKkZOcEh2xBucigdl9Jo1cW0 V94fV26MNxriXEWaktzIxuc= X-Google-Smtp-Source: APiQypIE3NnhVIIWmHInD6C3QjxS21/kjvOOYBbRR6eRrmBzANsib0A8qE0C3s1Dbtoni/H9AWpWyg== X-Received: by 2002:a17:90a:32ea:: with SMTP id l97mr6067769pjb.50.1587054547892; Thu, 16 Apr 2020 09:29:07 -0700 (PDT) Received: from 42.do-not-panic.com (42.do-not-panic.com. [157.230.128.187]) by smtp.gmail.com with ESMTPSA id r16sm2590313pfl.176.2020.04.16.09.29.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Apr 2020 09:29:06 -0700 (PDT) Received: by 42.do-not-panic.com (Postfix, from userid 1000) id 10AAF40277; Thu, 16 Apr 2020 16:29:06 +0000 (UTC) From: "Luis R. Rodriguez" To: gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk Cc: slyfox@gentoo.org, ast@kernel.org, keescook@chromium.org, josh@joshtriplett.org, ravenexp@gmail.com, chainsaw@gentoo.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Luis Chamberlain , stable@vger.kernel.org Subject: [PATCH] coredump: fix crash when umh is disabled Date: Thu, 16 Apr 2020 16:28:59 +0000 Message-Id: <20200416162859.26518-1-mcgrof@kernel.org> X-Mailer: git-send-email 2.23.0.rc1 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Luis Chamberlain Commit 64e90a8acb859 ("Introduce STATIC_USERMODEHELPER to mediate call_usermodehelper()") added the optiont to disable all call_usermodehelper() calls by setting STATIC_USERMODEHELPER_PATH to an empty string. When this is done, and crashdump is triggered, it will crash on null pointer dereference, since we make assumptions over what call_usermodehelper_exec() did. This has been reported by Sergey when one triggers a a coredump with the following configuration: ``` CONFIG_STATIC_USERMODEHELPER=y CONFIG_STATIC_USERMODEHELPER_PATH="" kernel.core_pattern = |/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h %e ``` The way disabling the umh was designed was that call_usermodehelper_exec() would just return early, without an error. But coredump assumes certain variables are set up for us when this happens, and calls ile_start_write(cprm.file) with a NULL file. [ 2.819676] BUG: kernel NULL pointer dereference, address: 0000000000000020 [ 2.819859] #PF: supervisor read access in kernel mode [ 2.820035] #PF: error_code(0x0000) - not-present page [ 2.820188] PGD 0 P4D 0 [ 2.820305] Oops: 0000 [#1] SMP PTI [ 2.820436] CPU: 2 PID: 89 Comm: a Not tainted 5.7.0-rc1+ #7 [ 2.820680] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190711_202441-buildvm-armv7-10.arm.fedoraproject.org-2.fc31 04/01/2014 [ 2.821150] RIP: 0010:do_coredump+0xd80/0x1060 [ 2.821385] Code: e8 95 11 ed ff 48 c7 c6 cc a7 b4 81 48 8d bd 28 ff ff ff 89 c2 e8 70 f1 ff ff 41 89 c2 85 c0 0f 84 72 f7 ff ff e9 b4 fe ff ff <48> 8b 57 20 0f b7 02 66 25 00 f0 66 3d 00 8 0 0f 84 9c 01 00 00 44 [ 2.822014] RSP: 0000:ffffc9000029bcb8 EFLAGS: 00010246 [ 2.822339] RAX: 0000000000000000 RBX: ffff88803f860000 RCX: 000000000000000a [ 2.822746] RDX: 0000000000000009 RSI: 0000000000000282 RDI: 0000000000000000 [ 2.823141] RBP: ffffc9000029bde8 R08: 0000000000000000 R09: ffffc9000029bc00 [ 2.823508] R10: 0000000000000001 R11: ffff88803dec90be R12: ffffffff81c39da0 [ 2.823902] R13: ffff88803de84400 R14: 0000000000000000 R15: 0000000000000000 [ 2.824285] FS: 00007fee08183540(0000) GS:ffff88803e480000(0000) knlGS:0000000000000000 [ 2.824767] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2.825111] CR2: 0000000000000020 CR3: 000000003f856005 CR4: 0000000000060ea0 [ 2.825479] Call Trace: [ 2.825790] get_signal+0x11e/0x720 [ 2.826087] do_signal+0x1d/0x670 [ 2.826361] ? force_sig_info_to_task+0xc1/0xf0 [ 2.826691] ? force_sig_fault+0x3c/0x40 [ 2.826996] ? do_trap+0xc9/0x100 [ 2.827179] exit_to_usermode_loop+0x49/0x90 [ 2.827359] prepare_exit_to_usermode+0x77/0xb0 [ 2.827559] ? invalid_op+0xa/0x30 [ 2.827747] ret_from_intr+0x20/0x20 [ 2.827921] RIP: 0033:0x55e2c76d2129 [ 2.828107] Code: 2d ff ff ff e8 68 ff ff ff 5d c6 05 18 2f 00 00 01 c3 0f 1f 80 00 00 00 00 c3 0f 1f 80 00 00 00 00 e9 7b ff ff ff 55 48 89 e5 <0f> 0b b8 00 00 00 00 5d c3 66 2e 0f 1f 84 0 0 00 00 00 00 0f 1f 40 [ 2.828603] RSP: 002b:00007fffeba5e080 EFLAGS: 00010246 [ 2.828801] RAX: 000055e2c76d2125 RBX: 0000000000000000 RCX: 00007fee0817c718 [ 2.829034] RDX: 00007fffeba5e188 RSI: 00007fffeba5e178 RDI: 0000000000000001 [ 2.829257] RBP: 00007fffeba5e080 R08: 0000000000000000 R09: 00007fee08193c00 [ 2.829482] R10: 0000000000000009 R11: 0000000000000000 R12: 000055e2c76d2040 [ 2.829727] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 [ 2.829964] CR2: 0000000000000020 [ 2.830149] ---[ end trace ceed83d8c68a1bf1 ]--- ``` Cc: # v4.11+ Fixes: 64e90a8acb859 ("Introduce STATIC_USERMODEHELPER to mediate call_usermodehelper()") BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=199795 Reported-by: Tony Vroon Reported-by: Sergey Kvachonok Tested-by: Sergei Trofimovich Signed-off-by: Luis Chamberlain --- fs/coredump.c | 8 ++++++++ kernel/umh.c | 5 +++++ 2 files changed, 13 insertions(+) diff --git a/fs/coredump.c b/fs/coredump.c index f8296a82d01d..c92074fb152d 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -786,6 +786,14 @@ void do_coredump(const kernel_siginfo_t *siginfo) if (displaced) put_files_struct(displaced); if (!dump_interrupted()) { + /* + * umh disabled with CONFIG_STATIC_USERMODEHELPER_PATH="" would + * have this set to NULL. + */ + if (!cprm.file) { + pr_info("Core dump to |%s disabled\n", cn.corename); + goto close_fail; + } file_start_write(cprm.file); core_dumped = binfmt->core_dump(&cprm); file_end_write(cprm.file); diff --git a/kernel/umh.c b/kernel/umh.c index 7f255b5a8845..11bf5eea474c 100644 --- a/kernel/umh.c +++ b/kernel/umh.c @@ -544,6 +544,11 @@ EXPORT_SYMBOL_GPL(fork_usermode_blob); * Runs a user-space application. The application is started * asynchronously if wait is not set, and runs as a child of system workqueues. * (ie. it runs with full root capabilities and optimized affinity). + * + * Note: successful return value does not guarantee the helper was called at + * all. You can't rely on sub_info->{init,cleanup} being called even for + * UMH_WAIT_* wait modes as STATIC_USERMODEHELPER_PATH="" turns all helpers + * into a successful no-op. */ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait) {