From mboxrd@z Thu Jan 1 00:00:00 1970 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=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 3DF47C2BA19 for ; Wed, 15 Apr 2020 20:21:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1D1CA2076D for ; Wed, 15 Apr 2020 20:21:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2441996AbgDOUU7 (ORCPT ); Wed, 15 Apr 2020 16:20:59 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:41016 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2437924AbgDOUU4 (ORCPT ); Wed, 15 Apr 2020 16:20:56 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jOoWV-0002mn-Gy; Wed, 15 Apr 2020 14:20:39 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jOoWH-0000TQ-TH; Wed, 15 Apr 2020 14:20:39 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Christian Brauner Cc: syzbot , adobriyan@gmail.com, akpm@linux-foundation.org, avagin@gmail.com, bernd.edlinger@hotmail.de, christian@brauner.io, guro@fb.com, kent.overstreet@gmail.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mhocko@suse.com, syzkaller-bugs@googlegroups.com, tglx@linutronix.de, Alexey Gladkov References: <0000000000001c5eaa05a357f2e1@google.com> <878siwioxj.fsf@x220.int.ebiederm.org> <20200415193612.7cmmbwfpof6pvsqv@wittgenstein> Date: Wed, 15 Apr 2020 15:17:26 -0500 In-Reply-To: <20200415193612.7cmmbwfpof6pvsqv@wittgenstein> (Christian Brauner's message of "Wed, 15 Apr 2020 21:36:12 +0200") Message-ID: <873694ijvt.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1jOoWH-0000TQ-TH;;;mid=<873694ijvt.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18DPCq9Nz2frtDug5iGSOpxqL8ILPXh+aw= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH] proc: Handle umounts cleanly X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christian Brauner writes: > On Wed, Apr 15, 2020 at 01:28:24PM -0500, Eric W. Biederman wrote: >> syzbot writes: >> > KASAN: use-after-free Read in dput (2) >> > >> > proc_fill_super: allocate dentry failed >> > ================================================================== >> > BUG: KASAN: use-after-free in fast_dput fs/dcache.c:727 [inline] >> > BUG: KASAN: use-after-free in dput+0x53e/0xdf0 fs/dcache.c:846 >> > Read of size 4 at addr ffff88808a618cf0 by task syz-executor.0/8426 >> > >> > CPU: 0 PID: 8426 Comm: syz-executor.0 Not tainted 5.6.0-next-20200412-syzkaller #0 >> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 >> > Call Trace: >> > __dump_stack lib/dump_stack.c:77 [inline] >> > dump_stack+0x188/0x20d lib/dump_stack.c:118 >> > print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:382 >> > __kasan_report.cold+0x35/0x4d mm/kasan/report.c:511 >> > kasan_report+0x33/0x50 mm/kasan/common.c:625 >> > fast_dput fs/dcache.c:727 [inline] >> > dput+0x53e/0xdf0 fs/dcache.c:846 >> > proc_kill_sb+0x73/0xf0 fs/proc/root.c:195 >> > deactivate_locked_super+0x8c/0xf0 fs/super.c:335 >> > vfs_get_super+0x258/0x2d0 fs/super.c:1212 >> > vfs_get_tree+0x89/0x2f0 fs/super.c:1547 >> > do_new_mount fs/namespace.c:2813 [inline] >> > do_mount+0x1306/0x1b30 fs/namespace.c:3138 >> > __do_sys_mount fs/namespace.c:3347 [inline] >> > __se_sys_mount fs/namespace.c:3324 [inline] >> > __x64_sys_mount+0x18f/0x230 fs/namespace.c:3324 >> > do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 >> > entry_SYSCALL_64_after_hwframe+0x49/0xb3 >> > RIP: 0033:0x45c889 >> > Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 >> > RSP: 002b:00007ffc1930ec48 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 >> > RAX: ffffffffffffffda RBX: 0000000001324914 RCX: 000000000045c889 >> > RDX: 0000000020000140 RSI: 0000000020000040 RDI: 0000000000000000 >> > RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000 >> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003 >> > R13: 0000000000000749 R14: 00000000004ca15a R15: 0000000000000013 >> >> Looking at the code now that it the internal mount of proc is no >> longer used it is possible to unmount proc. If proc is unmounted >> the fields of the pid namespace that were used for filesystem >> specific state are not reinitialized. >> >> Which means that proc_self and proc_thread_self can be pointers to >> already freed dentries. >> >> The reported user after free appears to be from mounting and >> unmounting proc followed by mounting proc again and using error >> injection to cause the new root dentry allocation to fail. This in >> turn results in proc_kill_sb running with proc_self and >> proc_thread_self still retaining their values from the previous mount >> of proc. Then calling dput on either proc_self of proc_thread_self >> will result in double put. Which KASAN sees as a use after free. >> >> Solve this by always reinitializing the filesystem state stored >> in the struct pid_namespace, when proc is unmounted. >> >> Reported-by: syzbot+72868dd424eb66c6b95f@syzkaller.appspotmail.com >> Fixes: 69879c01a0c3 ("proc: Remove the now unnecessary internal mount of proc") >> Signed-off-by: "Eric W. Biederman" > > Was looking at that earlier right before eod briefly here as well. > Acked-by: Christian Brauner The syzbot report or did you see the failure another way? Eric