linux-kernel - Re: KCSAN: data-race in common_perm_cond / task_dump

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Message-ID: <CACT4Y+Y0W9Zm6Re6jC9f59Rm=f7P-dKtE-OUCAOD0ubwPZA_Uw@mail.gmail.com>
Date:   Thu, 24 Oct 2019 10:34:12 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+109584edb0b8511d7dad@...kaller.appspotmail.com>
Cc:     Marco Elver <elver@...gle.com>, James Morris <jmorris@...ei.org>,
        John Johansen <john.johansen@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: KCSAN: data-race in common_perm_cond / task_dump_owner

On Thu, Oct 24, 2019 at 9:30 AM syzbot
<syzbot+109584edb0b8511d7dad@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    05f22368 x86, kcsan: Enable KCSAN for x86
> git tree:       https://github.com/google/ktsan.git kcsan
> console output: https://syzkaller.appspot.com/x/log.txt?x=155db950e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
> dashboard link: https://syzkaller.appspot.com/bug?extid=109584edb0b8511d7dad
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+109584edb0b8511d7dad@...kaller.appspotmail.com

This may be pretty bad if I am not missing something, see:
https://groups.google.com/d/msg/syzkaller-bugs/mzwiXt4ml68/GuAUQrWtBQAJ

> ==================================================================
> BUG: KCSAN: data-race in common_perm_cond / task_dump_owner
>
> read to 0xffff888124ca931c of 4 bytes by task 7605 on cpu 0:
>   common_perm_cond+0x65/0x110 security/apparmor/lsm.c:217
>   apparmor_inode_getattr+0x2b/0x40 security/apparmor/lsm.c:389
>   security_inode_getattr+0x9b/0xd0 security/security.c:1222
>   vfs_getattr+0x2e/0x70 fs/stat.c:115
>   vfs_statx+0x102/0x190 fs/stat.c:191
>   vfs_stat include/linux/fs.h:3242 [inline]
>   __do_sys_newstat+0x51/0xb0 fs/stat.c:341
>   __se_sys_newstat fs/stat.c:337 [inline]
>   __x64_sys_newstat+0x3a/0x50 fs/stat.c:337
>   do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> write to 0xffff888124ca931c of 4 bytes by task 7608 on cpu 1:
>   task_dump_owner+0xd8/0x260 fs/proc/base.c:1742
>   pid_update_inode+0x3c/0x70 fs/proc/base.c:1818
>   pid_revalidate+0x91/0xd0 fs/proc/base.c:1841
>   d_revalidate fs/namei.c:758 [inline]
>   d_revalidate fs/namei.c:755 [inline]
>   lookup_fast+0x6f2/0x700 fs/namei.c:1607
>   walk_component+0x6d/0xe80 fs/namei.c:1796
>   link_path_walk.part.0+0x5d3/0xa90 fs/namei.c:2131
>   link_path_walk fs/namei.c:2062 [inline]
>   path_openat+0x14f/0x36e0 fs/namei.c:3524
>   do_filp_open+0x11e/0x1b0 fs/namei.c:3555
>   do_sys_open+0x3b3/0x4f0 fs/open.c:1097
>   __do_sys_open fs/open.c:1115 [inline]
>   __se_sys_open fs/open.c:1110 [inline]
>   __x64_sys_open+0x55/0x70 fs/open.c:1110
>   do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 7608 Comm: ps Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
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