Re: kmsan boot error: KMSAN: uninit-value in proc_task_name

[Alexander Potapenko]

On Thu, Dec 5, 2019 at 6:45 AM syzbot
<syzbot+c0d17fd100b00692b701@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    818fcf71 Revert "kmsan: disable strscpy() optimization und..
> git tree:       https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=11b8bb7ae00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fde150fb1e865232
> dashboard link: https://syzkaller.appspot.com/bug?extid=c0d17fd100b00692b701
> compiler:       clang version 9.0.0 (/home/glider/llvm/clang
> 80fee25776c2fb61e74c1ecb1a523375c2500b69)
>
> 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+c0d17fd100b00692b701@xxxxxxxxxxxxxxxxxxxxxxxxx
#syz-fix: kmsan: disable strscpy() optimization under KMSAN

This is a false positive that was accidentally sent upstream.

> =====================================================
> BUG: KMSAN: uninit-value in seq_commit include/linux/seq_file.h:89 [inline]
> BUG: KMSAN: uninit-value in proc_task_name+0x574/0x590 fs/proc/array.c:121
> CPU: 1 PID: 5202 Comm: ps Not tainted 5.4.0-rc8-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+0x1c9/0x220 lib/dump_stack.c:118
>   kmsan_report+0x128/0x220 mm/kmsan/kmsan_report.c:108
>   __msan_warning+0x57/0xa0 mm/kmsan/kmsan_instr.c:245
>   seq_commit include/linux/seq_file.h:89 [inline]
>   proc_task_name+0x574/0x590 fs/proc/array.c:121
>   do_task_stat+0x1a7b/0x3090 fs/proc/array.c:540
>   proc_tgid_stat+0xbe/0xf0 fs/proc/array.c:632
>   proc_single_show+0x1a8/0x2b0 fs/proc/base.c:756
>   seq_read+0xac6/0x1d90 fs/seq_file.c:229
>   __vfs_read+0x1a9/0xc90 fs/read_write.c:425
>   vfs_read+0x359/0x6f0 fs/read_write.c:461
>   ksys_read+0x265/0x430 fs/read_write.c:587
>   __do_sys_read fs/read_write.c:597 [inline]
>   __se_sys_read+0x92/0xb0 fs/read_write.c:595
>   __x64_sys_read+0x4a/0x70 fs/read_write.c:595
>   do_syscall_64+0xb6/0x160 arch/x86/entry/common.c:291
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7fd34fa40310
> Code: 73 01 c3 48 8b 0d 28 4b 2b 00 31 d2 48 29 c2 64 89 11 48 83 c8 ff eb
> ea 90 90 83 3d e5 a2 2b 00 00 75 10 b8 00 00 00 00 0f 05 <48> 3d 01 f0 ff
> ff 73 31 c3 48 83 ec 08 e8 6e 8a 01 00 48 89 04 24
> RSP: 002b:00007ffc157facf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007fd34fa40310
> RDX: 0000000000000fff RSI: 00007fd34ff0dd00 RDI: 0000000000000006
> RBP: 0000000000000fff R08: 0000000000000000 R09: 00007fd34fd08a10
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd34ff0dd00
> R13: 0000000001a59150 R14: 0000000000000005 R15: 0000000000000000
>
> Local variable description: ----tcomm@proc_task_name
> Variable was created at:
>   proc_task_name+0x8d/0x590 fs/proc/array.c:103
>   proc_task_name+0x8d/0x590 fs/proc/array.c:103
> =====================================================
>
>
> ---
> 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@xxxxxxxxxxxxxxxxx
>
> syzbot will keep track of this bug report. See:
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-- 
Alexander Potapenko
Software Engineer

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