Re: [syzbot] KASAN: out-of-bounds Read in do_exit

[Eric W. Biederman]

syzbot <syzbot+b80bbdcca4c4dfaa189e@xxxxxxxxxxxxxxxxxxxxxxxxx> writes:

> Hello,
>
> syzbot found the following issue on:

This looks like dueling debug mechanism.  At a quick glance
stack_no_used is deliberately looking for an uninitialized part of the
stack.

Perhaps the fix is to make KASAN and DEBUG_STACK_USAGE impossible to
select at the same time in Kconfig?

Eric

>
> HEAD commit:    9ed13a17 Merge tag 'net-5.13-rc7' of git://git.kernel.org/..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=116c517bd00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bf635d6d1c7ebabc
> dashboard link: https://syzkaller.appspot.com/bug?extid=b80bbdcca4c4dfaa189e
> compiler:       Debian clang version 11.0.1-2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b80bbdcca4c4dfaa189e@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ==================================================================
> BUG: KASAN: out-of-bounds in stack_not_used include/linux/sched/task_stack.h:101 [inline]
> BUG: KASAN: out-of-bounds in check_stack_usage kernel/exit.c:711 [inline]
> BUG: KASAN: out-of-bounds in do_exit+0x1c6b/0x23d0 kernel/exit.c:869
> Read of size 8 at addr ffffc90017d60400 by task loop0/31717
>
> CPU: 0 PID: 31717 Comm: loop0 Not tainted 5.13.0-rc6-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x202/0x31e lib/dump_stack.c:120
>  print_address_description+0x5f/0x3b0 mm/kasan/report.c:233
>  __kasan_report mm/kasan/report.c:419 [inline]
>  kasan_report+0x15c/0x200 mm/kasan/report.c:436
>  stack_not_used include/linux/sched/task_stack.h:101 [inline]
>  check_stack_usage kernel/exit.c:711 [inline]
>  do_exit+0x1c6b/0x23d0 kernel/exit.c:869
>  kthread+0x3b8/0x3c0 kernel/kthread.c:315
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>
>
> Memory state around the buggy address:
>  ffffc90017d60300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffffc90017d60380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>ffffc90017d60400: 07 07 07 07 07 07 07 07 00 00 00 00 00 00 00 00
>                    ^
>  ffffc90017d60480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffffc90017d60500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ==================================================================
>
>
> ---
> This report 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@xxxxxxxxxxxxxxxx.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.