Re: KASAN: stack-out-of-bounds Read in locks_remove_flock

[Dmitry Vyukov]

On Tue, Nov 6, 2018 at 9:03 PM, syzbot
<syzbot+1818cd833edc063452c6@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    d881de30d29e Add linux-next specific files for 20181107
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14aa485d400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=caa433e1c8778437
> dashboard link: https://syzkaller.appspot.com/bug?extid=1818cd833edc063452c6
> compiler:       gcc (GCC) 8.0.1 20180413 (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+1818cd833edc063452c6@xxxxxxxxxxxxxxxxxxxxxxxxx

This is another manifestation of the following report, right?

#syz dup: KASAN: use-after-free Read in locks_delete_block

> ==================================================================
> BUG: KASAN: stack-out-of-bounds in locks_remove_flock+0x33c/0x350
> fs/locks.c:2567
> Read of size 8 at addr ffff8801c71c7a08 by task syz-executor5/20562
>
> CPU: 0 PID: 20562 Comm: syz-executor5 Not tainted 4.20.0-rc1-next-20181107+
> #107
> 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+0x244/0x39d lib/dump_stack.c:113
>  print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>  locks_remove_flock+0x33c/0x350 fs/locks.c:2567
>  locks_remove_file+0x148/0x5c0 fs/locks.c:2607
>  __fput+0x2f0/0xa70 fs/file_table.c:271
>  ____fput+0x15/0x20 fs/file_table.c:312
>  task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>  exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
>  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>  do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x411021
> Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 34 19 00 00 c3 48
> 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89
> c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
> RSP: 002b:00007ffdb42509a0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 0000000000000005 RCX: 0000000000411021
> RDX: 0000000000000000 RSI: 0000000000732ea0 RDI: 0000000000000004
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 00007ffdb42508c0 R11: 0000000000000293 R12: 0000000000000000
> R13: 0000000000000001 R14: 0000000000000201 R15: 0000000000000005
>
> The buggy address belongs to the page:
> page:ffffea00071c71c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
> flags: 0x2fffc0000000000()
> raw: 02fffc0000000000 0000000000000000 ffffffff071c0101 0000000000000000
> raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff8801c71c7900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff8801c71c7980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>
>> ffff8801c71c7a00: f2 f2 f2 00 00 00 00 00 00 00 00 00 00 00 00 00
>
>                       ^
>  ffff8801c71c7a80: 00 f1 f1 f1 f1 00 00 f2 f2 f2 f2 f2 f2 f8 f2 f2
>  ffff8801c71c7b00: f2 f2 f2 f2 f2 00 f2 f2 f2 00 00 00 00 00 00 00
> ==================================================================
>
>
> ---
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