WARNING in ovl_rename

WARNING in ovl_rename

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    037904a2 Merge branch 'x86-urgent-for-linus' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11f58ecca00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a42d110b47dd6b36
dashboard link: https://syzkaller.appspot.com/bug?extid=bb1836a212e69f8e201a
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ba097ca00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10be1ceca00000

The bug was bisected to:

commit 6eaf011144af10cad34c0d46f82e50d382c8e926
Author: Amir Goldstein <amir73il@gmail.com>
Date:   Thu Oct 12 16:03:04 2017 +0000

     ovl: fix EIO from lookup of non-indexed upper

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1430a262a00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1630a262a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1230a262a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+bb1836a212e69f8e201a@syzkaller.appspotmail.com
Fixes: 6eaf011144af ("ovl: fix EIO from lookup of non-indexed upper")

overlayfs: workdir and upperdir must reside under the same mount
WARNING: CPU: 0 PID: 8323 at fs/overlayfs/dir.c:1176  
ovl_rename+0x159c/0x1940 fs/overlayfs/dir.c:1176
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 8323 Comm: syz-executor156 Not tainted 5.1.0-rc6+ #89
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+0x172/0x1f0 lib/dump_stack.c:113
  panic+0x2cb/0x65c kernel/panic.c:214
  __warn.cold+0x20/0x45 kernel/panic.c:571
  report_bug+0x263/0x2b0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:179 [inline]
  fixup_bug arch/x86/kernel/traps.c:174 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:ovl_rename+0x159c/0x1940 fs/overlayfs/dir.c:1176
Code: 80 00 00 00 e8 45 f7 19 ff 8b b4 24 80 00 00 00 85 f6 0f 85 cd f6 ff  
ff e8 b1 f5 19 ff 4c 89 f7 e9 a5 f6 ff ff e8 a4 f5 19 ff <0f> 0b e9 a4 f3  
ff ff e8 98 f5 19 ff 48 8b 54 24 70 b8 ff ff 37 00
RSP: 0018:ffff88809366fad8 EFLAGS: 00010293
RAX: ffff88808bb781c0 RBX: 0000000000000000 RCX: ffff888095efc6e0
RDX: 0000000000000000 RSI: ffffffff8256970c RDI: ffff888095efc738
RBP: ffff88809366fbf8 R08: ffff88808bb781c0 R09: 0000000000000008
R10: ffffed1015d05bc7 R11: ffff8880ae82de3b R12: ffff88808b22f160
R13: 0000000000000000 R14: ffff888095efc580 R15: ffff88809366fb90
  vfs_rename+0x803/0x1ac0 fs/namei.c:4475
  do_renameat2+0xb0f/0xc40 fs/namei.c:4625
  __do_sys_rename fs/namei.c:4671 [inline]
  __se_sys_rename fs/namei.c:4669 [inline]
  __x64_sys_rename+0x61/0x80 fs/namei.c:4669
  do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x446d89
Code: e8 ec b9 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 db 06 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8603ed4d98 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
RAX: ffffffffffffffda RBX: 00000000006dcc28 RCX: 0000000000446d89
RDX: 0000000000446d89 RSI: 0000000020000140 RDI: 00000000200000c0
RBP: 00000000006dcc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc2c
R13: 69647265776f6c2c R14: 30656c69662f2e3d R15: 7269647265707075
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot will keep track of this bug report. See:
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: WARNING in ovl_rename

[syzbot]

syzbot suspects this bug was fixed by commit:

commit 146d62e5a5867fbf84490d82455718bfb10fe824
Author: Amir Goldstein <amir73il@gmail.com>
Date:   Thu Apr 18 14:42:08 2019 +0000

     ovl: detect overlapping layers

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=138841dae00000
start commit:   037904a2 Merge branch 'x86-urgent-for-linus' of git://git...
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=a42d110b47dd6b36
dashboard link: https://syzkaller.appspot.com/bug?extid=bb1836a212e69f8e201a
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ba097ca00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10be1ceca00000

If the result looks correct, please mark the bug fixed by replying with:

#syz fix: ovl: detect overlapping layers

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: WARNING in ovl_rename

[Amir Goldstein]

On Fri, Dec 6, 2019 at 3:54 AM syzbot
<syzbot+bb1836a212e69f8e201a@syzkaller.appspotmail.com> wrote:
>
> syzbot suspects this bug was fixed by commit:
>
> commit 146d62e5a5867fbf84490d82455718bfb10fe824
> Author: Amir Goldstein <amir73il@gmail.com>
> Date:   Thu Apr 18 14:42:08 2019 +0000
>
>      ovl: detect overlapping layers
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=138841dae00000
> start commit:   037904a2 Merge branch 'x86-urgent-for-linus' of git://git...
> git tree:       upstream
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a42d110b47dd6b36
> dashboard link: https://syzkaller.appspot.com/bug?extid=bb1836a212e69f8e201a
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ba097ca00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10be1ceca00000
>
> If the result looks correct, please mark the bug fixed by replying with:
>
> #syz fix: ovl: detect overlapping layers
>

Not exactly. Depends how you define "the bug".

The actual bug wasn't introduced by:
     ovl: fix EIO from lookup of non-indexed upper

Nor was it fixed by:
     ovl: detect overlapping layers

It would be more accurate to say that the former commit exposed the bug
to this specific repro and the latter commit has masked it from this repro.

The actual bug was introduced by:
    804032fabb3b ("ovl: don't check rename to self")

Which did not take into account hardlinking underneath overlayfs.

I posted a fix to relax this WARN_ON(), which is marked for stable 4.9+,
because I see that the repro is also reported on kernel 4.14.y and
"ovl: detect overlapping layers" is not expected to land in 4.14.y.

Thanks,
Amir.