WARNING in filldir64

WARNING in filldir64

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    43b815c6 Merge tag 'armsoc-fixes' of git://git.kernel.org/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10721dfb600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fb0b431ccdf08c1c
dashboard link: https://syzkaller.appspot.com/bug?extid=3031f712c7ad5dd4d926
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+3031f712c7ad5dd4d926@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 1 PID: 10405 at fs/readdir.c:150 verify_dirent_name  
fs/readdir.c:150 [inline]
WARNING: CPU: 1 PID: 10405 at fs/readdir.c:150 filldir64+0x524/0x620  
fs/readdir.c:356
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 10405 Comm: syz-executor.2 Not tainted 5.4.0-rc1+ #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+0x1d8/0x2f8 lib/dump_stack.c:113
  panic+0x25c/0x799 kernel/panic.c:220
  __warn+0x20e/0x210 kernel/panic.c:581
  report_bug+0x1b6/0x2f0 lib/bug.c:195
  fixup_bug arch/x86/kernel/traps.c:179 [inline]
  do_error_trap+0xd7/0x440 arch/x86/kernel/traps.c:272
  do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:291
  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028
RIP: 0010:verify_dirent_name fs/readdir.c:150 [inline]
RIP: 0010:filldir64+0x524/0x620 fs/readdir.c:356
Code: 00 00 c7 03 f2 ff ff ff b8 f2 ff ff ff 48 83 c4 60 5b 41 5c 41 5d 41  
5e 41 5f 5d c3 e8 55 2c b9 ff 0f 0b eb 07 e8 4c 2c b9 ff <0f> 0b 49 83 c6  
24 4c 89 f0 48 c1 e8 03 42 8a 04 20 84 c0 0f 85 b6
RSP: 0018:ffff8880a3dc7b88 EFLAGS: 00010283
RAX: ffffffff81ba0624 RBX: 000000000000000c RCX: 0000000000040000
RDX: ffffc9000a588000 RSI: 00000000000021f1 RDI: 00000000000021f2
RBP: ffff8880a3dc7c10 R08: ffffffff81ba0134 R09: 0000000000000004
R10: fffffbfff1120afb R11: 0000000000000000 R12: dffffc0000000000
R13: ffff8880a3dc7d30 R14: ffff8880a3dc7e88 R15: 000000000000000c
  dir_emit include/linux/fs.h:3542 [inline]
  __fat_readdir+0x1320/0x1a50 fs/fat/dir.c:677
  fat_readdir+0x46/0x50 fs/fat/dir.c:704
  iterate_dir+0x2a4/0x520 fs/readdir.c:107
  ksys_getdents64+0x1ea/0x3f0 fs/readdir.c:412
  __do_sys_getdents64 fs/readdir.c:431 [inline]
  __se_sys_getdents64 fs/readdir.c:428 [inline]
  __x64_sys_getdents64+0x7a/0x90 fs/readdir.c:428
  do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459a59
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f943ff4bc78 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459a59
RDX: 0000000000001000 RSI: 00000000200005c0 RDI: 0000000000000005
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f943ff4c6d4
R13: 00000000004c0533 R14: 00000000004d2c58 R15: 00000000ffffffff
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.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

Re: WARNING in filldir64

[Eric Biggers]

[+Linus]

On Mon, Oct 07, 2019 at 07:30:07AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    43b815c6 Merge tag 'armsoc-fixes' of git://git.kernel.org/..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10721dfb600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fb0b431ccdf08c1c
> dashboard link: https://syzkaller.appspot.com/bug?extid=3031f712c7ad5dd4d926
> 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+3031f712c7ad5dd4d926@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 10405 at fs/readdir.c:150 verify_dirent_name
> fs/readdir.c:150 [inline]
> WARNING: CPU: 1 PID: 10405 at fs/readdir.c:150 filldir64+0x524/0x620
> fs/readdir.c:356
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 10405 Comm: syz-executor.2 Not tainted 5.4.0-rc1+ #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+0x1d8/0x2f8 lib/dump_stack.c:113
>  panic+0x25c/0x799 kernel/panic.c:220
>  __warn+0x20e/0x210 kernel/panic.c:581
>  report_bug+0x1b6/0x2f0 lib/bug.c:195
>  fixup_bug arch/x86/kernel/traps.c:179 [inline]
>  do_error_trap+0xd7/0x440 arch/x86/kernel/traps.c:272
>  do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:291
>  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028
> RIP: 0010:verify_dirent_name fs/readdir.c:150 [inline]
> RIP: 0010:filldir64+0x524/0x620 fs/readdir.c:356
> Code: 00 00 c7 03 f2 ff ff ff b8 f2 ff ff ff 48 83 c4 60 5b 41 5c 41 5d 41
> 5e 41 5f 5d c3 e8 55 2c b9 ff 0f 0b eb 07 e8 4c 2c b9 ff <0f> 0b 49 83 c6 24
> 4c 89 f0 48 c1 e8 03 42 8a 04 20 84 c0 0f 85 b6
> RSP: 0018:ffff8880a3dc7b88 EFLAGS: 00010283
> RAX: ffffffff81ba0624 RBX: 000000000000000c RCX: 0000000000040000
> RDX: ffffc9000a588000 RSI: 00000000000021f1 RDI: 00000000000021f2
> RBP: ffff8880a3dc7c10 R08: ffffffff81ba0134 R09: 0000000000000004
> R10: fffffbfff1120afb R11: 0000000000000000 R12: dffffc0000000000
> R13: ffff8880a3dc7d30 R14: ffff8880a3dc7e88 R15: 000000000000000c
>  dir_emit include/linux/fs.h:3542 [inline]
>  __fat_readdir+0x1320/0x1a50 fs/fat/dir.c:677
>  fat_readdir+0x46/0x50 fs/fat/dir.c:704
>  iterate_dir+0x2a4/0x520 fs/readdir.c:107
>  ksys_getdents64+0x1ea/0x3f0 fs/readdir.c:412
>  __do_sys_getdents64 fs/readdir.c:431 [inline]
>  __se_sys_getdents64 fs/readdir.c:428 [inline]
>  __x64_sys_getdents64+0x7a/0x90 fs/readdir.c:428
>  do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x459a59
> Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f943ff4bc78 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459a59
> RDX: 0000000000001000 RSI: 00000000200005c0 RDI: 0000000000000005
> RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f943ff4c6d4
> R13: 00000000004c0533 R14: 00000000004d2c58 R15: 00000000ffffffff
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 

This WARN_ON was added by:

	commit 8a23eb804ca4f2be909e372cf5a9e7b30ae476cd
	Author: Linus Torvalds <torvalds@linux-foundation.org>
	Date:   Sat Oct 5 11:32:52 2019 -0700

	    Make filldir[64]() verify the directory entry filename is valid

Seems this indicates a corrupt filesystem rather than a kernel bug, so using
WARN_ON is not appropriate.  It should either use pr_warn_once(), or be silent.

- Eric

Re: WARNING in filldir64

[Linus Torvalds]

On Mon, Oct 7, 2019 at 12:07 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> Seems this indicates a corrupt filesystem rather than a kernel bug, so using
> WARN_ON is not appropriate.  It should either use pr_warn_once(), or be silent.

I was going to silence it for the actual 5.4 release, but I wanted to
see if anybody actually triggers it.

I didn't really _expect_ it to be triggered, to be honest, so it's
interesting that it did. What is syzbot doing?

If this is syzbot doing filesystem image randomization, then it falls
under "ok, expected, ignore it, we'll silence it for 5.4"

But if it's syzbot doing something else, then it would be interesting
to hear what it's up to.

                Linus

Re: WARNING in filldir64

[Eric Biggers]

On Mon, Oct 07, 2019 at 12:14:33PM -0700, Linus Torvalds wrote:
> On Mon, Oct 7, 2019 at 12:07 PM Eric Biggers <ebiggers@kernel.org> wrote:
> >
> > Seems this indicates a corrupt filesystem rather than a kernel bug, so using
> > WARN_ON is not appropriate.  It should either use pr_warn_once(), or be silent.
> 
> I was going to silence it for the actual 5.4 release, but I wanted to
> see if anybody actually triggers it.
> 
> I didn't really _expect_ it to be triggered, to be honest, so it's
> interesting that it did. What is syzbot doing?
> 
> If this is syzbot doing filesystem image randomization, then it falls
> under "ok, expected, ignore it, we'll silence it for 5.4"
> 
> But if it's syzbot doing something else, then it would be interesting
> to hear what it's up to.
> 

It got there via fat_readdir(), and in the console log there is:

syz_mount_image$vfat(&(0x7f0000000540)='vfat\x00', &(0x7f00000002c0)='./file0\x00', 0x800000000e004, 0x1, &(0x7f0000000140)=[{&(0x7f0000010000)="eb3c906d6b66732e666174000204010002000270fff8", 0x16}], 0x0, 0x0)

So it seems to have generated a corrupt filesystem image and tried to mount it.

- Eric

Re: WARNING in filldir64

[Linus Torvalds]

On Mon, Oct 7, 2019 at 12:19 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> So it seems to have generated a corrupt filesystem image and tried to mount it.

Ok, then everything is working as expected.

Let's ignore the syzbot one for now, and see if some other load triggers this.

             Linus