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@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ 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@xxxxxxxxxxxxxxxxxxxx>
	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