linux-kernel - Re: [syzbot] [exfat?] [ocfs2?] kernel BUG in link_path

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Message-ID: <CAGudoHE0Q-Loi_rsbk5rnzgtGfbvY+Fpo9g=NPJHqLP5G_AaUg@mail.gmail.com>
Date: Thu, 4 Dec 2025 08:45:08 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: syzbot <syzbot+d222f4b7129379c3d5bc@...kaller.appspotmail.com>
Cc: brauner@...nel.org, jack@...e.cz, jlbec@...lplan.org, 
	joseph.qi@...ux.alibaba.com, linkinjeon@...nel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, mark@...heh.com, 
	ocfs2-devel@...ts.linux.dev, sj1557.seo@...sung.com, 
	syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [syzbot] [exfat?] [ocfs2?] kernel BUG in link_path_walk

On Thu, Dec 4, 2025 at 2:21 AM syzbot
<syzbot+d222f4b7129379c3d5bc@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> kernel BUG in link_path_walk
>
> (syz.0.73,6964,1):ocfs2_find_entry_id:420 ERROR: status = -30
> ------------[ cut here ]------------
> kernel BUG at fs/namei.c:2532!

On the commit syzbot is testing on (b2c27842) and with the patch, the
triggered assert is the second one on S_ISDIR:
       VFS_BUG_ON(!d_can_lookup(nd->path.dentry));
       VFS_BUG_ON(!S_ISDIR(nd->path.dentry->d_inode->i_mode));

d_can_lookup is  __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;

Or to put it differently, lookup got entered with a bogus state of a
dentry claiming it is a directory, with an inode which is not. Per the
i_mode reported in the opening mail it is a regular file instead.

While I don't see how this can happen, I don't think it is *my* bug
either -- merely nothing else asserted on the 2 things being in
tandem.

syzbot likes to operate on corrupted filesystems, so I'm going to
assume things are going haywire in ocfs2 until proven otherwise.

> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
> CPU: 1 UID: 0 PID: 6964 Comm: syz.0.73 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
> RIP: 0010:link_path_walk+0x1a57/0x1a90 fs/namei.c:2532
> Code: 89 e9 80 e1 07 fe c1 38 c1 0f 8c be fd ff ff 4c 89 ef e8 2c e5 e9 ff e9 b1 fd ff ff e8 62 90 83 ff 90 0f 0b e8 5a 90 83 ff 90 <0f> 0b e8 52 90 83 ff 90 0f 0b e8 4a 90 83 ff 4c 89 ff 48 c7 c6 40
> RSP: 0018:ffffc9000491f8a0 EFLAGS: 00010293
> RAX: ffffffff823e22d6 RBX: dffffc0000000000 RCX: ffff8880250f3d00
> RDX: 0000000000000000 RSI: 0000000000008000 RDI: 0000000000004000
> RBP: ffff888079181120 R08: ffff8880299ef520 R09: ffff88807acd2000
> R10: ffff8880299ef520 R11: ffff88807acd2000 R12: ffffc9000491fc58
> R13: ffffc9000491fc28 R14: 0000000000008000 R15: 0000000000100000
> FS:  00007ff92e2e36c0(0000) GS:ffff888125f49000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000555575344808 CR3: 0000000025c92000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  path_openat+0x2b3/0x3dd0 fs/namei.c:4787
>  do_filp_open+0x1fa/0x410 fs/namei.c:4818
>  do_sys_openat2+0x121/0x200 fs/open.c:1430
>  do_sys_open fs/open.c:1436 [inline]
>  __do_sys_open fs/open.c:1444 [inline]
>  __se_sys_open fs/open.c:1440 [inline]
>  __x64_sys_open+0x11e/0x150 fs/open.c:1440
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7ff92d38f749
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ff92e2e3038 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
> RAX: ffffffffffffffda RBX: 00007ff92d5e5fa0 RCX: 00007ff92d38f749
> RDX: 0000000000000000 RSI: 0000000000145142 RDI: 0000200000000240
> RBP: 00007ff92d413f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007ff92d5e6038 R14: 00007ff92d5e5fa0 R15: 00007ffda4bd0278
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:link_path_walk+0x1a57/0x1a90 fs/namei.c:2532
> Code: 89 e9 80 e1 07 fe c1 38 c1 0f 8c be fd ff ff 4c 89 ef e8 2c e5 e9 ff e9 b1 fd ff ff e8 62 90 83 ff 90 0f 0b e8 5a 90 83 ff 90 <0f> 0b e8 52 90 83 ff 90 0f 0b e8 4a 90 83 ff 4c 89 ff 48 c7 c6 40
> RSP: 0018:ffffc9000491f8a0 EFLAGS: 00010293
> RAX: ffffffff823e22d6 RBX: dffffc0000000000 RCX: ffff8880250f3d00
> RDX: 0000000000000000 RSI: 0000000000008000 RDI: 0000000000004000
> RBP: ffff888079181120 R08: ffff8880299ef520 R09: ffff88807acd2000
> R10: ffff8880299ef520 R11: ffff88807acd2000 R12: ffffc9000491fc58
> R13: ffffc9000491fc28 R14: 0000000000008000 R15: 0000000000100000
> FS:  00007ff92e2e36c0(0000) GS:ffff888125e49000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f1310116e9c CR3: 0000000025c92000 CR4: 00000000003526f0
>
>
> Tested on:
>
> commit:         b2c27842 Add linux-next specific files for 20251203
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=15d7801a580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=caadf525b0ab8d17
> dashboard link: https://syzkaller.appspot.com/bug?extid=d222f4b7129379c3d5bc
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=1281d4c2580000
>