linux-kernel - Re: [syzbot] [overlayfs?] WARNING in ovl_create

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <CAOQ4uxhMO1kt1aMWcZaUi-AVqWPY=xYEuK_EgmEhvJhG-B9YDQ@mail.gmail.com>
Date: Tue, 20 Jan 2026 13:41:13 +0100
From: Amir Goldstein <amir73il@...il.com>
To: syzbot <syzbot+2214f6a425ea963a605b@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org, 
	miklos@...redi.hu, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [overlayfs?] WARNING in ovl_create_real (4)

On Tue, Jan 20, 2026 at 2:13 AM syzbot
<syzbot+2214f6a425ea963a605b@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    603c05a1639f Merge tag 'nfs-for-6.19-2' of git://git.linux..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17b8339a580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1859476832863c41
> dashboard link: https://syzkaller.appspot.com/bug?extid=2214f6a425ea963a605b
> compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-603c05a1.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/0fd1a1c47d69/vmlinux-603c05a1.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/152f657b1f0a/bzImage-603c05a1.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2214f6a425ea963a605b@...kaller.appspotmail.com
>
> overlayfs: ...falling back to redirect_dir=nofollow.
> overlayfs: ...falling back to index=off.
> overlayfs: ...falling back to uuid=null.
> ------------[ cut here ]------------
> WARNING: fs/overlayfs/dir.c:214 at ovl_create_real+0x9af/0xbd0 fs/overlayfs/dir.c:214, CPU#2: syz.2.9540/3063
> Modules linked in:
> CPU: 2 UID: 0 PID: 3063 Comm: syz.2.9540 Tainted: G             L      syzkaller #0 PREEMPT(full)
> Tainted: [L]=SOFTLOCKUP
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:ovl_create_real+0x9af/0xbd0 fs/overlayfs/dir.c:214
> Code: 8b 48 c7 c7 c8 2b 79 90 e8 1e 42 98 01 44 0f b6 3d 41 5a 31 0d e9 dc fa ff ff e8 fc 05 e1 fe e9 67 f8 ff ff e8 12 2a 77 fe 90 <0f> 0b 90 49 c7 c4 fb ff ff ff e9 ac f8 ff ff 49 c7 c4 fe ff ff ff
> RSP: 0018:ffffc9000518f4b0 EFLAGS: 00010283
> RAX: 000000000001eb61 RBX: ffff88802d846758 RCX: ffffc9002830b000
> RDX: 0000000000080000 RSI: ffffffff8347d1be RDI: 0000000000000005
> RBP: ffff88803bd2f490 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000000 R11: ffff888033102ff0 R12: 0000000000000000
> R13: ffff888034d2a800 R14: ffff88802d8467c0 R15: ffff888035c6e2e0
> FS:  00007f0d6ec506c0(0000) GS:ffff8880d6af2000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b333dcff8 CR3: 000000005d5af000 CR4: 0000000000352ef0
> DR0: ffffffffffffffff DR1: 00000000000001f8 DR2: 0000000000000083
> DR3: ffffffffefffff15 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  ovl_create_temp+0x54/0xb0 fs/overlayfs/dir.c:253
>  ovl_copy_up_workdir fs/overlayfs/copy_up.c:778 [inline]
>  ovl_do_copy_up fs/overlayfs/copy_up.c:988 [inline]
>  ovl_copy_up_one+0xc4e/0x3c40 fs/overlayfs/copy_up.c:1189
>  ovl_copy_up_flags+0x18f/0x240 fs/overlayfs/copy_up.c:1243
>  ovl_rename_start fs/overlayfs/dir.c:1161 [inline]
>  ovl_rename+0x270/0x6b0 fs/overlayfs/dir.c:1348
>  vfs_rename+0x1021/0x2390 fs/namei.c:5938
>  do_renameat2+0x71c/0x9b0 fs/namei.c:6056
>  __do_sys_rename fs/namei.c:6099 [inline]
>  __se_sys_rename fs/namei.c:6097 [inline]
>  __x64_sys_rename+0x7d/0xa0 fs/namei.c:6097
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f0d6dd8f7c9
> 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:00007f0d6ec50038 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
> RAX: ffffffffffffffda RBX: 00007f0d6dfe5fa0 RCX: 00007f0d6dd8f7c9
> RDX: 0000000000000000 RSI: 0000200000000180 RDI: 0000200000000000
> RBP: 00007f0d6de13f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f0d6dfe6038 R14: 00007f0d6dfe5fa0 R15: 00007fffee2fe808
>  </TASK>
>
>
> ---
> This report 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@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report

#syz dup: WARNING in ovl_create_real (3)

Looks like an upper fs which creates a newdentry with NULL d_inode
I think that overlayfs is just the messenger here.

We could maybe remove this WARN_ON if it is not helpful.

Thanks,
Amir.