[moderation] [media?] WARNING: kobject bug in v4l2_open

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e98d21c170b0 Add linux-next specific files for 20260508
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17f740ec580000
kernel config: https://syzkaller.appspot.com/x/.config?x=76d40e8423bfbf00
dashboard link: https://syzkaller.appspot.com/bug?extid=cf28ffddd0e9a2dd7d89
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [linux-...@vger.kernel.org linux...@vger.kernel.org mch...@kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d6f17cfff258/disk-e98d21c1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e6a9264935ba/vmlinux-e98d21c1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dae7a84315a9/bzImage-e98d21c1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cf28ff...@syzkaller.appspotmail.com

------------[ cut here ]------------
kobject: '(null)' (ffff8880554282f0): is not initialized, yet kobject_put() is being called.
WARNING: lib/kobject.c:736 at kobject_put+0x66/0x560 lib/kobject.c:734, CPU#1: v4l_id/11606
Modules linked in:
CPU: 1 UID: 0 PID: 11606 Comm: v4l_id Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:kobject_put+0x8e/0x560 lib/kobject.c:734
Code: 7d 04 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 48 89 df e8 db 63 0f f7 48 8b 33 4c 89 f7 48 89 da <67> 48 0f b9 3a eb 05 e8 c6 c9 a5 f6 4c 8d 73 38 4c 89 f7 be 04 00
RSP: 0018:ffffc900047ef6b8 EFLAGS: 00010246
RAX: 1ffff1100aa8505e RBX: ffff8880554282f0 RCX: dffffc0000000000
RDX: ffff8880554282f0 RSI: 0000000000000000 RDI: ffffffff8f9c65c0
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1f1597f R12: 1ffff1100aa85065
R13: ffff888055428930 R14: ffffffff8f9c65c0 R15: ffff88805542832c
FS: 00007f7774808880(0000) GS:ffff88812601f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6e1bda56b8 CR3: 0000000056c78000 CR4: 00000000003526f0
Call Trace:
<TASK>
video_put drivers/media/v4l2-core/v4l2-dev.c:173 [inline]
v4l2_open+0x269/0x3a0 drivers/media/v4l2-core/v4l2-dev.c:450
chrdev_open+0x4d0/0x5f0 fs/char_dev.c:411
do_dentry_open+0x83d/0x13e0 fs/open.c:947
vfs_open+0x3b/0x350 fs/open.c:1079
do_open fs/namei.c:4699 [inline]
path_openat+0x2e43/0x38a0 fs/namei.c:4858
do_file_open+0x23e/0x4a0 fs/namei.c:4887
do_sys_openat2+0x113/0x200 fs/open.c:1364
do_sys_open fs/open.c:1370 [inline]
__do_sys_openat fs/open.c:1386 [inline]
__se_sys_openat fs/open.c:1381 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1381
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f77748f6407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffe595dc770 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f7774808880 RCX: 00007f77748f6407
RDX: 0000000000000000 RSI: 00007ffe595dcf1b RDI: ffffffffffffff9c
RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007ffe595dc9c0 R14: 00007f777508c000 R15: 000055586421a4d8
</TASK>
----------------
Code disassembly (best guess):
0: 7d 04 jge 0x6
2: 48 89 d8 mov %rbx,%rax
5: 48 c1 e8 03 shr $0x3,%rax
9: 48 b9 00 00 00 00 00 movabs $0xdffffc0000000000,%rcx
10: fc ff df
13: 80 3c 08 00 cmpb $0x0,(%rax,%rcx,1)
17: 74 08 je 0x21
19: 48 89 df mov %rbx,%rdi
1c: e8 db 63 0f f7 call 0xf70f63fc
21: 48 8b 33 mov (%rbx),%rsi
24: 4c 89 f7 mov %r14,%rdi
27: 48 89 da mov %rbx,%rdx
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: eb 05 jmp 0x36
31: e8 c6 c9 a5 f6 call 0xf6a5c9fc
36: 4c 8d 73 38 lea 0x38(%rbx),%r14
3a: 4c 89 f7 mov %r14,%rdi
3d: be .byte 0xbe
3e: 04 00 add $0x0,%al


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