[syzbot] [media?] WARNING: refcount bug in dvb_device_open (3)

[syzbot] [media?] WARNING: refcount bug in dvb_device_open (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    c22e26bd0906 Merge tag 'landlock-7.0-rc1' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=133fa722580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6428d17febdfb14e
dashboard link: https://syzkaller.appspot.com/bug?extid=2e428058cafb408fb695
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b33c549157ca/disk-c22e26bd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/34c7ded19553/vmlinux-c22e26bd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/66faec2158ed/bzImage-c22e26bd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2e428058cafb408fb695@syzkaller.appspotmail.com

netlink: 104 bytes leftover after parsing attributes in process `syz.8.4164'.
------------[ cut here ]------------
refcount_t: saturated; leaking memory.
WARNING: lib/refcount.c:22 at refcount_warn_saturate+0x8c/0x110 lib/refcount.c:22, CPU#0: syz.8.4164/19520
Modules linked in:
CPU: 0 UID: 0 PID: 19520 Comm: syz.8.4164 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:refcount_warn_saturate+0x8c/0x110 lib/refcount.c:22
Code: 75 68 e8 d7 88 2e fd 48 8d 3d d0 b7 be 0a 67 48 0f b9 3a eb 66 85 db 74 3e 83 fb 01 75 4c e8 bb 88 2e fd 48 8d 3d c4 b7 be 0a <67> 48 0f b9 3a eb 4a e8 a8 88 2e fd 48 8d 3d c1 b7 be 0a 67 48 0f
RSP: 0000:ffffc90004a176f8 EFLAGS: 00010287
RAX: ffffffff84948cc5 RBX: 0000000000000001 RCX: 0000000000080000
RDX: ffffc9000f978000 RSI: 00000000000018cb RDI: ffffffff8f534490
RBP: 00000000ffffffff R08: ffff88802cbfbc00 R09: 0000000000000005
R10: 0000000000000100 R11: 0000000000000004 R12: ffff88802b964418
R13: ffffffff9933f940 R14: ffff88802b964410 R15: ffff88802b964400
FS:  00007f7a552556c0(0000) GS:ffff888126595000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c3cfd8b CR3: 000000009f294000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:-1 [inline]
 __refcount_inc include/linux/refcount.h:366 [inline]
 refcount_inc include/linux/refcount.h:383 [inline]
 kref_get include/linux/kref.h:45 [inline]
 dvb_device_get drivers/media/dvb-core/dvbdev.c:624 [inline]
 dvb_device_open+0x31f/0x360 drivers/media/dvb-core/dvbdev.c:106
 chrdev_open+0x4d0/0x5f0 fs/char_dev.c:411
 do_dentry_open+0x83d/0x13e0 fs/open.c:949
 vfs_open+0x3b/0x350 fs/open.c:1081
 do_open fs/namei.c:4671 [inline]
 path_openat+0x2e3d/0x38a0 fs/namei.c:4830
 do_file_open+0x23e/0x4a0 fs/namei.c:4859
 do_sys_openat2+0x113/0x200 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1383
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7a56fdc84e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007f7a55254b28 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f7a552556c0 RCX: 00007f7a56fdc84e
RDX: 0000000000000002 RSI: 00007f7a55254c00 RDI: ffffffffffffff9c
RBP: 00007f7a55254c00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: cccccccccccccccd
R13: 00007f7a57296128 R14: 00007f7a57296090 R15: 00007fff6ac46eb8
 </TASK>
----------------
Code disassembly (best guess):
   0:	75 68                	jne    0x6a
   2:	e8 d7 88 2e fd       	call   0xfd2e88de
   7:	48 8d 3d d0 b7 be 0a 	lea    0xabeb7d0(%rip),%rdi        # 0xabeb7de
   e:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  13:	eb 66                	jmp    0x7b
  15:	85 db                	test   %ebx,%ebx
  17:	74 3e                	je     0x57
  19:	83 fb 01             	cmp    $0x1,%ebx
  1c:	75 4c                	jne    0x6a
  1e:	e8 bb 88 2e fd       	call   0xfd2e88de
  23:	48 8d 3d c4 b7 be 0a 	lea    0xabeb7c4(%rip),%rdi        # 0xabeb7ee
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 4a                	jmp    0x7b
  31:	e8 a8 88 2e fd       	call   0xfd2e88de
  36:	48 8d 3d c1 b7 be 0a 	lea    0xabeb7c1(%rip),%rdi        # 0xabeb7fe
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf


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