[v6.1] WARNING: refcount bug in dvb_device_open

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ad16b162f21d Linux 6.1.172
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10d77bce580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0605c5af04d7603
dashboard link: https://syzkaller.appspot.com/bug?extid=118d909b3c98fda97c46
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/2188b271cf45/disk-ad16b162.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/356336b9737c/vmlinux-ad16b162.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3453b10f11f7/bzImage-ad16b162.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+118d90...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: saturated; leaking memory.
WARNING: CPU: 0 PID: 11783 at lib/refcount.c:22 refcount_warn_saturate+0x153/0x1a0 lib/refcount.c:22
Modules linked in:
CPU: 0 PID: 11783 Comm: syz.4.1575 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:refcount_warn_saturate+0x153/0x1a0 lib/refcount.c:22
Code: 09 01 48 c7 c7 40 cf de 8a e8 79 a1 3c fd 0f 0b eb 8c e8 90 31 71 fd c6 05 3e 46 fa 09 01 48 c7 c7 40 cf de 8a e8 5d a1 3c fd <0f> 0b e9 6d ff ff ff e8 71 31 71 fd c6 05 23 46 fa 09 01 48 c7 c7
RSP: 0018:ffffc90003917798 EFLAGS: 00010246
RAX: 0bd63ac84f448c00 RBX: 0000000000000001 RCX: 0000000000080000
RDX: ffffc900106a0000 RSI: 0000000000003749 RDI: 000000000000374a
RBP: 00000000ffffffff R08: ffffc90003917427 R09: 1ffff92000722e84
R10: dffffc0000000000 R11: fffff52000722e85 R12: ffff888142279e18
R13: ffffffff96c53860 R14: 0000000000000001 R15: ffff888142279e00
FS: 00007f5591cfa6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5590d85f40 CR3: 0000000038c6a000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__refcount_add include/linux/refcount.h:-1 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
kref_get include/linux/kref.h:45 [inline]
dvb_device_get drivers/media/dvb-core/dvbdev.c:631 [inline]
dvb_device_open+0x330/0x370 drivers/media/dvb-core/dvbdev.c:106
chrdev_open+0x5c5/0x6a0 fs/char_dev.c:414
do_dentry_open+0x7e9/0x10d0 fs/open.c:882
do_open fs/namei.c:3634 [inline]
path_openat+0x2635/0x2ee0 fs/namei.c:3791
do_filp_open+0x1f1/0x430 fs/namei.c:3818
do_sys_openat2+0x150/0x4b0 fs/open.c:1320
do_sys_open fs/open.c:1336 [inline]
__do_sys_openat fs/open.c:1352 [inline]
__se_sys_openat fs/open.c:1347 [inline]
__x64_sys_openat+0x135/0x160 fs/open.c:1347
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f5590d5d60e
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:00007f5591cf9b28 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f5591cfa6c0 RCX: 00007f5590d5d60e
RDX: 0000000000000000 RSI: 00007f5591cf9c00 RDI: ffffffffffffff9c
RBP: 00007f5591cf9c00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: cccccccccccccccd
R13: 00007f5591016218 R14: 00007f5591016180 R15: 00007ffd3231d058
</TASK>


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