[v5.15] WARNING: refcount bug in dvb_device_open

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7b232985052f Linux 5.15.199
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1647865a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=51a2e1546f1a0739057c
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/97a23052e207/disk-7b232985.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e9871fb1bda3/vmlinux-7b232985.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b08e48f5be44/bzImage-7b232985.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+51a2e1...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: saturated; leaking memory.
WARNING: CPU: 1 PID: 5103 at lib/refcount.c:22 refcount_warn_saturate+0x153/0x1a0 lib/refcount.c:22
Modules linked in:
CPU: 1 PID: 5103 Comm: syz.4.235 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:refcount_warn_saturate+0x153/0x1a0 lib/refcount.c:22
Code: 09 01 48 c7 c7 00 b8 79 8a e8 69 68 cd 05 0f 0b eb 8c e8 d0 5f 95 fd c6 05 ca 72 92 09 01 48 c7 c7 00 b8 79 8a e8 4d 68 cd 05 <0f> 0b e9 6d ff ff ff e8 b1 5f 95 fd c6 05 af 72 92 09 01 48 c7 c7
RSP: 0018:ffffc9000375f798 EFLAGS: 00010246
RAX: 25aa356a47451100 RBX: 0000000000000001 RCX: 0000000000080000
RDX: ffffc9000e7fa000 RSI: 0000000000004a72 RDI: 0000000000004a73
RBP: 00000000ffffffff R08: ffff8880b9133d7f R09: 1ffff110172267af
R10: dffffc0000000000 R11: ffffed10172267b0 R12: ffff88802910aa18
R13: ffffffff9632be78 R14: 0000000000000001 R15: ffff88802910aa00
FS: 00007f0e5578d6c0(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000404030 CR3: 000000005785b000 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:641 [inline]
dvb_device_open+0x330/0x370 drivers/media/dvb-core/dvbdev.c:116
chrdev_open+0x5c5/0x6a0 fs/char_dev.c:414
do_dentry_open+0x7ff/0xf80 fs/open.c:826
do_open fs/namei.c:3616 [inline]
path_openat+0x26f5/0x2fa0 fs/namei.c:3750
do_filp_open+0x1e2/0x410 fs/namei.c:3777
do_sys_openat2+0x150/0x4b0 fs/open.c:1255
do_sys_open fs/open.c:1271 [inline]
__do_sys_openat fs/open.c:1287 [inline]
__se_sys_openat fs/open.c:1282 [inline]
__x64_sys_openat+0x135/0x160 fs/open.c:1282
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f0e574f278e
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:00007f0e5578cb28 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f0e5578d6c0 RCX: 00007f0e574f278e
RDX: 0000000000000000 RSI: 00007f0e5578cc00 RDI: ffffffffffffff9c
RBP: 00007f0e5578cc00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: cccccccccccccccd
R13: 00007f0e577ad038 R14: 00007f0e577acfa0 R15: 00007ffc395664c8
</TASK>


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