[moderation] [media?] WARNING: refcount bug in dvb_device_get

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a52d6c7160f7 selftests/arm64: fix spelling errors in comme..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=16c908b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ecdef466b08b9772
dashboard link: https://syzkaller.appspot.com/bug?extid=df25983d45d7c6891ca9
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
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/af2ea186884f/disk-a52d6c71.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/cef93b18732f/vmlinux-a52d6c71.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b9f9b8922f14/Image-a52d6c71.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+df2598...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x134/0x1f8 lib/refcount.c:25, CPU#0: syz.6.545/8047
Modules linked in:
CPU: 0 UID: 0 PID: 8047 Comm: syz.6.545 Tainted: G L syzkaller #0 PREEMPT
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/02/2026
pstate: 63400005 (nZCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : refcount_warn_saturate+0x134/0x1f8 lib/refcount.c:25
lr : refcount_warn_saturate+0x134/0x1f8 lib/refcount.c:25
sp : ffff800099927640
x29: ffff800099927640 x28: dfff800000000000 x27: 1fffe00019353751
x26: dfff800000000000 x25: ffff700013324edc x24: dfff800000000000
x23: ffff80008742cca8 x22: ffff0000d9e83a10 x21: ffff0000cbbc9e00
x20: ffff0000cbbc9e10 x19: ffff80008a116000 x18: 1fffe00035bce428
x17: 0000000000000003 x16: ffff800088ac7000 x15: ffff800088b7cfa0
x14: ffff0001ade7214c x13: 0000000000000001 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000003 x9 : 2b8a9c5458a86c00
x8 : 2b8a9c5458a86c00 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000008 x3 : ffff8000803b7a0c
x2 : 0000000000000001 x1 : ffff000105b99d40 x0 : 0000000000000001
Call trace:
refcount_warn_saturate+0x134/0x1f8 lib/refcount.c:25 (P)
__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+0x9c/0xc0 drivers/media/dvb-core/dvbdev.c:621
dvb_device_open+0x100/0x254 drivers/media/dvb-core/dvbdev.c:106
chrdev_open+0x398/0x3e8 fs/char_dev.c:411
do_dentry_open+0x5c4/0xfc0 fs/open.c:947
vfs_open+0x44/0x2dc fs/open.c:1052
do_open fs/namei.c:4700 [inline]
path_openat+0x21fc/0x2a60 fs/namei.c:4859
do_file_open+0x1c8/0x2e8 fs/namei.c:4888
do_sys_openat2+0x114/0x1e8 fs/open.c:1368
do_sys_open+0xb0/0xe0 fs/open.c:1374
__do_sys_openat fs/open.c:1390 [inline]
__se_sys_openat fs/open.c:1385 [inline]
__arm64_sys_openat+0xa0/0xbc fs/open.c:1385
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
irq event stamp: 140
hardirqs last enabled at (139): [<ffff8000803b79bc>] raw_spin_rq_unlock_irq kernel/sched/sched.h:1673 [inline]
hardirqs last enabled at (139): [<ffff8000803b79bc>] finish_lock_switch kernel/sched/core.c:5241 [inline]
hardirqs last enabled at (139): [<ffff8000803b79bc>] finish_task_switch+0x234/0x858 kernel/sched/core.c:5359
hardirqs last disabled at (140): [<ffff8000868bf3a0>] el1_brk64+0x20/0x54 arch/arm64/kernel/entry-common.c:425
softirqs last enabled at (108): [<ffff800080139980>] local_bh_enable include/linux/bottom_half.h:33 [inline]
softirqs last enabled at (108): [<ffff800080139980>] put_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:251 [inline]
softirqs last enabled at (108): [<ffff800080139980>] do_sve_acc+0x32c/0x4b8 arch/arm64/kernel/fpsimd.c:1349
softirqs last disabled at (106): [<ffff800080139760>] local_bh_disable include/linux/bottom_half.h:20 [inline]
softirqs last disabled at (106): [<ffff800080139760>] get_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:234 [inline]
softirqs last disabled at (106): [<ffff800080139760>] do_sve_acc+0x10c/0x4b8 arch/arm64/kernel/fpsimd.c:1325
---[ end trace 0000000000000000 ]---
Internal error: SP/PC alignment exception: 000000008a000000 [#1] SMP
Modules linked in:
CPU: 0 UID: 0 PID: 8047 Comm: syz.6.545 Tainted: G W L syzkaller #0 PREEMPT
Tainted: [W]=WARN, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/02/2026
pstate: 83400805 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=-c)
pc : 0x1
lr : vfs_ioctl fs/ioctl.c:51 [inline]
lr : __do_sys_ioctl fs/ioctl.c:597 [inline]
lr : __se_sys_ioctl fs/ioctl.c:583 [inline]
lr : __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
sp : ffff800099927d30
x29: ffff800099927d30 x28: ffff000105b99d40 x27: 0000000000000003
x26: 1fffe00020b733a8 x25: dfff800000000000 x24: 00000000fffffdfd
x23: 0000000000000001 x22: 0000000020000000 x21: 0000000080106f53
x20: ffff0000c9a9ba40 x19: ffff0000c9a9ba41 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
x14: 00000000ffff8000 x13: 0000000000000005 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000080000 x9 : 000000000000091d
x8 : ffff800099f99000 x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 0000000000000000 x3 : ffff800080ce6e14
x2 : 0000000020000000 x1 : 0000000080106f53 x0 : ffff0000c9a9ba40
Call trace:
0x1 (P)
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
---[ end trace 0000000000000000 ]---


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