[syzbot] [media?] general protection fault in vidtv_s302m_encode

Hello,

syzbot found the following issue on:

HEAD commit:    3b5f4b83c4ab Merge tag 'for-7.2-rc5-tag' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11068aea580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=e9ce4d4ff55ba65e3980
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f99ca00b02a2/disk-3b5f4b83.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5caff5208bfc/vmlinux-3b5f4b83.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c0e941f5f816/bzImage-3b5f4b83.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 UID: 0 PID: 5713 Comm: kworker/0:5 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: events vidtv_mux_tick
RIP: 0010:vidtv_s302m_encode+0x269/0x1860 drivers/media/test-drivers/vidtv/vidtv_s302m.c:414
Code: 31 aa f9 31 ff 89 de e8 95 2b aa f9 84 db 0f 85 37 0d 00 00 e8 78 31 aa f9 4c 89 e2 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e e7 14 00 00 48 8b 44 24 08 41
RSP: 0018:ffffc9000454f830 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000400
RDX: 0000000000000000 RSI: ffffffff88602ec8 RDI: ffff88813fe238c0
RBP: 0000000000000000 R08: 0000000000000dc0 R09: 00000000ffffffff
R10: ffffffff8edee673 R11: 0000000000000001 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff888076157200 R15: ffff88802e6f2000
FS:  0000000000000000(0000) GS:ffff888123ddc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f89c38f7ff8 CR3: 0000000038e49000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 vidtv_mux_poll_encoders drivers/media/test-drivers/vidtv/vidtv_mux.c:339 [inline]
 vidtv_mux_tick+0x4e4/0x1460 drivers/media/test-drivers/vidtv/vidtv_mux.c:416
 process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
 process_scheduled_works kernel/workqueue.c:3405 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:vidtv_s302m_encode+0x269/0x1860 drivers/media/test-drivers/vidtv/vidtv_s302m.c:414
Code: 31 aa f9 31 ff 89 de e8 95 2b aa f9 84 db 0f 85 37 0d 00 00 e8 78 31 aa f9 4c 89 e2 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e e7 14 00 00 48 8b 44 24 08 41
----------------
Code disassembly (best guess):
   0:	31 aa f9 31 ff 89    	xor    %ebp,-0x7600ce07(%rdx)
   6:	de e8                	fsubrp %st,%st(0)
   8:	95                   	xchg   %eax,%ebp
   9:	2b aa f9 84 db 0f    	sub    0xfdb84f9(%rdx),%ebp
   f:	85 37                	test   %esi,(%rdi)
  11:	0d 00 00 e8 78       	or     $0x78e80000,%eax
  16:	31 aa f9 4c 89 e2    	xor    %ebp,-0x1d76b307(%rdx)
  1c:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  23:	fc ff df
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	0f b6 04 02          	movzbl (%rdx,%rax,1),%eax <-- trapping instruction
  2e:	84 c0                	test   %al,%al
  30:	74 08                	je     0x3a
  32:	3c 03                	cmp    $0x3,%al
  34:	0f 8e e7 14 00 00    	jle    0x1521
  3a:	48 8b 44 24 08       	mov    0x8(%rsp),%rax
  3f:	41                   	rex.B


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