BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
IP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline]
IP: vb2_vmalloc_put+0x9/0x60 drivers/media/v4l2-core/videobuf2-vmalloc.c:68
PGD 99a7c067 P4D 99a7c067 PUD 98c6b067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 1 PID: 3883 Comm: syz-executor.1 Not tainted 4.14.266-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff88809c462240 task.stack: ffff888096e98000
RIP: 0010:refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline]
RIP: 0010:vb2_vmalloc_put+0x9/0x60 drivers/media/v4l2-core/videobuf2-vmalloc.c:68
RSP: 0018:ffff888096e9f900 EFLAGS: 00010297
RAX: ffff88809c462240 RBX: ffff8880a52da780 RCX: 1ffff1101388c562
RDX: 0000000000000000 RSI: ffff88809c462af0 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff8880a52da794 R14: 0000000000000000 R15: ffffffff84c24b70
FS:  00007f60a5147700(0000) GS:ffff8880ba500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000020 CR3: 00000000afca2000 CR4: 00000000003406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __vb2_buf_mem_free+0xfa/0x1d0 drivers/media/v4l2-core/videobuf2-core.c:240
 __vb2_free_mem drivers/media/v4l2-core/videobuf2-core.c:409 [inline]
 __vb2_queue_free+0x60d/0x7a0 drivers/media/v4l2-core/videobuf2-core.c:454
 vb2_core_reqbufs+0x1cc/0x910 drivers/media/v4l2-core/videobuf2-core.c:687
 vb2_ioctl_reqbufs+0x1b6/0x320 drivers/media/v4l2-core/videobuf2-v4l2.c:718
 v4l_reqbufs drivers/media/v4l2-core/v4l2-ioctl.c:1863 [inline]
 v4l_reqbufs+0x98/0xc0 drivers/media/v4l2-core/v4l2-ioctl.c:1852
 __video_do_ioctl+0x65b/0x6a0 drivers/media/v4l2-core/v4l2-ioctl.c:2738
 video_usercopy+0xfd/0xe70 drivers/media/v4l2-core/v4l2-ioctl.c:2908
 v4l2_ioctl+0x1bb/0x2f0 drivers/media/v4l2-core/v4l2-dev.c:360
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xff0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f60a67d2059
RSP: 002b:00007f60a5147168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f60a68e4f60 RCX: 00007f60a67d2059
RDX: 0000000020000080 RSI: 00000000c0145608 RDI: 0000000000000003
RBP: 00007f60a682c08d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffdfc7b390f R14: 00007f60a5147300 R15: 0000000000022000
Code: e9 ca fc ff ff e8 28 a5 bc fc e9 96 fc ff ff e8 4e a7 bc fc e9 fd fe ff ff 66 0f 1f 84 00 00 00 00 00 55 48 89 fd e8 37 f4 92 fc <f0> ff 4d 20 0f 88 34 62 5f 02 74 06 5d e9 25 f4 92 fc e8 20 f4 
RIP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline] RSP: ffff888096e9f900
RIP: vb2_vmalloc_put+0x9/0x60 drivers/media/v4l2-core/videobuf2-vmalloc.c:68 RSP: ffff888096e9f900
CR2: 0000000000000020
---[ end trace dacc9cd9f7fca2fa ]---
----------------
Code disassembly (best guess):
   0:	e9 ca fc ff ff       	jmpq   0xfffffccf
   5:	e8 28 a5 bc fc       	callq  0xfcbca532
   a:	e9 96 fc ff ff       	jmpq   0xfffffca5
   f:	e8 4e a7 bc fc       	callq  0xfcbca762
  14:	e9 fd fe ff ff       	jmpq   0xffffff16
  19:	66 0f 1f 84 00 00 00 	nopw   0x0(%rax,%rax,1)
  20:	00 00
  22:	55                   	push   %rbp
  23:	48 89 fd             	mov    %rdi,%rbp
  26:	e8 37 f4 92 fc       	callq  0xfc92f462
* 2b:	f0 ff 4d 20          	lock decl 0x20(%rbp) <-- trapping instruction
  2f:	0f 88 34 62 5f 02    	js     0x25f6269
  35:	74 06                	je     0x3d
  37:	5d                   	pop    %rbp
  38:	e9 25 f4 92 fc       	jmpq   0xfc92f462
  3d:	e8                   	.byte 0xe8
  3e:	20 f4                	and    %dh,%ah