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 b4dce067 P4D b4dce067 PUD b4e49067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 1 PID: 18319 Comm: syz-executor.0 Not tainted 4.14.267-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8880b1afa080 task.stack: ffff888096fc0000
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:ffff888096fc7ca8 EFLAGS: 00010297
RAX: ffff8880b1afa080 RBX: ffff8880aaffa800 RCX: 1ffff1101635f52a
RDX: 0000000000000000 RSI: ffff8880b1afa930 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff8880aaffa814 R14: 0000000000000000 R15: ffffffff84c253f0
FS:  000055555612c400(0000) GS:ffff8880ba500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000020 CR3: 00000000aa5dd000 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_queue_release+0x5b/0x70 drivers/media/v4l2-core/videobuf2-core.c:2054
 v4l2_m2m_ctx_release+0x26/0x30 drivers/media/v4l2-core/v4l2-mem2mem.c:674
 vim2m_release+0xd4/0x120 drivers/media/platform/vim2m.c:959
 v4l2_release+0xf4/0x190 drivers/media/v4l2-core/v4l2-dev.c:446
 __fput+0x25f/0x7a0 fs/file_table.c:210
 task_work_run+0x11f/0x190 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x1ad/0x200 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
 do_syscall_64+0x4a3/0x640 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f390a991c9b
RSP: 002b:00007ffd14998030 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f390a991c9b
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 00007f390aaf3960 R08: 0000000000000000 R09: 00007f390aaf7758
R10: 0000000000000000 R11: 0000000000000293 R12: 000000000008d3fc
R13: 00007f390aaf7a60 R14: 00007f390aaf1f60 R15: 0000000000000000
Code: e9 ca fc ff ff e8 28 a1 bc fc e9 96 fc ff ff e8 4e a3 bc fc e9 fd fe ff ff 66 0f 1f 84 00 00 00 00 00 55 48 89 fd e8 07 ef 92 fc <f0> ff 4d 20 0f 88 ae 69 5f 02 74 06 5d e9 f5 ee 92 fc e8 f0 ee 
RIP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline] RSP: ffff888096fc7ca8
RIP: vb2_vmalloc_put+0x9/0x60 drivers/media/v4l2-core/videobuf2-vmalloc.c:68 RSP: ffff888096fc7ca8
CR2: 0000000000000020
---[ end trace 85d090cc5e738c22 ]---
----------------
Code disassembly (best guess):
   0:	e9 ca fc ff ff       	jmpq   0xfffffccf
   5:	e8 28 a1 bc fc       	callq  0xfcbca132
   a:	e9 96 fc ff ff       	jmpq   0xfffffca5
   f:	e8 4e a3 bc fc       	callq  0xfcbca362
  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 07 ef 92 fc       	callq  0xfc92ef32
* 2b:	f0 ff 4d 20          	lock decl 0x20(%rbp) <-- trapping instruction
  2f:	0f 88 ae 69 5f 02    	js     0x25f69e3
  35:	74 06                	je     0x3d
  37:	5d                   	pop    %rbp
  38:	e9 f5 ee 92 fc       	jmpq   0xfc92ef32
  3d:	e8                   	.byte 0xe8
  3e:	f0 ee                	lock out %al,(%dx)