BUG: kernel NULL pointer dereference, address: 0000000000000018
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 11637d067 P4D 11637d067 PUD 1166ee067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP
CPU: 1 PID: 3323 Comm: kworker/1:2 Not tainted 5.11.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events l2cap_chan_timeout
RIP: 0010:arch_atomic_fetch_sub arch/x86/include/asm/atomic.h:190 [inline]
RIP: 0010:atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:221 [inline]
RIP: 0010:__refcount_sub_and_test include/linux/refcount.h:272 [inline]
RIP: 0010:__refcount_dec_and_test include/linux/refcount.h:315 [inline]
RIP: 0010:refcount_dec_and_test include/linux/refcount.h:333 [inline]
RIP: 0010:kref_put include/linux/kref.h:64 [inline]
RIP: 0010:l2cap_chan_put+0x9/0x30 net/bluetooth/l2cap_core.c:502
Code: 31 db 48 89 d8 5b 5d 41 5c c3 4c 89 e7 e8 7f cc fd ff eb a9 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 48 8d 57 18 b8 ff ff ff ff <f0> 0f c1 47 18 83 f8 01 74 05 85 c0 7e 09 c3 48 89 d7 e9 50 f7 ff
RSP: 0018:ffffc900059afe18 EFLAGS: 00010246
RAX: 00000000ffffffff RBX: ffff888116639000 RCX: dead000000000122
RDX: 0000000000000018 RSI: ffff888116639c88 RDI: 0000000000000000
RBP: ffff888116639800 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000000 R12: ffff888116210a70
R13: ffff888116639cb8 R14: ffff888116639910 R15: ffff888116639918
FS:  0000000000000000(0000) GS:ffff888237d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000018 CR3: 00000001167ee000 CR4: 0000000000350ee0
Call Trace:
 l2cap_sock_kill.part.11+0x10/0x50 net/bluetooth/l2cap_sock.c:1217
 l2cap_chan_timeout+0x7d/0xe0 net/bluetooth/l2cap_core.c:438
 process_one_work+0x293/0x600 kernel/workqueue.c:2275
 worker_thread+0x38/0x380 kernel/workqueue.c:2421
 kthread+0x145/0x170 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Modules linked in:
CR2: 0000000000000018
---[ end trace 7d0bd3157aba206d ]---
RIP: 0010:arch_atomic_fetch_sub arch/x86/include/asm/atomic.h:190 [inline]
RIP: 0010:atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:221 [inline]
RIP: 0010:__refcount_sub_and_test include/linux/refcount.h:272 [inline]
RIP: 0010:__refcount_dec_and_test include/linux/refcount.h:315 [inline]
RIP: 0010:refcount_dec_and_test include/linux/refcount.h:333 [inline]
RIP: 0010:kref_put include/linux/kref.h:64 [inline]
RIP: 0010:l2cap_chan_put+0x9/0x30 net/bluetooth/l2cap_core.c:502
Code: 31 db 48 89 d8 5b 5d 41 5c c3 4c 89 e7 e8 7f cc fd ff eb a9 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 48 8d 57 18 b8 ff ff ff ff <f0> 0f c1 47 18 83 f8 01 74 05 85 c0 7e 09 c3 48 89 d7 e9 50 f7 ff
RSP: 0018:ffffc900059afe18 EFLAGS: 00010246
RAX: 00000000ffffffff RBX: ffff888116639000 RCX: dead000000000122
RDX: 0000000000000018 RSI: ffff888116639c88 RDI: 0000000000000000
RBP: ffff888116639800 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000000 R12: ffff888116210a70
R13: ffff888116639cb8 R14: ffff888116639910 R15: ffff888116639918
FS:  0000000000000000(0000) GS:ffff888237d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000018 CR3: 00000001167ee000 CR4: 0000000000350ee0