==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: null-ptr-deref in atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
BUG: KASAN: null-ptr-deref in __refcount_sub_and_test include/linux/refcount.h:272 [inline]
BUG: KASAN: null-ptr-deref in __refcount_dec_and_test include/linux/refcount.h:315 [inline]
BUG: KASAN: null-ptr-deref in refcount_dec_and_test include/linux/refcount.h:333 [inline]
BUG: KASAN: null-ptr-deref in kref_put include/linux/kref.h:64 [inline]
BUG: KASAN: null-ptr-deref in l2cap_chan_put+0x1c/0x1c0 net/bluetooth/l2cap_core.c:504
Write of size 4 at addr 0000000000000018 by task kworker/0:0/5

CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.13.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events l2cap_chan_timeout
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x10c/0x14b lib/dump_stack.c:120
 __kasan_report mm/kasan/report.c:423 [inline]
 kasan_report.cold+0x5f/0xd8 mm/kasan/report.c:436
 check_region_inline mm/kasan/generic.c:180 [inline]
 kasan_check_range+0x13d/0x180 mm/kasan/generic.c:186
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
 __refcount_sub_and_test include/linux/refcount.h:272 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 kref_put include/linux/kref.h:64 [inline]
 l2cap_chan_put+0x1c/0x1c0 net/bluetooth/l2cap_core.c:504
 l2cap_sock_kill+0x95/0x110 net/bluetooth/l2cap_sock.c:1225
 l2cap_chan_timeout+0x171/0x3a0 net/bluetooth/l2cap_core.c:438
 process_one_work+0x84c/0x13b0 kernel/workqueue.c:2276
 worker_thread+0x598/0xf80 kernel/workqueue.c:2422
 kthread+0x36f/0x450 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
==================================================================
BUG: kernel NULL pointer dereference, address: 0000000000000018
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 0 P4D 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5 Comm: kworker/0:0 Tainted: G    B             5.13.0-rc6-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+0x21/0x1c0 net/bluetooth/l2cap_core.c:504
Code: d5 be 0f fb eb ad 0f 1f 00 41 56 be 04 00 00 00 41 55 41 54 4c 8d 67 18 55 48 89 fd 4c 89 e7 53 e8 34 c2 0f fb b8 ff ff ff ff <f0> 0f c1 45 18 83 f8 01 74 11 85 c0 0f 8e 2b 01 00 00 5b 5d 41 5c
RSP: 0018:ffffc9000006fca0 EFLAGS: 00010246
RAX: 00000000ffffffff RBX: ffff8881034da110 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000004 RDI: 0000000000000001
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: fffffbfff12b24a4 R11: 6e696c6261736944 R12: 0000000000000018
R13: ffff8881034da4b8 R14: ffffffff8889bca0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881f6400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000018 CR3: 000000010d18a000 CR4: 0000000000350ef0
Call Trace:
 l2cap_sock_kill+0x95/0x110 net/bluetooth/l2cap_sock.c:1225
 l2cap_chan_timeout+0x171/0x3a0 net/bluetooth/l2cap_core.c:438
 process_one_work+0x84c/0x13b0 kernel/workqueue.c:2276
 worker_thread+0x598/0xf80 kernel/workqueue.c:2422
 kthread+0x36f/0x450 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Modules linked in:
CR2: 0000000000000018
---[ end trace 46c6f91767477cea ]---
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+0x21/0x1c0 net/bluetooth/l2cap_core.c:504
Code: d5 be 0f fb eb ad 0f 1f 00 41 56 be 04 00 00 00 41 55 41 54 4c 8d 67 18 55 48 89 fd 4c 89 e7 53 e8 34 c2 0f fb b8 ff ff ff ff <f0> 0f c1 45 18 83 f8 01 74 11 85 c0 0f 8e 2b 01 00 00 5b 5d 41 5c
RSP: 0018:ffffc9000006fca0 EFLAGS: 00010246
RAX: 00000000ffffffff RBX: ffff8881034da110 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000004 RDI: 0000000000000001
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: fffffbfff12b24a4 R11: 6e696c6261736944 R12: 0000000000000018
R13: ffff8881034da4b8 R14: ffffffff8889bca0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881f6400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000018 CR3: 000000010d18a000 CR4: 0000000000350ef0