syzbot

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refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 6889 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 6889 Comm: kworker/u5:2 Not tainted 5.8.0-rc7-next-20200731-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: hci0 hci_rx_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:231
 __warn.cold+0x20/0x4a kernel/panic.c:600
 report_bug+0x1bd/0x210 lib/bug.c:198
 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
 exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Code: 07 31 ff 89 de e8 67 f4 d8 fd 84 db 0f 85 36 ff ff ff e8 1a f8 d8 fd 48 c7 c7 20 ca 93 88 c6 05 e3 6e 19 07 01 e8 a9 e7 a9 fd <0f> 0b e9 17 ff ff ff e8 fb f7 d8 fd 0f b6 1d c8 6e 19 07 31 ff 89
RSP: 0018:ffffc900057df908 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff8880897ac240 RSI: ffffffff815d86e7 RDI: fffff52000afbf13
RBP: 0000000000000002 R08: 0000000000000001 R09: ffff8880ae6318a7
R10: 0000000000000000 R11: 746e756f63666572 R12: dffffc0000000000
R13: 0000000000000001 R14: ffff88809eda2000 R15: 0000000000000003
 refcount_add include/linux/refcount.h:204 [inline]
 refcount_inc include/linux/refcount.h:241 [inline]
 kref_get include/linux/kref.h:45 [inline]
 l2cap_chan_hold net/bluetooth/l2cap_core.c:495 [inline]
 l2cap_global_chan_by_psm+0x53f/0x5b0 net/bluetooth/l2cap_core.c:1978
 l2cap_conless_channel net/bluetooth/l2cap_core.c:7595 [inline]
 l2cap_recv_frame+0xc3b/0xae10 net/bluetooth/l2cap_core.c:7665
 l2cap_recv_acldata+0x7f6/0x8e0 net/bluetooth/l2cap_core.c:8314
 hci_acldata_packet net/bluetooth/hci_core.c:4703 [inline]
 hci_rx_work+0x4c7/0xb50 net/bluetooth/hci_core.c:4894
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Kernel Offset: disabled
Rebooting in 86400 seconds..