WARNING: refcount bug in l2cap_global_chan_by_psm

[syzbot <syzbot+39ad9f042519082fcec9@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    c0842fbc random32: move the pseudo-random 32-bit definitio..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=142980c2900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=76cacb0fe58c4a1e
dashboard link: https://syzkaller.appspot.com/bug?extid=39ad9f042519082fcec9
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1100fc58900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13a9d662900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+39ad9f042519082fcec9@syzkaller.appspotmail.com

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refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 6830 at lib/refcount.c:25 refcount_warn_saturate+0x13d/0x1a0 lib/refcount.c:25
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 6830 Comm: kworker/u5:2 Not tainted 5.8.0-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+0x1f0/0x31e lib/dump_stack.c:118
 panic+0x264/0x7a0 kernel/panic.c:231
 __warn+0x227/0x250 kernel/panic.c:600
 report_bug+0x1b1/0x2e0 lib/bug.c:198
 handle_bug+0x42/0x80 arch/x86/kernel/traps.c:235
 exc_invalid_op+0x16/0x40 arch/x86/kernel/traps.c:255
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:547
RIP: 0010:refcount_warn_saturate+0x13d/0x1a0 lib/refcount.c:25
Code: c7 c3 ca 14 89 31 c0 e8 41 c0 a9 fd 0f 0b eb a3 e8 f8 0a d8 fd c6 05 38 a8 ec 05 01 48 c7 c7 fa ca 14 89 31 c0 e8 23 c0 a9 fd <0f> 0b eb 85 e8 da 0a d8 fd c6 05 1b a8 ec 05 01 48 c7 c7 26 cb 14
RSP: 0018:ffffc90001607a70 EFLAGS: 00010246
RAX: 94a8124281310300 RBX: 0000000000000002 RCX: ffff888092562280
RDX: 0000000000000000 RSI: 0000000080000001 RDI: 0000000000000000
RBP: 0000000000000002 R08: ffffffff815e07c9 R09: ffffed1015d262c0
R10: ffffed1015d262c0 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: ffff8880a948e018 R15: 0000000000000001
 refcount_add include/linux/refcount.h:206 [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+0x4aa/0x4e0 net/bluetooth/l2cap_core.c:1978
 l2cap_conless_channel net/bluetooth/l2cap_core.c:7596 [inline]
 l2cap_recv_frame+0x530/0x8f10 net/bluetooth/l2cap_core.c:7666
 hci_acldata_packet net/bluetooth/hci_core.c:4520 [inline]
 hci_rx_work+0x7d7/0x9c0 net/bluetooth/hci_core.c:4710
 process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
 worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
 kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
Kernel Offset: disabled
Rebooting in 86400 seconds..


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