======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/u5:2/5779 is trying to acquire lock:
ffffffff8e562248 (rfcomm_mutex){+.+.}-{3:3}, at: rfcomm_security_cfm+0x41/0x550 net/bluetooth/rfcomm/core.c:2214

but task is already holding lock:
ffffffff8e53eb68 (hci_cb_list_lock){+.+.}-{3:3}, at: hci_encrypt_cfm+0x2fe/0x4d0 include/net/bluetooth/hci_core.h:2077

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (hci_cb_list_lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
       hci_connect_cfm include/net/bluetooth/hci_core.h:2001 [inline]
       hci_remote_features_evt+0x535/0x900 net/bluetooth/hci_event.c:3719
       hci_event_func net/bluetooth/hci_event.c:7500 [inline]
       hci_event_packet+0x807/0x1280 net/bluetooth/hci_event.c:7552
       hci_rx_work+0x43a/0xd60 net/bluetooth/hci_core.c:4017
       process_one_work kernel/workqueue.c:2657 [inline]
       process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
       worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
       kthread+0x2fa/0x390 kernel/kthread.c:388
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
       ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

-> #1 (&hdev->lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
       l2cap_chan_connect+0xfc/0xe30 net/bluetooth/l2cap_core.c:7171
       l2cap_sock_connect+0x586/0x760 net/bluetooth/l2cap_sock.c:257
       kernel_connect+0x142/0x1c0 net/socket.c:3636
       rfcomm_session_create net/bluetooth/rfcomm/core.c:811 [inline]
       __rfcomm_dlc_open net/bluetooth/rfcomm/core.c:388 [inline]
       rfcomm_dlc_open+0xa1f/0xec0 net/bluetooth/rfcomm/core.c:431
       rfcomm_sock_connect+0x2ed/0x600 net/bluetooth/rfcomm/sock.c:421
       __sys_connect_file net/socket.c:2057 [inline]
       __sys_connect+0x3da/0x470 net/socket.c:2074
       __do_sys_connect net/socket.c:2084 [inline]
       __se_sys_connect net/socket.c:2081 [inline]
       __x64_sys_connect+0x7a/0x90 net/socket.c:2081
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (rfcomm_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain kernel/locking/lockdep.c:3869 [inline]
       __lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137
       lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5756
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
       rfcomm_security_cfm+0x41/0x550 net/bluetooth/rfcomm/core.c:2214
       hci_encrypt_cfm+0x363/0x4d0 include/net/bluetooth/hci_core.h:2080
       hci_cc_read_enc_key_size+0x219/0x380 net/bluetooth/hci_event.c:763
       hci_cc_func net/bluetooth/hci_event.c:4187 [inline]
       hci_cmd_complete_evt+0x4e7/0xa40 net/bluetooth/hci_event.c:4204
       hci_event_func net/bluetooth/hci_event.c:7497 [inline]
       hci_event_packet+0x7b4/0x1280 net/bluetooth/hci_event.c:7552
       hci_rx_work+0x43a/0xd60 net/bluetooth/hci_core.c:4017
       process_one_work kernel/workqueue.c:2657 [inline]
       process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
       worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
       kthread+0x2fa/0x390 kernel/kthread.c:388
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
       ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

other info that might help us debug this:

Chain exists of:
  rfcomm_mutex --> &hdev->lock --> hci_cb_list_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(hci_cb_list_lock);
                               lock(&hdev->lock);
                               lock(hci_cb_list_lock);
  lock(rfcomm_mutex);

 *** DEADLOCK ***

4 locks held by kworker/u5:2/5779:
 #0: ffff88805ff1f538 ((wq_completion)hci4#2){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline]
 #0: ffff88805ff1f538 ((wq_completion)hci4#2){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734
 #1: ffffc900047afd00 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline]
 #1: ffffc900047afd00 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734
 #2: ffff8880262300b8 (&hdev->lock){+.+.}-{3:3}, at: hci_cc_read_enc_key_size+0x9c/0x380 net/bluetooth/hci_event.c:728
 #3: ffffffff8e53eb68 (hci_cb_list_lock){+.+.}-{3:3}, at: hci_encrypt_cfm+0x2fe/0x4d0 include/net/bluetooth/hci_core.h:2077

stack backtrace:
CPU: 1 PID: 5779 Comm: kworker/u5:2 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/08/2026
Workqueue: hci4 hci_rx_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
 check_noncircular+0x2fc/0x400 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain kernel/locking/lockdep.c:3869 [inline]
 __lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137
 lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5756
 __mutex_lock_common kernel/locking/mutex.c:603 [inline]
 __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
 rfcomm_security_cfm+0x41/0x550 net/bluetooth/rfcomm/core.c:2214
 hci_encrypt_cfm+0x363/0x4d0 include/net/bluetooth/hci_core.h:2080
 hci_cc_read_enc_key_size+0x219/0x380 net/bluetooth/hci_event.c:763
 hci_cc_func net/bluetooth/hci_event.c:4187 [inline]
 hci_cmd_complete_evt+0x4e7/0xa40 net/bluetooth/hci_event.c:4204
 hci_event_func net/bluetooth/hci_event.c:7497 [inline]
 hci_event_packet+0x7b4/0x1280 net/bluetooth/hci_event.c:7552
 hci_rx_work+0x43a/0xd60 net/bluetooth/hci_core.c:4017
 process_one_work kernel/workqueue.c:2657 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>