======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/4488 is trying to acquire lock:
ffff0000dbe3c428 (&hdev->lock){+.+.}-{3:3}, at: l2cap_chan_connect+0xd0/0xba0 net/bluetooth/l2cap_core.c:7284

but task is already holding lock:
ffff800017bb6ac8 (rfcomm_mutex){+.+.}-{3:3}, at: rfcomm_dlc_open+0xa8/0xcf4 net/bluetooth/rfcomm/core.c:425

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (rfcomm_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1a0/0x1f3c kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       rfcomm_security_cfm+0x9c/0x674 net/bluetooth/rfcomm/core.c:2210
       hci_encrypt_cfm+0x308/0x444 include/net/bluetooth/hci_core.h:1897
       hci_encrypt_change_evt+0x724/0xba4 net/bluetooth/hci_event.c:3664
       hci_event_func net/bluetooth/hci_event.c:7314 [inline]
       hci_event_packet+0x698/0xe60 net/bluetooth/hci_event.c:7366
       hci_rx_work+0x310/0xa70 net/bluetooth/hci_core.c:4006
       process_one_work+0x7e4/0x13bc kernel/workqueue.c:2292
       worker_thread+0x8cc/0xfe8 kernel/workqueue.c:2439
       kthread+0x254/0x2e0 kernel/kthread.c:376
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:850

-> #1 (hci_cb_list_lock){+.+.}-{3:3}:
       __mutex_lock_common+0x1a0/0x1f3c kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       hci_connect_cfm include/net/bluetooth/hci_core.h:1818 [inline]
       hci_remote_features_evt+0x410/0x840 net/bluetooth/hci_event.c:3734
       hci_event_func net/bluetooth/hci_event.c:7314 [inline]
       hci_event_packet+0x698/0xe60 net/bluetooth/hci_event.c:7366
       hci_rx_work+0x310/0xa70 net/bluetooth/hci_core.c:4006
       process_one_work+0x7e4/0x13bc kernel/workqueue.c:2292
       worker_thread+0x8cc/0xfe8 kernel/workqueue.c:2439
       kthread+0x254/0x2e0 kernel/kthread.c:376
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:850

-> #0 (&hdev->lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3095 [inline]
       check_prevs_add kernel/locking/lockdep.c:3214 [inline]
       validate_chain kernel/locking/lockdep.c:3830 [inline]
       __lock_acquire+0x2808/0x6634 kernel/locking/lockdep.c:5063
       lock_acquire+0x20c/0x638 kernel/locking/lockdep.c:5678
       __mutex_lock_common+0x1a0/0x1f3c kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       l2cap_chan_connect+0xd0/0xba0 net/bluetooth/l2cap_core.c:7284
       l2cap_sock_connect+0x414/0x600 net/bluetooth/l2cap_sock.c:257
       kernel_connect+0x124/0x190 net/socket.c:3555
       rfcomm_session_create net/bluetooth/rfcomm/core.c:807 [inline]
       __rfcomm_dlc_open net/bluetooth/rfcomm/core.c:384 [inline]
       rfcomm_dlc_open+0x4f4/0xcf4 net/bluetooth/rfcomm/core.c:427
       rfcomm_sock_connect+0x25c/0x57c net/bluetooth/rfcomm/sock.c:421
       __sys_connect_file net/socket.c:2011 [inline]
       __sys_connect+0x28c/0x2b4 net/socket.c:2028
       __do_sys_connect net/socket.c:2038 [inline]
       __se_sys_connect net/socket.c:2035 [inline]
       __arm64_sys_connect+0x7c/0x94 net/socket.c:2035
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz.0.17/4488:
 #0: ffff800017bb6ac8 (rfcomm_mutex){+.+.}-{3:3}, at: rfcomm_dlc_open+0xa8/0xcf4 net/bluetooth/rfcomm/core.c:425

stack backtrace:
CPU: 1 PID: 4488 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026
Call trace:
 dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
 dump_stack+0x1c/0x5c lib/dump_stack.c:113
 print_circular_bug+0x148/0x1b0 kernel/locking/lockdep.c:2048
 check_noncircular+0x264/0x2f8 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3095 [inline]
 check_prevs_add kernel/locking/lockdep.c:3214 [inline]
 validate_chain kernel/locking/lockdep.c:3830 [inline]
 __lock_acquire+0x2808/0x6634 kernel/locking/lockdep.c:5063
 lock_acquire+0x20c/0x638 kernel/locking/lockdep.c:5678
 __mutex_lock_common+0x1a0/0x1f3c kernel/locking/mutex.c:603
 __mutex_lock kernel/locking/mutex.c:747 [inline]
 mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
 l2cap_chan_connect+0xd0/0xba0 net/bluetooth/l2cap_core.c:7284
 l2cap_sock_connect+0x414/0x600 net/bluetooth/l2cap_sock.c:257
 kernel_connect+0x124/0x190 net/socket.c:3555
 rfcomm_session_create net/bluetooth/rfcomm/core.c:807 [inline]
 __rfcomm_dlc_open net/bluetooth/rfcomm/core.c:384 [inline]
 rfcomm_dlc_open+0x4f4/0xcf4 net/bluetooth/rfcomm/core.c:427
 rfcomm_sock_connect+0x25c/0x57c net/bluetooth/rfcomm/sock.c:421
 __sys_connect_file net/socket.c:2011 [inline]
 __sys_connect+0x28c/0x2b4 net/socket.c:2028
 __do_sys_connect net/socket.c:2038 [inline]
 __se_sys_connect net/socket.c:2035 [inline]
 __arm64_sys_connect+0x7c/0x94 net/socket.c:2035
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585