======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.1.20018/17851 is trying to acquire lock:
ffff8880800d00b8 (&hdev->lock){+.+.}-{4:4}, at: l2cap_chan_connect+0xac/0x2110 net/bluetooth/l2cap_core.c:7289

but task is already holding lock:
ffffffff90f871a0 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_dlc_open+0x92/0xac0 net/bluetooth/rfcomm/core.c:426

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (rfcomm_mutex){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       rfcomm_security_cfm+0x3f/0x4b0 net/bluetooth/rfcomm/core.c:2223
       hci_auth_cfm include/net/bluetooth/hci_core.h:2203 [inline]
       hci_auth_complete_evt+0x811/0x1180 net/bluetooth/hci_event.c:3554
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4087
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (hci_cb_list_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       hci_connect_cfm include/net/bluetooth/hci_core.h:2164 [inline]
       hci_remote_features_evt+0x485/0x9b0 net/bluetooth/hci_event.c:3786
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4087
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&hdev->lock){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       l2cap_chan_connect+0xac/0x2110 net/bluetooth/l2cap_core.c:7289
       l2cap_sock_connect+0x37a/0x770 net/bluetooth/l2cap_sock.c:255
       kernel_connect+0x107/0x160 net/socket.c:3755
       rfcomm_session_create net/bluetooth/rfcomm/core.c:808 [inline]
       __rfcomm_dlc_open net/bluetooth/rfcomm/core.c:385 [inline]
       rfcomm_dlc_open+0x838/0xac0 net/bluetooth/rfcomm/core.c:428
       rfcomm_dev_activate+0x83/0x110 net/bluetooth/rfcomm/tty.c:112
       tty_port_open+0x161/0x220 drivers/tty/tty_port.c:798
       rfcomm_tty_open+0xad/0x490 net/bluetooth/rfcomm/tty.c:744
       tty_open+0x2cc/0xe20 drivers/tty/tty_io.c:2112
       chrdev_open+0x234/0x6a0 fs/char_dev.c:411
       do_dentry_open+0x6ab/0x14d0 fs/open.c:996
       vfs_open+0x82/0x3f0 fs/open.c:1101
       do_open fs/namei.c:4837 [inline]
       path_openat+0x19fa/0x2440 fs/namei.c:5000
       do_file_open+0x20e/0x430 fs/namei.c:5029
       do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
       do_sys_open fs/open.c:1423 [inline]
       __do_sys_openat fs/open.c:1439 [inline]
       __se_sys_openat fs/open.c:1434 [inline]
       __x64_sys_openat+0x12d/0x210 fs/open.c:1434
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

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 ***

locks held by syz.1.20018/17851: 3, last CPU#0:
 #0: ffff88802b51e1b0 (&tty->legacy_mutex){+.+.}-{4:4}, at: tty_init_dev.part.0+0x39/0x470 drivers/tty/tty_io.c:1381
 #1: ffff888053c382a0 (&port->mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
 #1: ffff888053c382a0 (&port->mutex){+.+.}-{4:4}, at: tty_port_open+0x92/0x220 drivers/tty/tty_port.c:793
 #2: ffffffff90f871a0 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_dlc_open+0x92/0xac0 net/bluetooth/rfcomm/core.c:426

stack backtrace:
CPU: 0 UID: 0 PID: 17851 Comm: syz.1.20018 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2087
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
 lock_acquire kernel/locking/lockdep.c:5942 [inline]
 lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
 l2cap_chan_connect+0xac/0x2110 net/bluetooth/l2cap_core.c:7289
 l2cap_sock_connect+0x37a/0x770 net/bluetooth/l2cap_sock.c:255
 kernel_connect+0x107/0x160 net/socket.c:3755
 rfcomm_session_create net/bluetooth/rfcomm/core.c:808 [inline]
 __rfcomm_dlc_open net/bluetooth/rfcomm/core.c:385 [inline]
 rfcomm_dlc_open+0x838/0xac0 net/bluetooth/rfcomm/core.c:428
 rfcomm_dev_activate+0x83/0x110 net/bluetooth/rfcomm/tty.c:112
 tty_port_open+0x161/0x220 drivers/tty/tty_port.c:798
 rfcomm_tty_open+0xad/0x490 net/bluetooth/rfcomm/tty.c:744
 tty_open+0x2cc/0xe20 drivers/tty/tty_io.c:2112
 chrdev_open+0x234/0x6a0 fs/char_dev.c:411
 do_dentry_open+0x6ab/0x14d0 fs/open.c:996
 vfs_open+0x82/0x3f0 fs/open.c:1101
 do_open fs/namei.c:4837 [inline]
 path_openat+0x19fa/0x2440 fs/namei.c:5000
 do_file_open+0x20e/0x430 fs/namei.c:5029
 do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
 do_sys_open fs/open.c:1423 [inline]
 __do_sys_openat fs/open.c:1439 [inline]
 __se_sys_openat fs/open.c:1434 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1434
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6532f9e199
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6533f33028 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f6533225fa0 RCX: 00007f6532f9e199
RDX: 0000000000000802 RSI: 0000200000000300 RDI: ffffffffffffff9c
RBP: 00007f65330350b8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6533226038 R14: 00007f6533225fa0 R15: 00007ffe5746b488
 </TASK>