In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: RFCOMM: connect the session socket without rfcomm_mutex

An RFCOMM connect() issued while a BR/EDR link is being authenticated makes lockdep report a circular dependency, and the reported cycle is a real AB/BA between rfcomm_mutex and hdev->lock.

rfcomm_security_cfm() is called from the HCI event path, which already holds hdev->lock:

hci_rx_work() hci_event_packet() hci_cc_read_enc_key_size() [hdev->lock] hci_encrypt_cfm() [hci_cb_list_lock] rfcomm_security_cfm() [rfcomm_mutex]

while an RFCOMM connect() from userspace takes the same two locks the other way round:

rfcomm_sock_connect() rfcomm_dlc_open() [rfcomm_mutex] __rfcomm_dlc_open() rfcomm_session_create() kernel_connect() l2cap_sock_connect() l2cap_chan_connect() [hdev->lock]

WARNING: possible circular locking dependency detected kworker/u131:1/1128 is trying to acquire lock: rfcomm_mutex, at: rfcomm_security_cfm+0x31/0x3e0 [rfcomm] but task is already holding lock: hci_cb_list_lock, at: hci_cc_read_enc_key_size+0x1d2/0xcc0 Chain exists of: rfcomm_mutex --> &hdev->lock --> hci_cb_list_lock

hci_auth_complete_evt() and hci_encrypt_change_evt() reach the callback the same way.

Both orders have to be seen in the same boot, which is why a BR/EDR connection alone is not enough to show it: a session set up by the r…

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: RFCOMM: connect the session socket without rfcomm_mutex

An RFCOMM connect() issued while a BR/EDR link is being authenticated makes lockdep report a circular dependency, and the reported cycle is a real AB/BA between rfcomm_mutex and hdev->lock.

rfcomm_security_cfm() is called from the HCI event path, which already holds hdev->lock:

hci_rx_work() hci_event_packet() hci_cc_read_enc_key_size() [hdev->lock] hci_encrypt_cfm() [hci_cb_list_lock] rfcomm_security_cfm() [rfcomm_mutex]

while an RFCOMM connect() from userspace takes the same two locks the other way round:

rfcomm_sock_connect() rfcomm_dlc_open() [rfcomm_mutex] __rfcomm_dlc_open() rfcomm_session_create() kernel_connect() l2cap_sock_connect() l2cap_chan_connect() [hdev->lock]

WARNING: possible circular locking dependency detected kworker/u131:1/1128 is trying to acquire lock: rfcomm_mutex, at: rfcomm_security_cfm+0x31/0x3e0 [rfcomm] but task is already holding lock: hci_cb_list_lock, at: hci_cc_read_enc_key_size+0x1d2/0xcc0 Chain exists of: rfcomm_mutex --> &hdev->lock --> hci_cb_list_lock

hci_auth_complete_evt() and hci_encrypt_change_evt() reach the callback the same way.

Both orders have to be seen in the same boot, which is why a BR/EDR connection alone is not enough to show it: a session set up by the r…