Bluetooth: SCO: fix race conditions in sco_sock_connect()

Overview

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

Bluetooth: SCO: fix race conditions in sco_sock_connect()

sco_sock_connect() checks sk_state and sk_type without holding the socket lock. Two concurrent connect() syscalls on the same socket can both pass the check and enter sco_connect(), leading to use-after-free.

The buggy scenario involves three participants and was confirmed with additional logging instrumentation:

Thread A (connect): HCI disconnect: Thread B (connect):

sco_sock_connect(sk) sco_sock_connect(sk) sk_state==BT_OPEN sk_state==BT_OPEN (pass, no lock) (pass, no lock) sco_connect(sk): sco_connect(sk): hci_dev_lock hci_dev_lock hci_connect_sco <- blocked -> hcon1 sco_conn_add->conn1 lock_sock(sk) sco_chan_add: conn1->sk = sk sk->conn = conn1 sk_state=BT_CONNECT release_sock hci_dev_unlock hci_dev_lock sco_conn_del: lock_sock(sk) sco_chan_del: sk->conn=NULL conn1->sk=NULL sk_state= BT_CLOSED SOCK_ZAPPED release_sock hci_dev_unlock (unblocked) hci_connect_sco -> hcon2 sco_conn_add -> conn2 lock_sock(sk) sco_chan_add: sk->conn=conn2 sk_state= BT_CONNECT // zombie sk! release_sock hci_dev_unlock

Thread B revives a BT_CLOSED + SOCK_ZAPPED socket back to BT_CONNECT. Subsequent cleanup triggers double sock_put() and use-after-free. Meanwhile conn1 is leaked as it was orphaned when sco_conn_del() cleared the association.

Fix this by:

• Moving lock_sock() before the sk_state/sk_type checks in sco_sock_connect() to serialize concurrent connect attempts
• Fixing the sk_type != SOCK_SEQPACKET check to actually return the error instead of just assigning it
• Adding a state re-check in sco_connect() after lock_sock() to catch state changes during the window between the locks
• Adding sco_pi(sk)->conn check in sco_chan_add() to prevent double-attach of a socket to multiple connections
• Adding hci_conn_drop() on sco_chan_add failure to prevent HCI connection leaks

Affected

• Linux >= 70a13b1e25fef37c87c8a1228ddb8900efbca7cf < dabf22269242e2f2bf44c43fcdc2fa763df7f9cc
• Linux >= 9a8ec9e8ebb5a7c0cfbce2d6b4a6b67b2b78e8f3 < adb90cd0f9f7a8d438fcb93354040fbafc5ae2a0
• Linux >= 9a8ec9e8ebb5a7c0cfbce2d6b4a6b67b2b78e8f3 < 7e296ffdab5bdab718dff7c14288fdcb9154fa27
• Linux >= 9a8ec9e8ebb5a7c0cfbce2d6b4a6b67b2b78e8f3 < 98c8d3bfdaa657d8f472dbbebd7ea8cd816d8a8d
• Linux >= 9a8ec9e8ebb5a7c0cfbce2d6b4a6b67b2b78e8f3 < d002bd11024bd231bcb606877e33951ffb7bed14
• Linux >= 9a8ec9e8ebb5a7c0cfbce2d6b4a6b67b2b78e8f3 < 8a5b0135d4a5d9683203a3d9a12a711ccec5936b
• Linux >= 6.1.109 < 6.1.168
• Linux 6.3

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.