[PATCH 6.12 081/242] Bluetooth: SCO: fix race conditions in sco_sock_connect()

Greg Kroah-Hartman
2026-04-08T18:42:44Z

From: Cen Zhang <zzzccc427@gmail.com>

[ Upstream commit 8a5b0135d4a5d9683203a3d9a12a711ccec5936b ]

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

Fixes: 9a8ec9e8ebb5 ("Bluetooth: SCO: Fix possible circular locking dependency on sco_connect_cfm")
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/bluetooth/sco.c | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index ad3439bd4d51a..ded0c52ccf0b9 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -238,7 +238,7 @@ static int sco_chan_add(struct sco_conn *conn, struct sock *sk,
int err = 0;

sco_conn_lock(conn);
- if (conn->sk)
+ if (conn->sk || sco_pi(sk)->conn)
err = -EBUSY;
else
__sco_chan_add(conn, sk, parent);
@@ -293,9 +293,20 @@ static int sco_connect(struct sock *sk)

lock_sock(sk);

+ /* Recheck state after reacquiring the socket lock, as another
+ * thread may have changed it (e.g., closed the socket).
+ */
+ if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
+ release_sock(sk);
+ hci_conn_drop(hcon);
+ err = -EBADFD;
+ goto unlock;
+ }
+
err = sco_chan_add(conn, sk, NULL);
if (err) {
release_sock(sk);
+ hci_conn_drop(hcon);
goto unlock;
}

@@ -602,13 +613,18 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr *addr, int alen
addr->sa_family != AF_BLUETOOTH)
return -EINVAL;

- if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND)
+ lock_sock(sk);
+
+ if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
+ release_sock(sk);
return -EBADFD;
+ }

- if (sk->sk_type != SOCK_SEQPACKET)
- err = -EINVAL;
+ if (sk->sk_type != SOCK_SEQPACKET) {
+ release_sock(sk);
+ return -EINVAL;
+ }

- lock_sock(sk);
/* Set destination address and psm */
bacpy(&sco_pi(sk)->dst, &sa->sco_bdaddr);
release_sock(sk);
--
2.53.0