[PATCH] Bluetooth: SCO: fix race conditions in sco_sock_connect()

[Cen Zhang <zzzccc427@gmail.com>]

sco_sock_connect() checks sk_state and sk_type without holding the
socket lock, creating a TOCTOU race where two threads can both pass the
state check and proceed to sco_connect() concurrently.

This causes multiple issues:
1. Both threads create separate HCI and SCO connections
2. The second thread's sco_chan_add() overwrites sco_pi(sk)->conn,
   orphaning the first connection (memory/resource leak)
3. If the socket is closed between the state check and sco_connect()'s
   inner lock_sock(), the connect proceeds on a dead socket (UAF)

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 detect
  state changes during the lock gap
- Adding sco_pi(sk)->conn check in sco_chan_add() to prevent
  double-attach of the 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>
---
 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 e7db50165879..689788ad26a4 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -298,7 +298,7 @@ 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);
@@ -353,9 +353,20 @@ 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;
 	}
 
@@ -652,13 +663,18 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr_unsized *addr,
 	    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);
-- 
2.34.1