Bluetooth: Lock the L2CAP channel when sending

The ERTM and streaming mode transmit queue must only be accessed while
the L2CAP channel lock is held.  Locking the channel before calling
l2cap_chan_send ensures that multiple threads cannot simultaneously
manipulate the queue when sending and receiving concurrently.

L2CAP channel locking had previously moved to the l2cap_chan struct
instead of the associated socket, so some of the old socket locking
can also be removed in this patch.
Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
Signed-off-by: Gustavo Padovan <gustavo@padovan.org>

include/net/bluetooth/bluetooth.h

@@ -257,12 +257,10 @@ static inline struct sk_buff *bt_skb_send_alloc(struct sock *sk,
 {
 	struct sk_buff *skb;
 
-	release_sock(sk);
 	if ((skb = sock_alloc_send_skb(sk, len + BT_SKB_RESERVE, nb, err))) {
 		skb_reserve(skb, BT_SKB_RESERVE);
 		bt_cb(skb)->incoming  = 0;
 	}
-	lock_sock(sk);
 
 	if (!skb && *err)
 		return NULL;

net/bluetooth/l2cap_sock.c

@@ -720,16 +720,13 @@ static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
 	if (msg->msg_flags & MSG_OOB)
 		return -EOPNOTSUPP;
 
-	lock_sock(sk);
-
-	if (sk->sk_state != BT_CONNECTED) {
-		release_sock(sk);
+	if (sk->sk_state != BT_CONNECTED)
 		return -ENOTCONN;
-	}
 
+	l2cap_chan_lock(chan);
 	err = l2cap_chan_send(chan, msg, len, sk->sk_priority);
+	l2cap_chan_unlock(chan);
 
-	release_sock(sk);
 	return err;
 }
 
@@ -940,7 +937,10 @@ static struct sk_buff *l2cap_sock_alloc_skb_cb(struct l2cap_chan *chan,
 	struct sk_buff *skb;
 	int err;
 
+	l2cap_chan_unlock(chan);
 	skb = bt_skb_send_alloc(chan->sk, len, nb, &err);
+	l2cap_chan_lock(chan);
+
 	if (!skb)
 		return ERR_PTR(err);