Bluetooth: Make better use of l2cap_chan reference counting

L2CAP sockets contain a pointer to l2cap_chan that needs to be
reference counted in order to prevent a possible dangling pointer when
the channel is freed.

There were a few other cases where an l2cap_chan pointer on the stack
was dereferenced after a call to l2cap_chan_del. Those pointers are
also now reference counted.
Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
Signed-off-by: Gustavo Padovan <gustavo@padovan.org>

net/bluetooth/l2cap_core.c

@@ -1256,6 +1256,7 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
 
 	/* Kill channels */
 	list_for_each_entry_safe(chan, l, &conn->chan_l, list) {
+		l2cap_chan_hold(chan);
 		l2cap_chan_lock(chan);
 
 		l2cap_chan_del(chan, err);
@@ -1263,6 +1264,7 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
 		l2cap_chan_unlock(chan);
 
 		chan->ops->close(chan->data);
+		l2cap_chan_put(chan);
 	}
 
 	mutex_unlock(&conn->chan_lock);
@@ -3375,11 +3377,13 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, struct l2cap_cmd
 	sk->sk_shutdown = SHUTDOWN_MASK;
 	release_sock(sk);
 
+	l2cap_chan_hold(chan);
 	l2cap_chan_del(chan, ECONNRESET);
 
 	l2cap_chan_unlock(chan);
 
 	chan->ops->close(chan->data);
+	l2cap_chan_put(chan);
 
 	mutex_unlock(&conn->chan_lock);
 
@@ -3407,11 +3411,13 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, struct l2cap_cmd
 
 	l2cap_chan_lock(chan);
 
+	l2cap_chan_hold(chan);
 	l2cap_chan_del(chan, 0);
 
 	l2cap_chan_unlock(chan);
 
 	chan->ops->close(chan->data);
+	l2cap_chan_put(chan);
 
 	mutex_unlock(&conn->chan_lock);
 

net/bluetooth/l2cap_sock.c

@@ -956,6 +956,7 @@ static void l2cap_sock_destruct(struct sock *sk)
 {
 	BT_DBG("sk %p", sk);
 
+	l2cap_chan_put(l2cap_pi(sk)->chan);
 	if (l2cap_pi(sk)->rx_busy_skb) {
 		kfree_skb(l2cap_pi(sk)->rx_busy_skb);
 		l2cap_pi(sk)->rx_busy_skb = NULL;
@@ -1057,6 +1058,8 @@ static struct sock *l2cap_sock_alloc(struct net *net, struct socket *sock, int p
 		return NULL;
 	}
 
+	l2cap_chan_hold(chan);
+
 	chan->sk = sk;
 
 	l2cap_pi(sk)->chan = chan;