Bluetooth: Fix disconnecting L2CAP when a credits overflow occurs

The L2CAP specification requires us to disconnect an L2CAP channel if
the remote side gives us credits beyond 65535. This patch makes sure we
disconnect the channel in such a situation.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/l2cap_core.c

@@ -42,6 +42,8 @@
 #include "amp.h"
 #include "6lowpan.h"
 
+#define LE_FLOWCTL_MAX_CREDITS 65535
+
 bool disable_ertm;
 
 static u32 l2cap_feat_mask = L2CAP_FEAT_FIXED_CHAN | L2CAP_FEAT_UCD;
@@ -5473,7 +5475,7 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
 {
 	struct l2cap_le_credits *pkt;
 	struct l2cap_chan *chan;
-	u16 cid, credits;
+	u16 cid, credits, max_credits;
 
 	if (cmd_len != sizeof(*pkt))
 		return -EPROTO;
@@ -5488,6 +5490,17 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
 	if (!chan)
 		return -EBADSLT;
 
+	max_credits = LE_FLOWCTL_MAX_CREDITS - chan->tx_credits;
+	if (credits > max_credits) {
+		BT_ERR("LE credits overflow");
+		l2cap_send_disconn_req(chan, ECONNRESET);
+
+		/* Return 0 so that we don't trigger an unnecessary
+		 * command reject packet.
+		 */
+		return 0;
+	}
+
 	chan->tx_credits += credits;
 
 	while (chan->tx_credits && !skb_queue_empty(&chan->tx_q)) {