Bluetooth: Check if SDU size is greater than MTU on L2CAP

After reassembly the SDU we need to check his size. It can't overflow
the MTU size.
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/l2cap.c

@@ -3277,15 +3277,19 @@ static int l2cap_sar_reassembly_sdu(struct sock *sk, struct sk_buff *skb, u16 co
 		pi->conn_state &= ~L2CAP_CONN_SAR_SDU;
 		pi->partial_sdu_len += skb->len;
 
+		if (pi->partial_sdu_len > pi->imtu)
+			goto drop;
+
 		if (pi->partial_sdu_len == pi->sdu_len) {
 			_skb = skb_clone(pi->sdu, GFP_ATOMIC);
 			err = sock_queue_rcv_skb(sk, _skb);
 			if (err < 0)
 				kfree_skb(_skb);
 		}
-		kfree_skb(pi->sdu);
 		err = 0;
 
+drop:
+		kfree_skb(pi->sdu);
 		break;
 	}