Bluetooth: L2CAP: Fix not checking for maximum number of DCID

When receiving L2CAP_CREDIT_BASED_CONNECTION_REQ the remote may request
more channels than allowed by the spec (10 octecs = 5 CIDs) so this
checks if the number of channels is bigger than the maximum allowed and
respond with an error.
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/l2cap.h

@@ -494,6 +494,7 @@ struct l2cap_le_credits {
 
 #define L2CAP_ECRED_MIN_MTU		64
 #define L2CAP_ECRED_MIN_MPS		64
+#define L2CAP_ECRED_MAX_CID		5
 
 struct l2cap_ecred_conn_req {
 	__le16 psm;

net/bluetooth/l2cap_core.c

@@ -5921,7 +5921,7 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 	struct l2cap_ecred_conn_req *req = (void *) data;
 	struct {
 		struct l2cap_ecred_conn_rsp rsp;
-		__le16 dcid[5];
+		__le16 dcid[L2CAP_ECRED_MAX_CID];
 	} __packed pdu;
 	struct l2cap_chan *chan, *pchan;
 	u16 mtu, mps;
@@ -5938,6 +5938,14 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 		goto response;
 	}
 
+	cmd_len -= sizeof(*req);
+	num_scid = cmd_len / sizeof(u16);
+
+	if (num_scid > ARRAY_SIZE(pdu.dcid)) {
+		result = L2CAP_CR_LE_INVALID_PARAMS;
+		goto response;
+	}
+
 	mtu  = __le16_to_cpu(req->mtu);
 	mps  = __le16_to_cpu(req->mps);
 
@@ -5970,8 +5978,6 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 	}
 
 	result = L2CAP_CR_LE_SUCCESS;
-	cmd_len -= sizeof(*req);
-	num_scid = cmd_len / sizeof(u16);
 
 	for (i = 0; i < num_scid; i++) {
 		u16 scid = __le16_to_cpu(req->scid[i]);