[Bluetooth] Add packet size checks for CAPI messages

With malformed packets it might be possible to overwrite internal
CMTP and CAPI data structures. This patch adds additional length
checks to prevent these kinds of remote attacks.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/cmtp/capi.c

@@ -196,6 +196,9 @@ static void cmtp_recv_interopmsg(struct cmtp_session *session, struct sk_buff *s
 
 	switch (CAPIMSG_SUBCOMMAND(skb->data)) {
 	case CAPI_CONF:
+		if (skb->len < CAPI_MSG_BASELEN + 10)
+			break;
+
 		func = CAPIMSG_U16(skb->data, CAPI_MSG_BASELEN + 5);
 		info = CAPIMSG_U16(skb->data, CAPI_MSG_BASELEN + 8);
 
@@ -226,6 +229,9 @@ static void cmtp_recv_interopmsg(struct cmtp_session *session, struct sk_buff *s
 			break;
 
 		case CAPI_FUNCTION_GET_PROFILE:
+			if (skb->len < CAPI_MSG_BASELEN + 11 + sizeof(capi_profile))
+				break;
+
 			controller = CAPIMSG_U16(skb->data, CAPI_MSG_BASELEN + 11);
 			msgnum = CAPIMSG_MSGID(skb->data);
 
@@ -246,17 +252,26 @@ static void cmtp_recv_interopmsg(struct cmtp_session *session, struct sk_buff *s
 			break;
 
 		case CAPI_FUNCTION_GET_MANUFACTURER:
+			if (skb->len < CAPI_MSG_BASELEN + 15)
+				break;
+
 			controller = CAPIMSG_U32(skb->data, CAPI_MSG_BASELEN + 10);
 
 			if (!info && ctrl) {
-				strncpy(ctrl->manu,
-					skb->data + CAPI_MSG_BASELEN + 15,
+				int len = min_t(uint, CAPI_MANUFACTURER_LEN,
 						skb->data[CAPI_MSG_BASELEN + 14]);
+
+				memset(ctrl->manu, 0, CAPI_MANUFACTURER_LEN);
+				strncpy(ctrl->manu,
+					skb->data + CAPI_MSG_BASELEN + 15, len);
 			}
 
 			break;
 
 		case CAPI_FUNCTION_GET_VERSION:
+			if (skb->len < CAPI_MSG_BASELEN + 32)
+				break;
+
 			controller = CAPIMSG_U32(skb->data, CAPI_MSG_BASELEN + 12);
 
 			if (!info && ctrl) {
@@ -269,13 +284,18 @@ static void cmtp_recv_interopmsg(struct cmtp_session *session, struct sk_buff *s
 			break;
 
 		case CAPI_FUNCTION_GET_SERIAL_NUMBER:
+			if (skb->len < CAPI_MSG_BASELEN + 17)
+				break;
+
 			controller = CAPIMSG_U32(skb->data, CAPI_MSG_BASELEN + 12);
 
 			if (!info && ctrl) {
+				int len = min_t(uint, CAPI_SERIAL_LEN,
+						skb->data[CAPI_MSG_BASELEN + 16]);
+
 				memset(ctrl->serial, 0, CAPI_SERIAL_LEN);
 				strncpy(ctrl->serial,
-					skb->data + CAPI_MSG_BASELEN + 17,
-					skb->data[CAPI_MSG_BASELEN + 16]);
+					skb->data + CAPI_MSG_BASELEN + 17, len);
 			}
 
 			break;
@@ -284,14 +304,18 @@ static void cmtp_recv_interopmsg(struct cmtp_session *session, struct sk_buff *s
 		break;
 
 	case CAPI_IND:
+		if (skb->len < CAPI_MSG_BASELEN + 6)
+			break;
+
 		func = CAPIMSG_U16(skb->data, CAPI_MSG_BASELEN + 3);
 
 		if (func == CAPI_FUNCTION_LOOPBACK) {
+			int len = min_t(uint, skb->len - CAPI_MSG_BASELEN - 6,
+						skb->data[CAPI_MSG_BASELEN + 5]);
 			appl = CAPIMSG_APPID(skb->data);
 			msgnum = CAPIMSG_MSGID(skb->data);
 			cmtp_send_interopmsg(session, CAPI_RESP, appl, msgnum, func,
-						skb->data + CAPI_MSG_BASELEN + 6,
-						skb->data[CAPI_MSG_BASELEN + 5]);
+						skb->data + CAPI_MSG_BASELEN + 6, len);
 		}
 
 		break;
@@ -309,6 +333,9 @@ void cmtp_recv_capimsg(struct cmtp_session *session, struct sk_buff *skb)
 
 	BT_DBG("session %p skb %p len %d", session, skb, skb->len);
 
+	if (skb->len < CAPI_MSG_BASELEN)
+		return;
+
 	if (CAPIMSG_COMMAND(skb->data) == CAPI_INTEROPERABILITY) {
 		cmtp_recv_interopmsg(session, skb);
 		return;