TLS: Avoid undefined behavior in pointer arithmetic

Reorder terms in a way that no invalid pointers are generated with
pos+len operations. end-pos is always defined (with a valid pos pointer)
while pos+len could end up pointing beyond the end pointer which would
be undefined behavior.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/tls/tlsv1_client_write.c

@@ -134,6 +134,11 @@ static int tls_write_client_certificate(struct tlsv1_client *conn,
 	struct x509_certificate *cert;
 
 	pos = *msgpos;
+	if (TLS_RECORD_HEADER_LEN + 1 + 3 + 3 > end - pos) {
+		tls_alert(conn, TLS_ALERT_LEVEL_FATAL,
+			  TLS_ALERT_INTERNAL_ERROR);
+		return -1;
+	}
 
 	wpa_printf(MSG_DEBUG, "TLSv1: Send Certificate");
 	rhdr = pos;
@@ -154,7 +159,7 @@ static int tls_write_client_certificate(struct tlsv1_client *conn,
 	pos += 3;
 	cert = conn->cred ? conn->cred->cert : NULL;
 	while (cert) {
-		if (pos + 3 + cert->cert_len > end) {
+		if (3 + cert->cert_len > (size_t) (end - pos)) {
 			wpa_printf(MSG_DEBUG, "TLSv1: Not enough buffer space "
 				   "for Certificate (cert_len=%lu left=%lu)",
 				   (unsigned long) cert->cert_len,
@@ -265,9 +270,16 @@ static int tlsv1_key_x_dh(struct tlsv1_client *conn, u8 **pos, u8 *end)
 	wpa_hexdump(MSG_DEBUG, "TLSv1: DH Yc (client's public value)",
 		    dh_yc, dh_yc_len);
 
+	if (end - *pos < 2) {
+		tls_alert(conn, TLS_ALERT_LEVEL_FATAL,
+			  TLS_ALERT_INTERNAL_ERROR);
+		os_free(csecret);
+		os_free(dh_yc);
+		return -1;
+	}
 	WPA_PUT_BE16(*pos, dh_yc_len);
 	*pos += 2;
-	if (*pos + dh_yc_len > end) {
+	if (dh_yc_len > (size_t) (end - *pos)) {
 		wpa_printf(MSG_DEBUG, "TLSv1: Not enough room in the "
 			   "message buffer for Yc");
 		tls_alert(conn, TLS_ALERT_LEVEL_FATAL,

src/tls/tlsv1_server_write.c

@@ -168,6 +168,11 @@ static int tls_write_server_certificate(struct tlsv1_server *conn,
 	}
 
 	pos = *msgpos;
+	if (TLS_RECORD_HEADER_LEN + 1 + 3 + 3 > end - pos) {
+		tlsv1_server_alert(conn, TLS_ALERT_LEVEL_FATAL,
+				   TLS_ALERT_INTERNAL_ERROR);
+		return -1;
+	}
 
 	tlsv1_server_log(conn, "Send Certificate");
 	rhdr = pos;
@@ -188,7 +193,7 @@ static int tls_write_server_certificate(struct tlsv1_server *conn,
 	pos += 3;
 	cert = conn->cred->cert;
 	while (cert) {
-		if (pos + 3 + cert->cert_len > end) {
+		if (3 + cert->cert_len > (size_t) (end - pos)) {
 			wpa_printf(MSG_DEBUG, "TLSv1: Not enough buffer space "
 				   "for Certificate (cert_len=%lu left=%lu)",
 				   (unsigned long) cert->cert_len,
@@ -371,7 +376,7 @@ static int tls_write_server_key_exchange(struct tlsv1_server *conn,
 	/* body - ServerDHParams */
 	server_params = pos;
 	/* dh_p */
-	if (pos + 2 + dh_p_len > end) {
+	if (2 + dh_p_len > (size_t) (end - pos)) {
 		wpa_printf(MSG_DEBUG, "TLSv1: Not enough buffer space for "
 			   "dh_p");
 		tlsv1_server_alert(conn, TLS_ALERT_LEVEL_FATAL,
@@ -385,7 +390,7 @@ static int tls_write_server_key_exchange(struct tlsv1_server *conn,
 	pos += dh_p_len;
 
 	/* dh_g */
-	if (pos + 2 + conn->cred->dh_g_len > end) {
+	if (2 + conn->cred->dh_g_len > (size_t) (end - pos)) {
 		wpa_printf(MSG_DEBUG, "TLSv1: Not enough buffer space for "
 			   "dh_g");
 		tlsv1_server_alert(conn, TLS_ALERT_LEVEL_FATAL,
@@ -399,7 +404,7 @@ static int tls_write_server_key_exchange(struct tlsv1_server *conn,
 	pos += conn->cred->dh_g_len;
 
 	/* dh_Ys */
-	if (pos + 2 + dh_ys_len > end) {
+	if (2 + dh_ys_len > (size_t) (end - pos)) {
 		wpa_printf(MSG_DEBUG, "TLSv1: Not enough buffer space for "
 			   "dh_Ys");
 		tlsv1_server_alert(conn, TLS_ALERT_LEVEL_FATAL,
@@ -457,7 +462,7 @@ static int tls_write_server_key_exchange(struct tlsv1_server *conn,
 			 *   SignatureAlgorithm signature;
 			 * } SignatureAndHashAlgorithm;
 			 */
-			if (hlen < 0 || pos + 2 > end) {
+			if (hlen < 0 || end - pos < 2) {
 				tlsv1_server_alert(conn, TLS_ALERT_LEVEL_FATAL,
 						   TLS_ALERT_INTERNAL_ERROR);
 				return -1;

src/tls/x509v3.c

@@ -199,12 +199,11 @@ static int x509_parse_algorithm_identifier(
 			   hdr.class, hdr.tag);
 		return -1;
 	}
+	if (hdr.length > buf + len - hdr.payload)
+		return -1;
 	pos = hdr.payload;
 	end = pos + hdr.length;
 
-	if (end > buf + len)
-		return -1;
-
 	*next = end;
 
 	if (asn1_get_oid(pos, end - pos, &id->oid, &pos))
@@ -243,7 +242,7 @@ static int x509_parse_public_key(const u8 *buf, size_t len,
 	}
 	pos = hdr.payload;
 
-	if (pos + hdr.length > end)
+	if (hdr.length > end - pos)
 		return -1;
 	end = pos + hdr.length;
 	*next = end;
@@ -319,7 +318,7 @@ static int x509_parse_name(const u8 *buf, size_t len, struct x509_name *name,
 	}
 	pos = hdr.payload;
 
-	if (pos + hdr.length > buf + len)
+	if (hdr.length > buf + len - pos)
 		return -1;
 
 	end = *next = pos + hdr.length;
@@ -677,7 +676,7 @@ static int x509_parse_validity(const u8 *buf, size_t len,
 	pos = hdr.payload;
 	plen = hdr.length;
 
-	if (pos + plen > buf + len)
+	if (plen > (size_t) (buf + len - pos))
 		return -1;
 
 	*next = pos + plen;
@@ -801,7 +800,7 @@ static int x509_parse_ext_basic_constraints(struct x509_certificate *cert,
 		}
 		cert->ca = hdr.payload[0];
 
-		if (hdr.payload + hdr.length == pos + len) {
+		if (hdr.length == pos + len - hdr.payload) {
 			wpa_printf(MSG_DEBUG, "X509: BasicConstraints - cA=%d",
 				   cert->ca);
 			return 0;
@@ -1503,12 +1502,12 @@ struct x509_certificate * x509_certificate_parse(const u8 *buf, size_t len)
 	}
 	pos = hdr.payload;
 
-	if (pos + hdr.length > end) {
+	if (hdr.length > end - pos) {
 		x509_certificate_free(cert);
 		return NULL;
 	}
 
-	if (pos + hdr.length < end) {
+	if (hdr.length < end - pos) {
 		wpa_hexdump(MSG_MSGDUMP, "X509: Ignoring extra data after DER "
 			    "encoded certificate",
 			    pos + hdr.length, end - (pos + hdr.length));