RSN: 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/rsn_supp/wpa.c

@@ -1003,8 +1003,8 @@ static int wpa_supplicant_validate_ie_ft(struct wpa_sm *sm,
 	if (sm->assoc_resp_ies) {
 		pos = sm->assoc_resp_ies;
 		end = pos + sm->assoc_resp_ies_len;
-		while (pos + 2 < end) {
-			if (pos + 2 + pos[1] > end)
+		while (end - pos > 2) {
+			if (2 + pos[1] > end - pos)
 				break;
 			switch (*pos) {
 			case WLAN_EID_MOBILITY_DOMAIN:

src/rsn_supp/wpa_ie.c

@@ -378,7 +378,7 @@ static int wpa_parse_generic(const u8 *pos, const u8 *end,
 		return 0;
 	}
 
-	if (pos + 1 + RSN_SELECTOR_LEN < end &&
+	if (1 + RSN_SELECTOR_LEN < end - pos &&
 	    pos[1] >= RSN_SELECTOR_LEN + PMKID_LEN &&
 	    RSN_SELECTOR_GET(pos + 2) == RSN_KEY_DATA_PMKID) {
 		ie->pmkid = pos + 2 + RSN_SELECTOR_LEN;
@@ -491,13 +491,13 @@ int wpa_supplicant_parse_ies(const u8 *buf, size_t len,
 	int ret = 0;
 
 	os_memset(ie, 0, sizeof(*ie));
-	for (pos = buf, end = pos + len; pos + 1 < end; pos += 2 + pos[1]) {
+	for (pos = buf, end = pos + len; end - pos > 1; pos += 2 + pos[1]) {
 		if (pos[0] == 0xdd &&
 		    ((pos == buf + len - 1) || pos[1] == 0)) {
 			/* Ignore padding */
 			break;
 		}
-		if (pos + 2 + pos[1] > end) {
+		if (2 + pos[1] > end - pos) {
 			wpa_printf(MSG_DEBUG, "WPA: EAPOL-Key Key Data "
 				   "underflow (ie=%d len=%d pos=%d)",
 				   pos[0], pos[1], (int) (pos - buf));