SAE: 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/common/sae.c

@@ -923,7 +923,7 @@ static void sae_parse_commit_token(struct sae_data *sae, const u8 **pos,
 				   const u8 *end, const u8 **token,
 				   size_t *token_len)
 {
-	if (*pos + (sae->tmp->ec ? 3 : 2) * sae->tmp->prime_len < end) {
+	if ((sae->tmp->ec ? 3 : 2) * sae->tmp->prime_len < end - *pos) {
 		size_t tlen = end - (*pos + (sae->tmp->ec ? 3 : 2) *
 				     sae->tmp->prime_len);
 		wpa_hexdump(MSG_DEBUG, "SAE: Anti-Clogging Token", *pos, tlen);
@@ -946,7 +946,7 @@ static u16 sae_parse_commit_scalar(struct sae_data *sae, const u8 **pos,
 {
 	struct crypto_bignum *peer_scalar;
 
-	if (*pos + sae->tmp->prime_len > end) {
+	if (sae->tmp->prime_len > end - *pos) {
 		wpa_printf(MSG_DEBUG, "SAE: Not enough data for scalar");
 		return WLAN_STATUS_UNSPECIFIED_FAILURE;
 	}
@@ -994,7 +994,7 @@ static u16 sae_parse_commit_element_ecc(struct sae_data *sae, const u8 *pos,
 {
 	u8 prime[SAE_MAX_ECC_PRIME_LEN];
 
-	if (pos + 2 * sae->tmp->prime_len > end) {
+	if (2 * sae->tmp->prime_len > end - pos) {
 		wpa_printf(MSG_DEBUG, "SAE: Not enough data for "
 			   "commit-element");
 		return WLAN_STATUS_UNSPECIFIED_FAILURE;
@@ -1040,7 +1040,7 @@ static u16 sae_parse_commit_element_ffc(struct sae_data *sae, const u8 *pos,
 	struct crypto_bignum *res, *one;
 	const u8 one_bin[1] = { 0x01 };
 
-	if (pos + sae->tmp->prime_len > end) {
+	if (sae->tmp->prime_len > end - pos) {
 		wpa_printf(MSG_DEBUG, "SAE: Not enough data for "
 			   "commit-element");
 		return WLAN_STATUS_UNSPECIFIED_FAILURE;
@@ -1098,7 +1098,7 @@ u16 sae_parse_commit(struct sae_data *sae, const u8 *data, size_t len,
 	u16 res;
 
 	/* Check Finite Cyclic Group */
-	if (pos + 2 > end)
+	if (end - pos < 2)
 		return WLAN_STATUS_UNSPECIFIED_FAILURE;
 	res = sae_group_allowed(sae, allowed_groups, WPA_GET_LE16(pos));
 	if (res != WLAN_STATUS_SUCCESS)