privsep: 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/drivers/driver_privsep.c

@@ -161,11 +161,11 @@ wpa_driver_privsep_get_scan_results2(void *priv)
 		return NULL;
 	}
 
-	while (results->num < (size_t) num && pos + sizeof(int) < end) {
+	while (results->num < (size_t) num && end - pos > sizeof(int)) {
 		int len;
 		os_memcpy(&len, pos, sizeof(int));
 		pos += sizeof(int);
-		if (len < 0 || len > 10000 || pos + len > end)
+		if (len < 0 || len > 10000 || len > end - pos)
 			break;
 
 		r = os_malloc(len);