Patch for bug #61660

When the hexadecimal string has an odd length, the resulting binary data must be left padded with 0s in order to be aligned on 8 bits.
To avoid extraneous if test on each iteration, we distinguish the special case by pointing the source data iterator the the NUL bytes at the end which we can then detect and act accordingly.

ext/standard/string.c

@@ -150,17 +150,23 @@ static char *php_bin2hex(const unsigned char *old, const size_t oldlen, size_t *
  */
 static char *php_hex2bin(const unsigned char *old, const size_t oldlen, size_t *newlen)
 {
-	size_t target_length = oldlen >> 1;
+	size_t target_length = (oldlen + 1) >> 1;
 	register unsigned char *str = (unsigned char *)safe_emalloc(target_length, sizeof(char), 1);
 	size_t i, j;
-	for (i = j = 0; i < target_length; i++) {
+	/* if we have an odd length, point to the end of the string to distinguish the special case */
+	j = oldlen & 1 ? oldlen + 1: 0;
+	for (i = 0; i < target_length; i++) {
 		char c = old[j++];
 		if (c >= '0' && c <= '9') {
 			str[i] = (c - '0') << 4;
 		} else if (c >= 'a' && c <= 'f') {
 			str[i] = (c - 'a' + 10) << 4;
 		} else if (c >= 'A' && c <= 'F') {
 			str[i] = (c - 'A' + 10) << 4;
+		} else if(c == '\0') {
+			/* odd length, put the first 4 bits to 0 and restart at the beginning of the string */
+			str[i] = 0;
+			j= 0;
 		} else {
 			efree(str);
 			return NULL;