Add array size maximum to array_diff()

This silences some reports about the equivalence to array_merge()'s
issue. However, this is different as no packed fill is used in this
code, so it doesn't have the same bug that array_merge() had.

Closes GH-21449.

Author: ndossche

NEWS

@@ -134,6 +134,7 @@ PHP                                                                        NEWS
     null destination). (David Carlier)
   . Fixed bug GH-13204 (glob() fails if square bracket is in current directory).
     (ndossche)
+  . Add array size maximum to array_diff(). (ndossche)
 
 - Streams:
   . Added so_keepalive, tcp_keepidle, tcp_keepintvl and tcp_keepcnt stream

ext/standard/array.c

@@ -5741,7 +5741,7 @@ PHP_FUNCTION(array_diff)
 {
 	zval *args;
 	uint32_t argc, i;
-	uint32_t num;
+	uint64_t num;
 	HashTable exclude;
 	zval *value;
 	zend_string *str, *tmp_str, *key;
@@ -5831,6 +5831,11 @@ PHP_FUNCTION(array_diff)
 		return;
 	}
 
+	if (UNEXPECTED(num >= HT_MAX_SIZE)) {
+		zend_throw_error(NULL, "The total number of elements must be lower than %u", HT_MAX_SIZE);
+		RETURN_THROWS();
+	}
+
 	ZVAL_NULL(&dummy);
 	/* create exclude map */
 	zend_hash_init(&exclude, num, NULL, NULL, 0);