Fix GH-9008: mb_detect_encoding(): wrong results with null $encodings

Passing `null` to `$encodings` is supposed to behave like passing the
result of `mb_detect_order()`.  Therefore, we need to remove the non-
encodings from the `elist` in this case as well.  Thus, we duplicate
the global `elist`, so we can modify it.

Closes GH-9063.

NEWS

@@ -5,6 +5,10 @@ PHP                                                                        NEWS
 - Core:
   . Fixed --CGI-- support of run-tests.php. (cmb)
 
+- MBString:
+  . Fix bug GH-9008 (mb_detect_encoding(): wrong results with null $encodings).
+    (cmb)
+
 04 Aug 2022, PHP 8.1.9
 
 - CLI:

ext/mbstring/mbstring.c

@@ -2694,6 +2694,13 @@ PHP_FUNCTION(mb_strtolower)
 }
 /* }}} */
 
+static const mbfl_encoding **duplicate_elist(const mbfl_encoding **elist, size_t size)
+{
+	const mbfl_encoding **new_elist = safe_emalloc(size, sizeof(mbfl_encoding*), 0);
+	memcpy(ZEND_VOIDP(new_elist), elist, size * sizeof(mbfl_encoding*));
+	return new_elist;
+}
+
 /* {{{ Encodings of the given string is returned (as a string) */
 PHP_FUNCTION(mb_detect_encoding)
 {
@@ -2707,7 +2714,6 @@ PHP_FUNCTION(mb_detect_encoding)
 	const mbfl_encoding *ret;
 	const mbfl_encoding **elist;
 	size_t size;
-	bool free_elist;
 
 	ZEND_PARSE_PARAMETERS_START(1, 3)
 		Z_PARAM_STRING(str, str_len)
@@ -2721,16 +2727,13 @@ PHP_FUNCTION(mb_detect_encoding)
 		if (FAILURE == php_mb_parse_encoding_array(encoding_ht, &elist, &size, 2)) {
 			RETURN_THROWS();
 		}
-		free_elist = 1;
 	} else if (encoding_str) {
 		if (FAILURE == php_mb_parse_encoding_list(ZSTR_VAL(encoding_str), ZSTR_LEN(encoding_str), &elist, &size, /* persistent */ 0, /* arg_num */ 2, /* allow_pass_encoding */ 0)) {
 			RETURN_THROWS();
 		}
-		free_elist = 1;
 	} else {
-		elist = MBSTRG(current_detect_order_list);
+		elist = duplicate_elist(MBSTRG(current_detect_order_list), MBSTRG(current_detect_order_list_size));
 		size = MBSTRG(current_detect_order_list_size);
-		free_elist = 0;
 	}
 
 	if (size == 0) {
@@ -2739,12 +2742,10 @@ PHP_FUNCTION(mb_detect_encoding)
 		RETURN_THROWS();
 	}
 
-	if (free_elist) {
-		remove_non_encodings_from_elist(elist, &size);
-		if (size == 0) {
-			efree(ZEND_VOIDP(elist));
-			RETURN_FALSE;
-		}
+	remove_non_encodings_from_elist(elist, &size);
+	if (size == 0) {
+		efree(ZEND_VOIDP(elist));
+		RETURN_FALSE;
 	}
 
 	if (ZEND_NUM_ARGS() < 3) {
@@ -2761,9 +2762,7 @@ PHP_FUNCTION(mb_detect_encoding)
 		ret = mbfl_identify_encoding(&string, elist, size, strict);
 	}
 
-	if (free_elist) {
-		efree(ZEND_VOIDP(elist));
-	}
+	efree(ZEND_VOIDP(elist));
 
 	if (ret == NULL) {
 		RETURN_FALSE;

ext/mbstring/tests/gh9008.phpt

@@ -0,0 +1,24 @@
+--TEST--
+GH-9008 (mb_detect_encoding(): wrong results with null $encodings)
+--EXTENSIONS--
+mbstring
+--FILE--
+<?php
+$string = "<?php
+
+function test()
+{
+
+}
+";
+
+mb_detect_order(["ASCII", "UUENCODE"]);
+
+var_dump(
+    mb_detect_encoding($string, null, true),
+    mb_detect_encoding($string, mb_detect_order(), true),
+);
+?>
+--EXPECT--
+string(5) "ASCII"
+string(5) "ASCII"