Fix GH-17187: unreachable program point in zend_hash

A bunch of different issues:
1) The referenced value is copied without incrementing the refcount.
   The reason the refcount isn't incremented is because otherwise
   the array modifications would violate the RC1 constraints.
   Solve this by copying the reference itself instead and always
   read the referenced value.
2) No type checks on the array data, so malicious scripts could
   cause type confusion bugs.
3) Potential overflow when the arrays resize and we access ctag.

Author: ndossche

ext/xml/tests/gh17187_1.phpt

@@ -0,0 +1,93 @@
+--TEST--
+GH-17187 (unreachable program point in zend_hash)
+--EXTENSIONS--
+xml
+--CREDITS--
+chongwick
+--FILE--
+<?php
+class ImmutableParser {
+    private $parser;
+    private $immutableData;
+    private $arrayCopy;
+
+    public function __construct() {
+        $this->parser = xml_parser_create();
+        xml_set_element_handler($this->parser, function ($parser, $name, $attrs) {
+            echo "open\n";
+            var_dump($name, $attrs);
+            $this->arrayCopy = [$this]; // Create cycle intentionally
+            $this->immutableData = $this->arrayCopy;
+        }, function ($parser, $name) {
+            echo "close\n";
+            var_dump($name);
+        });
+    }
+
+    public function parseXml($xml) {
+        $this->immutableData = array();
+        xml_parse_into_struct($this->parser, $xml, $this->immutableData, $this->immutableData);
+        return $this->immutableData;
+    }
+}
+$immutableParser = new ImmutableParser();
+$xml = "<container><child/></container>";
+$immutableData = $immutableParser->parseXml($xml);
+var_dump($immutableData);
+?>
+--EXPECT--
+open
+string(9) "CONTAINER"
+array(0) {
+}
+open
+string(5) "CHILD"
+array(0) {
+}
+close
+string(5) "CHILD"
+close
+string(9) "CONTAINER"
+array(5) {
+  [0]=>
+  object(ImmutableParser)#1 (3) {
+    ["parser":"ImmutableParser":private]=>
+    object(XMLParser)#2 (0) {
+    }
+    ["immutableData":"ImmutableParser":private]=>
+    *RECURSION*
+    ["arrayCopy":"ImmutableParser":private]=>
+    array(1) {
+      [0]=>
+      *RECURSION*
+    }
+  }
+  ["CHILD"]=>
+  array(1) {
+    [0]=>
+    int(1)
+  }
+  [1]=>
+  array(3) {
+    ["tag"]=>
+    string(5) "CHILD"
+    ["type"]=>
+    string(8) "complete"
+    ["level"]=>
+    int(2)
+  }
+  ["CONTAINER"]=>
+  array(1) {
+    [0]=>
+    int(2)
+  }
+  [2]=>
+  array(3) {
+    ["tag"]=>
+    string(9) "CONTAINER"
+    ["type"]=>
+    string(5) "close"
+    ["level"]=>
+    int(1)
+  }
+}

ext/xml/tests/gh17187_2.phpt

@@ -0,0 +1,53 @@
+--TEST--
+GH-17187 (unreachable program point in zend_hash)
+--EXTENSIONS--
+xml
+--CREDITS--
+chongwick
+--FILE--
+<?php
+class ImmutableParser {
+    public $parser;
+    public $immutableData1;
+    public $immutableData2;
+
+    public function __construct() {
+        $this->parser = xml_parser_create();
+        xml_set_element_handler($this->parser, function ($parser, $name, $attrs) {
+            echo "open\n";
+            var_dump($name, $attrs);
+            $this->immutableData1 = 0xdead;
+            $this->immutableData2 = 0xbeef;
+        }, function ($parser, $name) {
+            echo "close\n";
+            var_dump($name);
+        });
+    }
+
+    public function parseXml($xml) {
+        $this->immutableData1 = array();
+        $this->immutableData2 = array();
+        xml_parse_into_struct($this->parser, $xml, $this->immutableData1, $this->immutableData2);
+    }
+}
+$immutableParser = new ImmutableParser();
+$xml = "<container><child/></container>";
+$immutableParser->parseXml($xml);
+var_dump($immutableParser->immutableData1);
+var_dump($immutableParser->immutableData2);
+?>
+--EXPECT--
+open
+string(9) "CONTAINER"
+array(0) {
+}
+open
+string(5) "CHILD"
+array(0) {
+}
+close
+string(5) "CHILD"
+close
+string(9) "CONTAINER"
+int(57005)
+int(48879)

ext/xml/xml.c

@@ -72,7 +72,7 @@ typedef struct {
 	/* We return a pointer to these zvals in get_gc(), so it's
 	 * important that a) they are adjacent b) object is the first
 	 * and c) the number of zvals is kept up to date. */
-#define XML_PARSER_NUM_ZVALS 12
+#define XML_PARSER_NUM_ZVALS 14
 	zval object;
 	zval startElementHandler;
 	zval endElementHandler;
@@ -85,6 +85,8 @@ typedef struct {
 	zval unknownEncodingHandler;
 	zval startNamespaceDeclHandler;
 	zval endNamespaceDeclHandler;
+	zval data;
+	zval info;
 
 	zend_function *startElementPtr;
 	zend_function *endElementPtr;
@@ -98,12 +100,10 @@ typedef struct {
 	zend_function *startNamespaceDeclPtr;
 	zend_function *endNamespaceDeclPtr;
 
-	zval data;
-	zval info;
 	int level;
 	int toffset;
 	int curtag;
-	zval *ctag;
+	zend_long ctag_index;
 	char **ltags;
 	int lastwasopen;
 	int skipwhite;
@@ -326,6 +326,8 @@ static void xml_parser_free_obj(zend_object *object)
 {
 	xml_parser *parser = xml_parser_from_obj(object);
 
+	zval_ptr_dtor(&parser->info);
+	zval_ptr_dtor(&parser->data);
 	if (parser->parser) {
 		XML_ParserFree(parser->parser);
 	}
@@ -551,15 +553,18 @@ static void _xml_add_to_info(xml_parser *parser, const char *name)
 {
 	zval *element;
 
-	if (Z_ISUNDEF(parser->info)) {
+	if (Z_ISUNDEF(parser->info) || UNEXPECTED(Z_TYPE_P(Z_REFVAL(parser->info)) != IS_ARRAY)) {
 		return;
 	}
 
+	SEPARATE_ARRAY(Z_REFVAL(parser->info));
+	zend_array *arr = Z_ARRVAL_P(Z_REFVAL(parser->info));
+
 	size_t name_len = strlen(name);
-	if ((element = zend_hash_str_find(Z_ARRVAL(parser->info), name, name_len)) == NULL) {
+	if ((element = zend_hash_str_find(arr, name, name_len)) == NULL) {
 		zval values;
 		array_init(&values);
-		element = zend_hash_str_update(Z_ARRVAL(parser->info), name, name_len, &values);
+		element = zend_hash_str_update(arr, name, name_len, &values);
 	}
 
 	add_next_index_long(element, parser->curtag);
@@ -583,6 +588,33 @@ static zend_string *_xml_decode_tag(xml_parser *parser, const XML_Char *tag)
 }
 /* }}} */
 
+static zval *xml_get_separated_data(xml_parser *parser)
+{
+	if (EXPECTED(Z_TYPE_P(Z_REFVAL(parser->data)) == IS_ARRAY)) {
+		SEPARATE_ARRAY(Z_REFVAL(parser->data));
+		return Z_REFVAL(parser->data);
+	}
+	return NULL;
+}
+
+static zval *xml_get_ctag(xml_parser *parser)
+{
+	zval *data = xml_get_separated_data(parser);
+	if (EXPECTED(data)) {
+		zval *zv = zend_hash_index_find(Z_ARRVAL_P(data), parser->ctag_index);
+		if (UNEXPECTED(!zv)) {
+			return NULL;
+		}
+		ZVAL_DEREF(zv);
+		if (UNEXPECTED(Z_TYPE_P(zv) != IS_ARRAY)) {
+			return NULL;
+		}
+		SEPARATE_ARRAY(zv);
+		return zv;
+	}
+	return NULL;
+}
+
 /* {{{ _xml_startElementHandler() */
 void _xml_startElementHandler(void *userData, const XML_Char *name, const XML_Char **attributes)
 {
@@ -662,7 +694,19 @@ void _xml_startElementHandler(void *userData, const XML_Char *name, const XML_Ch
 				zval_ptr_dtor(&atr);
 			}
 
-			parser->ctag = zend_hash_next_index_insert(Z_ARRVAL(parser->data), &tag);
+			zval *data = xml_get_separated_data(parser);
+			if (EXPECTED(data)) {
+				/* Note: due to array resizes or user interference,
+				 * we have to store an index instead of a zval into the array's memory. */
+				zend_array *arr = Z_ARRVAL_P(data);
+				if (EXPECTED(zend_hash_next_index_insert(arr, &tag))) {
+					parser->ctag_index = arr->nNextFreeElement - 1;
+				} else {
+					zval_ptr_dtor(&tag);
+				}
+			} else {
+				zval_ptr_dtor(&tag);
+			}
 		} else if (parser->level == (XML_MAXLEVEL + 1)) {
 						php_error_docref(NULL, E_WARNING, "Maximum depth exceeded - Results truncated");
 		}
@@ -695,19 +739,26 @@ void _xml_endElementHandler(void *userData, const XML_Char *name)
 
 	if (!Z_ISUNDEF(parser->data) && !EG(exception)) {
 		zval tag;
+		zval *data = xml_get_separated_data(parser);
 
 		if (parser->lastwasopen) {
-			add_assoc_string(parser->ctag, "type", "complete");
+			if (EXPECTED(data)) {
+				zval *zv = zend_hash_index_find_deref(Z_ARRVAL_P(data), parser->ctag_index);
+				if (EXPECTED(zv && Z_TYPE_P(zv) == IS_ARRAY)) {
+					SEPARATE_ARRAY(zv);
+					add_assoc_string(zv, "type", "complete");
+				}
+			}
 		} else {
-			array_init(&tag);
-
 			_xml_add_to_info(parser, ZSTR_VAL(tag_name) + parser->toffset);
 
-			add_assoc_string(&tag, "tag", SKIP_TAGSTART(ZSTR_VAL(tag_name))); /* cast to avoid gcc-warning */
-			add_assoc_string(&tag, "type", "close");
-			add_assoc_long(&tag, "level", parser->level);
-
-			zend_hash_next_index_insert(Z_ARRVAL(parser->data), &tag);
+			if (EXPECTED(data)) {
+				array_init(&tag);
+				add_assoc_string(&tag, "tag", SKIP_TAGSTART(ZSTR_VAL(tag_name))); /* cast to avoid gcc-warning */
+				add_assoc_string(&tag, "type", "close");
+				add_assoc_long(&tag, "level", parser->level);
+				zend_hash_next_index_insert(Z_ARRVAL_P(data), &tag);
+			}
 		}
 
 		parser->lastwasopen = 0;
@@ -765,27 +816,41 @@ void _xml_characterDataHandler(void *userData, const XML_Char *s, int len)
 		}
 	}
 	if (parser->lastwasopen) {
+		zval *ctag = xml_get_ctag(parser);
+		if (UNEXPECTED(!ctag)) {
+			zend_string_release_ex(decoded_value, false);
+			return;
+		}
+
 		zval *myval;
 		/* check if the current tag already has a value - if yes append to that! */
-		if ((myval = zend_hash_find(Z_ARRVAL_P(parser->ctag), ZSTR_KNOWN(ZEND_STR_VALUE)))) {
+		if ((myval = zend_hash_find(Z_ARRVAL_P(ctag), ZSTR_KNOWN(ZEND_STR_VALUE))) && Z_TYPE_P(myval) == IS_STRING) {
 			size_t newlen = Z_STRLEN_P(myval) + ZSTR_LEN(decoded_value);
 			Z_STR_P(myval) = zend_string_extend(Z_STR_P(myval), newlen, 0);
 			strncpy(Z_STRVAL_P(myval) + Z_STRLEN_P(myval) - ZSTR_LEN(decoded_value),
 					ZSTR_VAL(decoded_value), ZSTR_LEN(decoded_value) + 1);
 			zend_string_release_ex(decoded_value, 0);
 		} else {
 			if (doprint || (! parser->skipwhite)) {
-				add_assoc_str(parser->ctag, "value", decoded_value);
+				add_assoc_str(ctag, "value", decoded_value);
 			} else {
 				zend_string_release_ex(decoded_value, 0);
 			}
 		}
 	} else {
 		zval tag;
 		zval *curtag, *mytype, *myval;
-		ZEND_HASH_REVERSE_FOREACH_VAL(Z_ARRVAL(parser->data), curtag) {
-			if ((mytype = zend_hash_str_find(Z_ARRVAL_P(curtag),"type", sizeof("type") - 1))) {
-				if (zend_string_equals_literal(Z_STR_P(mytype), "cdata")) {
+
+		zval *data = xml_get_separated_data(parser);
+		if (UNEXPECTED(!data)) {
+			zend_string_release_ex(decoded_value, false);
+			return;
+		}
+
+		ZEND_HASH_REVERSE_FOREACH_VAL(Z_ARRVAL_P(data), curtag) {
+			if (EXPECTED(Z_TYPE_P(curtag) == IS_ARRAY) && (mytype = zend_hash_str_find(Z_ARRVAL_P(curtag),"type", sizeof("type") - 1))) {
+				if (EXPECTED(Z_TYPE_P(mytype) == IS_STRING) && zend_string_equals_literal(Z_STR_P(mytype), "cdata")) {
+					SEPARATE_ARRAY(curtag);
 					if ((myval = zend_hash_find(Z_ARRVAL_P(curtag), ZSTR_KNOWN(ZEND_STR_VALUE)))) {
 						size_t newlen = Z_STRLEN_P(myval) + ZSTR_LEN(decoded_value);
 						Z_STR_P(myval) = zend_string_extend(Z_STR_P(myval), newlen, 0);
@@ -805,7 +870,7 @@ void _xml_characterDataHandler(void *userData, const XML_Char *s, int len)
 			add_assoc_str(&tag, "value", decoded_value);
 			add_assoc_string(&tag, "type", "cdata");
 			add_assoc_long(&tag, "level", parser->level);
-			zend_hash_next_index_insert(Z_ARRVAL(parser->data), &tag);
+			zend_hash_next_index_insert(Z_ARRVAL_P(data), &tag);
 		} else if (parser->level == (XML_MAXLEVEL + 1)) {
 								php_error_docref(NULL, E_WARNING, "Maximum depth exceeded - Results truncated");
 		} else {
@@ -1266,21 +1331,21 @@ PHP_FUNCTION(xml_parse_into_struct)
 	}
 
 	if (info) {
-		info = zend_try_array_init(info);
-		if (!info) {
+		if (!zend_try_array_init(info)) {
 			RETURN_THROWS();
 		}
 	}
 
-	xdata = zend_try_array_init(xdata);
-	if (!xdata) {
+	if (!zend_try_array_init(xdata)) {
 		RETURN_THROWS();
 	}
 
-	ZVAL_COPY_VALUE(&parser->data, xdata);
+	zval_ptr_dtor(&parser->data);
+	ZVAL_COPY(&parser->data, xdata);
 
 	if (info) {
-		ZVAL_COPY_VALUE(&parser->info, info);
+		zval_ptr_dtor(&parser->info);
+		ZVAL_COPY(&parser->info, info);
 	}
 
 	parser->level = 0;