zend_string_init with NULL pointer in simplexml (UB)

[YuanchengJiang]

Description

The following code:

<?php
class AdvancedXMLElement extends SimpleXMLElement {
}
$sxe = simplexml_load_file(__DIR__ . '/53965/collection.xml', AdvancedXMLElement::class);
$processor = new XSLTProcessor;
$dom = new DOMDocument;
$dom->load(__DIR__ . '/53965/collection.xsl');
$processor->importStylesheet($dom);
$result = $processor->transformToDoc($sxe, AdvancedXMLElement::class);
$fusion = $result;
var_dump($fusion->getName());

Resulted in this output:

/home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend_string.h:191:24: runtime error: null pointer passed as argument 2, which is declared to never be null
/usr/include/string.h:44:28: note: nonnull attribute specified here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend_string.h:191:24 in 

To reproduce:

./php-src/sapi/cli/php  ./test.php

Commit:

ee2da6d9e9745ec83b02b1e5c5a07e8dbd5f9f98

Configurations:

CC="clang-12" CXX="clang++-12" CFLAGS="-DZEND_VERIFY_TYPE_INFERENCE" CXXFLAGS="-DZEND_VERIFY_TYPE_INFERENCE" ./configure --enable-debug --enable-address-sanitizer --enable-undefined-sanitizer --enable-re2c-cgoto --enable-fpm --enable-litespeed --enable-phpdbg-debug --enable-zts --enable-bcmath --enable-calendar --enable-dba --enable-dl-test --enable-exif --enable-ftp --enable-gd --enable-gd-jis-conv --enable-mbstring --enable-pcntl --enable-shmop --enable-soap --enable-sockets --enable-sysvmsg --enable-zend-test --with-zlib --with-bz2 --with-curl --with-enchant --with-gettext --with-gmp --with-mhash --with-ldap --with-libedit --with-readline --with-snmp --with-sodium --with-xsl --with-zip --with-mysqli --with-pdo-mysql --with-pdo-pgsql --with-pgsql --with-sqlite3 --with-pdo-sqlite --with-webp --with-jpeg --with-freetype --enable-sigchild --with-readline --with-pcre-jit --with-iconv

Operating System:

Ubuntu 20.04 Host, Docker 0599jiangyc/flowfusion:latest

This report is automatically generated by FlowFusion

PHP Version

nightly

Operating System

No response

[nielsdos]

Slightly reduced and easier:

<?php
$sxe = simplexml_load_file(__DIR__ . '/ext/xsl/tests/53965/collection.xml');
$processor = new XSLTProcessor;
$dom = new DOMDocument;
$dom->load(__DIR__ . '/ext/xsl/tests/53965/collection.xsl');
$processor->importStylesheet($dom);
$result = $processor->transformToDoc($sxe, SimpleXMLElement::class);
var_dump($result->getName());

[nielsdos]

Not sure why this is NULL in the first place, I'll have to figure it out. If it is legit that this is NULL then the following patch would work:

diff --git a/ext/simplexml/simplexml.c b/ext/simplexml/simplexml.c
index 78653cf7ef6..aa903668152 100644
--- a/ext/simplexml/simplexml.c
+++ b/ext/simplexml/simplexml.c
@@ -1628,10 +1628,11 @@ PHP_METHOD(SimpleXMLElement, getName)
 	node = php_sxe_get_first_node_non_destructive(sxe, node);
 	if (node) {
 		namelen = xmlStrlen(node->name);
-		RETURN_STRINGL((char*)node->name, namelen);
-	} else {
-		RETURN_EMPTY_STRING();
+		if (namelen) {
+			RETURN_STRINGL((char*)node->name, namelen);
+		}
 	}
+	RETURN_EMPTY_STRING();
 }
 /* }}} */
 

[nielsdos]

It's also not a SEGV, this does not crash my system but it's UB.

[nielsdos]

It may also be worthwhile to use ZVAL_STRINGL_FAST as many tags tend to be one char.

[nielsdos]

The problem is that the SimpleXMLElement is a document... Normally this isn't possible, i.e. it's always the root of a document that is pointed at, but xsl allows you to bypass this apparently. You can see this when you try importing a document via simplexml_import_dom.
A document indeed has no name.
Changing this to use the root element is breaking, and I see now technical reason why the importing of document nodes should be disallowed, so I'll just fix getName() probably.