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Fix negative SimpleXML offsets aliasing the first element #23068

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Fix negative SimpleXML offsets aliasing the first element #23068

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3 changes: 3 additions & 0 deletions NEWS
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,9 @@ PHP NEWS
. Fixed bug GH-23043 (broken session id code can cause zend_mm_heap
corrupted). (ndossche)

- SimpleXML:
. Fixed negative element offsets aliasing the first element. (iliaal)

- Sockets:
. Fixed various memory related issues in ext/sockets. (David Carlier)

Expand Down
18 changes: 12 additions & 6 deletions ext/simplexml/simplexml.c
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Expand Up @@ -134,7 +134,7 @@ static xmlNodePtr sxe_get_element_by_offset(php_sxe_object *sxe, zend_long offse
return NULL;
}
}
while (node && nodendx <= offset) {
while (node && (offset < 0 || nodendx <= offset)) {
if (node->type == XML_ELEMENT_NODE && match_ns(node, sxe->iter.nsprefix, sxe->iter.isprefix)) {
if (sxe->iter.type == SXE_ITER_CHILD || (
sxe->iter.type == SXE_ITER_ELEMENT && xmlStrEqual(node->name, BAD_CAST ZSTR_VAL(sxe->iter.name)))) {
Expand Down Expand Up @@ -319,11 +319,13 @@ static zval *sxe_prop_dim_read(zend_object *object, zval *member, bool elements,
if (node) {
node_as_zval(sxe, node, rv, SXE_ITER_NONE, NULL, sxe->iter.nsprefix, sxe->iter.isprefix);
} else if (type == BP_VAR_W || type == BP_VAR_RW) {
if (member && cnt < Z_LVAL_P(member)) {
if (member && (Z_LVAL_P(member) < 0 || cnt < Z_LVAL_P(member))) {
php_error_docref(NULL, E_WARNING, "Cannot add element %s number " ZEND_LONG_FMT " when only " ZEND_LONG_FMT " such elements exist", mynode->name, Z_LVAL_P(member), cnt);
}
node = xmlNewTextChild(mynode->parent, mynode->ns, mynode->name, NULL);
node_as_zval(sxe, node, rv, SXE_ITER_NONE, NULL, sxe->iter.nsprefix, sxe->iter.isprefix);
if (!member || Z_LVAL_P(member) >= 0) {
node = xmlNewTextChild(mynode->parent, mynode->ns, mynode->name, NULL);
node_as_zval(sxe, node, rv, SXE_ITER_NONE, NULL, sxe->iter.nsprefix, sxe->iter.isprefix);
}
}
} else {
/* In BP_VAR_IS mode only return a proper node if it actually exists. */
Expand Down Expand Up @@ -586,10 +588,14 @@ static zval *sxe_prop_dim_write(zend_object *object, zval *member, zval *value,
newnode = xmlNewTextChild(mynode, NULL, (xmlChar *)Z_STRVAL_P(member), value_str ? (xmlChar *)ZSTR_VAL(value_str) : NULL);
}
} else if (!member || Z_TYPE_P(member) == IS_LONG) {
if (member && cnt < Z_LVAL_P(member)) {
if (member && (Z_LVAL_P(member) < 0 || cnt < Z_LVAL_P(member))) {
php_error_docref(NULL, E_WARNING, "Cannot add element %s number " ZEND_LONG_FMT " when only " ZEND_LONG_FMT " such elements exist", mynode->name, Z_LVAL_P(member), cnt);
}
newnode = xmlNewTextChild(mynode->parent, mynode->ns, mynode->name, value_str ? (xmlChar *)ZSTR_VAL(value_str) : NULL);
if (member && Z_LVAL_P(member) < 0) {
value = &EG(error_zval);
} else {
newnode = xmlNewTextChild(mynode->parent, mynode->ns, mynode->name, value_str ? (xmlChar *)ZSTR_VAL(value_str) : NULL);
}
}
} else if (attribs) {
if (Z_TYPE_P(member) == IS_LONG) {
Expand Down
34 changes: 34 additions & 0 deletions ext/simplexml/tests/bug_sxe_negative_offset.phpt
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@@ -0,0 +1,34 @@
--TEST--
Negative SimpleXML element offsets must not alias the first element
--EXTENSIONS--
simplexml
--FILE--
<?php
$xml = simplexml_load_string('<r><item>a</item><item>b</item><item>c</item></r>');
$items = $xml->item;

echo "isset[-1]: ";
var_dump(isset($items[-1]));
echo "read[-1]: ";
var_dump($items[-1]);
echo "read[0]: ";
var_dump((string)$items[0]);

$items[-1] = 'Z';
echo "after negative write: ", $xml->asXML();

$items[5] = 'P';
echo "after out-of-range write: ", $xml->asXML();
?>
--EXPECTF--
isset[-1]: bool(false)
read[-1]: NULL
read[0]: string(1) "a"

Warning: main(): Cannot add element item number -1 when only 3 such elements exist in %s on line %d
after negative write: <?xml version="1.0"?>
<r><item>a</item><item>b</item><item>c</item></r>

Warning: main(): Cannot add element item number 5 when only 3 such elements exist in %s on line %d
after out-of-range write: <?xml version="1.0"?>
<r><item>a</item><item>b</item><item>c</item><item>P</item></r>
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