Fix GHSA-55rc-7hww-hf4p

Author: DarkaMaul

Lib/test/test_xml_etree.py

@@ -16,6 +16,7 @@
 import pyexpat
 import sys
 import textwrap
+import time
 import types
 import unittest
 import unittest.mock as mock
@@ -3477,6 +3478,29 @@ def test_find_xpath(self):
         self.assertRaisesRegex(SyntaxError, 'XPath', e.find, './tag[last()-0]')
         self.assertRaisesRegex(SyntaxError, 'XPath', e.find, './tag[last()+1]')
 
+    def test_find_xpath_index_no_quadratic_complexity(self):
+        root = ET.Element("root")
+        first_a = ET.SubElement(root, "a")
+        first_a.set("pos", "first")
+        n = 2 ** 15
+        for i in range(n):
+            ET.SubElement(root, "a")
+        last_a = ET.SubElement(root, "a")
+        last_a.set("pos", "last")
+
+        for pattern in [".//a[1]", ".//a[last()]"]:
+            start = time.time()
+            result = root.findall(pattern)
+            end = time.time()
+
+            # Before the fix these took 30+ seconds.
+            self.assertLess(end - start, 1)
+
+        self.assertIs(root.find(".//a[1]"), first_a)
+        self.assertEqual(root.find(".//a[1]").get("pos"), "first")
+        self.assertIs(root.find(".//a[last()]"), last_a)
+        self.assertEqual(root.find(".//a[last()]").get("pos"), "last")
+
     def test_findall(self):
         e = ET.XML(SAMPLE_XML)
         e[2] = ET.XML(SAMPLE_SECTION)

Lib/xml/etree/ElementPath.py

@@ -324,11 +324,15 @@ def select_negated(context, result):
                 index = -1
         def select(context, result):
             parent_map = get_parent_map(context)
+            sibling_cache = {}
             for elem in result:
                 try:
                     parent = parent_map[elem]
                     # FIXME: what if the selector is "*" ?
-                    elems = list(parent.findall(elem.tag))
+                    cache_key = (parent, elem.tag)
+                    if cache_key not in sibling_cache:
+                        sibling_cache[cache_key] = list(parent.findall(elem.tag))
+                    elems = sibling_cache[cache_key]
                     if elems[index] is elem:
                         yield elem
                 except (IndexError, KeyError):