gh-94938: Fix errror detection of unexpected keyword arguments (GH-94999)

When keyword argument name is an instance of a str subclass with
overloaded methods __eq__ and __hash__, the former code could not find
the name of an extraneous keyword argument to report an error, and
_PyArg_UnpackKeywords() returned success without setting the
corresponding cell in the linearized arguments array. But since the number
of expected initialized cells is determined as the total number of passed
arguments, this lead to reading NULL as a keyword parameter value, that
caused SystemError or crash or other undesired behavior.

1 files changed, 25 insertions, 0 deletions

diff --git a/Lib/test/test_call.py b/Lib/test/test_call.py
index 07355e8..a2eec41 100644
--- a/Lib/test/test_call.py
+++ b/Lib/test/test_call.py
@@ -11,6 +11,19 @@ import gc
 import contextlib
 
 
+class BadStr(str):
+    def __eq__(self, other):
+        return True
+    def __hash__(self):
+        # Guaranteed different hash
+        return str.__hash__(self) ^ 3
+
+    def __eq__(self, other):
+        return False
+    def __hash__(self):
+        return str.__hash__(self)
+
+
 class FunctionCalls(unittest.TestCase):
 
     def test_kwargs_order(self):
@@ -145,6 +158,18 @@ class CFunctionCallsErrorMessages(unittest.TestCase):
         self.assertRaisesRegex(TypeError, msg,
                                print, 0, sep=1, end=2, file=3, flush=4, foo=5)
 
+    def test_varargs18_kw(self):
+        # _PyArg_UnpackKeywordsWithVararg()
+        msg = r"invalid keyword argument for print\(\)$"
+        with self.assertRaisesRegex(TypeError, msg):
+            print(0, 1, **{BadStr('foo'): ','})
+
+    def test_varargs19_kw(self):
+        # _PyArg_UnpackKeywords()
+        msg = r"invalid keyword argument for round\(\)$"
+        with self.assertRaisesRegex(TypeError, msg):
+            round(1.75, **{BadStr('foo'): 1})
+
     def test_oldargs0_1(self):
         msg = r"keys\(\) takes no arguments \(1 given\)"
         self.assertRaisesRegex(TypeError, msg, {}.keys, 0)