gh-141778: add missing validation in ast.literal_eval() for non-string input

This also changes parsing of the private `__text_signature__` attribute
by inspect.signature().  Now we accept here only types, valid for
ast.Constant().

Lib/ast.py

@@ -59,17 +59,26 @@ def literal_eval(node_or_string):
     """
     if isinstance(node_or_string, str):
         node_or_string = parse(node_or_string.lstrip(" \t"), mode='eval').body
+        return _convert_literal(node_or_string, True)
     elif isinstance(node_or_string, Expression):
         node_or_string = node_or_string.body
     return _convert_literal(node_or_string)
 
 
-def _convert_literal(node):
+_type_None = type(None)
+_type_Ellipsis = type(...)
+
+
+def _convert_literal(node, omit_validation=False):
     """
     Used by `literal_eval` to convert an AST node into a value.
     """
     if isinstance(node, Constant):
-        return node.value
+        if omit_validation:
+            return node.value
+        if type(value := node.value) in (str, bytes, int, float, complex,
+                                         bool, _type_None, _type_Ellipsis):
+            return value
     if isinstance(node, Dict) and len(node.keys) == len(node.values):
         return dict(zip(
             map(_convert_literal, node.keys),

Lib/inspect.py

@@ -2216,7 +2216,8 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
             except NameError:
                 raise ValueError
 
-        if isinstance(value, (str, int, float, bytes, bool, type(None))):
+        if type(value) in (str, int, float, bytes, bool, complex,
+                           type(None), type(...)):
             return ast.Constant(value)
         raise ValueError
 

Lib/test/test_ast/test_ast.py

@@ -1890,6 +1890,10 @@ Module(
         self.assertRaises(ValueError, ast.literal_eval, '++6')
         self.assertRaises(ValueError, ast.literal_eval, '+True')
         self.assertRaises(ValueError, ast.literal_eval, '2+3')
+        # gh-141778: reject values of invalid types
+        node = ast.Expression(body=ast.Constant(object()))
+        ast.fix_missing_locations(node)
+        self.assertRaises(ValueError, ast.literal_eval, node)
 
     def test_literal_eval_str_int_limit(self):
         with support.adjust_int_max_str_digits(4000):

Lib/test/test_inspect/test_inspect.py

@@ -6286,7 +6286,9 @@ class TestSignatureDefinitions(unittest.TestCase):
     def test_thread_module_has_signatures(self):
         import _thread
         no_signature = {'RLock'}
-        self._test_module_has_signatures(_thread, no_signature)
+        unsupported_signature = {'interrupt_main'}
+        self._test_module_has_signatures(_thread, no_signature,
+                                         unsupported_signature)
 
     def test_time_module_has_signatures(self):
         no_signature = {

Misc/NEWS.d/next/Library/2025-12-19-07-09-02.gh-issue-141778.VdSWcy.rst

@@ -0,0 +1,2 @@
+Validate value types of :class:`ast.Constant` nodes in the
+:func:`ast.literal_eval`.  Patch by Sergey B Kirpichev.