bpo-25532: Protect against infinite loops in inspect.unwrap() (#1717)

Some objects (like test mocks) auto-generate new objects on
attribute access, which can lead to an infinite loop in
inspect.unwrap().

Ensuring references are retained to otherwise temporary objects
and capping the size of the memo dict turns this case into a
conventional exception instead.

1 files changed, 18 insertions, 0 deletions

diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index c55efd6942..350d5dbd77 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -3554,6 +3554,19 @@ class TestSignatureDefinitions(unittest.TestCase):
                 self.assertIsNone(obj.__text_signature__)
 
 
+class NTimesUnwrappable:
+    def __init__(self, n):
+        self.n = n
+        self._next = None
+
+    @property
+    def __wrapped__(self):
+        if self.n <= 0:
+            raise Exception("Unwrapped too many times")
+        if self._next is None:
+            self._next = NTimesUnwrappable(self.n - 1)
+        return self._next
+
 class TestUnwrap(unittest.TestCase):
 
     def test_unwrap_one(self):
@@ -3609,6 +3622,11 @@ class TestUnwrap(unittest.TestCase):
             __wrapped__ = func
         self.assertIsNone(inspect.unwrap(C()))
 
+    def test_recursion_limit(self):
+        obj = NTimesUnwrappable(sys.getrecursionlimit() + 1)
+        with self.assertRaisesRegex(ValueError, 'wrapper loop'):
+            inspect.unwrap(obj)
+
 class TestMain(unittest.TestCase):
     def test_only_source(self):
         module = importlib.import_module('unittest')