From 377d01be39ae46f13fe436539b0a116ef03a1af9 Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 16:41:46 +0300
Subject: [PATCH 1/9] bpo-34441: Fix ABC.__subclasscheck__ crash on a class
 with non-callable __subclasses__

The missing NULL check was reported by Svace static analyzer.
---
 Lib/test/test_abc.py                                       | 7 +++++++
 .../next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst  | 2 ++
 Modules/_abc.c                                             | 3 +++
 3 files changed, 12 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index 6fc3c95e4a645e..bc67efb8ecb74e 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -410,6 +410,13 @@ class C:
             with self.assertRaises(TypeError):
                 issubclass(C(), A)
 
+            # bpo-34441: Check that issubclass() doesn't crash on bogus classes
+            class S(metaclass=abc_ABCMeta):
+                __subclasses__ = None
+
+            with self.assertRaises(TypeError):
+                issubclass(int, S)
+
         def test_all_new_methods_are_called(self):
             class A(metaclass=abc_ABCMeta):
                 pass
diff --git a/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst b/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
new file mode 100644
index 00000000000000..9fe619818d6a5e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
@@ -0,0 +1,2 @@
+Fix crash when an ``ABC``-derived class with non-callable ``__subclasses__`` is passed as the
+second argument to ``issubclass()``.
diff --git a/Modules/_abc.c b/Modules/_abc.c
index 562a2e6d730dd3..ce9140fd03ccc4 100644
--- a/Modules/_abc.c
+++ b/Modules/_abc.c
@@ -665,6 +665,9 @@ _abc__abc_subclasscheck_impl(PyObject *module, PyObject *self,
 
     /* 6. Check if it's a subclass of a subclass (recursive). */
     subclasses = PyObject_CallMethod(self, "__subclasses__", NULL);
+    if (subclasses == NULL) {
+        goto end;
+    }
     if (!PyList_Check(subclasses)) {
         PyErr_SetString(PyExc_TypeError, "__subclasses__() must return a list");
         goto end;

From fa3bdaece1367c0bfb6839a4a4aa49d67c84392f Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 18:21:26 +0300
Subject: [PATCH 2/9] Add tests for various unusual __subclasses__

---
 Lib/test/test_abc.py | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index bc67efb8ecb74e..5064f5ba2f2496 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -411,10 +411,31 @@ class C:
                 issubclass(C(), A)
 
             # bpo-34441: Check that issubclass() doesn't crash on bogus classes
+            bogus_subclasses = [
+                None,
+                lambda x: None,
+                lambda: 42,
+                lambda: [42],
+            ]
+
+            for bs in bogus_subclasses:
+                class S(metaclass=abc_ABCMeta):
+                    __subclasses__ = bs
+
+                with self.assertRaises(TypeError):
+                    issubclass(int, S)
+
+            # Also check that issubclass() propagates exceptions raised by
+            # __subclasses__
+            exc_msg = "exception from __subclasses__"
+
+            def raise_exc():
+                raise Exception(exc_msg)
+
             class S(metaclass=abc_ABCMeta):
-                __subclasses__ = None
+                __subclasses__ = raise_exc
 
-            with self.assertRaises(TypeError):
+            with self.assertRaisesRegex(Exception, exc_msg):
                 issubclass(int, S)
 
         def test_all_new_methods_are_called(self):

From a3cd05068d1f3f4559c8e62ed42a88db4f1d55ce Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 20:03:09 +0300
Subject: [PATCH 3/9] Fix NEWS entry and reformat it with blurb

---
 .../next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst    | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst b/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
index 9fe619818d6a5e..1a74cfca46e626 100644
--- a/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
+++ b/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
@@ -1,2 +1,3 @@
-Fix crash when an ``ABC``-derived class with non-callable ``__subclasses__`` is passed as the
-second argument to ``issubclass()``.
+Fix crash when an ``ABC``-derived class with non-callable ``__subclasses__``
+is passed as the second argument to :func:`issubclass()`. Patch by Alexey
+Izbyshev.

From 432f6df196f6aa6dda1ee00747fc58f4fd94b5cf Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 20:20:05 +0300
Subject: [PATCH 4/9] End sentences with a full stop

---
 Lib/test/test_abc.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index 5064f5ba2f2496..fc34207a01443e 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -410,7 +410,8 @@ class C:
             with self.assertRaises(TypeError):
                 issubclass(C(), A)
 
-            # bpo-34441: Check that issubclass() doesn't crash on bogus classes
+            # bpo-34441: Check that issubclass() doesn't crash on bogus
+            # classes.
             bogus_subclasses = [
                 None,
                 lambda x: None,
@@ -426,7 +427,7 @@ class S(metaclass=abc_ABCMeta):
                     issubclass(int, S)
 
             # Also check that issubclass() propagates exceptions raised by
-            # __subclasses__
+            # __subclasses__.
             exc_msg = "exception from __subclasses__"
 
             def raise_exc():

From 56b21e8a8c6b9ff7d5ec472975e288e3a1a58eee Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 20:20:56 +0300
Subject: [PATCH 5/9] Test an invalid __subclasses__ signature with a valid
 return type

---
 Lib/test/test_abc.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index fc34207a01443e..e19c2661cecfe5 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -414,7 +414,7 @@ class C:
             # classes.
             bogus_subclasses = [
                 None,
-                lambda x: None,
+                lambda x: [],
                 lambda: 42,
                 lambda: [42],
             ]

From 7df825eb9b7c8a4fb4f98cc1d2b233eddc114d3e Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 20:23:38 +0300
Subject: [PATCH 6/9] Use subTest() to distinguish iterations

---
 Lib/test/test_abc.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index e19c2661cecfe5..177278d3984730 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -419,11 +419,12 @@ class C:
                 lambda: [42],
             ]
 
-            for bs in bogus_subclasses:
+            for i, bs in enumerate(bogus_subclasses):
                 class S(metaclass=abc_ABCMeta):
                     __subclasses__ = bs
 
-                with self.assertRaises(TypeError):
+                with self.subTest(i=i), \
+                        self.assertRaises(TypeError):
                     issubclass(int, S)
 
             # Also check that issubclass() propagates exceptions raised by

From dcf2e04a8ebc0d683d43f0e36f0adf43ec36d8d8 Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 20:35:53 +0300
Subject: [PATCH 7/9] Generalize NEWS entry

---
 .../next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst     | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst b/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
index 1a74cfca46e626..6db095bdf0c67c 100644
--- a/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
+++ b/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
@@ -1,3 +1,3 @@
-Fix crash when an ``ABC``-derived class with non-callable ``__subclasses__``
-is passed as the second argument to :func:`issubclass()`. Patch by Alexey
+Fix crash when an ``ABC``-derived class with invalid ``__subclasses__`` is
+passed as the second argument to :func:`issubclass()`. Patch by Alexey
 Izbyshev.

From 7d3c5ec097f3ba75c17a9bf56ca9d6ae1412b385 Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 20:37:04 +0300
Subject: [PATCH 8/9] bs -> func

---
 Lib/test/test_abc.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index 177278d3984730..8fc2f4cdde2fd4 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -419,9 +419,9 @@ class C:
                 lambda: [42],
             ]
 
-            for i, bs in enumerate(bogus_subclasses):
+            for i, func in enumerate(bogus_subclasses):
                 class S(metaclass=abc_ABCMeta):
-                    __subclasses__ = bs
+                    __subclasses__ = func
 
                 with self.subTest(i=i), \
                         self.assertRaises(TypeError):

From 72cb03187d272c48d8b6c0f547cbdb615caa8127 Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Mon, 20 Aug 2018 20:51:17 +0300
Subject: [PATCH 9/9] Use nested with statements for readability

---
 Lib/test/test_abc.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index 8fc2f4cdde2fd4..9f5afb241aea3a 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -423,9 +423,9 @@ class C:
                 class S(metaclass=abc_ABCMeta):
                     __subclasses__ = func
 
-                with self.subTest(i=i), \
-                        self.assertRaises(TypeError):
-                    issubclass(int, S)
+                with self.subTest(i=i):
+                    with self.assertRaises(TypeError):
+                        issubclass(int, S)
 
             # Also check that issubclass() propagates exceptions raised by
             # __subclasses__.