[Python-checkins] bpo-45826: Fix a crash in suggestions.c by checking for `traceback is None` (GH-29590)

[ambv]

https://github.com/python/cpython/commit/5d90c467c02ffefdb13c1abc83a171db1a99ffad
commit: 5d90c467c02ffefdb13c1abc83a171db1a99ffad
branch: main
author: Dennis Sweeney <36520290+sweeneyde at users.noreply.github.com>
committer: ambv <lukasz at langa.pl>
date: 2021-11-18T00:03:52+01:00
summary:

bpo-45826: Fix a crash in suggestions.c by checking for `traceback is None` (GH-29590)

files:
A Misc/NEWS.d/next/Core and Builtins/2021-11-17-08-05-27.bpo-45826.OERoTm.rst
M Lib/test/test_exceptions.py
M Python/suggestions.c

diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 0f8a8f134b61f..098804fad5e2d 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -1885,6 +1885,37 @@ def foo():
 
         self.assertNotIn("something", err.getvalue())
 
+    def test_issue45826(self):
+        # regression test for bpo-45826
+        def f():
+            with self.assertRaisesRegex(NameError, 'aaa'):
+                aab
+
+        try:
+            f()
+        except self.failureException:
+            with support.captured_stderr() as err:
+                sys.__excepthook__(*sys.exc_info())
+
+        self.assertIn("aab", err.getvalue())
+
+    def test_issue45826_focused(self):
+        def f():
+            try:
+                nonsense
+            except BaseException as E:
+                E.with_traceback(None)
+                raise ZeroDivisionError()
+
+        try:
+            f()
+        except ZeroDivisionError:
+            with support.captured_stderr() as err:
+                sys.__excepthook__(*sys.exc_info())
+
+        self.assertIn("nonsense", err.getvalue())
+        self.assertIn("ZeroDivisionError", err.getvalue())
+
 
 class AttributeErrorTests(unittest.TestCase):
     def test_attributes(self):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-11-17-08-05-27.bpo-45826.OERoTm.rst b/Misc/NEWS.d/next/Core and Builtins/2021-11-17-08-05-27.bpo-45826.OERoTm.rst
new file mode 100644
index 0000000000000..f04373bf2fc59
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-11-17-08-05-27.bpo-45826.OERoTm.rst	
@@ -0,0 +1 @@
+Fixed a crash when calling ``.with_traceback(None)`` on ``NameError``. This occurs internally in ``unittest.TestCase.assertRaises()``.
\ No newline at end of file
diff --git a/Python/suggestions.c b/Python/suggestions.c
index 81976ff4f2eb4..d9e69fa7e0db2 100644
--- a/Python/suggestions.c
+++ b/Python/suggestions.c
@@ -202,13 +202,21 @@ offer_suggestions_for_name_error(PyNameErrorObject *exc)
     PyTracebackObject *traceback = (PyTracebackObject *) exc->traceback; // borrowed reference
     // Abort if we don't have a variable name or we have an invalid one
     // or if we don't have a traceback to work with
-    if (name == NULL || traceback == NULL || !PyUnicode_CheckExact(name)) {
+    if (name == NULL || !PyUnicode_CheckExact(name) ||
+        traceback == NULL || !Py_IS_TYPE(traceback, &PyTraceBack_Type)
+    ) {
         return NULL;
     }
 
     // Move to the traceback of the exception
-    while (traceback->tb_next != NULL) {
-        traceback = traceback->tb_next;
+    while (1) {
+        PyTracebackObject *next = traceback->tb_next;
+        if (next == NULL || !Py_IS_TYPE(next, &PyTraceBack_Type)) {
+            break;
+        }
+        else {
+            traceback = next;
+        }
     }
 
     PyFrameObject *frame = traceback->tb_frame;