[Python-checkins] [3.8] bpo-35714: Reject null characters in struct format strings (GH-16928) (GH-20419)

[Zackery Spytz]

https://github.com/python/cpython/commit/5ff5edfef63b3dbc1abb004b3fa4b3db87e79ff9
commit: 5ff5edfef63b3dbc1abb004b3fa4b3db87e79ff9
branch: 3.8
author: Zackery Spytz <zspytz at gmail.com>
committer: GitHub <noreply at github.com>
date: 2020-05-26T11:57:09+03:00
summary:

[3.8] bpo-35714: Reject null characters in struct format strings (GH-16928) (GH-20419)

struct.error is now raised if there is a null character in a struct
format string.
(cherry picked from commit 3f59b55316f4c6ab451997902579aa69020b537c)

files:
A Misc/NEWS.d/next/Library/2019-10-25-23-45-49.bpo-35714.fw3xb7.rst
M Lib/test/test_struct.py
M Modules/_struct.c

diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py
index 454082e66d3f8..67e7c559d9f1d 100644
--- a/Lib/test/test_struct.py
+++ b/Lib/test/test_struct.py
@@ -652,6 +652,13 @@ def test_format_attr(self):
         s2 = struct.Struct(s.format.encode())
         self.assertEqual(s2.format, s.format)
 
+    def test_issue35714(self):
+        # Embedded null characters should not be allowed in format strings.
+        for s in '\0', '2\0i', b'\0':
+            with self.assertRaisesRegex(struct.error,
+                                        'embedded null character'):
+                struct.calcsize(s)
+
 
 class UnpackIteratorTest(unittest.TestCase):
     """
diff --git a/Misc/NEWS.d/next/Library/2019-10-25-23-45-49.bpo-35714.fw3xb7.rst b/Misc/NEWS.d/next/Library/2019-10-25-23-45-49.bpo-35714.fw3xb7.rst
new file mode 100644
index 0000000000000..39102065ca7b5
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-10-25-23-45-49.bpo-35714.fw3xb7.rst
@@ -0,0 +1,2 @@
+:exc:`struct.error` is now raised if there is a null character in a
+:mod:`struct` format string.
diff --git a/Modules/_struct.c b/Modules/_struct.c
index 1c917b7513f46..64a9827e83aae 100644
--- a/Modules/_struct.c
+++ b/Modules/_struct.c
@@ -1285,6 +1285,10 @@ prepare_s(PyStructObject *self)
     size_t ncodes;
 
     fmt = PyBytes_AS_STRING(self->s_format);
+    if (strlen(fmt) != (size_t)PyBytes_GET_SIZE(self->s_format)) {
+        PyErr_SetString(StructError, "embedded null character");
+        return -1;
+    }
 
     f = whichtable(&fmt);