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[3.7] bpo-35714: Reject null characters in struct format strings (GH-16928) #20375

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[3.7] bpo-35714: Reject null characters in struct format strings (GH-16928) #20375

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bpo-35714: Reject null characters in struct format strings (GH-16928) 
struct.error is now raised if there is a null character in a struct
format string.
(cherry picked from commit 3f59b55)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>
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@ZackerySpytz @miss-islington
ZackerySpytz authored and miss-islington committed May 25, 2020
commit 90b0d96fe1c9d5bf56e14c6cf195e80962172a03
8 changes: 8 additions & 0 deletions Lib/test/test_struct.py
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Expand Up @@ -627,6 +627,14 @@ def test_format_attr(self):
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):
"""
Tests for iterative unpacking (struct.Struct.iter_unpack).
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2019-10-25-23-45-49.bpo-35714.fw3xb7.rst
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@@ -0,0 +1,2 @@
:exc:`struct.error` is now raised if there is a null character in a
:mod:`struct` format string.
5 changes: 5 additions & 0 deletions Modules/_struct.c
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Expand Up @@ -1285,6 +1285,11 @@ 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(_structmodulestate_global->StructError,
"embedded null character");
return -1;
}

f = whichtable(&fmt);

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