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gh-124248: Fix crash in struct when processing 0p fields #124251

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Merged
merged 5 commits into from
Sep 20, 2024
Merged

gh-124248: Fix crash in struct when processing 0p fields #124251

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e707f5d
Fix handling of 0p fields in struct
brianschubert Sep 19, 2024
55c3e1b
Use PEP 7 braces
brianschubert Sep 19, 2024
e0ce3ec
Update NEWS
brianschubert Sep 19, 2024
7346b0d
Update ACKS
brianschubert Sep 19, 2024
0f78c80
Fix PEP 7 brace style
brianschubert Sep 19, 2024
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9 changes: 9 additions & 0 deletions Lib/test/test_struct.py
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Original file line number Diff line number Diff line change
Expand Up @@ -96,6 +96,13 @@ def test_new_features(self):
('10s', b'helloworld', b'helloworld', b'helloworld', 0),
('11s', b'helloworld', b'helloworld\0', b'helloworld\0', 1),
('20s', b'helloworld', b'helloworld'+10*b'\0', b'helloworld'+10*b'\0', 1),
('0p', b'helloworld', b'', b'', 1),
('1p', b'helloworld', b'\x00', b'\x00', 1),
('2p', b'helloworld', b'\x01h', b'\x01h', 1),
('10p', b'helloworld', b'\x09helloworl', b'\x09helloworl', 1),
('11p', b'helloworld', b'\x0Ahelloworld', b'\x0Ahelloworld', 0),
('12p', b'helloworld', b'\x0Ahelloworld\0', b'\x0Ahelloworld\0', 1),
('20p', b'helloworld', b'\x0Ahelloworld'+9*b'\0', b'\x0Ahelloworld'+9*b'\0', 1),
('b', 7, b'\7', b'\7', 0),
('b', -7, b'\371', b'\371', 0),
('B', 7, b'\7', b'\7', 0),
Expand Down Expand Up @@ -339,6 +346,7 @@ def assertStructError(func, *args, **kwargs):
def test_p_code(self):
# Test p ("Pascal string") code.
for code, input, expected, expectedback in [
('0p', b'abc', b'', b''),
('p', b'abc', b'\x00', b''),
('1p', b'abc', b'\x00', b''),
('2p', b'abc', b'\x01a', b'a'),
Expand Down Expand Up @@ -580,6 +588,7 @@ def test__sizeof__(self):
self.check_sizeof('187s', 1)
self.check_sizeof('20p', 1)
self.check_sizeof('0s', 1)
self.check_sizeof('0p', 1)
self.check_sizeof('0c', 0)

def test_boundary_error_message(self):
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2024-09-19-11-47-39.gh-issue-124248.g7rufd.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fixed potential crash when using :mod:`struct` to process zero-width
'Pascal string' fields (``0p``).
17 changes: 13 additions & 4 deletions Modules/_struct.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1669,9 +1669,15 @@ s_unpack_internal(PyStructObject *soself, const char *startfrom,
if (e->format == 's') {
v = PyBytes_FromStringAndSize(res, code->size);
} else if (e->format == 'p') {
Py_ssize_t n = *(unsigned char*)res;
if (n >= code->size)
n = code->size - 1;
Py_ssize_t n;
if (code->size == 0) {
n = 0;
} else {
n = *(unsigned char*)res;
if (n >= code->size) {
n = code->size - 1;
}
}
v = PyBytes_FromStringAndSize(res + 1, n);
} else {
v = e->unpack(state, res, e);
Expand Down Expand Up @@ -1982,8 +1988,11 @@ s_pack_internal(PyStructObject *soself, PyObject *const *args, int offset,
n = PyByteArray_GET_SIZE(v);
p = PyByteArray_AS_STRING(v);
}
if (n > (code->size - 1))
if (code->size == 0) {
n = 0;
} else if (n > (code->size - 1)) {
n = code->size - 1;
}
if (n > 0)
memcpy(res + 1, p, n);
if (n > 255)
Expand Down
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