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gh-124248: Fix crash in struct when processing 0p fields (#124251) · python/cpython@63f1960 · GitHub

  1. python
  2. cpython

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Commit 63f1960

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brianschubert
authored
gh-124248: Fix crash in struct when processing 0p fields (#124251)
1 parent baa3550 commit 63f1960

4 files changed

Lines changed: 27 additions & 4 deletions

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‎Lib/test/test_struct.py‎

Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -96,6 +96,13 @@ def test_new_features(self):
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('10s', b'helloworld', b'helloworld', b'helloworld', 0),
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('11s', b'helloworld', b'helloworld\0', b'helloworld\0', 1),
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('20s', b'helloworld', b'helloworld'+10*b'\0', b'helloworld'+10*b'\0', 1),
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('0p', b'helloworld', b'', b'', 1),
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('1p', b'helloworld', b'\x00', b'\x00', 1),
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('2p', b'helloworld', b'\x01h', b'\x01h', 1),
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('10p', b'helloworld', b'\x09helloworl', b'\x09helloworl', 1),
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('11p', b'helloworld', b'\x0Ahelloworld', b'\x0Ahelloworld', 0),
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('12p', b'helloworld', b'\x0Ahelloworld\0', b'\x0Ahelloworld\0', 1),
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('20p', b'helloworld', b'\x0Ahelloworld'+9*b'\0', b'\x0Ahelloworld'+9*b'\0', 1),
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('b', 7, b'\7', b'\7', 0),
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('b', -7, b'\371', b'\371', 0),
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('B', 7, b'\7', b'\7', 0),
@@ -339,6 +346,7 @@ def assertStructError(func, *args, **kwargs):
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def test_p_code(self):
340347
# Test p ("Pascal string") code.
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for code, input, expected, expectedback in [
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('0p', b'abc', b'', b''),
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('p', b'abc', b'\x00', b''),
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('1p', b'abc', b'\x00', b''),
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('2p', b'abc', b'\x01a', b'a'),
@@ -580,6 +588,7 @@ def test__sizeof__(self):
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self.check_sizeof('187s', 1)
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self.check_sizeof('20p', 1)
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self.check_sizeof('0s', 1)
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self.check_sizeof('0p', 1)
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self.check_sizeof('0c', 0)
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def test_boundary_error_message(self):

‎Misc/ACKS‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1653,6 +1653,7 @@ Scott Schram
16531653
Robin Schreiber
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Chad J. Schroeder
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Simon-Martin Schroeder
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Brian Schubert
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Christian Schubert
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Sam Schulenburg
16581659
Andreas Schwab

‎Misc/NEWS.d/next/Library/2024-09-19-11-47-39.gh-issue-124248.g7rufd.rst‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
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Fixed potential crash when using :mod:`struct` to process zero-width
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'Pascal string' fields (``0p``).

‎Modules/_struct.c‎

Lines changed: 15 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1669,9 +1669,16 @@ s_unpack_internal(PyStructObject *soself, const char *startfrom,
16691669
if (e->format == 's') {
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v = PyBytes_FromStringAndSize(res, code->size);
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} else if (e->format == 'p') {
1672-
Py_ssize_t n = *(unsigned char*)res;
1673-
if (n >= code->size)
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n = code->size - 1;
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Py_ssize_t n;
1673+
if (code->size == 0) {
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n = 0;
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}
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else {
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n = *(unsigned char*)res;
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if (n >= code->size) {
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n = code->size - 1;
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}
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}
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v = PyBytes_FromStringAndSize(res + 1, n);
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} else {
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v = e->unpack(state, res, e);
@@ -1982,8 +1989,12 @@ s_pack_internal(PyStructObject *soself, PyObject *const *args, int offset,
19821989
n = PyByteArray_GET_SIZE(v);
19831990
p = PyByteArray_AS_STRING(v);
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}
1985-
if (n > (code->size - 1))
1992+
if (code->size == 0) {
1993+
n = 0;
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}
1995+
else if (n > (code->size - 1)) {
19861996
n = code->size - 1;
1997+
}
19871998
if (n > 0)
19881999
memcpy(res + 1, p, n);
19892000
if (n > 255)

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