8000 gh-96735: Fix undefined behaviour in struct unpacking functions by mdickinson · Pull Request #96739 · python/cpython · GitHub
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gh-96735: Fix undefined behaviour in struct unpacking functions #96739

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Merged
merged 10 commits into from
Sep 25, 2022
Merged

gh-96735: Fix undefined behaviour in struct unpacking functions #96739

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22fdce6
Fix undefined behaviour in bu_ulonglong
mdickinson Sep 10, 2022
e12943b
Add regression test
mdickinson Sep 10, 2022
8efefd8
Also apply the fix to lu_longlong
mdickinson Sep 10, 2022
cba4b8b
Merge branch 'main' into fix-struct-unpack-undefined-behaviour
mdickinson Sep 10, 2022
0d49e73
Fix similar undefined behaviour issues in bu_int and lu_int
mdickinson Sep 10, 2022
bfd714f
Merge remote-tracking branch 'mdickinson/fix-struct-unpack-undefined-…
mdickinson Sep 10, 2022
5aeef09
Remove redundant test
mdickinson Sep 10, 2022
204e924
Fix accumulator type
mdickinson Sep 10, 2022
994703e
Branch-free sign-extension
mdickinson Sep 13, 2022
1294440
Fix unconventional spacing
mdickinson Sep 13, 2022
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Fix undefined behaviour in bu_ulonglong
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@mdickinson
mdickinson committed Sep 10, 2022
commit 22fdce61d61a6b68f84c3e6e263de2860429ccea
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-09-10-16-46-16.gh-issue-96735.0YzJuG.rst
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@@ -0,0 +1 @@
Fix undefined behaviour in :func:`struct.unpack`.
15 changes: 9 additions & 6 deletions Modules/_struct.c
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Expand Up @@ -835,16 +835,19 @@ bu_uint(_structmodulestate *state, const char *p, const formatdef *f)
static PyObject *
bu_longlong(_structmodulestate *state, const char *p, const formatdef *f)
{
long long x = 0;
Py_ssize_t i = f->size;
unsigned long long x = 0;

/* This function is only ever used in the case f->size == 8. */
assert(f->size == 8);
Py_ssize_t i = 8;
const unsigned char *bytes = (const unsigned char *)p;
do {
x = (x<<8) | *bytes++;
} while (--i > 0);
/* Extend the sign bit. */
if (SIZEOF_LONG_LONG > f->size)
x |= -(x & ((long long)1 << ((8 * f->size) - 1)));
return PyLong_FromLongLong(x);

/* Extend sign, avoiding implementation-defined or undefined behaviour. */
return PyLong_FromLongLong(x & 0x8000000000000000 ?
-1 - (long long)(0xFFFFFFFFFFFFFFFF - x) : (long long)x);
}

static PyObject *
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0