https://github.com/python/cpython/commit/a9020589de6321310720ca550f48793ab5b42d93 commit: a9020589de6321310720ca550f48793ab5b42d93 branch: 3.13 author: Miss Islington (bot) <[email protected]> committer: vstinner <[email protected]> date: 2025-09-14T09:49:23Z summary:
[3.13] gh-71810: Fix _PyLong_AsByteArray() undefined behavior (GH-138873) (#138884) gh-71810: Fix _PyLong_AsByteArray() undefined behavior (GH-138873) Don't read p[-1] when p is an empty string: when n==0. (cherry picked from commit 8b5ce31c2b44d9bf82e6119e90a52dd530bfd1db) Co-authored-by: Victor Stinner <[email protected]> files: M Objects/longobject.c diff --git a/Objects/longobject.c b/Objects/longobject.c index 98bf50d01cc079..23f50c7ed28abb 100644 --- a/Objects/longobject.c +++ b/Objects/longobject.c @@ -1046,8 +1046,14 @@ _PyLong_AsByteArray(PyLongObject* v, just above didn't get to ensure there's a sign bit, and the loop below wouldn't add one either. Make sure a sign bit exists. */ - unsigned char msb = *(p - pincr); - int sign_bit_set = msb >= 0x80; + int sign_bit_set; + if (n > 0) { + unsigned char msb = *(p - pincr); + sign_bit_set = msb >= 0x80; + } + else { + sign_bit_set = 0; + } assert(accumbits == 0); if (sign_bit_set == do_twos_comp) return 0; _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
