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gh-136660: fix UB in dictobject memcpy when there are 0 entries #136662

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gh-136660: fix UB in dictobject memcpy when there are 0 entries #136662

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5 changes: 4 additions & 1 deletion Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2095,7 +2095,10 @@ dictresize(PyInterpreterState *interp, PyDictObject *mp,
if (unicode) { // combined unicode -> combined unicode
PyDictUnicodeEntry *newentries = DK_UNICODE_ENTRIES(newkeys);
if (oldkeys->dk_nentries == numentries && mp->ma_keys->dk_kind == DICT_KEYS_UNICODE) {
memcpy(newentries, oldentries, numentries * sizeof(PyDictUnicodeEntry));
/* avoid memcpy on 0 entries to avoid UB on oldentries */
if (numentries > 0) {
memcpy(newentries, oldentries, numentries * sizeof(PyDictUnicodeEntry));
}
}
else {
PyDictUnicodeEntry *ep = oldentries;
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