fix out-of-bounds read in DecodeNormLookup::decode#686
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kevina
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Jul 6, 2026
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In common/convert.cpp, DecodeNormLookup::decode walks the normalization output with the guard
ret.to[i] && i < E::max_to, so it dereferences ret.to[i] before the index is bounds-checked. When a decoded entry fills all three output slots with non-zero values, i reaches max_to and the loop reads ret.to[max_to], one Uni16 past the end of the max_to-sized to[] array (ToUniNormEntry::to is Uni16 to[3]). This path is reached when normalization is enabled and a to_uni norm form is selected, decoding untrusted input text.Reorder the two conditions so the bounds test short-circuits first, matching the three sibling loops in EncodeNormLookup a few lines down that already read as
i < E::max_to && ret.to[i]. Keeping the check on the same side as its siblings is the least surprising place for it.