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MeshPredictionSchemeTexCoordsPortableDecoder::DecodePredictionData() reads the number of orientations as an int32_t from the stream and checks only that it is not negative. The count then sizes the orientation storage and drives a loop that cannot stop early, since RAnsBitDecoder::DecodeNextBit() returns false for a zero bit and for an exhausted buffer alike. A 224-byte stream declaring about two billion orientations, found by fuzzing the decoder, takes 2 s to decode with a release build of 1.5.7 and 14 s with main under AddressSanitizer, and reports success. Each predicted entry consumes at most one orientation, so a count above the number of entries can never be used whatever the stream contains. The count is now refused when it exceeds the size of the data-to-corner map. The bound is structural rather than a guess from the remaining buffer size: the orientations are rANS-coded, and a run of equal ones takes far less than a bit each. TestTexCoordOrientationCountIsBounded decodes that stream and expects a failure, which now comes in 1 ms.
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MeshPredictionSchemeTexCoordsPortableDecoder::DecodePredictionData() reads the number of orientations as an int32_t from the stream and checks only that it is not negative. The count then sizes the orientation storage and drives a loop that cannot stop early, since RAnsBitDecoder::DecodeNextBit() returns false for a zero bit and for an exhausted buffer alike. A 224-byte stream declaring about two billion orientations, found by fuzzing the decoder, takes 2 s to decode with a release build of 1.5.7 and 14 s with main under AddressSanitizer, and reports success.
Each predicted entry consumes at most one orientation, so a count above the number of entries can never be used whatever the stream contains. The count is now refused when it exceeds the size of the data-to-corner map. The bound is structural rather than a guess from the remaining buffer size: the orientations are rANS-coded, and a run of equal ones takes far less than a bit each.
TestTexCoordOrientationCountIsBounded decodes that stream and expects a failure, which now comes in 1 ms.