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A compressed block with an original size of 0 made CompressedInput::Decompress allocate Buffer(0), whose data() is null, and pass it as the LZ4/ZSTD destination; LZ4 does pointer arithmetic on it before it checks the capacity, which is undefined behaviour. A well-formed empty block also left CompressedInput::DoNext without data, so it reported end of stream, and Decompress ignored how many bytes LZ4/ZSTD actually produced, so a block that decoded short exposed a zero-filled tail as data. Decompress empty blocks into a zero-capacity stack target, keep reading blocks until one yields data, and reject output whose length differs from the declared original size.
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CompressedInput::Decompressinbase/compressed.cpptrusts the declared original size in three ways:Buffer(0), whosedata()is null, and passes it to LZ4/ZSTD as the destination. LZ4 does pointer arithmetic on it before checking capacity, which is undefined behaviour (UBSan: "applying non-zero offset to null pointer" inlz4.c).DoNextwith no data, so the stream reports end of input mid-packet.Decompressignores how many bytes LZ4/ZSTD actually produced. A block that decodes to 19 bytes while declaring 20 exposes a zero-filled tail as row data, a silent wrong value.Fix: decompress empty blocks into a zero-capacity stack target, keep reading blocks until one yields data, and throw
CompressionErrorwhen the output length differs from the declared original size, for both LZ4 and ZSTD.Reproducer: a checksum-valid LZ4 block with original size 20 whose payload decodes to 19 bytes, or an LZ4 block with original size 0 and a non-empty payload.
Tests:
CompressedInputCase.SkipsEmptyBlocksandRejectsBlockShorterThanDeclaredOriginalSizefail on master.RejectsEmptyBlockWithNonEmptyContentfails on master in a UBSan build.