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Fix & fuzz ZSTD_generateSequences

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This function was seriously flawed:
* It didn't do output bounds checks
* It produced invalid sequences when an uncompressed or RLE block was emitted
* It produced invalid sequences when the block splitter was enabled
* It produced invalid sequences when ZSTD_c_targetCBlockSize was enabled

I've attempted to fix these issues, but this function is just a bad idea,
so I've marked it as deprecated and unsafe. We should replace it with
`ZSTD_extractSequences()` which operates on a compressed frame.
This commit is contained in:
Nick Terrell
2024-03-21 07:18:05 -07:00
parent 741b87bbe1
commit 731f4b70fc
8 changed files with 231 additions and 56 deletions
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lib/zstd.h
+23 -10
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@@ -1538,25 +1538,38 @@ typedef enum {
ZSTDLIB_STATIC_API size_t ZSTD_sequenceBound(size_t srcSize);
/*! ZSTD_generateSequences() :
* WARNING: This function is meant for debugging and informational purposes ONLY!
* Its implementation is flawed, and it will be deleted in a future version.
* It is not guaranteed to succeed, as there are several cases where it will give
* up and fail. You should NOT use this function in production code.
*
* This function is deprecated, and will be removed in a future version.
*
* Generate sequences using ZSTD_compress2(), given a source buffer.
*
* @param zc The compression context to be used for ZSTD_compress2(). Set any
* compression parameters you need on this context.
* @param outSeqs The output sequences buffer of size @p outSeqsSize
* @param outSeqsSize The size of the output sequences buffer.
* ZSTD_sequenceBound(srcSize) is an upper bound on the number
* of sequences that can be generated.
* @param src The source buffer to generate sequences from of size @p srcSize.
* @param srcSize The size of the source buffer.
*
* Each block will end with a dummy sequence
* with offset == 0, matchLength == 0, and litLength == length of last literals.
* litLength may be == 0, and if so, then the sequence of (of: 0 ml: 0 ll: 0)
* simply acts as a block delimiter.
*
* @zc can be used to insert custom compression params.
* This function invokes ZSTD_compress2().
*
* The output of this function can be fed into ZSTD_compressSequences() with CCtx
* setting of ZSTD_c_blockDelimiters as ZSTD_sf_explicitBlockDelimiters
* @return : number of sequences generated
* @returns The number of sequences generated, necessarily less than
* ZSTD_sequenceBound(srcSize), or an error code that can be checked
* with ZSTD_isError().
*/
ZSTD_DEPRECATED("For debugging only, will be replaced by ZSTD_extractSequences()")
ZSTDLIB_STATIC_API size_t
ZSTD_generateSequences( ZSTD_CCtx* zc,
ZSTD_Sequence* outSeqs, size_t outSeqsSize,
const void* src, size_t srcSize);
ZSTD_generateSequences(ZSTD_CCtx* zc,
ZSTD_Sequence* outSeqs, size_t outSeqsSize,
const void* src, size_t srcSize);
/*! ZSTD_mergeBlockDelimiters() :
* Given an array of ZSTD_Sequence, remove all sequences that represent block delimiters/last literals