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Drop single-use prefix in ZSTD_DCtx_reset if frame started #4848

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Drop single-use prefix in ZSTD_DCtx_reset if frame started #4848

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4 changes: 4 additions & 0 deletions lib/decompress/zstd_decompress.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1947,6 +1947,10 @@ size_t ZSTD_DCtx_reset(ZSTD_DCtx* dctx, ZSTD_ResetDirective reset)
{
if ( (reset == ZSTD_reset_session_only)
|| (reset == ZSTD_reset_session_and_parameters) ) {
/* A prefix is only used once : if a frame was started, it is abandoned now,
* so the prefix must not leak into the next frame */
if (dctx->streamStage != zdss_init && dctx->dictUses == ZSTD_use_once)
ZSTD_clearDict(dctx);
dctx->streamStage = zdss_init;
dctx->noForwardProgress = 0;
dctx->isFrameDecompression = 1;
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33 changes: 33 additions & 0 deletions tests/zstreamtest.c
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Expand Up @@ -1406,6 +1406,39 @@ static int basicUnitTests(U32 seed, double compressibility, int bigTests)
DISPLAYLEVEL(3, "OK (%s)\n", ZSTD_getErrorName(r));
}

DISPLAYLEVEL(3, "test%3i : prefix is dropped by session reset after a rejected frame header : ", testNb++);
{ BYTE const badHeader[6] = { 0x28, 0xB5, 0x2F, 0xFD, 0x08, 0x00 }; /* reserved bit set */
CHECK_Z( ZSTD_DCtx_refPrefix(zd, dictionary.start, dictionary.filled) );
outBuff.dst = decodedBuffer;
outBuff.size = CNBufferSize;
outBuff.pos = 0;
inBuff.src = badHeader;
inBuff.size = sizeof(badHeader);
inBuff.pos = 0;
if (!ZSTD_isError(ZSTD_decompressStream(zd, &outBuff, &inBuff))) goto _output_error;
CHECK_Z( ZSTD_DCtx_reset(zd, ZSTD_reset_session_only) );
outBuff.pos = 0;
inBuff.src = compressedBuffer;
inBuff.size = cSize;
inBuff.pos = 0;
if (!ZSTD_isError(ZSTD_decompressStream(zd, &outBuff, &inBuff))) goto _output_error; /* prefix must be gone */
CHECK_Z( ZSTD_DCtx_reset(zd, ZSTD_reset_session_only) );
}
DISPLAYLEVEL(3, "OK \n");

DISPLAYLEVEL(3, "test%3i : prefix survives session reset before any input : ", testNb++);
CHECK_Z( ZSTD_DCtx_refPrefix(zd, dictionary.start, dictionary.filled) );
CHECK_Z( ZSTD_DCtx_reset(zd, ZSTD_reset_session_only) );
outBuff.dst = decodedBuffer;
outBuff.size = CNBufferSize;
outBuff.pos = 0;
inBuff.src = compressedBuffer;
inBuff.size = cSize;
inBuff.pos = 0;
CHECK_Z( ZSTD_decompressStream(zd, &outBuff, &inBuff) );
if (outBuff.pos != CNBufferSize) goto _output_error; /* must regenerate whole input */
DISPLAYLEVEL(3, "OK \n");

DISPLAYLEVEL(3, "test%3i : compress again with ZSTD_compressStream2 : ", testNb++);
outBuff.dst = compressedBuffer;
outBuff.size = compressedBufferSize;
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