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decompress: check content size when an empty last block ends the frame #4885

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decompress: check content size when an empty last block ends the frame #4885

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7 changes: 7 additions & 0 deletions lib/decompress/zstd_decompress.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1321,6 +1321,13 @@ size_t ZSTD_decompressContinue(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, c
}
/* empty block */
if (bp.lastBlock) {
/* An empty last block ends the frame here, so the content size
* check that normally runs in ZSTDds_decompressLastBlock must
* be performed at this point as well. */
RETURN_ERROR_IF(
dctx->fParams.frameContentSize != ZSTD_CONTENTSIZE_UNKNOWN
&& dctx->decodedSize != dctx->fParams.frameContentSize,
corruption_detected, "");
if (dctx->fParams.checksumFlag) {
dctx->expected = 4;
dctx->stage = ZSTDds_checkChecksum;
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26 changes: 26 additions & 0 deletions tests/zstreamtest.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2512,6 +2512,32 @@ static int basicUnitTests(U32 seed, double compressibility, int bigTests)
}
DISPLAYLEVEL(3, "OK \n");

DISPLAYLEVEL(3, "test%3i : reject empty last block that underflows frame content size : ", testNb++);
{ /* Frame declares 1,000,000 bytes, but only decodes 5 bytes before an
* empty last block ends it. Streaming must report corruption. */
static const BYTE frame[] = {
0x28, 0xb5, 0x2f, 0xfd, /* magic number */
0xa0, /* single segment, 4-byte FCS */
0x40, 0x42, 0x0f, 0x00, /* frame content size: 1,000,000 */
0x28, 0x00, 0x00, 'h', 'e', 'l', 'l', 'o', /* non-last raw block, 5 bytes */
0x01, 0x00, 0x00, /* empty last raw block */
};
ZSTD_DStream* const dstream = ZSTD_createDStream();
BYTE out[16];
ZSTD_inBuffer input;
ZSTD_outBuffer output;
size_t r;
CHECK(dstream == NULL, "memory allocation failure");
input.src = frame; input.size = sizeof(frame); input.pos = 0;
output.dst = out; output.size = sizeof(out); output.pos = 0;
r = ZSTD_decompressStream(dstream, &output, &input);
ZSTD_freeDStream(dstream);
CHECK(!ZSTD_isError(r), "empty last block bypassed the content size check");
CHECK(ZSTD_getErrorCode(r) != ZSTD_error_corruption_detected,
"unexpected error : %s", ZSTD_getErrorName(r));
}
DISPLAYLEVEL(3, "OK \n");

_end:
FUZ_freeDictionary(dictionary);
ZSTD_freeCStream(zc);
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