[libzstd] Fix bug in Huffman decompresser

The zstd format specification doesn't enforce that Huffman compressed
literals (including the table) have to be smaller than the uncompressed
literals. The compressor will never Huffman compress literals if the
compressed size is larger than the uncompressed size. The decompresser
doesn't accept Huffman compressed literals with 4 streams whose compressed
size is at least as large as the uncompressed size.

* Make the decompresser accept Huffman compressed literals whose size
  increases.
* Add a test case that exposes the bug. The compressed file has to be
  statically generated, since the compressor won't normally produce files
  that expose the bug.

lib/decompress/huf_decompress.c

@@ -917,11 +917,11 @@ static const algo_time_t algoTime[16 /* Quantization */][3 /* single, double, qu
 *   Tells which decoder is likely to decode faster,
 *   based on a set of pre-determined metrics.
 *   @return : 0==HUF_decompress4X2, 1==HUF_decompress4X4 .
-*   Assumption : 0 < cSrcSize < dstSize <= 128 KB */
+*   Assumption : 0 < cSrcSize, dstSize <= 128 KB */
 U32 HUF_selectDecoder (size_t dstSize, size_t cSrcSize)
 {
     /* decoder timing evaluation */
-    U32 const Q = (U32)(cSrcSize * 16 / dstSize);   /* Q < 16 since dstSize > cSrcSize */
+    U32 const Q = cSrcSize >= dstSize ? 15 : (U32)(cSrcSize * 16 / dstSize);   /* Q < 16 */
     U32 const D256 = (U32)(dstSize >> 8);
     U32 const DTime0 = algoTime[Q][0].tableTime + (algoTime[Q][0].decode256Time * D256);
     U32 DTime1 = algoTime[Q][1].tableTime + (algoTime[Q][1].decode256Time * D256);
@@ -977,7 +977,7 @@ size_t HUF_decompress4X_hufOnly_wksp(HUF_DTable* dctx, void* dst,
 {
     /* validation checks */
     if (dstSize == 0) return ERROR(dstSize_tooSmall);
-    if ((cSrcSize >= dstSize) || (cSrcSize <= 1)) return ERROR(corruption_detected);   /* invalid */
+    if (cSrcSize == 0) return ERROR(corruption_detected);
 
     {   U32 const algoNb = HUF_selectDecoder(dstSize, cSrcSize);
         return algoNb ? HUF_decompress4X4_DCtx_wksp(dctx, dst, dstSize, cSrc, cSrcSize, workSpace, wkspSize):

tests/playTests.sh

@@ -386,6 +386,13 @@ $ZSTD -t tmpSplit.* && die "bad file not detected !"
 ./datagen | $ZSTD -c | $ZSTD -t
 
 
+
+$ECHO "\n**** golden files tests **** "
+
+$ZSTD -t -r files
+$ZSTD -c -r files | $ZSTD -t
+
+
 $ECHO "\n**** benchmark mode tests **** "
 
 $ECHO "bench one file"