fix : huge (>4GB) stream of blocks

experimental function ZSTD_compressBlock() is designed for very small data in mind,
for situation where saving the ~12 bytes of frame header can actually make a difference.

Some systems though may have to deal with small and large data entangled.
If it's larger than a block (> 128KB), compressBlock() cannot compress them in one round.

That's why it's possible to compress in multiple rounds.
This is a chain of compressed blocks.

Some users push this capability to the limit, encoding gigantic chain of blocks.
On crossing the 4GB limit, some internal overflow occurs.

This fix moves the overflow correction mechanism higher in the call chain,
so that it's applied also to gigantic chains of blocks.

Added a test case in fuzzer.c, which crashes before the fix, and pass now.

lib/compress/zstd_compress.c

@@ -2454,19 +2454,6 @@ static size_t ZSTD_compress_frameChunk (ZSTD_CCtx* cctx,
             return ERROR(dstSize_tooSmall);   /* not enough space to store compressed block */
         if (remaining < blockSize) blockSize = remaining;
 
-        if (ZSTD_window_needOverflowCorrection(ms->window, ip + blockSize)) {
-            U32 const cycleLog = ZSTD_cycleLog(cctx->appliedParams.cParams.chainLog, cctx->appliedParams.cParams.strategy);
-            U32 const correction = ZSTD_window_correctOverflow(&ms->window, cycleLog, maxDist, ip);
-            ZSTD_STATIC_ASSERT(ZSTD_CHAINLOG_MAX <= 30);
-            ZSTD_STATIC_ASSERT(ZSTD_WINDOWLOG_MAX_32 <= 30);
-            ZSTD_STATIC_ASSERT(ZSTD_WINDOWLOG_MAX <= 31);
-
-            ZSTD_reduceIndex(cctx, correction);
-            if (ms->nextToUpdate < correction) ms->nextToUpdate = 0;
-            else ms->nextToUpdate -= correction;
-            ms->loadedDictEnd = 0;
-            ms->dictMatchState = NULL;
-        }
         ZSTD_window_enforceMaxDist(&ms->window, ip + blockSize, maxDist, &ms->loadedDictEnd, &ms->dictMatchState);
         if (ms->nextToUpdate < ms->window.lowLimit) ms->nextToUpdate = ms->window.lowLimit;
 
@@ -2603,6 +2590,20 @@ static size_t ZSTD_compressContinue_internal (ZSTD_CCtx* cctx,
     if (cctx->appliedParams.ldmParams.enableLdm)
         ZSTD_window_update(&cctx->ldmState.window, src, srcSize);
 
+    if (ZSTD_window_needOverflowCorrection(ms->window, (const char*)src + srcSize)) {
+        U32 const cycleLog = ZSTD_cycleLog(cctx->appliedParams.cParams.chainLog, cctx->appliedParams.cParams.strategy);
+        U32 const correction = ZSTD_window_correctOverflow(&ms->window, cycleLog, 1 << cctx->appliedParams.cParams.windowLog, src);
+        ZSTD_STATIC_ASSERT(ZSTD_CHAINLOG_MAX <= 30);
+        ZSTD_STATIC_ASSERT(ZSTD_WINDOWLOG_MAX_32 <= 30);
+        ZSTD_STATIC_ASSERT(ZSTD_WINDOWLOG_MAX <= 31);
+
+        ZSTD_reduceIndex(cctx, correction);
+        if (ms->nextToUpdate < correction) ms->nextToUpdate = 0;
+        else ms->nextToUpdate -= correction;
+        ms->loadedDictEnd = 0;
+        ms->dictMatchState = NULL;
+    }
+
     DEBUGLOG(5, "ZSTD_compressContinue_internal (blockSize=%u)", (U32)cctx->blockSize);
     {   size_t const cSize = frame ?
                              ZSTD_compress_frameChunk (cctx, dst, dstCapacity, src, srcSize, lastFrameChunk) :

lib/compress/zstd_fast.c

@@ -172,6 +172,7 @@ size_t ZSTD_compressBlock_fast_generic(
 
         if (ip <= ilimit) {
             /* Fill Table */
+            assert(base+current+2 > istart);  /* check base overflow */
             hashTable[ZSTD_hashPtr(base+current+2, hlog, mls)] = current+2;  /* here because current+2 could be > iend-8 */
             hashTable[ZSTD_hashPtr(ip-2, hlog, mls)] = (U32)(ip-2-base);
 

tests/fuzzer.c

@@ -1291,6 +1291,20 @@ static int basicUnitTests(U32 seed, double compressibility)
           if (r != blockSize) goto _output_error; }
         DISPLAYLEVEL(3, "OK \n");
 
+        /* very long stream of block compression */
+        DISPLAYLEVEL(3, "test%3i : Huge block streaming compression test : ", testNb++);
+        CHECK( ZSTD_compressBegin(cctx, -99) );  /* we just want to quickly overflow internal U32 index */
+        CHECK( ZSTD_getBlockSize(cctx) >= blockSize);
+        {   U64 const toCompress = 5000000000ULL;   /* > 4 GB */
+            U64 compressed = 0;
+            while (compressed < toCompress) {
+                size_t const blockCSize = ZSTD_compressBlock(cctx, compressedBuffer, ZSTD_compressBound(blockSize), CNBuffer, blockSize);
+                if (ZSTD_isError(cSize)) goto _output_error;
+                compressed += blockCSize;
+            }
+        }
+        DISPLAYLEVEL(3, "OK \n");
+
         /* dictionary block compression */
         DISPLAYLEVEL(3, "test%3i : Dictionary Block compression test : ", testNb++);
         CHECK( ZSTD_compressBegin_usingDict(cctx, CNBuffer, dictSize, 5) );