Merge pull request facebook#4129 from facebook/mitigate_32bit

Limit range of operations on Indexes in 32-bit mode

lib/compress/zstd_compress_internal.h

@@ -918,11 +918,12 @@ MEM_STATIC U64 ZSTD_rollingHash_rotate(U64 hash, BYTE toRemove, BYTE toAdd, U64
 /*-*************************************
 * Round buffer management
 ***************************************/
-#if (ZSTD_WINDOWLOG_MAX_64 > 31)
-# error "ZSTD_WINDOWLOG_MAX is too large : would overflow ZSTD_CURRENT_MAX"
-#endif
-/* Max current allowed */
-#define ZSTD_CURRENT_MAX ((3U << 29) + (1U << ZSTD_WINDOWLOG_MAX))
+/* Max @current value allowed:
+ * In 32-bit mode: we want to avoid crossing the 2 GB limit,
+ * reducing risks of side effects in case of signed operations on indexes.
+ * In 64-bit mode: we want to ensure that adding the maximum job size (512 MB)
+ * doesn't overflow U32 index capacity (4 GB) */
+#define ZSTD_CURRENT_MAX (MEM_64bits() ? 3500U MB : 2000U MB)
 /* Maximum chunk size before overflow correction needs to be called again */
 #define ZSTD_CHUNKSIZE_MAX \
  ( ((U32)-1) /* Maximum ending current index */ \
@@ -1274,8 +1275,9 @@ U32 ZSTD_window_update(ZSTD_window_t* window,
  /* if input and dictionary overlap : reduce dictionary (area presumed modified by input) */
  if ( (ip+srcSize > window->dictBase + window->lowLimit)
  & (ip < window->dictBase + window->dictLimit)) {
- ptrdiff_t const highInputIdx = (ip + srcSize) - window->dictBase;
- U32 const lowLimitMax = (highInputIdx > (ptrdiff_t)window->dictLimit) ? window->dictLimit : (U32)highInputIdx;
+ size_t const highInputIdx = (size_t)((ip + srcSize) - window->dictBase);
+ U32 const lowLimitMax = (highInputIdx > (size_t)window->dictLimit) ? window->dictLimit : (U32)highInputIdx;
+ assert(highInputIdx < UINT_MAX);
  window->lowLimit = lowLimitMax;
  DEBUGLOG(5, "Overlapping extDict and input : new lowLimit = %u", window->lowLimit);
  }