fixed fuzzer test

and removed one blind copy, since there is no more guarantee that at least 4 bytes are still available in output buffer

2 files changed, 10 insertions, 7 deletions

diff --git a/lib/lz4.c b/lib/lz4.c
index 6febb90..dbda4f1 100644
--- a/lib/lz4.c
+++ b/lib/lz4.c
@@ -1398,8 +1398,7 @@ typedef enum { decode_full_block = 0, partial_decode = 1 } earlyEnd_directive;
  *  Note that it is important for performance that this function really get inlined,
  *  in order to remove useless branches during compilation optimization.
  */
-LZ4_FORCE_INLINE
-int
+LZ4_FORCE_INLINE int
 LZ4_decompress_generic(
                  const char* const src,
                  char* const dst,
@@ -1432,7 +1431,7 @@ LZ4_decompress_generic(
     const BYTE* const shortiend = iend - (endOnInput ? 14 : 8) /*maxLL*/ - 2 /*offset*/;
     const BYTE* const shortoend = oend - (endOnInput ? 14 : 8) /*maxLL*/ - 18 /*maxML*/;
 
-    DEBUGLOG(5, "LZ4_decompress_generic (srcSize:%i)", srcSize);
+    DEBUGLOG(5, "LZ4_decompress_generic (srcSize:%i, dstSize:%i)", srcSize, outputSize);
 
     /* Special cases */
     assert(src != NULL);
@@ -1537,7 +1536,7 @@ LZ4_decompress_generic(
 
 _copy_match:
         if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) goto _output_error;   /* Error : offset outside buffers */
-        LZ4_write32(op, (U32)offset);   /* costs ~1%; silence an msan warning when offset==0 */
+        // LZ4_write32(op, (U32)offset);   /* costs ~1%; silence an msan warning when offset==0 */   /* note : no longer valid with partialDecoding, since there is no guarantee that at least 4 bytes are available */
 
         if (length == ML_MASK) {
             unsigned s;
@@ -1584,15 +1583,18 @@ _copy_match:
         /* specific : partial decode : does not respect end parsing restrictions */
         assert(op<=oend);
         if (partialDecoding && (cpy > oend-12)) {
+            DEBUGLOG(2, "match copy close to the end");
             size_t const mlen = MIN(length, (size_t)(oend-op));
             const BYTE* const matchEnd = match + mlen;
             BYTE* const copyEnd = op + mlen;
             if (matchEnd > op) {   /* overlap copy */
                 while (op < copyEnd) *op++ = *match++;
             } else {
+                DEBUGLOG(2, "let's memcopy %zu bytes (non overlapping)", mlen);
                 memcpy(op, match, mlen);
             }
             op = copyEnd;
+            if (op==oend) break;
             continue;
         }
 
diff --git a/tests/fuzzer.c b/tests/fuzzer.c
index bdb7841..d6a5f51 100644
--- a/tests/fuzzer.c
+++ b/tests/fuzzer.c
@@ -582,11 +582,12 @@ static int FUZ_test(U32 seed, U32 nbCycles, const U32 startCycle, const double c
         FUZ_DISPLAYTEST("test LZ4_decompress_safe_partial");
         {   size_t const missingBytes = FUZ_rand(&randState) % blockSize;
             int const targetSize = (int)(blockSize - missingBytes);
-            char const sentinel = compressedBuffer[targetSize] = block[targetSize] ^ 0x5A;
+            char const sentinel = decodedBuffer[targetSize] = block[targetSize] ^ 0x5A;
+            assert(decodedBuffer[targetSize] == sentinel);
             int const decResult = LZ4_decompress_safe_partial(compressedBuffer, decodedBuffer, compressedSize, targetSize, blockSize);
-            FUZ_CHECKTEST(decResult<0, "LZ4_decompress_safe_partial failed despite valid input data");
+            FUZ_CHECKTEST(decResult<0, "LZ4_decompress_safe_partial failed despite valid input data (error:%i)", decResult);
             FUZ_CHECKTEST(decResult != targetSize, "LZ4_decompress_safe_partial did not regenerated required amount of data (%i < %i <= %i)", decResult, targetSize, blockSize);
-            FUZ_CHECKTEST(compressedBuffer[targetSize] != sentinel, "LZ4_decompress_safe_partial overwrite beyond requested size (though %i <= %i <= %i)", decResult, targetSize, blockSize);
+            FUZ_CHECKTEST(decodedBuffer[targetSize] != sentinel, "LZ4_decompress_safe_partial overwrite beyond requested size (though %i <= %i <= %i)", decResult, targetSize, blockSize);
         }
 
         /* Test Compression with limited output size */