Fix input size validation edge cases

The bug is a read up to 2 bytes past the end of the buffer.
There are three cases for this bug, one for each test case added.

* An empty input causes `token = *ip++` to read one byte too far.
* A one byte input with `(token >> ML_BITS) == RUN_MASK` causes
  one extra byte to be read without validation. This could be
  combined with the first bug to cause 2 extra bytes to be read.
* The case pointed out in issue #508, where `ip == iend` at the
  beginning of the loop after taking the shortcut.

Benchmarks show no regressions on clang or gcc-7 on both my mac
and devserver.

Fixes #508.

1 files changed, 26 insertions, 0 deletions

diff --git a/tests/fuzzer.c b/tests/fuzzer.c
index 244cc4f..def5230 100644
--- a/tests/fuzzer.c
+++ b/tests/fuzzer.c
@@ -487,6 +487,32 @@ static int FUZ_test(U32 seed, U32 nbCycles, const U32 startCycle, const double c
         ret = LZ4_decompress_fast(compressedBuffer, decodedBuffer, blockSize+1);
         FUZ_CHECKTEST(ret>=0, "LZ4_decompress_fast should have failed, due to Output Size being too large");
 
+        /* Test decoding with empty input */
+        FUZ_DISPLAYTEST("LZ4_decompress_safe() with empty input");
+        LZ4_decompress_safe(NULL, decodedBuffer, 0, blockSize);
+
+        /* Test decoding with a one byte input */
+        FUZ_DISPLAYTEST("LZ4_decompress_safe() with one byte input");
+        {   char const tmp = 0xFF;
+            LZ4_decompress_safe(&tmp, decodedBuffer, 1, blockSize);
+        }
+
+        /* Test decoding shortcut edge case */
+        FUZ_DISPLAYTEST("LZ4_decompress_safe() with shortcut edge case");
+        {   char tmp[17];
+            unsigned long i;
+            /* 14 bytes of literals, followed by a 14 byte match.
+             * Should not read beyond the end of the buffer.
+             * See https://github.com/lz4/lz4/issues/508. */
+            *tmp = 0xEE;
+            memset(tmp + 1, 0, 14);
+            tmp[15] = 14;
+            tmp[16] = 0;
+            ret = LZ4_decompress_safe(tmp, decodedBuffer, sizeof(tmp), blockSize);
+            FUZ_CHECKTEST(ret >= 0, "LZ4_decompress_safe() should fail");
+        }
+
+
         /* Test decoding with output size exactly what's necessary => must work */
         FUZ_DISPLAYTEST();
         decodedBuffer[blockSize] = 0;