[ossfuzz] Improve the fuzzers

* Run more decompression variants
* Round trip the compression fuzzer and do partial decompression as well
* Add a compression fuzzer that compresses into a smaller output buffer
  and test the destSize variant

These fuzzers caught 2 bugs that were fixed in the previous commit.
* Input buffer over-read in partial decompress
* Partial decompress fails if output size is 0

1 files changed, 50 insertions, 0 deletions

diff --git a/ossfuzz/round_trip_fuzzer.c b/ossfuzz/round_trip_fuzzer.c
new file mode 100644
index 0000000..3a66e80
--- /dev/null
+++ b/ossfuzz/round_trip_fuzzer.c
@@ -0,0 +1,50 @@
+/**
+ * This fuzz target performs a lz4 round-trip test (compress & decompress),
+ * compares the result with the original, and calls abort() on corruption.
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "fuzz_helpers.h"
+#include "lz4.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+    uint32_t seed = FUZZ_seed(&data, &size);
+    size_t const dstCapacity = LZ4_compressBound(size);
+    char* const dst = (char*)malloc(dstCapacity);
+    char* const rt = (char*)malloc(size);
+
+    FUZZ_ASSERT(dst);
+    FUZZ_ASSERT(rt);
+
+    /* Compression must succeed and round trip correctly. */
+    int const dstSize = LZ4_compress_default((const char*)data, dst,
+                                             size, dstCapacity);
+    FUZZ_ASSERT(dstSize > 0);
+
+    int const rtSize = LZ4_decompress_safe(dst, rt, dstSize, size);
+    FUZZ_ASSERT_MSG(rtSize == size, "Incorrect size");
+    FUZZ_ASSERT_MSG(!memcmp(data, rt, size), "Corruption!");
+
+    /* Partial decompression must succeed. */
+    {
+        size_t const partialCapacity = FUZZ_rand32(&seed, 0, size);
+        char* const partial = (char*)malloc(partialCapacity);
+        FUZZ_ASSERT(partial);
+        int const partialSize = LZ4_decompress_safe_partial(
+                dst, partial, dstSize, partialCapacity, partialCapacity);
+        FUZZ_ASSERT(partialSize >= 0);
+        FUZZ_ASSERT_MSG(partialSize == partialCapacity, "Incorrect size");
+        FUZZ_ASSERT_MSG(!memcmp(data, partial, partialSize), "Corruption!");
+        free(partial);
+    }
+
+    free(dst);
+    free(rt);
+
+    return 0;
+}