[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, 48 insertions, 0 deletions

diff --git a/ossfuzz/fuzz.h b/ossfuzz/fuzz.h
new file mode 100644
index 0000000..eefac63
--- /dev/null
+++ b/ossfuzz/fuzz.h
@@ -0,0 +1,48 @@
+/**
+ * Fuzz target interface.
+ * Fuzz targets have some common parameters passed as macros during compilation.
+ * Check the documentation for each individual fuzzer for more parameters.
+ *
+ * @param FUZZ_RNG_SEED_SIZE:
+ *        The number of bytes of the source to look at when constructing a seed
+ *        for the deterministic RNG. These bytes are discarded before passing
+ *        the data to lz4 functions. Every fuzzer initializes the RNG exactly
+ *        once before doing anything else, even if it is unused.
+ *        Default: 4.
+ * @param LZ4_DEBUG:
+ *        This is a parameter for the lz4 library. Defining `LZ4_DEBUG=1`
+ *        enables assert() statements in the lz4 library. Higher levels enable
+ *        logging, so aren't recommended. Defining `LZ4_DEBUG=1` is
+ *        recommended.
+ * @param LZ4_FORCE_MEMORY_ACCESS:
+ *        This flag controls how the zstd library accesses unaligned memory.
+ *        It can be undefined, or 0 through 2. If it is undefined, it selects
+ *        the method to use based on the compiler. If testing with UBSAN set
+ *        MEM_FORCE_MEMORY_ACCESS=0 to use the standard compliant method.
+ * @param FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+ *        This is the canonical flag to enable deterministic builds for fuzzing.
+ *        Changes to zstd for fuzzing are gated behind this define.
+ *        It is recommended to define this when building zstd for fuzzing.
+ */
+
+#ifndef FUZZ_H
+#define FUZZ_H
+
+#ifndef FUZZ_RNG_SEED_SIZE
+#  define FUZZ_RNG_SEED_SIZE 4
+#endif
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif