[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, 45 insertions, 15 deletions

diff --git a/ossfuzz/decompress_fuzzer.c b/ossfuzz/decompress_fuzzer.c
index e6e14c4..0267c93 100644
--- a/ossfuzz/decompress_fuzzer.c
+++ b/ossfuzz/decompress_fuzzer.c
@@ -1,28 +1,58 @@
+/**
+ * This fuzz target attempts to decompress the fuzzed data with the simple
+ * decompression function to ensure the decompressor never crashes.
+ */
+
 #include <stddef.h>
 #include <stdint.h>
 #include <stdlib.h>
-#include "lz4.h"
+#include <string.h>
 
-#define CHECK(COND)   if (!(COND)) { abort(); }
+#include "fuzz_helpers.h"
+#include "lz4.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
-  // TODO: Size input buffer pseudo-randomly based on seed extracted from input
-  size_t const buffer_size = 10 * 1024 * 1024;
-  char *const dest_buffer = (char *)malloc(buffer_size);
 
-  CHECK(dest_buffer != NULL);
+    uint32_t seed = FUZZ_seed(&data, &size);
+    size_t const dstCapacity = FUZZ_rand32(&seed, 0, 4 * size);
+    size_t const smallDictSize = size + 1;
+    size_t const largeDictSize = 64 * 1024 - 1;
+    size_t const dictSize = MAX(smallDictSize, largeDictSize);
+    char* const dst = (char*)malloc(dstCapacity);
+    char* const dict = (char*)malloc(dictSize + size);
+    char* const largeDict = dict;
+    char* const dataAfterDict = dict + dictSize;
+    char* const smallDict = dataAfterDict - smallDictSize;
 
-  // Allocation succeeded, try decompressing the incoming data.
-  int result = LZ4_decompress_safe((const char*)data,
-                                   dest_buffer,
-                                   size,
-                                   buffer_size);
+    FUZZ_ASSERT(dst);
+    FUZZ_ASSERT(dict);
 
-  // Ignore the result of decompression.
-  (void)result;
+    /* Prepare the dictionary. The data doesn't matter for decompression. */
+    memset(dict, 0, dictSize);
+    memcpy(dataAfterDict, data, size);
 
-  free(dest_buffer);
+    /* Decompress using each possible dictionary configuration. */
+    /* No dictionary. */
+    LZ4_decompress_safe_usingDict((char const*)data, dst, size,
+                                  dstCapacity, NULL, 0);
+    /* Small external dictonary. */
+    LZ4_decompress_safe_usingDict((char const*)data, dst, size,
+                                  dstCapacity, smallDict, smallDictSize);
+    /* Large external dictionary. */
+    LZ4_decompress_safe_usingDict((char const*)data, dst, size,
+                                  dstCapacity, largeDict, largeDictSize);
+    /* Small prefix. */
+    LZ4_decompress_safe_usingDict((char const*)dataAfterDict, dst, size,
+                                  dstCapacity, smallDict, smallDictSize);
+    /* Large prefix. */
+    LZ4_decompress_safe_usingDict((char const*)data, dst, size,
+                                  dstCapacity, largeDict, largeDictSize);
+    /* Partial decompression. */
+    LZ4_decompress_safe_partial((char const*)data, dst, size,
+                                dstCapacity, dstCapacity);
+    free(dst);
+    free(dict);
 
-  return 0;
+    return 0;
 }