Add American Fuzzy Lop (afl) to third_party/afl/

third_party/afl/src/experimental/post_library/post_library_png.so.c

+/*
+   american fuzzy lop - postprocessor for PNG
+   ------------------------------------------
+
+   Written and maintained by Michal Zalewski <lcamtuf@google.com>
+
+   Copyright 2015 Google Inc. All rights reserved.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at:
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+   See post_library.so.c for a general discussion of how to implement
+   postprocessors. This specific postprocessor attempts to fix up PNG
+   checksums, providing a slightly more complicated example than found
+   in post_library.so.c.
+
+   Compile with:
+
+     gcc -shared -Wall -O3 post_library_png.so.c -o post_library_png.so -lz
+
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <zlib.h>
+
+#include <arpa/inet.h>
+
+/* A macro to round an integer up to 4 kB. */
+
+#define UP4K(_i) ((((_i) >> 12) + 1) << 12)
+
+const unsigned char* afl_postprocess(const unsigned char* in_buf,
+                                     unsigned int* len) {
+
+  static unsigned char* saved_buf;
+  static unsigned int   saved_len;
+
+  unsigned char* new_buf = (unsigned char*)in_buf;
+  unsigned int pos = 8;
+
+  /* Don't do anything if there's not enough room for the PNG header
+     (8 bytes). */
+
+  if (*len < 8) return in_buf;
+
+  /* Minimum size of a zero-length PNG chunk is 12 bytes; if we
+     don't have that, we can bail out. */
+
+  while (pos + 12 <= *len) {
+
+    unsigned int chunk_len, real_cksum, file_cksum;
+
+    /* Chunk length is the first big-endian dword in the chunk. */
+
+    chunk_len = ntohl(*(uint32_t*)(in_buf + pos));
+
+    /* Bail out if chunk size is too big or goes past EOF. */
+
+    if (chunk_len > 1024 * 1024 || pos + 12 + chunk_len > *len) break;
+
+    /* Chunk checksum is calculated for chunk ID (dword) and the actual
+       payload. */
+
+    real_cksum = htonl(crc32(0, in_buf + pos + 4, chunk_len + 4));
+
+    /* The in-file checksum is the last dword past the chunk data. */
+
+    file_cksum = *(uint32_t*)(in_buf + pos + 8 + chunk_len);
+
+    /* If the checksums do not match, we need to fix the file. */
+
+    if (real_cksum != file_cksum) {
+
+      /* First modification? Make a copy of the input buffer. Round size
+         up to 4 kB to minimize the number of reallocs needed. */
+
+      if (new_buf == in_buf) {
+
+        if (*len <= saved_len) {
+
+          new_buf = saved_buf;
+
+        } else {
+
+          new_buf = realloc(saved_buf, UP4K(*len));
+          if (!new_buf) return in_buf;
+          saved_buf = new_buf;
+          saved_len = UP4K(*len);
+          memcpy(new_buf, in_buf, *len);
+
+        }
+
+      }
+
+      *(uint32_t*)(new_buf + pos + 8 + chunk_len) = real_cksum;
+
+    }
+
+    /* Skip the entire chunk and move to the next one. */
+
+    pos += 12 + chunk_len;
+
+  }
+
+  return new_buf;
+
+}