1 files changed, 163 insertions, 0 deletions
diff --git a/custom_mutators/examples/post_library_png.so.c b/custom_mutators/examples/post_library_png.so.c
new file mode 100644
index 00000000..941f7e55
--- /dev/null
+++ b/custom_mutators/examples/post_library_png.so.c
@@ -0,0 +1,163 @@
+/*
+   american fuzzy lop++ - postprocessor for PNG
+   ------------------------------------------
+
+   Originally written by Michal Zalewski
+
+   Copyright 2015 Google Inc. All rights reserved.
+   Adapted to the new API, 2020 by Dominik Maier
+
+   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)
+
+typedef struct post_state {
+
+  unsigned char *buf;
+  size_t         size;
+
+} post_state_t;
+
+void *afl_custom_init(void *afl) {
+
+  post_state_t *state = malloc(sizeof(post_state_t));
+  if (!state) {
+
+    perror("malloc");
+    return NULL;
+
+  }
+
+  state->buf = calloc(sizeof(unsigned char), 4096);
+  if (!state->buf) {
+
+    free(state);
+    perror("calloc");
+    return NULL;
+
+  }
+
+  return state;
+
+}
+
+size_t afl_custom_post_process(post_state_t *data, const unsigned char *in_buf,
+                               unsigned int          len,
+                               const unsigned char **out_buf) {
+
+  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) {
+
+    *out_buf = in_buf;
+    return len;
+
+  }
+
+  /* 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 <= data->size) {
+
+          new_buf = data->buf;
+
+        } else {
+
+          new_buf = realloc(data->buf, UP4K(len));
+          if (!new_buf) {
+
+            *out_buf = in_buf;
+            return len;
+
+          }
+
+          data->buf = new_buf;
+          data->size = 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;
+
+  }
+
+  *out_buf = new_buf;
+  return len;
+
+}
+
+/* Gets called afterwards */
+void afl_custom_deinit(post_state_t *data) {
+
+  free(data->buf);
+  free(data);
+
+}
+