more custom mutator remodelling

4 files changed, 239 insertions, 90 deletions

diff --git a/examples/custom_mutators/custom_mutator_helpers.h b/examples/custom_mutators/custom_mutator_helpers.h
index cd3a15f0..0dc00d96 100644
--- a/examples/custom_mutators/custom_mutator_helpers.h
+++ b/examples/custom_mutators/custom_mutator_helpers.h
@@ -5,8 +5,18 @@
 #include "types.h"
 #include <stdlib.h>
 
+#define INITIAL_GROWTH_SIZE (64)
+
 #define RAND_BELOW(limit) (rand() % (limit))
 
+/* Use in a struct: creates a name_buf and a name_size variable. */
+#define BUF_VAR(type, name) \
+  type * name##_buf;        \
+  size_t name##_size;
+/* this filles in `&structptr->something_buf, &structptr->something_size`. */
+#define BUF_PARAMS(struct, name) \
+  (void **)&struct->name##_buf, &struct->name##_size
+
 typedef struct {
 
 } afl_t;
@@ -267,5 +277,56 @@ static void surgical_havoc_mutate(u8 *out_buf, s32 begin, s32 end) {
 
 }
 
+/* This function makes sure *size is > size_needed after call.
+ It changes buf and size in-place, if needed.
+ It will realloc *buf otherwise.
+ *size will grow exponentially as per:
+ https://blog.mozilla.org/nnethercote/2014/11/04/please-grow-your-buffers-exponentially/
+ Will return NULL if size_needed is <1 or *size is negative or malloc Failed.
+ @return For convenience, this function returns *buf. NULL on error.
+ */
+static inline void *maybe_grow(void **buf, size_t *size, size_t size_needed) {
+
+  /* Oops. found a bug? */
+  if (unlikely(size_needed < 1)) return NULL;
+
+  /* No need to realloc */
+  if (likely(*size >= size_needed)) return *buf;
+  if (unlikely(*size < 0)) return NULL;
+  /* No inital size was set */
+  if (*size == 0) *size = INITIAL_GROWTH_SIZE;
+  while (*size < size_needed) {
+
+    *size *= 2;
+    if ((*size) < 0) {
+
+      /* An overflow occurred. Fall back to size_needed */
+      *size = size_needed;
+
+    }
+
+  }
+
+  *buf = realloc(*buf, *size);
+
+  return *buf;
+
+}
+
+/* Swaps buf1 ptr and buf2 ptr, as well as their sizes */
+static inline void swap_bufs(void **buf1, size_t *size1, void **buf2,
+                             size_t *size2) {
+
+  void * scratch_buf = *buf1;
+  size_t scratch_size = *size1;
+  *buf1 = *buf2;
+  *size1 = *size2;
+  *buf2 = scratch_buf;
+  *size2 = scratch_size;
+
+}
+
+#undef INITIAL_GROWTH_SIZE
+
 #endif
 
diff --git a/examples/custom_mutators/example.c b/examples/custom_mutators/example.c
index 4b0a461b..54fc9d47 100644
--- a/examples/custom_mutators/example.c
+++ b/examples/custom_mutators/example.c
@@ -15,7 +15,6 @@
 #include <stdio.h>
 
 #define DATA_SIZE (100)
-#define INITIAL_BUF_SIZE (16384)
 
 static const char *commands[] = {
 
@@ -28,9 +27,19 @@ static const char *commands[] = {
 typedef struct my_mutator {
 
   afl_t *afl;
+
   // any additional data here!
-  size_t pre_save_size;
-  u8 *   pre_save_buf;
+  uint8_t *trim_buf;
+  size_t   trim_buf_size;
+  int      trimmming_steps;
+  int      cur_step;
+
+  // Reused buffers:
+  BUF_VAR(u8, fuzz);
+  BUF_VAR(u8, data);
+  BUF_VAR(u8, havoc);
+  BUF_VAR(u8, trim_out);
+  BUF_VAR(u8, pre_save);
 
 } my_mutator_t;
 
@@ -59,16 +68,6 @@ my_mutator_t *afl_custom_init(afl_t *afl, unsigned int seed) {
 
   data->afl = afl;
 
-  data->pre_save_buf = malloc(INITIAL_BUF_SIZE);
-  if (!data->pre_save_buf) {
-
-    free(data);
-    return NULL;
-
-  }
-
-  data->pre_save_size = INITIAL_BUF_SIZE;
-
   return data;
 
 }
@@ -85,20 +84,25 @@ my_mutator_t *afl_custom_init(afl_t *afl, unsigned int seed) {
  * @param[in] add_buf_size Size of the additional test case
  * @param[in] max_size Maximum size of the mutated output. The mutation must not
  *     produce data larger than max_size.
- * @return Size of the mutated output.
+ * @return Size of the mutated output. Negative return will abort fuzzing.
  */
-size_t afl_custom_fuzz(my_mutator_t *data, uint8_t **buf, size_t buf_size,
-                       uint8_t *add_buf,
-                       size_t   add_buf_size,  // add_buf can be NULL
-                       size_t   max_size) {
+size_t afl_custom_fuzz(my_mutator_t *data, uint8_t *buf, size_t buf_size,
+                       u8 **out_buf, uint8_t *add_buf,
+                       size_t add_buf_size,  // add_buf can be NULL
+                       size_t max_size) {
 
   // Make sure that the packet size does not exceed the maximum size expected by
   // the fuzzer
   size_t mutated_size = DATA_SIZE <= max_size ? DATA_SIZE : max_size;
 
-  if (mutated_size > buf_size) *buf = realloc(*buf, mutated_size);
+  // maybe_grow is optimized to be quick for reused buffers.
+  u8 *mutated_out = maybe_grow(BUF_PARAMS(data, fuzz), mutated_size);
+  if (!mutated_out) {
+
+    perror("custom mutator allocation (maybe_grow)");
+    return -1;           /* afl-fuzz will very likely error out after this. */
 
-  uint8_t *mutated_out = *buf;
+  }
 
   // Randomly select a command string to add as a header to the packet
   memcpy(mutated_out, commands[rand() % 3], 3);
@@ -112,6 +116,7 @@ size_t afl_custom_fuzz(my_mutator_t *data, uint8_t **buf, size_t buf_size,
 
   }
 
+  *out_buf = mutated_out;
   return mutated_size;
 
 }
@@ -137,11 +142,10 @@ size_t afl_custom_pre_save(my_mutator_t *data, uint8_t *buf, size_t buf_size,
 
   if (data->pre_save_size < buf_size + 5) {
 
-    data->pre_save_buf = realloc(data->pre_save_buf, buf_size + 5);
+    data->pre_save_buf = maybe_grow(BUF_PARAMS(data, pre_save), buf_size + 5);
     if (!data->pre_save_buf) {
 
-      perror("custom mutator realloc");
-      free(data);
+      perror("custom mutator realloc failed.");
       return -1;
 
     }
@@ -164,11 +168,6 @@ size_t afl_custom_pre_save(my_mutator_t *data, uint8_t *buf, size_t buf_size,
 
 }
 
-static uint8_t *trim_buf;
-static size_t   trim_buf_size;
-static int      trimmming_steps;
-static int      cur_step;
-
 /**
  * This method is called at the start of each trimming operation and receives
  * the initial buffer. It should return the amount of iteration steps possible
@@ -193,20 +192,20 @@ static int      cur_step;
 int afl_custom_init_trim(my_mutator_t *data, uint8_t *buf, size_t buf_size) {
 
   // We simply trim once
-  trimmming_steps = 1;
+  data->trimmming_steps = 1;
 
-  cur_step = 0;
-  trim_buf = buf;
-  trim_buf_size = buf_size;
+  data->cur_step = 0;
+  data->trim_buf = buf;
+  data->trim_buf_size = buf_size;
 
-  return trimmming_steps;
+  return data->trimmming_steps;
 
 }
 
 /**
  * This method is called for each trimming operation. It doesn't have any
  * arguments because we already have the initial buffer from init_trim and we
- * can memorize the current state in global variables. This can also save
+ * can memorize the current state in *data. This can also save
  * reparsing steps for each iteration. It should return the trimmed input
  * buffer, where the returned data must not exceed the initial input data in
  * length. Returning anything that is larger than the original data (passed
@@ -216,19 +215,18 @@ int afl_custom_init_trim(my_mutator_t *data, uint8_t *buf, size_t buf_size) {
  *
  * @param[in] data pointer returned in afl_custom_init for this fuzz case
  * @param[out] out_buf Pointer to the buffer containing the trimmed test case.
- *     External library should allocate memory for out_buf. AFL++ will release
- *     the memory after saving the test case.
- * @param[out] out_buf_size Pointer to the size of the trimmed test case
+ *     External library should allocate memory for out_buf.
+ *     AFL++ will not release the memory after saving the test case.
+ *     Keep a ref in *data.
+ * @return Pointer to the size of the trimmed test case
  */
-void afl_custom_trim(my_mutator_t *data, uint8_t **out_buf,
-                     size_t *out_buf_size) {
+size_t afl_custom_trim(my_mutator_t *data, uint8_t **out_buf) {
 
-  *out_buf_size = trim_buf_size - 1;
+  size_t ret = data->trim_buf_size - 1;
 
-  // External mutator should allocate memory for `out_buf`
-  *out_buf = malloc(*out_buf_size);
+  *out_buf = maybe_grow(BUF_PARAMS(data, trim_out), ret);
   // Remove the last byte of the trimming input
-  memcpy(*out_buf, trim_buf, *out_buf_size);
+  memcpy(*out_buf, data->trim_buf, ret);
 
 }
 
@@ -248,12 +246,12 @@ int afl_custom_post_trim(my_mutator_t *data, int success) {
 
   if (success) {
 
-    ++cur_step;
-    return cur_step;
+    ++data->cur_step;
+    return data->cur_step;
 
   }
 
-  return trimmming_steps;
+  return data->trimmming_steps;
 
 }
 
@@ -264,26 +262,33 @@ int afl_custom_post_trim(my_mutator_t *data, int success) {
  * (Optional)
  *
  * @param[in] data pointer returned in afl_custom_init for this fuzz case
- * @param[inout] buf Pointer to the input data to be mutated and the mutated
+ * @param[in] buf Pointer to the input data to be mutated and the mutated
  *     output
  * @param[in] buf_size Size of input data
+ * @param[out] out_buf The output buffer. buf can be reused, if the content
+ * fits.
  * @param[in] max_size Maximum size of the mutated output. The mutation must
  *     not produce data larger than max_size.
  * @return Size of the mutated output.
  */
-size_t afl_custom_havoc_mutation(my_mutator_t *data, uint8_t **buf,
-                                 size_t buf_size, size_t max_size) {
+size_t afl_custom_havoc_mutation(my_mutator_t *data, u8 *buf, size_t buf_size,
+                                 u8 **out_buf, size_t max_size) {
 
   if (buf_size == 0) {
 
-    *buf = realloc(*buf, 1);
-    **buf = rand() % 256;
+    *out_buf = maybe_grow(BUF_PARAMS(data, havoc), 1);
+    **out_buf = rand() % 256;
     buf_size = 1;
 
+  } else {
+
+    // We reuse buf here. It's legal and faster.
+    *out_buf = buf;
+
   }
 
   size_t victim = rand() % buf_size;
-  (*buf)[victim] += rand() % 10;
+  (*out_buf)[victim] += rand() % 10;
 
   return buf_size;
 
@@ -346,6 +351,10 @@ void afl_custom_queue_new_entry(my_mutator_t * data,
 void afl_custom_deinit(my_mutator_t *data) {
 
   free(data->pre_save_buf);
+  free(data->havoc_buf);
+  free(data->data_buf);
+  free(data->fuzz_buf);
+  free(data->trim_out_buf);
   free(data);
 
 }
diff --git a/examples/post_library/post_library.so.c b/examples/post_library/post_library.so.c
index 5d2685cd..735aae9b 100644
--- a/examples/post_library/post_library.so.c
+++ b/examples/post_library/post_library.so.c
@@ -3,6 +3,7 @@
    --------------------------------------------------
 
    Originally written by Michal Zalewski
+   Edited by Dominik Maier, 2020
 
    Copyright 2015 Google Inc. All rights reserved.
 
@@ -41,22 +42,23 @@
    AFL will call the afl_postprocess() function for every mutated output buffer.
    From there, you have three choices:
 
-   1) If you don't want to modify the test case, simply return the original
-      buffer pointer ('in_buf').
+   1) If you don't want to modify the test case, simply set `*out_buf = in_buf`
+      and return the original `len`.
 
    2) If you want to skip this test case altogether and have AFL generate a
-      new one, return NULL. Use this sparingly - it's faster than running
-      the target program with patently useless inputs, but still wastes CPU
-      time.
+      new one, return 0 or set `*out_buf = NULL`.
+      Use this sparingly - it's faster than running the target program
+      with patently useless inputs, but still wastes CPU time.
 
    3) If you want to modify the test case, allocate an appropriately-sized
       buffer, move the data into that buffer, make the necessary changes, and
-      then return the new pointer. You can update *len if necessary, too.
+      then return the new pointer as out_buf. Return an appropriate len
+   afterwards.
 
       Note that the buffer will *not* be freed for you. To avoid memory leaks,
       you need to free it or reuse it on subsequent calls (as shown below).
 
-      *** DO NOT MODIFY THE ORIGINAL 'in_buf' BUFFER. ***
+      *** Feel free to reuse the original 'in_buf' BUFFER and return it. ***
 
     Aight. The example below shows a simple postprocessor that tries to make
     sure that all input files start with "GIF89a".
@@ -74,47 +76,83 @@
 
 #define HEADER "GIF89a"
 
-/* The actual postprocessor routine called by afl-fuzz: */
+typedef struct post_state {
+
+  unsigned char *buf;
+  size_t         size;
+
+} post_state_t;
+
+void *afl_postprocess_init(void *afl) {
+
+  post_state_t *state = malloc(sizeof(post_state_t));
+  if (!state) {
 
-const unsigned char *afl_postprocess(const unsigned char *in_buf,
-                                     unsigned int *       len) {
+    perror("malloc");
+    return NULL;
 
-  static unsigned char *saved_buf;
-  unsigned char *       new_buf;
+  }
+
+  state->buf = calloc(sizeof(unsigned char), 4096);
+  if (!state->buf) { return NULL; }
+
+  return state;
+
+}
+
+/* The actual postprocessor routine called by afl-fuzz: */
+
+size_t afl_postprocess(post_state_t *data, unsigned char *in_buf,
+                       unsigned int len, unsigned char **out_buf) {
 
   /* Skip execution altogether for buffers shorter than 6 bytes (just to
-     show how it's done). We can trust *len to be sane. */
+     show how it's done). We can trust len to be sane. */
 
-  if (*len < strlen(HEADER)) return NULL;
+  if (len < strlen(HEADER)) return 0;
 
   /* Do nothing for buffers that already start with the expected header. */
 
-  if (!memcmp(in_buf, HEADER, strlen(HEADER))) return in_buf;
+  if (!memcmp(in_buf, HEADER, strlen(HEADER))) {
+
+    *out_buf = in_buf;
+    return len;
+
+  }
 
   /* Allocate memory for new buffer, reusing previous allocation if
      possible. */
 
-  new_buf = realloc(saved_buf, *len);
+  *out_buf = realloc(data->buf, len);
 
   /* If we're out of memory, the most graceful thing to do is to return the
      original buffer and give up on modifying it. Let AFL handle OOM on its
      own later on. */
 
-  if (!new_buf) return in_buf;
-  saved_buf = new_buf;
+  if (!*out_buf) {
+
+    *out_buf = in_buf;
+    return len;
+
+  }
 
   /* Copy the original data to the new location. */
 
-  memcpy(new_buf, in_buf, *len);
+  memcpy(*out_buf, in_buf, len);
 
   /* Insert the new header. */
 
-  memcpy(new_buf, HEADER, strlen(HEADER));
+  memcpy(*out_buf, HEADER, strlen(HEADER));
 
-  /* Return modified buffer. No need to update *len in this particular case,
-     as we're not changing it. */
+  /* Return the new len. It hasn't changed, so it's just len. */
 
-  return new_buf;
+  return len;
 
 }
 
+/* Gets called afterwards */
+void afl_postprocess_deinit(post_state_t *data) {
+
+  free(data->buf);
+  free(data);
+
+}
diff --git a/examples/post_library/post_library_png.so.c b/examples/post_library/post_library_png.so.c
index 60ab318f..8597c88c 100644
--- a/examples/post_library/post_library_png.so.c
+++ b/examples/post_library/post_library_png.so.c
@@ -5,6 +5,7 @@
    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.
@@ -35,11 +36,32 @@
 
 #define UP4K(_i) ((((_i) >> 12) + 1) << 12)
 
-const unsigned char *afl_postprocess(const unsigned char *in_buf,
-                                     unsigned int *       len) {
+typedef struct post_state {
 
-  static unsigned char *saved_buf;
-  static unsigned int   saved_len;
+  unsigned char *buf;
+  size_t         size;
+
+} post_state_t;
+
+void *afl_postprocess_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) { return NULL; }
+
+  return state;
+
+}
+
+size_t afl_postprocess(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;
@@ -47,12 +69,17 @@ const unsigned char *afl_postprocess(const unsigned char *in_buf,
   /* Don't do anything if there's not enough room for the PNG header
      (8 bytes). */
 
-  if (*len < 8) return in_buf;
+  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) {
+  while (pos + 12 <= len) {
 
     unsigned int chunk_len, real_cksum, file_cksum;
 
@@ -62,7 +89,7 @@ const unsigned char *afl_postprocess(const unsigned char *in_buf,
 
     /* Bail out if chunk size is too big or goes past EOF. */
 
-    if (chunk_len > 1024 * 1024 || pos + 12 + chunk_len > *len) break;
+    if (chunk_len > 1024 * 1024 || pos + 12 + chunk_len > len) break;
 
     /* Chunk checksum is calculated for chunk ID (dword) and the actual
        payload. */
@@ -82,17 +109,23 @@ const unsigned char *afl_postprocess(const unsigned char *in_buf,
 
       if (new_buf == in_buf) {
 
-        if (*len <= saved_len) {
+        if (len <= data->size) {
 
-          new_buf = saved_buf;
+          new_buf = data->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);
+          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);
 
         }
 
@@ -108,7 +141,15 @@ const unsigned char *afl_postprocess(const unsigned char *in_buf,
 
   }
 
-  return new_buf;
+  *out_buf = new_buf;
+  return len;
 
 }
 
+/* Gets called afterwards */
+void afl_postprocess_deinit(post_state_t *data) {
+
+  free(data->buf);
+  free(data);
+
+}