diff options
Diffstat (limited to 'examples')
| -rw-r--r-- | examples/post_library/post_library.so.c | 159 | ||||
| -rw-r--r-- | examples/post_library/post_library_png.so.c | 156 |
2 files changed, 0 insertions, 315 deletions
diff --git a/examples/post_library/post_library.so.c b/examples/post_library/post_library.so.c deleted file mode 100644 index d9504b23..00000000 --- a/examples/post_library/post_library.so.c +++ /dev/null @@ -1,159 +0,0 @@ -/* - american fuzzy lop++ - postprocessor library example - -------------------------------------------------- - - Originally written by Michal Zalewski - Edited by Dominik Maier, 2020 - - 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 - - Postprocessor libraries can be passed to afl-fuzz to perform final cleanup - of any mutated test cases - for example, to fix up checksums in PNG files. - - Please heed the following warnings: - - 1) In almost all cases, it is more productive to comment out checksum logic - in the targeted binary (as shown in ../libpng_no_checksum/). One possible - exception is the process of fuzzing binary-only software in QEMU mode. - - 2) The use of postprocessors for anything other than checksums is - questionable and may cause more harm than good. AFL is normally pretty good - about dealing with length fields, magic values, etc. - - 3) Postprocessors that do anything non-trivial must be extremely robust to - gracefully handle malformed data and other error conditions - otherwise, - they will crash and take afl-fuzz down with them. Be wary of reading past - *len and of integer overflows when calculating file offsets. - - In other words, THIS IS PROBABLY NOT WHAT YOU WANT - unless you really, - honestly know what you're doing =) - - With that out of the way: the postprocessor library is passed to afl-fuzz - via AFL_POST_LIBRARY. The library must be compiled with: - - gcc -shared -Wall -O3 post_library.so.c -o post_library.so - - 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 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 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 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). - - *** 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". - - PS. If you don't like C, you can try out the unix-based wrapper from - Ben Nagy instead: https://github.com/bnagy/aflfix - - */ - -#include <stdio.h> -#include <stdlib.h> -#include <string.h> - -/* Header that must be present at the beginning of every test case: */ - -#define HEADER "GIF89a" - -typedef struct post_state { - - unsigned char *buf; - size_t size; - -} post_state_t; - -void *afl_postprocess_init(void *afl, unsigned int seed) { - - 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; - -} - -/* 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. */ - - if (len < strlen(HEADER)) return 0; - - /* Do nothing for buffers that already start with the expected header. */ - - if (!memcmp(in_buf, HEADER, strlen(HEADER))) { - - *out_buf = in_buf; - return len; - - } - - /* Allocate memory for new buffer, reusing previous allocation if - possible. */ - - *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 (!*out_buf) { - - *out_buf = in_buf; - return len; - - } - - /* Copy the original data to the new location. */ - - memcpy(*out_buf, in_buf, len); - - /* Insert the new header. */ - - memcpy(*out_buf, HEADER, strlen(HEADER)); - - /* Return the new len. It hasn't changed, so it's just len. */ - - 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 deleted file mode 100644 index b29afd62..00000000 --- a/examples/post_library/post_library_png.so.c +++ /dev/null @@ -1,156 +0,0 @@ -/* - 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_postprocess_init(void *afl, unsigned int seed) { - - 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; - - /* 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_postprocess_deinit(post_state_t *data) { - - free(data->buf); - free(data); - -} - |