thodg/libgit2/fuzzers/midx_fuzzer.c

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• Hash : f0e693b1
  Author :
  Date : 2021-09-07T17:53:49
  

  str: introduce `git_str` for internal, `git_buf` is external libgit2 has two distinct requirements that were previously solved by `git_buf`. We require: 1. A general purpose string class that provides a number of utility APIs for manipulating data (eg, concatenating, truncating, etc). 2. A structure that we can use to return strings to callers that they can take ownership of. By using a single class (`git_buf`) for both of these purposes, we have confused the API to the point that refactorings are difficult and reasoning about correctness is also difficult. Move the utility class `git_buf` to be called `git_str`: this represents its general purpose, as an internal string buffer class. The name also is an homage to Junio Hamano ("gitstr"). The public API remains `git_buf`, and has a much smaller footprint. It is generally only used as an "out" param with strict requirements that follow the documentation. (Exceptions exist for some legacy APIs to avoid breaking callers unnecessarily.) Utility functions exist to convert a user-specified `git_buf` to a `git_str` so that we can call internal functions, then converting it back again.

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• fuzzers/midx_fuzzer.c

• /*
   * libgit2 multi-pack-index fuzzer target.
   *
   * Copyright (C) the libgit2 contributors. All rights reserved.
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   */
  
  #include <stdio.h>
  
  #include "git2.h"
  
  #include "common.h"
  #include "futils.h"
  #include "hash.h"
  #include "midx.h"
  
  int LLVMFuzzerInitialize(int *argc, char ***argv)
  {
  	GIT_UNUSED(argc);
  	GIT_UNUSED(argv);
  
  	if (git_libgit2_init() < 0) {
  		fprintf(stderr, "Failed to initialize libgit2\n");
  		abort();
  	}
  	return 0;
  }
  
  int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
  {
  	git_midx_file idx = {{0}};
  	git_midx_entry e;
  	git_str midx_buf = GIT_STR_INIT;
  	unsigned char hash[GIT_HASH_SHA1_SIZE];
  	git_oid oid = {{0}};
  	bool append_hash = false;
  
  	if (size < 4)
  		return 0;
  
  	/*
  	 * If the first byte in the stream has the high bit set, append the
  	 * SHA1 hash so that the packfile is somewhat valid.
  	 */
  	append_hash = *data & 0x80;
  	/* Keep a 4-byte alignment to avoid unaligned accesses. */
  	data += 4;
  	size -= 4;
  
  	if (append_hash) {
  		if (git_str_init(&midx_buf, size + GIT_HASH_SHA1_SIZE) < 0)
  			goto cleanup;
  		if (git_hash_buf(hash, data, size, GIT_HASH_ALGORITHM_SHA1) < 0) {
  			fprintf(stderr, "Failed to compute the SHA1 hash\n");
  			abort();
  		}
  		memcpy(midx_buf.ptr, data, size);
  		memcpy(midx_buf.ptr + size, hash, GIT_HASH_SHA1_SIZE);
  
  		memcpy(oid.id, hash, GIT_OID_RAWSZ);
  	} else {
  		git_str_attach_notowned(&midx_buf, (char *)data, size);
  	}
  
  	if (git_midx_parse(&idx, (const unsigned char *)git_str_cstr(&midx_buf), git_str_len(&midx_buf)) < 0)
  		goto cleanup;
  
  	/* Search for any oid, just to exercise that codepath. */
  	if (git_midx_entry_find(&e, &idx, &oid, GIT_OID_HEXSZ) < 0)
  		goto cleanup;
  
  cleanup:
  	git_midx_close(&idx);
  	git_str_dispose(&midx_buf);
  	return 0;
  }
  

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