thodg/libgit2/fuzzers/commit_graph_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/commit_graph_fuzzer.c

• /*
   * libgit2 commit-graph 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 "str.h"
  #include "futils.h"
  #include "hash.h"
  #include "commit_graph.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_commit_graph_file file = {{0}};
  	git_commit_graph_entry e;
  	git_str commit_graph_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 file 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(&commit_graph_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(commit_graph_buf.ptr, data, size);
  		memcpy(commit_graph_buf.ptr + size, hash, GIT_HASH_SHA1_SIZE);
  
  		memcpy(oid.id, hash, GIT_OID_RAWSZ);
  	} else {
  		git_str_attach_notowned(&commit_graph_buf, (char *)data, size);
  	}
  
  	if (git_commit_graph_file_parse(
  			    &file,
  			    (const unsigned char *)git_str_cstr(&commit_graph_buf),
  			    git_str_len(&commit_graph_buf))
  	    < 0)
  		goto cleanup;
  
  	/* Search for any oid, just to exercise that codepath. */
  	if (git_commit_graph_entry_find(&e, &file, &oid, GIT_OID_HEXSZ) < 0)
  		goto cleanup;
  
  cleanup:
  	git_commit_graph_file_close(&file);
  	git_str_dispose(&commit_graph_buf);
  	return 0;
  }
  

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