thodg/libgit2/tests/pack/filelimit.c

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• Hash : 322c15ee
  Author :
  Date : 2020-08-01T18:24:41
  

  Make the pack and mwindow implementations data-race-free This change fixes a packfile heap corruption that can happen when interacting with multiple packfiles concurrently across multiple threads. This is exacerbated by setting a lower mwindow open file limit. This change: * Renames most of the internal methods in pack.c to clearly indicate that they expect to be called with a certain lock held, making reasoning about the state of locks a bit easier. * Splits the `git_pack_file` lock in two: the one in `git_pack_file` only protects the `index_map`. The protection to `git_mwindow_file` is now in that struct. * Explicitly checks for freshness of the `git_pack_file` in `git_packfile_unpack_header`: this allows the mwindow implementation to close files whenever there is enough cache pressure, and `git_packfile_unpack_header` will reopen the packfile if needed. * After a call to `p_munmap()`, the `data` and `len` fields are poisoned with `NULL` to make use-after-frees more evident and crash rather than being open to the possibility of heap corruption. * Adds a test case to prevent this from regressing in the future. Fixes: #5591

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• tests/pack/filelimit.c

• #include "clar_libgit2.h"
  #include "mwindow.h"
  
  #include <git2.h>
  #include "git2/sys/commit.h"
  #include "git2/sys/mempack.h"
  
  static size_t expected_open_mwindow_files = 0;
  static size_t original_mwindow_file_limit = 0;
  
  extern git_mutex git__mwindow_mutex;
  extern git_mwindow_ctl git_mwindow__mem_ctl;
  
  void test_pack_filelimit__initialize_tiny(void)
  {
  	expected_open_mwindow_files = 1;
  	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_MWINDOW_FILE_LIMIT, &original_mwindow_file_limit));
  	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_MWINDOW_FILE_LIMIT, expected_open_mwindow_files));
  }
  
  void test_pack_filelimit__initialize_medium(void)
  {
  	expected_open_mwindow_files = 10;
  	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_MWINDOW_FILE_LIMIT, &original_mwindow_file_limit));
  	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_MWINDOW_FILE_LIMIT, expected_open_mwindow_files));
  }
  
  void test_pack_filelimit__initialize_unlimited(void)
  {
  	expected_open_mwindow_files = 15;
  	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_MWINDOW_FILE_LIMIT, &original_mwindow_file_limit));
  	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_MWINDOW_FILE_LIMIT, 0));
  }
  
  void test_pack_filelimit__cleanup(void)
  {
  	git_buf path = GIT_BUF_INIT;
  	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_MWINDOW_FILE_LIMIT, original_mwindow_file_limit));
  
  	cl_git_pass(git_buf_joinpath(&path, clar_sandbox_path(), "repo.git"));
  	cl_fixture_cleanup(path.ptr);
  	git_buf_dispose(&path);
  }
  
  /*
   * Create a packfile with one commit, one tree, and two blobs. The first blob
   * (README.md) has the same content in all commits, but the second one
   * (file.txt) has a different content in each commit.
   */
  void create_packfile_commit(
  		git_repository *repo,
  		git_oid *out_commit_id,
  		git_oid *parent_id,
  		size_t commit_index,
  		size_t commit_count)
  {
  	git_buf file_contents = GIT_BUF_INIT;
  	git_treebuilder *treebuilder;
  	git_packbuilder *packbuilder;
  	git_signature *s;
  	git_oid oid, tree_id, commit_id;
  	const git_oid *parents[] = { parent_id };
  	size_t parent_count = parent_id ? 1 : 0;
  
  	cl_git_pass(git_treebuilder_new(&treebuilder, repo, NULL));
  
  	cl_git_pass(git_blob_create_from_buffer(&oid, repo, "", 0));
  	cl_git_pass(git_treebuilder_insert(NULL, treebuilder, "README.md", &oid, 0100644));
  
  	cl_git_pass(git_buf_printf(&file_contents, "Commit %zd/%zd", commit_index, commit_count));
  	cl_git_pass(git_blob_create_from_buffer(&oid, repo, file_contents.ptr, file_contents.size));
  	cl_git_pass(git_treebuilder_insert(NULL, treebuilder, "file.txt", &oid, 0100644));
  
  	cl_git_pass(git_treebuilder_write(&tree_id, treebuilder));
  	cl_git_pass(git_signature_now(&s, "alice", "alice@example.com"));
  	cl_git_pass(git_commit_create_from_ids(&commit_id, repo, "refs/heads/master", s, s,
  			NULL, file_contents.ptr, &tree_id, parent_count, parents));
  
  	cl_git_pass(git_packbuilder_new(&packbuilder, repo));
  	cl_git_pass(git_packbuilder_insert_commit(packbuilder, &commit_id));
  	cl_git_pass(git_packbuilder_write(packbuilder, NULL, 0, NULL, NULL));
  
  	cl_git_pass(git_oid_cpy(out_commit_id, &commit_id));
  
  	git_buf_dispose(&file_contents);
  	git_treebuilder_free(treebuilder);
  	git_packbuilder_free(packbuilder);
  	git_signature_free(s);
  }
  
  void test_pack_filelimit__open_repo_with_multiple_packfiles(void)
  {
  	git_buf path = GIT_BUF_INIT;
  	git_mwindow_ctl *ctl = &git_mwindow__mem_ctl;
  	git_repository *repo;
  	git_revwalk *walk;
  	git_oid id, *parent_id = NULL;
  	size_t i;
  	const size_t commit_count = 16;
  	unsigned int open_windows;
  
  	/*
  	 * Create a repository and populate it with 16 commits, each in its own
  	 * packfile.
  	 */
  	cl_git_pass(git_buf_joinpath(&path, clar_sandbox_path(), "repo.git"));
  	cl_git_pass(git_repository_init(&repo, path.ptr, true));
  	for (i = 0; i < commit_count; ++i) {
  		create_packfile_commit(repo, &id, parent_id, i + 1, commit_count);
  		parent_id = &id;
  	}
  
  	cl_git_pass(git_revwalk_new(&walk, repo));
  	cl_git_pass(git_revwalk_sorting(walk, GIT_SORT_TOPOLOGICAL));
  	cl_git_pass(git_revwalk_push_ref(walk, "refs/heads/master"));
  
  	/* Walking the repository requires eventually opening each of the packfiles. */
  	i = 0;
  	while (git_revwalk_next(&id, walk) == 0)
  		++i;
  	cl_assert_equal_i(commit_count, i);
  
  	cl_git_pass(git_mutex_lock(&git__mwindow_mutex));
  	/*
  	 * Adding an assert while holding a lock will cause the whole process to
  	 * deadlock. Copy the value and do the assert after releasing the lock.
  	 */
  	open_windows = ctl->open_windows;
  	cl_git_pass(git_mutex_unlock(&git__mwindow_mutex));
  
  	cl_assert_equal_i(expected_open_mwindow_files, open_windows);
  
  	git_buf_dispose(&path);
  	git_revwalk_free(walk);
  	git_repository_free(repo);
  }
  

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