thodg/libgit2/src/filebuf.c

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• Hash : 18c4ae70
  Author :
  Date : 2016-03-10T17:05:30
  

  filebuf: handle write error in `lock_file` When writing to a file with locking not check if writing the locked file actually succeeds. Fix the issue by returning error code and message when writing fails.

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• src/filebuf.c

• /*
   * 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 "common.h"
  #include "filebuf.h"
  #include "fileops.h"
  
  static const size_t WRITE_BUFFER_SIZE = (4096 * 2);
  
  enum buferr_t {
  	BUFERR_OK = 0,
  	BUFERR_WRITE,
  	BUFERR_ZLIB,
  	BUFERR_MEM
  };
  
  #define ENSURE_BUF_OK(buf) if ((buf)->last_error != BUFERR_OK) { return -1; }
  
  static int verify_last_error(git_filebuf *file)
  {
  	switch (file->last_error) {
  	case BUFERR_WRITE:
  		giterr_set(GITERR_OS, "Failed to write out file");
  		return -1;
  
  	case BUFERR_MEM:
  		giterr_set_oom();
  		return -1;
  
  	case BUFERR_ZLIB:
  		giterr_set(GITERR_ZLIB,
  			"Buffer error when writing out ZLib data");
  		return -1;
  
  	default:
  		return 0;
  	}
  }
  
  static int lock_file(git_filebuf *file, int flags, mode_t mode)
  {
  	if (git_path_exists(file->path_lock) == true) {
  		if (flags & GIT_FILEBUF_FORCE)
  			p_unlink(file->path_lock);
  		else {
  			giterr_clear(); /* actual OS error code just confuses */
  			giterr_set(GITERR_OS,
  				"Failed to lock file '%s' for writing", file->path_lock);
  			return GIT_ELOCKED;
  		}
  	}
  
  	/* create path to the file buffer is required */
  	if (flags & GIT_FILEBUF_FORCE) {
  		/* XXX: Should dirmode here be configurable? Or is 0777 always fine? */
  		file->fd = git_futils_creat_locked_withpath(file->path_lock, 0777, mode);
  	} else {
  		file->fd = git_futils_creat_locked(file->path_lock, mode);
  	}
  
  	if (file->fd < 0)
  		return file->fd;
  
  	file->fd_is_open = true;
  
  	if ((flags & GIT_FILEBUF_APPEND) && git_path_exists(file->path_original) == true) {
  		git_file source;
  		char buffer[FILEIO_BUFSIZE];
  		ssize_t read_bytes;
  		int error;
  
  		source = p_open(file->path_original, O_RDONLY);
  		if (source < 0) {
  			giterr_set(GITERR_OS,
  				"Failed to open file '%s' for reading",
  				file->path_original);
  			return -1;
  		}
  
  		while ((read_bytes = p_read(source, buffer, sizeof(buffer))) > 0) {
  			if ((error = p_write(file->fd, buffer, read_bytes)) < 0)
  				break;
  			if (file->compute_digest)
  				git_hash_update(&file->digest, buffer, read_bytes);
  		}
  
  		p_close(source);
  
  		if (read_bytes < 0) {
  			giterr_set(GITERR_OS, "Failed to read file '%s'", file->path_original);
  			return -1;
  		} else if (error < 0) {
  			giterr_set(GITERR_OS, "Failed to write file '%s'", file->path_lock);
  			return -1;
  		}
  	}
  
  	return 0;
  }
  
  void git_filebuf_cleanup(git_filebuf *file)
  {
  	if (file->fd_is_open && file->fd >= 0)
  		p_close(file->fd);
  
  	if (file->created_lock && !file->did_rename && file->path_lock && git_path_exists(file->path_lock))
  		p_unlink(file->path_lock);
  
  	if (file->compute_digest) {
  		git_hash_ctx_cleanup(&file->digest);
  		file->compute_digest = 0;
  	}
  
  	if (file->buffer)
  		git__free(file->buffer);
  
  	/* use the presence of z_buf to decide if we need to deflateEnd */
  	if (file->z_buf) {
  		git__free(file->z_buf);
  		deflateEnd(&file->zs);
  	}
  
  	if (file->path_original)
  		git__free(file->path_original);
  	if (file->path_lock)
  		git__free(file->path_lock);
  
  	memset(file, 0x0, sizeof(git_filebuf));
  	file->fd = -1;
  }
  
  GIT_INLINE(int) flush_buffer(git_filebuf *file)
  {
  	int result = file->write(file, file->buffer, file->buf_pos);
  	file->buf_pos = 0;
  	return result;
  }
  
  int git_filebuf_flush(git_filebuf *file)
  {
  	return flush_buffer(file);
  }
  
  static int write_normal(git_filebuf *file, void *source, size_t len)
  {
  	if (len > 0) {
  		if (p_write(file->fd, (void *)source, len) < 0) {
  			file->last_error = BUFERR_WRITE;
  			return -1;
  		}
  
  		if (file->compute_digest)
  			git_hash_update(&file->digest, source, len);
  	}
  
  	return 0;
  }
  
  static int write_deflate(git_filebuf *file, void *source, size_t len)
  {
  	z_stream *zs = &file->zs;
  
  	if (len > 0 || file->flush_mode == Z_FINISH) {
  		zs->next_in = source;
  		zs->avail_in = (uInt)len;
  
  		do {
  			size_t have;
  
  			zs->next_out = file->z_buf;
  			zs->avail_out = (uInt)file->buf_size;
  
  			if (deflate(zs, file->flush_mode) == Z_STREAM_ERROR) {
  				file->last_error = BUFERR_ZLIB;
  				return -1;
  			}
  
  			have = file->buf_size - (size_t)zs->avail_out;
  
  			if (p_write(file->fd, file->z_buf, have) < 0) {
  				file->last_error = BUFERR_WRITE;
  				return -1;
  			}
  
  		} while (zs->avail_out == 0);
  
  		assert(zs->avail_in == 0);
  
  		if (file->compute_digest)
  			git_hash_update(&file->digest, source, len);
  	}
  
  	return 0;
  }
  
  #define MAX_SYMLINK_DEPTH 5
  
  static int resolve_symlink(git_buf *out, const char *path)
  {
  	int i, error, root;
  	ssize_t ret;
  	struct stat st;
  	git_buf curpath = GIT_BUF_INIT, target = GIT_BUF_INIT;
  
  	if ((error = git_buf_grow(&target, GIT_PATH_MAX + 1)) < 0 ||
  	    (error = git_buf_puts(&curpath, path)) < 0)
  		return error;
  
  	for (i = 0; i < MAX_SYMLINK_DEPTH; i++) {
  		error = p_lstat(curpath.ptr, &st);
  		if (error < 0 && errno == ENOENT) {
  			error = git_buf_puts(out, curpath.ptr);
  			goto cleanup;
  		}
  
  		if (error < 0) {
  			giterr_set(GITERR_OS, "failed to stat '%s'", curpath.ptr);
  			error = -1;
  			goto cleanup;
  		}
  
  		if (!S_ISLNK(st.st_mode)) {
  			error = git_buf_puts(out, curpath.ptr);
  			goto cleanup;
  		}
  
  		ret = p_readlink(curpath.ptr, target.ptr, GIT_PATH_MAX);
  		if (ret < 0) {
  			giterr_set(GITERR_OS, "failed to read symlink '%s'", curpath.ptr);
  			error = -1;
  			goto cleanup;
  		}
  
  		if (ret == GIT_PATH_MAX) {
  			giterr_set(GITERR_INVALID, "symlink target too long");
  			error = -1;
  			goto cleanup;
  		}
  
  		/* readlink(2) won't NUL-terminate for us */
  		target.ptr[ret] = '\0';
  		target.size = ret;
  
  		root = git_path_root(target.ptr);
  		if (root >= 0) {
  			if ((error = git_buf_puts(&curpath, target.ptr)) < 0)
  				goto cleanup;
  		} else {
  			git_buf dir = GIT_BUF_INIT;
  
  			if ((error = git_path_dirname_r(&dir, curpath.ptr)) < 0)
  				goto cleanup;
  
  			git_buf_swap(&curpath, &dir);
  			git_buf_free(&dir);
  
  			if ((error = git_path_apply_relative(&curpath, target.ptr)) < 0)
  				goto cleanup;
  		}
  	}
  
  	giterr_set(GITERR_INVALID, "maximum symlink depth reached");
  	error = -1;
  
  cleanup:
  	git_buf_free(&curpath);
  	git_buf_free(&target);
  	return error;
  }
  
  int git_filebuf_open(git_filebuf *file, const char *path, int flags, mode_t mode)
  {
  	int compression, error = -1;
  	size_t path_len, alloc_len;
  
  	/* opening an already open buffer is a programming error;
  	 * assert that this never happens instead of returning
  	 * an error code */
  	assert(file && path && file->buffer == NULL);
  
  	memset(file, 0x0, sizeof(git_filebuf));
  
  	if (flags & GIT_FILEBUF_DO_NOT_BUFFER)
  		file->do_not_buffer = true;
  
  	file->buf_size = WRITE_BUFFER_SIZE;
  	file->buf_pos = 0;
  	file->fd = -1;
  	file->last_error = BUFERR_OK;
  
  	/* Allocate the main cache buffer */
  	if (!file->do_not_buffer) {
  		file->buffer = git__malloc(file->buf_size);
  		GITERR_CHECK_ALLOC(file->buffer);
  	}
  
  	/* If we are hashing on-write, allocate a new hash context */
  	if (flags & GIT_FILEBUF_HASH_CONTENTS) {
  		file->compute_digest = 1;
  
  		if (git_hash_ctx_init(&file->digest) < 0)
  			goto cleanup;
  	}
  
  	compression = flags >> GIT_FILEBUF_DEFLATE_SHIFT;
  
  	/* If we are deflating on-write, */
  	if (compression != 0) {
  		/* Initialize the ZLib stream */
  		if (deflateInit(&file->zs, compression) != Z_OK) {
  			giterr_set(GITERR_ZLIB, "Failed to initialize zlib");
  			goto cleanup;
  		}
  
  		/* Allocate the Zlib cache buffer */
  		file->z_buf = git__malloc(file->buf_size);
  		GITERR_CHECK_ALLOC(file->z_buf);
  
  		/* Never flush */
  		file->flush_mode = Z_NO_FLUSH;
  		file->write = &write_deflate;
  	} else {
  		file->write = &write_normal;
  	}
  
  	/* If we are writing to a temp file */
  	if (flags & GIT_FILEBUF_TEMPORARY) {
  		git_buf tmp_path = GIT_BUF_INIT;
  
  		/* Open the file as temporary for locking */
  		file->fd = git_futils_mktmp(&tmp_path, path, mode);
  
  		if (file->fd < 0) {
  			git_buf_free(&tmp_path);
  			goto cleanup;
  		}
  		file->fd_is_open = true;
  		file->created_lock = true;
  
  		/* No original path */
  		file->path_original = NULL;
  		file->path_lock = git_buf_detach(&tmp_path);
  		GITERR_CHECK_ALLOC(file->path_lock);
  	} else {
  		git_buf resolved_path = GIT_BUF_INIT;
  
  		if ((error = resolve_symlink(&resolved_path, path)) < 0)
  			goto cleanup;
  
  		/* Save the original path of the file */
  		path_len = resolved_path.size;
  		file->path_original = git_buf_detach(&resolved_path);
  
  		/* create the locking path by appending ".lock" to the original */
  		GITERR_CHECK_ALLOC_ADD(&alloc_len, path_len, GIT_FILELOCK_EXTLENGTH);
  		file->path_lock = git__malloc(alloc_len);
  		GITERR_CHECK_ALLOC(file->path_lock);
  
  		memcpy(file->path_lock, file->path_original, path_len);
  		memcpy(file->path_lock + path_len, GIT_FILELOCK_EXTENSION, GIT_FILELOCK_EXTLENGTH);
  
  		if (git_path_isdir(file->path_original)) {
  			giterr_set(GITERR_FILESYSTEM, "path '%s' is a directory", file->path_original);
  			error = GIT_EDIRECTORY;
  			goto cleanup;
  		}
  
  		/* open the file for locking */
  		if ((error = lock_file(file, flags, mode)) < 0)
  			goto cleanup;
  
  		file->created_lock = true;
  	}
  
  	return 0;
  
  cleanup:
  	git_filebuf_cleanup(file);
  	return error;
  }
  
  int git_filebuf_hash(git_oid *oid, git_filebuf *file)
  {
  	assert(oid && file && file->compute_digest);
  
  	flush_buffer(file);
  
  	if (verify_last_error(file) < 0)
  		return -1;
  
  	git_hash_final(oid, &file->digest);
  	git_hash_ctx_cleanup(&file->digest);
  	file->compute_digest = 0;
  
  	return 0;
  }
  
  int git_filebuf_commit_at(git_filebuf *file, const char *path)
  {
  	git__free(file->path_original);
  	file->path_original = git__strdup(path);
  	GITERR_CHECK_ALLOC(file->path_original);
  
  	return git_filebuf_commit(file);
  }
  
  int git_filebuf_commit(git_filebuf *file)
  {
  	/* temporary files cannot be committed */
  	assert(file && file->path_original);
  
  	file->flush_mode = Z_FINISH;
  	flush_buffer(file);
  
  	if (verify_last_error(file) < 0)
  		goto on_error;
  
  	file->fd_is_open = false;
  
  	if (p_close(file->fd) < 0) {
  		giterr_set(GITERR_OS, "Failed to close file at '%s'", file->path_lock);
  		goto on_error;
  	}
  
  	file->fd = -1;
  
  	if (p_rename(file->path_lock, file->path_original) < 0) {
  		giterr_set(GITERR_OS, "Failed to rename lockfile to '%s'", file->path_original);
  		goto on_error;
  	}
  
  	file->did_rename = true;
  
  	git_filebuf_cleanup(file);
  	return 0;
  
  on_error:
  	git_filebuf_cleanup(file);
  	return -1;
  }
  
  GIT_INLINE(void) add_to_cache(git_filebuf *file, const void *buf, size_t len)
  {
  	memcpy(file->buffer + file->buf_pos, buf, len);
  	file->buf_pos += len;
  }
  
  int git_filebuf_write(git_filebuf *file, const void *buff, size_t len)
  {
  	const unsigned char *buf = buff;
  
  	ENSURE_BUF_OK(file);
  
  	if (file->do_not_buffer)
  		return file->write(file, (void *)buff, len);
  
  	for (;;) {
  		size_t space_left = file->buf_size - file->buf_pos;
  
  		/* cache if it's small */
  		if (space_left > len) {
  			add_to_cache(file, buf, len);
  			return 0;
  		}
  
  		add_to_cache(file, buf, space_left);
  		if (flush_buffer(file) < 0)
  			return -1;
  
  		len -= space_left;
  		buf += space_left;
  	}
  }
  
  int git_filebuf_reserve(git_filebuf *file, void **buffer, size_t len)
  {
  	size_t space_left = file->buf_size - file->buf_pos;
  
  	*buffer = NULL;
  
  	ENSURE_BUF_OK(file);
  
  	if (len > file->buf_size) {
  		file->last_error = BUFERR_MEM;
  		return -1;
  	}
  
  	if (space_left <= len) {
  		if (flush_buffer(file) < 0)
  			return -1;
  	}
  
  	*buffer = (file->buffer + file->buf_pos);
  	file->buf_pos += len;
  
  	return 0;
  }
  
  int git_filebuf_printf(git_filebuf *file, const char *format, ...)
  {
  	va_list arglist;
  	size_t space_left, len, alloclen;
  	int written, res;
  	char *tmp_buffer;
  
  	ENSURE_BUF_OK(file);
  
  	space_left = file->buf_size - file->buf_pos;
  
  	do {
  		va_start(arglist, format);
  		written = p_vsnprintf((char *)file->buffer + file->buf_pos, space_left, format, arglist);
  		va_end(arglist);
  
  		if (written < 0) {
  			file->last_error = BUFERR_MEM;
  			return -1;
  		}
  
  		len = written;
  		if (len + 1 <= space_left) {
  			file->buf_pos += len;
  			return 0;
  		}
  
  		if (flush_buffer(file) < 0)
  			return -1;
  
  		space_left = file->buf_size - file->buf_pos;
  
  	} while (len + 1 <= space_left);
  
  	if (GIT_ADD_SIZET_OVERFLOW(&alloclen, len, 1) ||
  		!(tmp_buffer = git__malloc(alloclen))) {
  		file->last_error = BUFERR_MEM;
  		return -1;
  	}
  
  	va_start(arglist, format);
  	written = p_vsnprintf(tmp_buffer, len + 1, format, arglist);
  	va_end(arglist);
  
  	if (written < 0) {
  		git__free(tmp_buffer);
  		file->last_error = BUFERR_MEM;
  		return -1;
  	}
  
  	res = git_filebuf_write(file, tmp_buffer, len);
  	git__free(tmp_buffer);
  
  	return res;
  }
  
  int git_filebuf_stats(time_t *mtime, size_t *size, git_filebuf *file)
  {
  	int res;
  	struct stat st;
  
  	if (file->fd_is_open)
  		res = p_fstat(file->fd, &st);
  	else
  		res = p_stat(file->path_original, &st);
  
  	if (res < 0) {
  		giterr_set(GITERR_OS, "Could not get stat info for '%s'",
  			file->path_original);
  		return res;
  	}
  
  	if (mtime)
  		*mtime = st.st_mtime;
  	if (size)
  		*size = (size_t)st.st_size;
  
  	return 0;
  }
  

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