/*
 unlink-directory.c : Safely unlink directory with everything under it.

    Copyright (c) 2002-2003 Timo Sirainen

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#define _GNU_SOURCE /* for O_NOFOLLOW with Linux */

#include "lib.h"
#include "unlink-directory.h"

#include <fcntl.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/stat.h>

#define close_save_errno(fd) \
	STMT_START { \
		old_errno = errno; \
		(void)close(fd); \
		errno = old_errno; \
	} STMT_END

static int unlink_directory_r(const char *dir)
{
	DIR *dirp;
	struct dirent *d;
	struct stat st;
        int dir_fd, old_errno;

	/* There's a bit tricky race condition with recursive deletion.
	   Suppose this happens:

	   lstat(dir, ..) -> OK, it's a directory
	   // attacker deletes dir, replaces it with symlink to /
	   opendir(dir) -> it actually opens /

	   Most portable solution is to lstat() the dir, chdir() there, then
	   check that "." points to same device/inode as we originally
	   lstat()ed. This assumes that the device has usable inodes, most
	   should except for some NFS implementations.

	   Filesystems may also reassign a deleted inode to another file
	   immediately after it's deleted. That in theory makes it possible to
	   exploit this race to delete the new directory. However, the new
	   inode is quite unlikely to be any important directory, and attacker
	   is quite unlikely to find out which directory even got the inode.
	   Maybe with some setuid program or daemon interaction something could
	   come out of it though.

	   Another less portable solution is to fchdir(open(dir, O_NOFOLLOW)).
	   This should be completely safe.

	   The actual file deletion also has to be done relative to current
	   directory, to make sure that the whole directory structure isn't
	   replaced with another one while we're deleting it. Going back to
	   parent directory isn't too easy either - safest (and easiest) way
	   again is to open() the directory and fchdir() back there.
	*/

#ifdef O_NOFOLLOW
	dir_fd = open(dir, O_RDONLY | O_NOFOLLOW);
	if (dir_fd == -1)
		return -1;
#else
	struct stat st2;

	if (lstat(dir, &st) < 0)
		return -1;

	if (!S_ISDIR(st.st_mode)) {
		errno = ENOTDIR;
		return -1;
	}

	dir_fd = open(dir, O_RDONLY);
	if (dir_fd == -1)
		return -1;

	if (fstat(dir_fd, &st2) < 0) {
		close_save_errno(dir_fd);
		return -1;
	}

	if (st.st_ino != st2.st_ino ||
	    !CMP_DEV_T(st.st_dev, st2.st_dev)) {
		/* directory was just replaced with something else. */
		(void)close(dir_fd);
		errno = ENOTDIR;
		return -1;
	}
#endif
	if (fchdir(dir_fd) < 0) {
                close_save_errno(dir_fd);
		return -1;
	}

	dirp = opendir(".");
	if (dirp == NULL) {
		close_save_errno(dir_fd);
		return -1;
	}

	errno = 0;
	while ((d = readdir(dirp)) != NULL) {
		if (d->d_name[0] == '.' &&
		    (d->d_name[1] == '\0' ||
		     (d->d_name[1] == '.' && d->d_name[2] == '\0'))) {
			/* skip . and .. */
			continue;
		}

		if (unlink(d->d_name) == -1 && errno != ENOENT) {
			old_errno = errno;

			if (lstat(d->d_name, &st) == 0 && S_ISDIR(st.st_mode)) {
				if (unlink_directory_r(d->d_name) < 0) {
					if (errno != ENOENT)
						break;
					errno = 0;
				}
				if (fchdir(dir_fd) < 0)
					break;

				if (rmdir(d->d_name) < 0) {
					if (errno != ENOENT)
						break;
					errno = 0;
				}
			} else {
				/* so it wasn't a directory */
				errno = old_errno;
				break;
			}
		}
	}

	(void)close(dir_fd);

	old_errno = errno;
	if (closedir(dirp) < 0)
		return -1;

	if (old_errno != 0) {
		errno = old_errno;
		return -1;
	}

	return 0;
}

int unlink_directory(const char *dir, int unlink_dir)
{
	int fd, ret;

	fd = open(".", O_RDONLY);
	if (fd == -1)
		return -1;

	ret = unlink_directory_r(dir);
	if (ret < 0 && errno == ENOENT)
		ret = 0;

	if (fchdir(fd) < 0) {
		i_fatal("unlink_directory(%s): "
			"Can't fchdir() back to our original dir: %m", dir);
	}
	(void)close(fd);

	if (unlink_dir) {
		if (rmdir(dir) < 0 && errno != ENOENT)
			return -1;
	}

	return ret;
}