Mercurial > dovecot > original-hg > dovecot-1.2
view src/lib/unlink-directory.c @ 9490:fd84592e817b HEAD
dovecot-example.conf: Updated dict comments.
author | Timo Sirainen <tss@iki.fi> |
---|---|
date | Mon, 23 Nov 2009 13:08:47 -0500 |
parents | 58630516a9d4 |
children | 00cd9aacd03c |
line wrap: on
line source
/* Copyright (c) 2002-2009 Dovecot authors, see the included COPYING file */ /* 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. */ #define _GNU_SOURCE /* for O_NOFOLLOW with Linux */ #include "lib.h" #include "close-keep-errno.h" #include "unlink-directory.h" #include <fcntl.h> #include <unistd.h> #include <dirent.h> #include <sys/stat.h> static int unlink_directory_r(const char *dir) { DIR *dirp; struct dirent *d; struct stat st; int dir_fd, old_errno; #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_keep_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_keep_errno(dir_fd); return -1; } dirp = opendir("."); if (dirp == NULL) { close_keep_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) < 0 && errno != ENOENT) { old_errno = errno; if (lstat(d->d_name, &st) < 0) { if (errno != ENOENT) break; errno = 0; } else if (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; i_error("unlink(%s/%s) failed: %m", dir, d->d_name); break; } } } old_errno = errno; (void)close(dir_fd); if (closedir(dirp) < 0) return -1; if (old_errno != 0) { errno = old_errno; return -1; } return 0; } int unlink_directory(const char *dir, bool unlink_dir) { int fd, ret, old_errno; fd = open(".", O_RDONLY); if (fd == -1) return -1; ret = unlink_directory_r(dir); if (ret < 0 && errno == ENOENT) ret = 0; old_errno = errno; if (fchdir(fd) < 0) { i_fatal("unlink_directory(%s): " "Can't fchdir() back to our original dir: %m", dir); } (void)close(fd); if (ret < 0) { errno = old_errno; return -1; } if (unlink_dir) { if (rmdir(dir) < 0 && errno != ENOENT) return -1; } return 0; }