Mercurial > dovecot > core-2.2
view src/lib/unlink-directory.c @ 23007:36e01285b5b8
lib: buffer - Improve header comment for buffer_insert() and buffer_delete().
author | Stephan Bosch <stephan.bosch@dovecot.fi> |
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date | Mon, 18 Mar 2019 00:52:37 +0100 |
parents | cb108f786fb4 |
children |
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/* Copyright (c) 2002-2018 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 "unlink-directory.h" #include <fcntl.h> #include <unistd.h> #include <dirent.h> #include <sys/stat.h> static int unlink_directory_r(const char *dir, enum unlink_directory_flags flags) { 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)) { if ((st.st_mode & S_IFMT) != S_IFLNK) errno = ENOTDIR; else { /* be compatible with O_NOFOLLOW */ errno = ELOOP; } return -1; } dir_fd = open(dir, O_RDONLY); if (dir_fd == -1) return -1; if (fstat(dir_fd, &st2) < 0) { i_close_fd(&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. */ i_close_fd(&dir_fd); errno = ENOTDIR; return -1; } #endif if (fchdir(dir_fd) < 0) { i_close_fd(&dir_fd); return -1; } dirp = opendir("."); if (dirp == NULL) { i_close_fd(&dir_fd); return -1; } errno = 0; while ((d = readdir(dirp)) != NULL) { if (d->d_name[0] == '.') { if ((d->d_name[1] == '\0' || (d->d_name[1] == '.' && d->d_name[2] == '\0'))) { /* skip . and .. */ continue; } if ((flags & UNLINK_DIRECTORY_FLAG_SKIP_DOTFILES) != 0) 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) && (flags & UNLINK_DIRECTORY_FLAG_FILES_ONLY) == 0) { if (unlink_directory_r(d->d_name, flags) < 0) { if (errno != ENOENT) break; errno = 0; } if (fchdir(dir_fd) < 0) break; if (rmdir(d->d_name) < 0) { if (errno != ENOENT) { if (errno == EEXIST) { /* standardize errno */ errno = ENOTEMPTY; } break; } errno = 0; } } else if (S_ISDIR(st.st_mode) && (flags & UNLINK_DIRECTORY_FLAG_FILES_ONLY) != 0) { /* skip directory */ } else if (old_errno == EBUSY && strncmp(d->d_name, ".nfs", 4) == 0) { /* can't delete NFS files that are still in use. let the caller decide if this error is worth logging about */ break; } 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; i_close_fd(&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, enum unlink_directory_flags flags) { int fd, ret, old_errno; fd = open(".", O_RDONLY); if (fd == -1) return -1; ret = unlink_directory_r(dir, flags); 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); } i_close_fd(&fd); if (ret < 0) { errno = old_errno; return -1; } if ((flags & UNLINK_DIRECTORY_FLAG_RMDIR) != 0) { if (rmdir(dir) < 0 && errno != ENOENT) { if (errno == EEXIST) { /* standardize errno */ errno = ENOTEMPTY; } return -1; } } return 0; }