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Systemd/src/basic/fs-util.c

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/***
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <time.h>
#include <unistd.h>
#include "alloc-util.h"
#include "dirent-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
#include "log.h"
#include "macro.h"
#include "missing.h"
#include "mkdir.h"
#include "parse-util.h"
#include "path-util.h"
#include "stat-util.h"
#include "stdio-util.h"
#include "string-util.h"
#include "strv.h"
#include "time-util.h"
#include "user-util.h"
#include "util.h"
int unlink_noerrno(const char *path) {
PROTECT_ERRNO;
int r;
r = unlink(path);
if (r < 0)
return -errno;
return 0;
}
int rmdir_parents(const char *path, const char *stop) {
size_t l;
int r = 0;
assert(path);
assert(stop);
l = strlen(path);
/* Skip trailing slashes */
while (l > 0 && path[l-1] == '/')
l--;
while (l > 0) {
char *t;
/* Skip last component */
while (l > 0 && path[l-1] != '/')
l--;
/* Skip trailing slashes */
while (l > 0 && path[l-1] == '/')
l--;
if (l <= 0)
break;
t = strndup(path, l);
if (!t)
return -ENOMEM;
if (path_startswith(stop, t)) {
free(t);
return 0;
}
r = rmdir(t);
free(t);
if (r < 0)
if (errno != ENOENT)
return -errno;
}
return 0;
}
int rename_noreplace(int olddirfd, const char *oldpath, int newdirfd, const char *newpath) {
struct stat buf;
int ret;
ret = renameat2(olddirfd, oldpath, newdirfd, newpath, RENAME_NOREPLACE);
if (ret >= 0)
return 0;
/* renameat2() exists since Linux 3.15, btrfs added support for it later.
* If it is not implemented, fallback to another method. */
if (!IN_SET(errno, EINVAL, ENOSYS))
return -errno;
/* The link()/unlink() fallback does not work on directories. But
* renameat() without RENAME_NOREPLACE gives the same semantics on
* directories, except when newpath is an *empty* directory. This is
* good enough. */
ret = fstatat(olddirfd, oldpath, &buf, AT_SYMLINK_NOFOLLOW);
if (ret >= 0 && S_ISDIR(buf.st_mode)) {
ret = renameat(olddirfd, oldpath, newdirfd, newpath);
return ret >= 0 ? 0 : -errno;
}
/* If it is not a directory, use the link()/unlink() fallback. */
ret = linkat(olddirfd, oldpath, newdirfd, newpath, 0);
if (ret < 0)
return -errno;
ret = unlinkat(olddirfd, oldpath, 0);
if (ret < 0) {
/* backup errno before the following unlinkat() alters it */
ret = errno;
(void) unlinkat(newdirfd, newpath, 0);
errno = ret;
return -errno;
}
return 0;
}
int readlinkat_malloc(int fd, const char *p, char **ret) {
size_t l = 100;
int r;
assert(p);
assert(ret);
for (;;) {
char *c;
ssize_t n;
c = new(char, l);
if (!c)
return -ENOMEM;
n = readlinkat(fd, p, c, l-1);
if (n < 0) {
r = -errno;
free(c);
return r;
}
if ((size_t) n < l-1) {
c[n] = 0;
*ret = c;
return 0;
}
free(c);
l *= 2;
}
}
int readlink_malloc(const char *p, char **ret) {
return readlinkat_malloc(AT_FDCWD, p, ret);
}
int readlink_value(const char *p, char **ret) {
_cleanup_free_ char *link = NULL;
char *value;
int r;
r = readlink_malloc(p, &link);
if (r < 0)
return r;
value = basename(link);
if (!value)
return -ENOENT;
value = strdup(value);
if (!value)
return -ENOMEM;
*ret = value;
return 0;
}
int readlink_and_make_absolute(const char *p, char **r) {
_cleanup_free_ char *target = NULL;
char *k;
int j;
assert(p);
assert(r);
j = readlink_malloc(p, &target);
if (j < 0)
return j;
k = file_in_same_dir(p, target);
if (!k)
return -ENOMEM;
*r = k;
return 0;
}
int readlink_and_canonicalize(const char *p, const char *root, char **ret) {
char *t, *s;
int r;
assert(p);
assert(ret);
r = readlink_and_make_absolute(p, &t);
if (r < 0)
return r;
r = chase_symlinks(t, root, 0, &s);
if (r < 0)
/* If we can't follow up, then let's return the original string, slightly cleaned up. */
*ret = path_kill_slashes(t);
else {
*ret = s;
free(t);
}
return 0;
}
int readlink_and_make_absolute_root(const char *root, const char *path, char **ret) {
_cleanup_free_ char *target = NULL, *t = NULL;
const char *full;
int r;
full = prefix_roota(root, path);
r = readlink_malloc(full, &target);
if (r < 0)
return r;
t = file_in_same_dir(path, target);
if (!t)
return -ENOMEM;
*ret = t;
t = NULL;
return 0;
}
int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid) {
assert(path);
/* Under the assumption that we are running privileged we
* first change the access mode and only then hand out
* ownership to avoid a window where access is too open. */
if (mode != MODE_INVALID)
if (chmod(path, mode) < 0)
return -errno;
if (uid != UID_INVALID || gid != GID_INVALID)
if (chown(path, uid, gid) < 0)
return -errno;
return 0;
}
int fchmod_umask(int fd, mode_t m) {
mode_t u;
int r;
u = umask(0777);
r = fchmod(fd, m & (~u)) < 0 ? -errno : 0;
umask(u);
return r;
}
int fd_warn_permissions(const char *path, int fd) {
struct stat st;
if (fstat(fd, &st) < 0)
return -errno;
if (st.st_mode & 0111)
log_warning("Configuration file %s is marked executable. Please remove executable permission bits. Proceeding anyway.", path);
if (st.st_mode & 0002)
log_warning("Configuration file %s is marked world-writable. Please remove world writability permission bits. Proceeding anyway.", path);
if (getpid() == 1 && (st.st_mode & 0044) != 0044)
log_warning("Configuration file %s is marked world-inaccessible. This has no effect as configuration data is accessible via APIs without restrictions. Proceeding anyway.", path);
return 0;
}
int touch_file(const char *path, bool parents, usec_t stamp, uid_t uid, gid_t gid, mode_t mode) {
_cleanup_close_ int fd;
int r;
assert(path);
if (parents)
mkdir_parents(path, 0755);
fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY,
(mode == 0 || mode == MODE_INVALID) ? 0644 : mode);
if (fd < 0)
return -errno;
if (mode != MODE_INVALID) {
r = fchmod(fd, mode);
if (r < 0)
return -errno;
}
if (uid != UID_INVALID || gid != GID_INVALID) {
r = fchown(fd, uid, gid);
if (r < 0)
return -errno;
}
if (stamp != USEC_INFINITY) {
struct timespec ts[2];
timespec_store(&ts[0], stamp);
ts[1] = ts[0];
r = futimens(fd, ts);
} else
r = futimens(fd, NULL);
if (r < 0)
return -errno;
return 0;
}
int touch(const char *path) {
return touch_file(path, false, USEC_INFINITY, UID_INVALID, GID_INVALID, MODE_INVALID);
}
int symlink_idempotent(const char *from, const char *to) {
_cleanup_free_ char *p = NULL;
int r;
assert(from);
assert(to);
if (symlink(from, to) < 0) {
if (errno != EEXIST)
return -errno;
r = readlink_malloc(to, &p);
if (r < 0)
return r;
if (!streq(p, from))
return -EINVAL;
}
return 0;
}
int symlink_atomic(const char *from, const char *to) {
_cleanup_free_ char *t = NULL;
int r;
assert(from);
assert(to);
r = tempfn_random(to, NULL, &t);
if (r < 0)
return r;
if (symlink(from, t) < 0)
return -errno;
if (rename(t, to) < 0) {
unlink_noerrno(t);
return -errno;
}
return 0;
}
int mknod_atomic(const char *path, mode_t mode, dev_t dev) {
_cleanup_free_ char *t = NULL;
int r;
assert(path);
r = tempfn_random(path, NULL, &t);
if (r < 0)
return r;
if (mknod(t, mode, dev) < 0)
return -errno;
if (rename(t, path) < 0) {
unlink_noerrno(t);
return -errno;
}
return 0;
}
int mkfifo_atomic(const char *path, mode_t mode) {
_cleanup_free_ char *t = NULL;
int r;
assert(path);
r = tempfn_random(path, NULL, &t);
if (r < 0)
return r;
if (mkfifo(t, mode) < 0)
return -errno;
if (rename(t, path) < 0) {
unlink_noerrno(t);
return -errno;
}
return 0;
}
int get_files_in_directory(const char *path, char ***list) {
_cleanup_closedir_ DIR *d = NULL;
struct dirent *de;
size_t bufsize = 0, n = 0;
_cleanup_strv_free_ char **l = NULL;
assert(path);
/* Returns all files in a directory in *list, and the number
* of files as return value. If list is NULL returns only the
* number. */
d = opendir(path);
if (!d)
return -errno;
FOREACH_DIRENT_ALL(de, d, return -errno) {
dirent_ensure_type(d, de);
if (!dirent_is_file(de))
continue;
if (list) {
/* one extra slot is needed for the terminating NULL */
if (!GREEDY_REALLOC(l, bufsize, n + 2))
return -ENOMEM;
l[n] = strdup(de->d_name);
if (!l[n])
return -ENOMEM;
l[++n] = NULL;
} else
n++;
}
if (list) {
*list = l;
l = NULL; /* avoid freeing */
}
return n;
}
static int getenv_tmp_dir(const char **ret_path) {
const char *n;
int r, ret = 0;
assert(ret_path);
/* We use the same order of environment variables python uses in tempfile.gettempdir():
* https://docs.python.org/3/library/tempfile.html#tempfile.gettempdir */
FOREACH_STRING(n, "TMPDIR", "TEMP", "TMP") {
const char *e;
e = secure_getenv(n);
if (!e)
continue;
if (!path_is_absolute(e)) {
r = -ENOTDIR;
goto next;
}
if (!path_is_safe(e)) {
r = -EPERM;
goto next;
}
r = is_dir(e, true);
if (r < 0)
goto next;
if (r == 0) {
r = -ENOTDIR;
goto next;
}
*ret_path = e;
return 1;
next:
/* Remember first error, to make this more debuggable */
if (ret >= 0)
ret = r;
}
if (ret < 0)
return ret;
*ret_path = NULL;
return ret;
}
static int tmp_dir_internal(const char *def, const char **ret) {
const char *e;
int r, k;
assert(def);
assert(ret);
r = getenv_tmp_dir(&e);
if (r > 0) {
*ret = e;
return 0;
}
k = is_dir(def, true);
if (k == 0)
k = -ENOTDIR;
if (k < 0)
return r < 0 ? r : k;
*ret = def;
return 0;
}
int var_tmp_dir(const char **ret) {
/* Returns the location for "larger" temporary files, that is backed by physical storage if available, and thus
* even might survive a boot: /var/tmp. If $TMPDIR (or related environment variables) are set, its value is
* returned preferably however. Note that both this function and tmp_dir() below are affected by $TMPDIR,
* making it a variable that overrides all temporary file storage locations. */
return tmp_dir_internal("/var/tmp", ret);
}
int tmp_dir(const char **ret) {
/* Similar to var_tmp_dir() above, but returns the location for "smaller" temporary files, which is usually
* backed by an in-memory file system: /tmp. */
return tmp_dir_internal("/tmp", ret);
}
int inotify_add_watch_fd(int fd, int what, uint32_t mask) {
char path[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
int r;
/* This is like inotify_add_watch(), except that the file to watch is not referenced by a path, but by an fd */
xsprintf(path, "/proc/self/fd/%i", what);
r = inotify_add_watch(fd, path, mask);
if (r < 0)
return -errno;
return r;
}
int chase_symlinks(const char *path, const char *original_root, unsigned flags, char **ret) {
_cleanup_free_ char *buffer = NULL, *done = NULL, *root = NULL;
_cleanup_close_ int fd = -1;
unsigned max_follow = 32; /* how many symlinks to follow before giving up and returning ELOOP */
bool exists = true;
char *todo;
int r;
assert(path);
/* This is a lot like canonicalize_file_name(), but takes an additional "root" parameter, that allows following
* symlinks relative to a root directory, instead of the root of the host.
*
* Note that "root" primarily matters if we encounter an absolute symlink. It is also used when following
* relative symlinks to ensure they cannot be used to "escape" the root directory. The path parameter passed is
* assumed to be already prefixed by it, except if the CHASE_PREFIX_ROOT flag is set, in which case it is first
* prefixed accordingly.
*
* Algorithmically this operates on two path buffers: "done" are the components of the path we already
* processed and resolved symlinks, "." and ".." of. "todo" are the components of the path we still need to
* process. On each iteration, we move one component from "todo" to "done", processing it's special meaning
* each time. The "todo" path always starts with at least one slash, the "done" path always ends in no
* slash. We always keep an O_PATH fd to the component we are currently processing, thus keeping lookup races
* at a minimum.
*
* Suggested usage: whenever you want to canonicalize a path, use this function. Pass the absolute path you got
* as-is: fully qualified and relative to your host's root. Optionally, specify the root parameter to tell this
* function what to do when encountering a symlink with an absolute path as directory: prefix it by the
* specified path.
*
* Note: there's also chase_symlinks_prefix() (see below), which as first step prefixes the passed path by the
* passed root. */
if (original_root) {
r = path_make_absolute_cwd(original_root, &root);
if (r < 0)
return r;
if (flags & CHASE_PREFIX_ROOT)
path = prefix_roota(root, path);
}
r = path_make_absolute_cwd(path, &buffer);
if (r < 0)
return r;
fd = open("/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
if (fd < 0)
return -errno;
todo = buffer;
for (;;) {
_cleanup_free_ char *first = NULL;
_cleanup_close_ int child = -1;
struct stat st;
size_t n, m;
/* Determine length of first component in the path */
n = strspn(todo, "/"); /* The slashes */
m = n + strcspn(todo + n, "/"); /* The entire length of the component */
/* Extract the first component. */
first = strndup(todo, m);
if (!first)
return -ENOMEM;
todo += m;
/* Just a single slash? Then we reached the end. */
if (isempty(first) || path_equal(first, "/"))
break;
/* Just a dot? Then let's eat this up. */
if (path_equal(first, "/."))
continue;
/* Two dots? Then chop off the last bit of what we already found out. */
if (path_equal(first, "/..")) {
_cleanup_free_ char *parent = NULL;
int fd_parent = -1;
/* If we already are at the top, then going up will not change anything. This is in-line with
* how the kernel handles this. */
if (isempty(done) || path_equal(done, "/"))
continue;
parent = dirname_malloc(done);
if (!parent)
return -ENOMEM;
/* Don't allow this to leave the root dir. */
if (root &&
path_startswith(done, root) &&
!path_startswith(parent, root))
continue;
free_and_replace(done, parent);
fd_parent = openat(fd, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH);
if (fd_parent < 0)
return -errno;
safe_close(fd);
fd = fd_parent;
continue;
}
/* Otherwise let's see what this is. */
child = openat(fd, first + n, O_CLOEXEC|O_NOFOLLOW|O_PATH);
if (child < 0) {
if (errno == ENOENT &&
(flags & CHASE_NONEXISTENT) &&
(isempty(todo) || path_is_safe(todo))) {
/* If CHASE_NONEXISTENT is set, and the path does not exist, then that's OK, return
* what we got so far. But don't allow this if the remaining path contains "../ or "./"
* or something else weird. */
if (!strextend(&done, first, todo, NULL))
return -ENOMEM;
exists = false;
break;
}
return -errno;
}
if (fstat(child, &st) < 0)
return -errno;
if (S_ISLNK(st.st_mode)) {
_cleanup_free_ char *destination = NULL;
/* This is a symlink, in this case read the destination. But let's make sure we don't follow
* symlinks without bounds. */
if (--max_follow <= 0)
return -ELOOP;
r = readlinkat_malloc(fd, first + n, &destination);
if (r < 0)
return r;
if (isempty(destination))
return -EINVAL;
if (path_is_absolute(destination)) {
/* An absolute destination. Start the loop from the beginning, but use the root
* directory as base. */
safe_close(fd);
fd = open(root ?: "/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
if (fd < 0)
return -errno;
free_and_replace(buffer, destination);
todo = buffer;
free(done);
/* Note that we do not revalidate the root, we take it as is. */
if (isempty(root))
done = NULL;
else {
done = strdup(root);
if (!done)
return -ENOMEM;
}
} else {
char *joined;
/* A relative destination. If so, this is what we'll prefix what's left to do with what
* we just read, and start the loop again, but remain in the current directory. */
joined = strjoin("/", destination, todo);
if (!joined)
return -ENOMEM;
free(buffer);
todo = buffer = joined;
}
continue;
}
/* If this is not a symlink, then let's just add the name we read to what we already verified. */
if (!done) {
done = first;
first = NULL;
} else {
if (!strextend(&done, first, NULL))
return -ENOMEM;
}
/* And iterate again, but go one directory further down. */
safe_close(fd);
fd = child;
child = -1;
}
if (!done) {
/* Special case, turn the empty string into "/", to indicate the root directory. */
done = strdup("/");
if (!done)
return -ENOMEM;
}
*ret = done;
done = NULL;
return exists;
}
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