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Systemd/src/core/mount-setup.c
Lennart Poettering 08c849815c label: rework label_fix() implementations (#8583) 
This reworks the SELinux and SMACK label fixing calls in a number of
ways:

1. The two separate boolean arguments of these functions are converted
   into a flags type LabelFixFlags.

2. The operations are now implemented based on O_PATH. This should
   resolve TTOCTTOU races between determining the label for the file
   system object and applying it, as it it allows to pin the object
   while we are operating on it.

3. When changing a label fails we'll query the label previously set, and
   if matches what we want to set anyway we'll suppress the error.

Also, all calls to label_fix() are now (void)ified, when we ignore the
return values.

Fixes: #8566
2018-03-27 07:38:26 +02:00

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/* SPDX-License-Identifier: LGPL-2.1+ */
/***
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 <ftw.h>
#include <stdlib.h>
#include <sys/mount.h>
#include <unistd.h>
#include "alloc-util.h"
#include "bus-util.h"
#include "cgroup-util.h"
#include "dev-setup.h"
#include "efivars.h"
#include "fileio.h"
#include "fs-util.h"
#include "label.h"
#include "log.h"
#include "macro.h"
#include "missing.h"
#include "mkdir.h"
#include "mount-setup.h"
#include "mount-util.h"
#include "path-util.h"
#include "set.h"
#include "smack-util.h"
#include "strv.h"
#include "user-util.h"
#include "util.h"
#include "virt.h"
typedef enum MountMode {
MNT_NONE = 0,
MNT_FATAL = 1 << 0,
MNT_IN_CONTAINER = 1 << 1,
MNT_CHECK_WRITABLE = 1 << 2,
} MountMode;
typedef struct MountPoint {
const char *what;
const char *where;
const char *type;
const char *options;
unsigned long flags;
bool (*condition_fn)(void);
MountMode mode;
} MountPoint;
/* The first three entries we might need before SELinux is up. The
* fourth (securityfs) is needed by IMA to load a custom policy. The
* other ones we can delay until SELinux and IMA are loaded. When
* SMACK is enabled we need smackfs, too, so it's a fifth one. */
#if ENABLE_SMACK
#define N_EARLY_MOUNT 5
#else
#define N_EARLY_MOUNT 4
#endif
static const MountPoint mount_table[] = {
{ "sysfs", "/sys", "sysfs", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
NULL, MNT_FATAL|MNT_IN_CONTAINER },
{ "proc", "/proc", "proc", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
NULL, MNT_FATAL|MNT_IN_CONTAINER },
{ "devtmpfs", "/dev", "devtmpfs", "mode=755", MS_NOSUID|MS_STRICTATIME,
NULL, MNT_FATAL|MNT_IN_CONTAINER },
{ "securityfs", "/sys/kernel/security", "securityfs", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
NULL, MNT_NONE },
#if ENABLE_SMACK
{ "smackfs", "/sys/fs/smackfs", "smackfs", "smackfsdef=*", MS_NOSUID|MS_NOEXEC|MS_NODEV,
mac_smack_use, MNT_FATAL },
{ "tmpfs", "/dev/shm", "tmpfs", "mode=1777,smackfsroot=*", MS_NOSUID|MS_NODEV|MS_STRICTATIME,
mac_smack_use, MNT_FATAL },
#endif
{ "tmpfs", "/dev/shm", "tmpfs", "mode=1777", MS_NOSUID|MS_NODEV|MS_STRICTATIME,
NULL, MNT_FATAL|MNT_IN_CONTAINER },
{ "devpts", "/dev/pts", "devpts", "mode=620,gid=" STRINGIFY(TTY_GID), MS_NOSUID|MS_NOEXEC,
NULL, MNT_IN_CONTAINER },
#if ENABLE_SMACK
{ "tmpfs", "/run", "tmpfs", "mode=755,smackfsroot=*", MS_NOSUID|MS_NODEV|MS_STRICTATIME,
mac_smack_use, MNT_FATAL },
#endif
{ "tmpfs", "/run", "tmpfs", "mode=755", MS_NOSUID|MS_NODEV|MS_STRICTATIME,
NULL, MNT_FATAL|MNT_IN_CONTAINER },
{ "cgroup2", "/sys/fs/cgroup", "cgroup2", "nsdelegate", MS_NOSUID|MS_NOEXEC|MS_NODEV,
cg_is_unified_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
{ "cgroup2", "/sys/fs/cgroup", "cgroup2", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
cg_is_unified_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
{ "tmpfs", "/sys/fs/cgroup", "tmpfs", "mode=755", MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_STRICTATIME,
cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
{ "cgroup2", "/sys/fs/cgroup/unified", "cgroup2", "nsdelegate", MS_NOSUID|MS_NOEXEC|MS_NODEV,
cg_is_hybrid_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
{ "cgroup2", "/sys/fs/cgroup/unified", "cgroup2", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
cg_is_hybrid_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
{ "cgroup", "/sys/fs/cgroup/systemd", "cgroup", "none,name=systemd,xattr", MS_NOSUID|MS_NOEXEC|MS_NODEV,
cg_is_legacy_wanted, MNT_IN_CONTAINER },
{ "cgroup", "/sys/fs/cgroup/systemd", "cgroup", "none,name=systemd", MS_NOSUID|MS_NOEXEC|MS_NODEV,
cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
{ "pstore", "/sys/fs/pstore", "pstore", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
NULL, MNT_NONE },
#if ENABLE_EFI
{ "efivarfs", "/sys/firmware/efi/efivars", "efivarfs", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
is_efi_boot, MNT_NONE },
#endif
{ "bpf", "/sys/fs/bpf", "bpf", "mode=700", MS_NOSUID|MS_NOEXEC|MS_NODEV,
NULL, MNT_NONE, },
};
/* These are API file systems that might be mounted by other software,
* we just list them here so that we know that we should ignore them */
static const char ignore_paths[] =
/* SELinux file systems */
"/sys/fs/selinux\0"
/* Container bind mounts */
"/proc/sys\0"
"/dev/console\0"
"/proc/kmsg\0";
bool mount_point_is_api(const char *path) {
unsigned i;
/* Checks if this mount point is considered "API", and hence
* should be ignored */
for (i = 0; i < ELEMENTSOF(mount_table); i ++)
if (path_equal(path, mount_table[i].where))
return true;
return path_startswith(path, "/sys/fs/cgroup/");
}
bool mount_point_ignore(const char *path) {
const char *i;
NULSTR_FOREACH(i, ignore_paths)
if (path_equal(path, i))
return true;
return false;
}
static int mount_one(const MountPoint *p, bool relabel) {
int r, priority;
assert(p);
priority = (p->mode & MNT_FATAL) ? LOG_ERR : LOG_DEBUG;
if (p->condition_fn && !p->condition_fn())
return 0;
/* Relabel first, just in case */
if (relabel)
(void) label_fix(p->where, LABEL_IGNORE_ENOENT|LABEL_IGNORE_EROFS);
r = path_is_mount_point(p->where, NULL, AT_SYMLINK_FOLLOW);
if (r < 0 && r != -ENOENT) {
log_full_errno(priority, r, "Failed to determine whether %s is a mount point: %m", p->where);
return (p->mode & MNT_FATAL) ? r : 0;
}
if (r > 0)
return 0;
/* Skip securityfs in a container */
if (!(p->mode & MNT_IN_CONTAINER) && detect_container() > 0)
return 0;
/* The access mode here doesn't really matter too much, since
* the mounted file system will take precedence anyway. */
if (relabel)
(void) mkdir_p_label(p->where, 0755);
else
(void) mkdir_p(p->where, 0755);
log_debug("Mounting %s to %s of type %s with options %s.",
p->what,
p->where,
p->type,
strna(p->options));
if (mount(p->what,
p->where,
p->type,
p->flags,
p->options) < 0) {
log_full_errno(priority, errno, "Failed to mount %s at %s: %m", p->type, p->where);
return (p->mode & MNT_FATAL) ? -errno : 0;
}
/* Relabel again, since we now mounted something fresh here */
if (relabel)
(void) label_fix(p->where, 0);
if (p->mode & MNT_CHECK_WRITABLE) {
if (access(p->where, W_OK) < 0) {
r = -errno;
(void) umount(p->where);
(void) rmdir(p->where);
log_full_errno(priority, r, "Mount point %s not writable after mounting: %m", p->where);
return (p->mode & MNT_FATAL) ? r : 0;
}
}
return 1;
}
static int mount_points_setup(unsigned n, bool loaded_policy) {
unsigned i;
int r = 0;
for (i = 0; i < n; i ++) {
int j;
j = mount_one(mount_table + i, loaded_policy);
if (j != 0 && r >= 0)
r = j;
}
return r;
}
int mount_setup_early(void) {
assert_cc(N_EARLY_MOUNT <= ELEMENTSOF(mount_table));
/* Do a minimal mount of /proc and friends to enable the most
* basic stuff, such as SELinux */
return mount_points_setup(N_EARLY_MOUNT, false);
}
int mount_cgroup_controllers(char ***join_controllers) {
_cleanup_set_free_free_ Set *controllers = NULL;
bool has_argument = !!join_controllers;
int r;
if (!cg_is_legacy_wanted())
return 0;
/* Mount all available cgroup controllers that are built into the kernel. */
if (!has_argument)
/* The defaults:
* mount "cpu" + "cpuacct" together, and "net_cls" + "net_prio".
*
* We'd like to add "cpuset" to the mix, but "cpuset" doesn't really
* work for groups with no initialized attributes.
*/
join_controllers = (char**[]) {
STRV_MAKE("cpu", "cpuacct"),
STRV_MAKE("net_cls", "net_prio"),
NULL,
};
r = cg_kernel_controllers(&controllers);
if (r < 0)
return log_error_errno(r, "Failed to enumerate cgroup controllers: %m");
for (;;) {
_cleanup_free_ char *options = NULL, *controller = NULL, *where = NULL;
MountPoint p = {
.what = "cgroup",
.type = "cgroup",
.flags = MS_NOSUID|MS_NOEXEC|MS_NODEV,
.mode = MNT_IN_CONTAINER,
};
char ***k = NULL;
controller = set_steal_first(controllers);
if (!controller)
break;
for (k = join_controllers; *k; k++)
if (strv_find(*k, controller))
break;
if (k && *k) {
char **i, **j;
for (i = *k, j = *k; *i; i++) {
if (!streq(*i, controller)) {
_cleanup_free_ char *t;
t = set_remove(controllers, *i);
if (!t) {
if (has_argument)
free(*i);
continue;
}
}
*(j++) = *i;
}
*j = NULL;
options = strv_join(*k, ",");
if (!options)
return log_oom();
} else
options = TAKE_PTR(controller);
where = strappend("/sys/fs/cgroup/", options);
if (!where)
return log_oom();
p.where = where;
p.options = options;
r = mount_one(&p, true);
if (r < 0)
return r;
if (r > 0 && k && *k) {
char **i;
for (i = *k; *i; i++) {
_cleanup_free_ char *t = NULL;
t = strappend("/sys/fs/cgroup/", *i);
if (!t)
return log_oom();
r = symlink(options, t);
if (r >= 0) {
#ifdef SMACK_RUN_LABEL
_cleanup_free_ char *src;
src = strappend("/sys/fs/cgroup/", options);
if (!src)
return log_oom();
r = mac_smack_copy(t, src);
if (r < 0 && r != -EOPNOTSUPP)
return log_error_errno(r, "Failed to copy smack label from %s to %s: %m", src, t);
#endif
} else if (errno != EEXIST)
return log_error_errno(errno, "Failed to create symlink %s: %m", t);
}
}
}
/* Now that we mounted everything, let's make the tmpfs the
* cgroup file systems are mounted into read-only. */
(void) mount("tmpfs", "/sys/fs/cgroup", "tmpfs", MS_REMOUNT|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_STRICTATIME|MS_RDONLY, "mode=755");
return 0;
}
#if HAVE_SELINUX || ENABLE_SMACK
static int nftw_cb(
const char *fpath,
const struct stat *sb,
int tflag,
struct FTW *ftwbuf) {
/* No need to label /dev twice in a row... */
if (_unlikely_(ftwbuf->level == 0))
return FTW_CONTINUE;
(void) label_fix(fpath, 0);
/* /run/initramfs is static data and big, no need to
* dynamically relabel its contents at boot... */
if (_unlikely_(ftwbuf->level == 1 &&
tflag == FTW_D &&
streq(fpath, "/run/initramfs")))
return FTW_SKIP_SUBTREE;
return FTW_CONTINUE;
};
#endif
int mount_setup(bool loaded_policy) {
int r = 0;
r = mount_points_setup(ELEMENTSOF(mount_table), loaded_policy);
if (r < 0)
return r;
#if HAVE_SELINUX || ENABLE_SMACK
/* Nodes in devtmpfs and /run need to be manually updated for
* the appropriate labels, after mounting. The other virtual
* API file systems like /sys and /proc do not need that, they
* use the same label for all their files. */
if (loaded_policy) {
usec_t before_relabel, after_relabel;
char timespan[FORMAT_TIMESPAN_MAX];
before_relabel = now(CLOCK_MONOTONIC);
nftw("/dev", nftw_cb, 64, FTW_MOUNT|FTW_PHYS|FTW_ACTIONRETVAL);
nftw("/dev/shm", nftw_cb, 64, FTW_MOUNT|FTW_PHYS|FTW_ACTIONRETVAL);
nftw("/run", nftw_cb, 64, FTW_MOUNT|FTW_PHYS|FTW_ACTIONRETVAL);
/* Temporarily remount the root cgroup filesystem to give it a proper label. */
r = cg_all_unified();
if (r == 0) {
(void) mount(NULL, "/sys/fs/cgroup", NULL, MS_REMOUNT, NULL);
(void) label_fix("/sys/fs/cgroup", 0);
nftw("/sys/fs/cgroup", nftw_cb, 64, FTW_MOUNT|FTW_PHYS|FTW_ACTIONRETVAL);
(void) mount(NULL, "/sys/fs/cgroup", NULL, MS_REMOUNT|MS_RDONLY, NULL);
} else if (r < 0)
return log_error_errno(r, "Failed to determine whether we are in all unified mode: %m");
after_relabel = now(CLOCK_MONOTONIC);
log_info("Relabelled /dev, /run and /sys/fs/cgroup in %s.",
format_timespan(timespan, sizeof(timespan), after_relabel - before_relabel, 0));
}
#endif
/* Create a few default symlinks, which are normally created
* by udevd, but some scripts might need them before we start
* udevd. */
dev_setup(NULL, UID_INVALID, GID_INVALID);
/* Mark the root directory as shared in regards to mount propagation. The kernel defaults to "private", but we
* think it makes more sense to have a default of "shared" so that nspawn and the container tools work out of
* the box. If specific setups need other settings they can reset the propagation mode to private if
* needed. Note that we set this only when we are invoked directly by the kernel. If we are invoked by a
* container manager we assume the container manager knows what it is doing (for example, because it set up
* some directories with different propagation modes). */
if (detect_container() <= 0)
if (mount(NULL, "/", NULL, MS_REC|MS_SHARED, NULL) < 0)
log_warning_errno(errno, "Failed to set up the root directory for shared mount propagation: %m");
/* Create a few directories we always want around, Note that sd_booted() checks for /run/systemd/system, so
* this mkdir really needs to stay for good, otherwise software that copied sd-daemon.c into their sources will
* misdetect systemd. */
(void) mkdir_label("/run/systemd", 0755);
(void) mkdir_label("/run/systemd/system", 0755);
/* Set up inaccessible items */
(void) mkdir_label("/run/systemd/inaccessible", 0000);
(void) mknod("/run/systemd/inaccessible/reg", S_IFREG | 0000, 0);
(void) mkdir_label("/run/systemd/inaccessible/dir", 0000);
(void) mknod("/run/systemd/inaccessible/chr", S_IFCHR | 0000, makedev(0, 0));
(void) mknod("/run/systemd/inaccessible/blk", S_IFBLK | 0000, makedev(0, 0));
(void) mkfifo("/run/systemd/inaccessible/fifo", 0000);
(void) mknod("/run/systemd/inaccessible/sock", S_IFSOCK | 0000, 0);
return 0;
}
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