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Systemd/src/core/namespace.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 <sched.h>
#include <stdio.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <unistd.h>
#include <linux/fs.h>
#include "alloc-util.h"
#include "dev-setup.h"
#include "fd-util.h"
#include "fs-util.h"
#include "loopback-setup.h"
#include "missing.h"
#include "mkdir.h"
#include "mount-util.h"
#include "namespace.h"
#include "path-util.h"
#include "selinux-util.h"
#include "socket-util.h"
#include "string-table.h"
#include "string-util.h"
#include "strv.h"
#include "umask-util.h"
#include "user-util.h"
#include "util.h"
#define DEV_MOUNT_OPTIONS (MS_NOSUID|MS_STRICTATIME|MS_NOEXEC)
typedef enum MountMode {
/* This is ordered by priority! */
INACCESSIBLE,
READONLY,
PRIVATE_TMP,
PRIVATE_VAR_TMP,
PRIVATE_DEV,
READWRITE,
} MountMode;
typedef struct BindMount {
const char *path; /* stack memory, doesn't need to be freed explicitly */
char *chased; /* malloc()ed memory, needs to be freed */
MountMode mode;
bool ignore;
} BindMount;
static int append_mounts(BindMount **p, char **strv, MountMode mode) {
char **i;
assert(p);
STRV_FOREACH(i, strv) {
(*p)->ignore = false;
if ((mode == INACCESSIBLE || mode == READONLY || mode == READWRITE) && (*i)[0] == '-') {
(*p)->ignore = true;
(*i)++;
}
if (!path_is_absolute(*i))
return -EINVAL;
(*p)->path = *i;
(*p)->mode = mode;
(*p)++;
}
return 0;
}
static int mount_path_compare(const void *a, const void *b) {
const BindMount *p = a, *q = b;
int d;
/* If the paths are not equal, then order prefixes first */
d = path_compare(p->path, q->path);
if (d != 0)
return d;
/* If the paths are equal, check the mode */
if (p->mode < q->mode)
return -1;
if (p->mode > q->mode)
return 1;
return 0;
}
static void drop_duplicates(BindMount *m, unsigned *n) {
BindMount *f, *t, *previous;
assert(m);
assert(n);
/* Drops duplicate entries. Expects that the array is properly ordered already. */
for (f = m, t = m, previous = NULL; f < m+*n; f++) {
/* The first one wins (which is the one with the more restrictive mode), see mount_path_compare()
* above. */
if (previous && path_equal(f->path, previous->path)) {
log_debug("%s is duplicate.", f->path);
continue;
}
*t = *f;
previous = t;
t++;
}
*n = t - m;
}
static void drop_inaccessible(BindMount *m, unsigned *n) {
BindMount *f, *t;
const char *clear = NULL;
assert(m);
assert(n);
/* Drops all entries obstructed by another entry further up the tree. Expects that the array is properly
* ordered already. */
for (f = m, t = m; f < m+*n; f++) {
/* If we found a path set for INACCESSIBLE earlier, and this entry has it as prefix we should drop
* it, as inaccessible paths really should drop the entire subtree. */
if (clear && path_startswith(f->path, clear)) {
log_debug("%s is masked by %s.", f->path, clear);
continue;
}
clear = f->mode == INACCESSIBLE ? f->path : NULL;
*t = *f;
t++;
}
*n = t - m;
}
static void drop_nop(BindMount *m, unsigned *n) {
BindMount *f, *t;
assert(m);
assert(n);
/* Drops all entries which have an immediate parent that has the same type, as they are redundant. Assumes the
* list is ordered by prefixes. */
for (f = m, t = m; f < m+*n; f++) {
/* Only suppress such subtrees for READONLY and READWRITE entries */
if (IN_SET(f->mode, READONLY, READWRITE)) {
BindMount *p;
bool found = false;
/* Now let's find the first parent of the entry we are looking at. */
for (p = t-1; p >= m; p--) {
if (path_startswith(f->path, p->path)) {
found = true;
break;
}
}
/* We found it, let's see if it's the same mode, if so, we can drop this entry */
if (found && p->mode == f->mode) {
log_debug("%s is redundant by %s", f->path, p->path);
continue;
}
}
*t = *f;
t++;
}
*n = t - m;
}
static int mount_dev(BindMount *m) {
static const char devnodes[] =
"/dev/null\0"
"/dev/zero\0"
"/dev/full\0"
"/dev/random\0"
"/dev/urandom\0"
"/dev/tty\0";
char temporary_mount[] = "/tmp/namespace-dev-XXXXXX";
const char *d, *dev = NULL, *devpts = NULL, *devshm = NULL, *devhugepages = NULL, *devmqueue = NULL, *devlog = NULL, *devptmx = NULL;
_cleanup_umask_ mode_t u;
int r;
assert(m);
u = umask(0000);
if (!mkdtemp(temporary_mount))
return -errno;
dev = strjoina(temporary_mount, "/dev");
(void) mkdir(dev, 0755);
if (mount("tmpfs", dev, "tmpfs", DEV_MOUNT_OPTIONS, "mode=755") < 0) {
r = -errno;
goto fail;
}
devpts = strjoina(temporary_mount, "/dev/pts");
(void) mkdir(devpts, 0755);
if (mount("/dev/pts", devpts, NULL, MS_BIND, NULL) < 0) {
r = -errno;
goto fail;
}
devptmx = strjoina(temporary_mount, "/dev/ptmx");
if (symlink("pts/ptmx", devptmx) < 0) {
r = -errno;
goto fail;
}
devshm = strjoina(temporary_mount, "/dev/shm");
(void) mkdir(devshm, 01777);
r = mount("/dev/shm", devshm, NULL, MS_BIND, NULL);
if (r < 0) {
r = -errno;
goto fail;
}
devmqueue = strjoina(temporary_mount, "/dev/mqueue");
(void) mkdir(devmqueue, 0755);
(void) mount("/dev/mqueue", devmqueue, NULL, MS_BIND, NULL);
devhugepages = strjoina(temporary_mount, "/dev/hugepages");
(void) mkdir(devhugepages, 0755);
(void) mount("/dev/hugepages", devhugepages, NULL, MS_BIND, NULL);
devlog = strjoina(temporary_mount, "/dev/log");
(void) symlink("/run/systemd/journal/dev-log", devlog);
NULSTR_FOREACH(d, devnodes) {
_cleanup_free_ char *dn = NULL;
struct stat st;
r = stat(d, &st);
if (r < 0) {
if (errno == ENOENT)
continue;
r = -errno;
goto fail;
}
if (!S_ISBLK(st.st_mode) &&
!S_ISCHR(st.st_mode)) {
r = -EINVAL;
goto fail;
}
if (st.st_rdev == 0)
continue;
dn = strappend(temporary_mount, d);
if (!dn) {
r = -ENOMEM;
goto fail;
}
mac_selinux_create_file_prepare(d, st.st_mode);
r = mknod(dn, st.st_mode, st.st_rdev);
mac_selinux_create_file_clear();
if (r < 0) {
r = -errno;
goto fail;
}
}
dev_setup(temporary_mount, UID_INVALID, GID_INVALID);
/* Create the /dev directory if missing. It is more likely to be
* missing when the service is started with RootDirectory. This is
* consistent with mount units creating the mount points when missing.
*/
(void) mkdir_p_label(m->path, 0755);
/* Unmount everything in old /dev */
umount_recursive(m->path, 0);
if (mount(dev, m->path, NULL, MS_MOVE, NULL) < 0) {
r = -errno;
goto fail;
}
rmdir(dev);
rmdir(temporary_mount);
return 0;
fail:
if (devpts)
umount(devpts);
if (devshm)
umount(devshm);
if (devhugepages)
umount(devhugepages);
if (devmqueue)
umount(devmqueue);
umount(dev);
rmdir(dev);
rmdir(temporary_mount);
return r;
}
static int apply_mount(
BindMount *m,
const char *tmp_dir,
const char *var_tmp_dir) {
const char *what;
int r;
assert(m);
log_debug("Applying namespace mount on %s", m->path);
switch (m->mode) {
case INACCESSIBLE: {
struct stat target;
/* First, get rid of everything that is below if there
* is anything... Then, overmount it with an
* inaccessible path. */
(void) umount_recursive(m->path, 0);
if (lstat(m->path, &target) < 0)
return log_debug_errno(errno, "Failed to lstat() %s to determine what to mount over it: %m", m->path);
what = mode_to_inaccessible_node(target.st_mode);
if (!what) {
log_debug("File type not supported for inaccessible mounts. Note that symlinks are not allowed");
return -ELOOP;
}
break;
}
case READONLY:
case READWRITE:
r = path_is_mount_point(m->path, 0);
if (r < 0)
return log_debug_errno(r, "Failed to determine whether %s is already a mount point: %m", m->path);
if (r > 0) /* Nothing to do here, it is already a mount. We just later toggle the MS_RDONLY bit for the mount point if needed. */
return 0;
/* This isn't a mount point yet, let's make it one. */
what = m->path;
break;
case PRIVATE_TMP:
what = tmp_dir;
break;
case PRIVATE_VAR_TMP:
what = var_tmp_dir;
break;
case PRIVATE_DEV:
return mount_dev(m);
default:
assert_not_reached("Unknown mode");
}
assert(what);
if (mount(what, m->path, NULL, MS_BIND|MS_REC, NULL) < 0)
return log_debug_errno(errno, "Failed to mount %s to %s: %m", what, m->path);
log_debug("Successfully mounted %s to %s", what, m->path);
return 0;
}
static int make_read_only(BindMount *m, char **blacklist) {
int r = 0;
assert(m);
if (IN_SET(m->mode, INACCESSIBLE, READONLY))
r = bind_remount_recursive(m->path, true, blacklist);
else if (m->mode == PRIVATE_DEV) { /* Can be readonly but the submounts can't*/
if (mount(NULL, m->path, NULL, MS_REMOUNT|DEV_MOUNT_OPTIONS|MS_RDONLY, NULL) < 0)
r = -errno;
} else
return 0;
/* Not that we only turn on the MS_RDONLY flag here, we never turn it off. Something that was marked read-only
* already stays this way. This improves compatibility with container managers, where we won't attempt to undo
* read-only mounts already applied. */
return r;
}
static int chase_all_symlinks(const char *root_directory, BindMount *m, unsigned *n) {
BindMount *f, *t;
int r;
assert(m);
assert(n);
/* Since mount() will always follow symlinks and we need to take the different root directory into account we
* chase the symlinks on our own first. This call wil do so for all entries and remove all entries where we
* can't resolve the path, and which have been marked for such removal. */
for (f = m, t = m; f < m+*n; f++) {
r = chase_symlinks(f->path, root_directory, &f->chased);
if (r == -ENOENT && f->ignore) /* Doesn't exist? Then remove it! */
continue;
if (r < 0)
return log_debug_errno(r, "Failed to chase symlinks for %s: %m", f->path);
if (path_equal(f->path, f->chased))
f->chased = mfree(f->chased);
else {
log_debug("Chased %s → %s", f->path, f->chased);
f->path = f->chased;
}
*t = *f;
t++;
}
*n = t - m;
return 0;
}
int setup_namespace(
const char* root_directory,
char** read_write_paths,
char** read_only_paths,
char** inaccessible_paths,
const char* tmp_dir,
const char* var_tmp_dir,
bool private_dev,
bool protect_sysctl,
bool protect_cgroups,
ProtectHome protect_home,
ProtectSystem protect_system,
unsigned long mount_flags) {
BindMount *m, *mounts = NULL;
bool make_slave = false;
unsigned n;
int r = 0;
if (mount_flags == 0)
mount_flags = MS_SHARED;
n = !!tmp_dir + !!var_tmp_dir +
strv_length(read_write_paths) +
strv_length(read_only_paths) +
strv_length(inaccessible_paths) +
private_dev +
(protect_sysctl ? 3 : 0) +
(protect_cgroups != protect_sysctl) +
(protect_home != PROTECT_HOME_NO || protect_system == PROTECT_SYSTEM_STRICT ? 3 : 0) +
(protect_system == PROTECT_SYSTEM_STRICT ?
(2 + !private_dev + !protect_sysctl) :
((protect_system != PROTECT_SYSTEM_NO ? 3 : 0) +
(protect_system == PROTECT_SYSTEM_FULL ? 1 : 0)));
if (root_directory || n > 0)
make_slave = true;
if (n > 0) {
m = mounts = (BindMount *) alloca0(n * sizeof(BindMount));
r = append_mounts(&m, read_write_paths, READWRITE);
if (r < 0)
return r;
r = append_mounts(&m, read_only_paths, READONLY);
if (r < 0)
return r;
r = append_mounts(&m, inaccessible_paths, INACCESSIBLE);
if (r < 0)
return r;
if (tmp_dir) {
m->path = prefix_roota(root_directory, "/tmp");
m->mode = PRIVATE_TMP;
m++;
}
if (var_tmp_dir) {
m->path = prefix_roota(root_directory, "/var/tmp");
m->mode = PRIVATE_VAR_TMP;
m++;
}
if (private_dev) {
m->path = prefix_roota(root_directory, "/dev");
m->mode = PRIVATE_DEV;
m++;
}
if (protect_sysctl) {
m->path = prefix_roota(root_directory, "/proc/sys");
m->mode = READONLY;
m++;
m->path = prefix_roota(root_directory, "/proc/sysrq-trigger");
m->mode = READONLY;
m->ignore = true; /* Not always compiled into the kernel */
m++;
m->path = prefix_roota(root_directory, "/sys");
m->mode = READONLY;
m++;
}
if (protect_cgroups != protect_sysctl) {
m->path = prefix_roota(root_directory, "/sys/fs/cgroup");
m->mode = protect_cgroups ? READONLY : READWRITE;
m++;
}
if (protect_home != PROTECT_HOME_NO || protect_system == PROTECT_SYSTEM_STRICT) {
const char *home_dir, *run_user_dir, *root_dir;
/* If protection of $HOME and $XDG_RUNTIME_DIR is requested, then go for it. If we are in
* strict system protection mode, then also add entries for these directories, but mark them
* writable. This is because we want ProtectHome= and ProtectSystem= to be fully orthogonal. */
home_dir = prefix_roota(root_directory, "/home");
home_dir = strjoina("-", home_dir);
run_user_dir = prefix_roota(root_directory, "/run/user");
run_user_dir = strjoina("-", run_user_dir);
root_dir = prefix_roota(root_directory, "/root");
root_dir = strjoina("-", root_dir);
r = append_mounts(&m, STRV_MAKE(home_dir, run_user_dir, root_dir),
protect_home == PROTECT_HOME_READ_ONLY ? READONLY :
protect_home == PROTECT_HOME_YES ? INACCESSIBLE : READWRITE);
if (r < 0)
return r;
}
if (protect_system == PROTECT_SYSTEM_STRICT) {
/* In strict mode, we mount everything read-only, except for /proc, /dev, /sys which are the
* kernel API VFS, which are left writable, but PrivateDevices= + ProtectKernelTunables=
* protect those, and these options should be fully orthogonal. (And of course /home and
* friends are also left writable, as ProtectHome= shall manage those, orthogonally, see
* above). */
m->path = prefix_roota(root_directory, "/");
m->mode = READONLY;
m++;
m->path = prefix_roota(root_directory, "/proc");
m->mode = READWRITE;
m++;
if (!private_dev) {
m->path = prefix_roota(root_directory, "/dev");
m->mode = READWRITE;
m++;
}
if (!protect_sysctl) {
m->path = prefix_roota(root_directory, "/sys");
m->mode = READWRITE;
m++;
}
} else if (protect_system != PROTECT_SYSTEM_NO) {
const char *usr_dir, *boot_dir, *efi_dir, *etc_dir;
/* In any other mode we simply mark the relevant three directories ready-only. */
usr_dir = prefix_roota(root_directory, "/usr");
boot_dir = prefix_roota(root_directory, "/boot");
boot_dir = strjoina("-", boot_dir);
efi_dir = prefix_roota(root_directory, "/efi");
efi_dir = strjoina("-", efi_dir);
etc_dir = prefix_roota(root_directory, "/etc");
r = append_mounts(&m, protect_system == PROTECT_SYSTEM_FULL
? STRV_MAKE(usr_dir, boot_dir, efi_dir, etc_dir)
: STRV_MAKE(usr_dir, boot_dir, efi_dir), READONLY);
if (r < 0)
return r;
}
assert(mounts + n == m);
/* Resolve symlinks manually first, as mount() will always follow them relative to the host's
* root. Moreover we want to suppress duplicates based on the resolved paths. This of course is a bit
* racy. */
r = chase_all_symlinks(root_directory, mounts, &n);
if (r < 0)
goto finish;
qsort(mounts, n, sizeof(BindMount), mount_path_compare);
drop_duplicates(mounts, &n);
drop_inaccessible(mounts, &n);
drop_nop(mounts, &n);
}
if (unshare(CLONE_NEWNS) < 0) {
r = -errno;
goto finish;
}
if (make_slave) {
/* Remount / as SLAVE so that nothing now mounted in the namespace
shows up in the parent */
if (mount(NULL, "/", NULL, MS_SLAVE|MS_REC, NULL) < 0) {
r = -errno;
goto finish;
}
}
if (root_directory) {
/* Turn directory into bind mount */
if (mount(root_directory, root_directory, NULL, MS_BIND|MS_REC, NULL) < 0) {
r = -errno;
goto finish;
}
}
if (n > 0) {
char **blacklist;
unsigned j;
/* First round, add in all special mounts we need */
for (m = mounts; m < mounts + n; ++m) {
r = apply_mount(m, tmp_dir, var_tmp_dir);
if (r < 0)
goto finish;
}
/* Create a blacklist we can pass to bind_mount_recursive() */
blacklist = newa(char*, n+1);
for (j = 0; j < n; j++)
blacklist[j] = (char*) mounts[j].path;
blacklist[j] = NULL;
/* Second round, flip the ro bits if necessary. */
for (m = mounts; m < mounts + n; ++m) {
r = make_read_only(m, blacklist);
if (r < 0)
goto finish;
}
}
if (root_directory) {
/* MS_MOVE does not work on MS_SHARED so the remount MS_SHARED will be done later */
r = mount_move_root(root_directory);
if (r < 0)
goto finish;
}
/* Remount / as the desired mode. Not that this will not
* reestablish propagation from our side to the host, since
* what's disconnected is disconnected. */
if (mount(NULL, "/", NULL, mount_flags | MS_REC, NULL) < 0) {
r = -errno;
goto finish;
}
r = 0;
finish:
for (m = mounts; m < mounts + n; m++)
free(m->chased);
return r;
}
static int setup_one_tmp_dir(const char *id, const char *prefix, char **path) {
_cleanup_free_ char *x = NULL;
char bid[SD_ID128_STRING_MAX];
sd_id128_t boot_id;
int r;
assert(id);
assert(prefix);
assert(path);
/* We include the boot id in the directory so that after a
* reboot we can easily identify obsolete directories. */
r = sd_id128_get_boot(&boot_id);
if (r < 0)
return r;
x = strjoin(prefix, "/systemd-private-", sd_id128_to_string(boot_id, bid), "-", id, "-XXXXXX", NULL);
if (!x)
return -ENOMEM;
RUN_WITH_UMASK(0077)
if (!mkdtemp(x))
return -errno;
RUN_WITH_UMASK(0000) {
char *y;
y = strjoina(x, "/tmp");
if (mkdir(y, 0777 | S_ISVTX) < 0)
return -errno;
}
*path = x;
x = NULL;
return 0;
}
int setup_tmp_dirs(const char *id, char **tmp_dir, char **var_tmp_dir) {
char *a, *b;
int r;
assert(id);
assert(tmp_dir);
assert(var_tmp_dir);
r = setup_one_tmp_dir(id, "/tmp", &a);
if (r < 0)
return r;
r = setup_one_tmp_dir(id, "/var/tmp", &b);
if (r < 0) {
char *t;
t = strjoina(a, "/tmp");
rmdir(t);
rmdir(a);
free(a);
return r;
}
*tmp_dir = a;
*var_tmp_dir = b;
return 0;
}
int setup_netns(int netns_storage_socket[2]) {
_cleanup_close_ int netns = -1;
int r, q;
assert(netns_storage_socket);
assert(netns_storage_socket[0] >= 0);
assert(netns_storage_socket[1] >= 0);
/* We use the passed socketpair as a storage buffer for our
* namespace reference fd. Whatever process runs this first
* shall create a new namespace, all others should just join
* it. To serialize that we use a file lock on the socket
* pair.
*
* It's a bit crazy, but hey, works great! */
if (lockf(netns_storage_socket[0], F_LOCK, 0) < 0)
return -errno;
netns = receive_one_fd(netns_storage_socket[0], MSG_DONTWAIT);
if (netns == -EAGAIN) {
/* Nothing stored yet, so let's create a new namespace */
if (unshare(CLONE_NEWNET) < 0) {
r = -errno;
goto fail;
}
loopback_setup();
netns = open("/proc/self/ns/net", O_RDONLY|O_CLOEXEC|O_NOCTTY);
if (netns < 0) {
r = -errno;
goto fail;
}
r = 1;
} else if (netns < 0) {
r = netns;
goto fail;
} else {
/* Yay, found something, so let's join the namespace */
if (setns(netns, CLONE_NEWNET) < 0) {
r = -errno;
goto fail;
}
r = 0;
}
q = send_one_fd(netns_storage_socket[1], netns, MSG_DONTWAIT);
if (q < 0) {
r = q;
goto fail;
}
fail:
(void) lockf(netns_storage_socket[0], F_ULOCK, 0);
return r;
}
static const char *const protect_home_table[_PROTECT_HOME_MAX] = {
[PROTECT_HOME_NO] = "no",
[PROTECT_HOME_YES] = "yes",
[PROTECT_HOME_READ_ONLY] = "read-only",
};
DEFINE_STRING_TABLE_LOOKUP(protect_home, ProtectHome);
static const char *const protect_system_table[_PROTECT_SYSTEM_MAX] = {
[PROTECT_SYSTEM_NO] = "no",
[PROTECT_SYSTEM_YES] = "yes",
[PROTECT_SYSTEM_FULL] = "full",
[PROTECT_SYSTEM_STRICT] = "strict",
};
DEFINE_STRING_TABLE_LOOKUP(protect_system, ProtectSystem);
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