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Merge pull request #3093 from poettering/nspawn-userns-magic

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nspawn automatic user namespaces
This commit is contained in:
Lennart Poettering
2016-04-26 14:57:04 +02:00
parent 6e3930c40f 4aeb20f5aa
commit d7fe83bbc2
17 changed files with 1088 additions and 72 deletions
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src/nspawn/nspawn.c
+309 -41
View File
@@ -22,7 +22,9 @@
#endif
#include <errno.h>
#include <getopt.h>
#include <grp.h>
#include <linux/loop.h>
#include <pwd.h>
#include <sched.h>
#ifdef HAVE_SECCOMP
#include <seccomp.h>
@@ -75,6 +77,7 @@
#include "nspawn-expose-ports.h"
#include "nspawn-mount.h"
#include "nspawn-network.h"
#include "nspawn-patch-uid.h"
#include "nspawn-register.h"
#include "nspawn-settings.h"
#include "nspawn-setuid.h"
@@ -101,6 +104,11 @@
#include "user-util.h"
#include "util.h"
/* Note that devpts's gid= parameter parses GIDs as signed values, hence we stay away from the upper half of the 32bit
* UID range here */
#define UID_SHIFT_PICK_MIN ((uid_t) UINT32_C(0x00080000))
#define UID_SHIFT_PICK_MAX ((uid_t) UINT32_C(0x6FFF0000))
typedef enum ContainerStatus {
CONTAINER_TERMINATED,
CONTAINER_REBOOTED
@@ -173,8 +181,9 @@ static char *arg_image = NULL;
static VolatileMode arg_volatile_mode = VOLATILE_NO;
static ExposePort *arg_expose_ports = NULL;
static char **arg_property = NULL;
static UserNamespaceMode arg_userns_mode = USER_NAMESPACE_NO;
static uid_t arg_uid_shift = UID_INVALID, arg_uid_range = 0x10000U;
static bool arg_userns = false;
static bool arg_userns_chown = false;
static int arg_kill_signal = 0;
static bool arg_unified_cgroup_hierarchy = false;
static SettingsMask arg_settings_mask = 0;
@@ -202,8 +211,10 @@ static void help(void) {
" --uuid=UUID Set a specific machine UUID for the container\n"
" -S --slice=SLICE Place the container in the specified slice\n"
" --property=NAME=VALUE Set scope unit property\n"
" -U --private-users=pick Run within user namespace, pick UID/GID range automatically\n"
" --private-users[=UIDBASE[:NUIDS]]\n"
" Run within user namespace\n"
" Run within user namespace, user configured UID/GID range\n"
" --private-user-chown Adjust OS tree file ownership for private UID/GID range\n"
" --private-network Disable network in container\n"
" --network-interface=INTERFACE\n"
" Assign an existing network interface to the\n"
@@ -272,9 +283,15 @@ static int custom_mounts_prepare(void) {
for (i = 0; i < arg_n_custom_mounts; i++) {
CustomMount *m = &arg_custom_mounts[i];
if (arg_userns && arg_uid_shift == UID_INVALID && path_equal(m->destination, "/")) {
log_error("--private-users with automatic UID shift may not be combined with custom root mounts.");
return -EINVAL;
if (path_equal(m->destination, "/") && arg_userns_mode != USER_NAMESPACE_NO) {
if (arg_userns_chown) {
log_error("--private-users-chown may not be combined with custom root mounts.");
return -EINVAL;
} else if (arg_uid_shift == UID_INVALID) {
log_error("--private-users with automatic UID shift may not be combined with custom root mounts.");
return -EINVAL;
}
}
if (m->type != CUSTOM_MOUNT_OVERLAY)
@@ -349,6 +366,7 @@ static int parse_argv(int argc, char *argv[]) {
ARG_KILL_SIGNAL,
ARG_SETTINGS,
ARG_CHDIR,
ARG_PRIVATE_USERS_CHOWN,
};
static const struct option options[] = {
@@ -392,6 +410,7 @@ static int parse_argv(int argc, char *argv[]) {
{ "port", required_argument, NULL, 'p' },
{ "property", required_argument, NULL, ARG_PROPERTY },
{ "private-users", optional_argument, NULL, ARG_PRIVATE_USERS },
{ "private-users-chown", optional_argument, NULL, ARG_PRIVATE_USERS_CHOWN},
{ "kill-signal", required_argument, NULL, ARG_KILL_SIGNAL },
{ "settings", required_argument, NULL, ARG_SETTINGS },
{ "chdir", required_argument, NULL, ARG_CHDIR },
@@ -406,7 +425,7 @@ static int parse_argv(int argc, char *argv[]) {
assert(argc >= 0);
assert(argv);
while ((c = getopt_long(argc, argv, "+hD:u:abL:M:jS:Z:qi:xp:n", options, NULL)) >= 0)
while ((c = getopt_long(argc, argv, "+hD:u:abL:M:jS:Z:qi:xp:nU", options, NULL)) >= 0)
switch (c) {
@@ -797,10 +816,29 @@ static int parse_argv(int argc, char *argv[]) {
break;
case ARG_PRIVATE_USERS:
if (optarg) {
r = optarg ? parse_boolean(optarg) : 1;
if (r == 0) {
/* no: User namespacing off */
arg_userns_mode = USER_NAMESPACE_NO;
arg_uid_shift = UID_INVALID;
arg_uid_range = UINT32_C(0x10000);
} else if (r > 0) {
/* yes: User namespacing on, UID range is read from root dir */
arg_userns_mode = USER_NAMESPACE_FIXED;
arg_uid_shift = UID_INVALID;
arg_uid_range = UINT32_C(0x10000);
} else if (streq(optarg, "pick")) {
/* pick: User namespacing on, UID range is picked randomly */
arg_userns_mode = USER_NAMESPACE_PICK;
arg_uid_shift = UID_INVALID;
arg_uid_range = UINT32_C(0x10000);
} else {
_cleanup_free_ char *buffer = NULL;
const char *range, *shift;
/* anything else: User namespacing on, UID range is explicitly configured */
range = strchr(optarg, ':');
if (range) {
buffer = strndup(optarg, range - optarg);
@@ -820,9 +858,28 @@ static int parse_argv(int argc, char *argv[]) {
log_error("Failed to parse UID: %s", optarg);
return -EINVAL;
}
arg_userns_mode = USER_NAMESPACE_FIXED;
}
arg_userns = true;
arg_settings_mask |= SETTING_USERNS;
break;
case 'U':
if (userns_supported()) {
arg_userns_mode = USER_NAMESPACE_PICK;
arg_uid_shift = UID_INVALID;
arg_uid_range = UINT32_C(0x10000);
arg_settings_mask |= SETTING_USERNS;
}
break;
case ARG_PRIVATE_USERS_CHOWN:
arg_userns_chown = true;
arg_settings_mask |= SETTING_USERNS;
break;
case ARG_KILL_SIGNAL:
@@ -893,6 +950,9 @@ static int parse_argv(int argc, char *argv[]) {
if (arg_share_system)
arg_register = false;
if (arg_userns_mode == USER_NAMESPACE_PICK)
arg_userns_chown = true;
if (arg_start_mode != START_PID1 && arg_share_system) {
log_error("--boot and --share-system may not be combined.");
return -EINVAL;
@@ -933,8 +993,15 @@ static int parse_argv(int argc, char *argv[]) {
return -EINVAL;
}
if (arg_userns && access("/proc/self/uid_map", F_OK) < 0)
return log_error_errno(EOPNOTSUPP, "--private-users= is not supported, kernel compiled without user namespace support.");
if (arg_userns_mode != USER_NAMESPACE_NO && !userns_supported()) {
log_error("--private-users= is not supported, kernel compiled without user namespace support.");
return -EOPNOTSUPP;
}
if (arg_userns_chown && arg_read_only) {
log_error("--read-only and --private-users-chown may not be combined.");
return -EINVAL;
}
if (argc > optind) {
arg_parameters = strv_copy(argv + optind);
@@ -993,7 +1060,7 @@ static int verify_arguments(void) {
static int userns_lchown(const char *p, uid_t uid, gid_t gid) {
assert(p);
if (!arg_userns)
if (arg_userns_mode == USER_NAMESPACE_NO)
return 0;
if (uid == UID_INVALID && gid == GID_INVALID)
@@ -2218,6 +2285,29 @@ static int setup_machine_id(const char *directory) {
return 0;
}
static int recursive_chown(const char *directory, uid_t shift, uid_t range) {
int r;
assert(directory);
if (arg_userns_mode == USER_NAMESPACE_NO || !arg_userns_chown)
return 0;
r = path_patch_uid(directory, arg_uid_shift, arg_uid_range);
if (r == -EOPNOTSUPP)
return log_error_errno(r, "Automatic UID/GID adjusting is only supported for UID/GID ranges starting at multiples of 2^16 with a range of 2^16.");
if (r == -EBADE)
return log_error_errno(r, "Upper 16 bits of root directory UID and GID do not match.");
if (r < 0)
return log_error_errno(r, "Failed to adjust UID/GID shift of OS tree: %m");
if (r == 0)
log_debug("Root directory of image is already owned by the right UID/GID range, skipping recursive chown operation.");
else
log_debug("Patched directory tree to match UID/GID range.");
return r;
}
static int mount_devices(
const char *where,
const char *root_device, bool root_device_rw,
@@ -2435,7 +2525,7 @@ static int determine_names(void) {
static int determine_uid_shift(const char *directory) {
int r;
if (!arg_userns) {
if (arg_userns_mode == USER_NAMESPACE_NO) {
arg_uid_shift = 0;
return 0;
}
@@ -2462,7 +2552,6 @@ static int determine_uid_shift(const char *directory) {
return -EINVAL;
}
log_info("Using user namespaces with base " UID_FMT " and range " UID_FMT ".", arg_uid_shift, arg_uid_range);
return 0;
}
@@ -2499,7 +2588,7 @@ static int inner_child(
cg_unified_flush();
if (arg_userns) {
if (arg_userns_mode != USER_NAMESPACE_NO) {
/* Tell the parent, that it now can write the UID map. */
(void) barrier_place(barrier); /* #1 */
@@ -2510,7 +2599,14 @@ static int inner_child(
}
}
r = mount_all(NULL, arg_userns, true, arg_uid_shift, arg_private_network, arg_uid_range, arg_selinux_apifs_context);
r = mount_all(NULL,
arg_userns_mode != USER_NAMESPACE_NO,
true,
arg_private_network,
arg_uid_shift,
arg_uid_range,
arg_selinux_apifs_context);
if (r < 0)
return r;
@@ -2749,7 +2845,8 @@ static int outer_child(
if (r < 0)
return r;
if (arg_userns) {
if (arg_userns_mode != USER_NAMESPACE_NO) {
/* Let the parent know which UID shift we read from the image */
l = send(uid_shift_socket, &arg_uid_shift, sizeof(arg_uid_shift), MSG_NOSIGNAL);
if (l < 0)
return log_error_errno(errno, "Failed to send UID shift: %m");
@@ -2757,17 +2854,49 @@ static int outer_child(
log_error("Short write while sending UID shift.");
return -EIO;
}
if (arg_userns_mode == USER_NAMESPACE_PICK) {
/* When we are supposed to pick the UID shift, the parent will check now whether the UID shift
* we just read from the image is available. If yes, it will send the UID shift back to us, if
* not it will pick a different one, and send it back to us. */
l = recv(uid_shift_socket, &arg_uid_shift, sizeof(arg_uid_shift), 0);
if (l < 0)
return log_error_errno(errno, "Failed to recv UID shift: %m");
if (l != sizeof(arg_uid_shift)) {
log_error("Short read while recieving UID shift.");
return -EIO;
}
}
log_info("Selected user namespace base " UID_FMT " and range " UID_FMT ".", arg_uid_shift, arg_uid_range);
}
/* Turn directory into bind mount */
if (mount(directory, directory, NULL, MS_BIND|MS_REC, NULL) < 0)
return log_error_errno(errno, "Failed to make bind mount: %m");
r = setup_volatile(directory, arg_volatile_mode, arg_userns, arg_uid_shift, arg_uid_range, arg_selinux_context);
r = recursive_chown(directory, arg_uid_shift, arg_uid_range);
if (r < 0)
return r;
r = setup_volatile_state(directory, arg_volatile_mode, arg_userns, arg_uid_shift, arg_uid_range, arg_selinux_context);
r = setup_volatile(
directory,
arg_volatile_mode,
arg_userns_mode != USER_NAMESPACE_NO,
arg_uid_shift,
arg_uid_range,
arg_selinux_context);
if (r < 0)
return r;
r = setup_volatile_state(
directory,
arg_volatile_mode,
arg_userns_mode != USER_NAMESPACE_NO,
arg_uid_shift,
arg_uid_range,
arg_selinux_context);
if (r < 0)
return r;
@@ -2781,7 +2910,13 @@ static int outer_child(
return log_error_errno(r, "Failed to make tree read-only: %m");
}
r = mount_all(directory, arg_userns, false, arg_private_network, arg_uid_shift, arg_uid_range, arg_selinux_apifs_context);
r = mount_all(directory,
arg_userns_mode != USER_NAMESPACE_NO,
false,
arg_private_network,
arg_uid_shift,
arg_uid_range,
arg_selinux_apifs_context);
if (r < 0)
return r;
@@ -2823,11 +2958,24 @@ static int outer_child(
if (r < 0)
return r;
r = mount_custom(directory, arg_custom_mounts, arg_n_custom_mounts, arg_userns, arg_uid_shift, arg_uid_range, arg_selinux_apifs_context);
r = mount_custom(
directory,
arg_custom_mounts,
arg_n_custom_mounts,
arg_userns_mode != USER_NAMESPACE_NO,
arg_uid_shift,
arg_uid_range,
arg_selinux_apifs_context);
if (r < 0)
return r;
r = mount_cgroups(directory, arg_unified_cgroup_hierarchy, arg_userns, arg_uid_shift, arg_uid_range, arg_selinux_apifs_context);
r = mount_cgroups(
directory,
arg_unified_cgroup_hierarchy,
arg_userns_mode != USER_NAMESPACE_NO,
arg_uid_shift,
arg_uid_range,
arg_selinux_apifs_context);
if (r < 0)
return r;
@@ -2838,7 +2986,7 @@ static int outer_child(
pid = raw_clone(SIGCHLD|CLONE_NEWNS|
(arg_share_system ? 0 : CLONE_NEWIPC|CLONE_NEWPID|CLONE_NEWUTS) |
(arg_private_network ? CLONE_NEWNET : 0) |
(arg_userns ? CLONE_NEWUSER : 0),
(arg_userns_mode != USER_NAMESPACE_NO ? CLONE_NEWUSER : 0),
NULL);
if (pid < 0)
return log_error_errno(errno, "Failed to fork inner child: %m");
@@ -2882,6 +3030,61 @@ static int outer_child(
return 0;
}
static int uid_shift_pick(uid_t *shift, LockFile *ret_lock_file) {
unsigned n_tries = 100;
uid_t candidate;
int r;
assert(shift);
assert(ret_lock_file);
assert(arg_userns_mode == USER_NAMESPACE_PICK);
assert(arg_uid_range == 0x10000U);
candidate = *shift;
(void) mkdir("/run/systemd/nspawn-uid", 0755);
for (;;) {
char lock_path[strlen("/run/systemd/nspawn-uid/") + DECIMAL_STR_MAX(uid_t) + 1];
_cleanup_release_lock_file_ LockFile lf = LOCK_FILE_INIT;
if (--n_tries <= 0)
return -EBUSY;
if (candidate < UID_SHIFT_PICK_MIN || candidate > UID_SHIFT_PICK_MAX)
goto next;
if ((candidate & UINT32_C(0xFFFF)) != 0)
goto next;
xsprintf(lock_path, "/run/systemd/nspawn-uid/" UID_FMT, candidate);
r = make_lock_file(lock_path, LOCK_EX|LOCK_NB, &lf);
if (r == -EBUSY) /* Range already taken by another nspawn instance */
goto next;
if (r < 0)
return r;
/* Make some superficial checks whether the range is currently known in the user database */
if (getpwuid(candidate))
goto next;
if (getpwuid(candidate + UINT32_C(0xFFFE)))
goto next;
if (getgrgid(candidate))
goto next;
if (getgrgid(candidate + UINT32_C(0xFFFE)))
goto next;
*ret_lock_file = lf;
lf = (struct LockFile) LOCK_FILE_INIT;
*shift = candidate;
return 0;
next:
random_bytes(&candidate, sizeof(candidate));
candidate = (candidate % (UID_SHIFT_PICK_MAX - UID_SHIFT_PICK_MIN)) + UID_SHIFT_PICK_MIN;
candidate &= (uid_t) UINT32_C(0xFFFF0000);
}
}
static int setup_uid_map(pid_t pid) {
char uid_map[strlen("/proc//uid_map") + DECIMAL_STR_MAX(uid_t) + 1], line[DECIMAL_STR_MAX(uid_t)*3+3+1];
int r;
@@ -3113,6 +3316,19 @@ static int load_settings(void) {
}
}
if ((arg_settings_mask & SETTING_USERNS) == 0 &&
settings->userns_mode != _USER_NAMESPACE_MODE_INVALID) {
if (!arg_settings_trusted)
log_warning("Ignoring PrivateUsers= and PrivateUsersChown= settings, file %s is not trusted.", p);
else {
arg_userns_mode = settings->userns_mode;
arg_uid_shift = settings->uid_shift;
arg_uid_range = settings->uid_range;
arg_userns_chown = settings->userns_chown;
}
}
return 0;
}
@@ -3351,20 +3567,42 @@ int main(int argc, char *argv[]) {
}
for (;;) {
_cleanup_close_pair_ int kmsg_socket_pair[2] = { -1, -1 }, rtnl_socket_pair[2] = { -1, -1 },
pid_socket_pair[2] = { -1, -1 }, uuid_socket_pair[2] = { -1, -1 }, uid_shift_socket_pair[2] = { -1, -1 };
ContainerStatus container_status;
_cleanup_(barrier_destroy) Barrier barrier = BARRIER_NULL;
static const struct sigaction sa = {
.sa_handler = nop_signal_handler,
.sa_flags = SA_NOCLDSTOP,
};
int ifi = 0;
ssize_t l;
_cleanup_release_lock_file_ LockFile uid_shift_lock = LOCK_FILE_INIT;
_cleanup_close_ int etc_passwd_lock = -1;
_cleanup_close_pair_ int
kmsg_socket_pair[2] = { -1, -1 },
rtnl_socket_pair[2] = { -1, -1 },
pid_socket_pair[2] = { -1, -1 },
uuid_socket_pair[2] = { -1, -1 },
uid_shift_socket_pair[2] = { -1, -1 };
_cleanup_(barrier_destroy) Barrier barrier = BARRIER_NULL;
_cleanup_(sd_event_unrefp) sd_event *event = NULL;
_cleanup_(pty_forward_freep) PTYForward *forward = NULL;
_cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
ContainerStatus container_status;
char last_char = 0;
int ifi = 0;
ssize_t l;
if (arg_userns_mode == USER_NAMESPACE_PICK) {
/* When we shall pick the UID/GID range, let's first lock /etc/passwd, so that we can safely
* check with getpwuid() if the specific user already exists. Note that /etc might be
* read-only, in which case this will fail with EROFS. But that's really OK, as in that case we
* can be reasonably sure that no users are going to be added. Note that getpwuid() checks are
* really just an extra safety net. We kinda assume that the UID range we allocate from is
* really ours. */
etc_passwd_lock = take_etc_passwd_lock(NULL);
if (etc_passwd_lock < 0 && etc_passwd_lock != -EROFS) {
log_error_errno(r, "Failed to take /etc/passwd lock: %m");
goto finish;
}
}
r = barrier_create(&barrier);
if (r < 0) {
@@ -3392,7 +3630,7 @@ int main(int argc, char *argv[]) {
goto finish;
}
if (arg_userns)
if (arg_userns_mode != USER_NAMESPACE_NO)
if (socketpair(AF_UNIX, SOCK_SEQPACKET|SOCK_CLOEXEC, 0, uid_shift_socket_pair) < 0) {
r = log_error_errno(errno, "Failed to create uid shift socket pair: %m");
goto finish;
@@ -3468,6 +3706,43 @@ int main(int argc, char *argv[]) {
uuid_socket_pair[1] = safe_close(uuid_socket_pair[1]);
uid_shift_socket_pair[1] = safe_close(uid_shift_socket_pair[1]);
if (arg_userns_mode != USER_NAMESPACE_NO) {
/* The child just let us know the UID shift it might have read from the image. */
l = recv(uid_shift_socket_pair[0], &arg_uid_shift, sizeof(arg_uid_shift), 0);
if (l < 0) {
r = log_error_errno(errno, "Failed to read UID shift: %m");
goto finish;
}
if (l != sizeof(arg_uid_shift)) {
log_error("Short read while reading UID shift.");
r = EIO;
goto finish;
}
if (arg_userns_mode == USER_NAMESPACE_PICK) {
/* If we are supposed to pick the UID shift, let's try to use the shift read from the
* image, but if that's already in use, pick a new one, and report back to the child,
* which one we now picked. */
r = uid_shift_pick(&arg_uid_shift, &uid_shift_lock);
if (r < 0) {
log_error_errno(r, "Failed to pick suitable UID/GID range: %m");
goto finish;
}
l = send(uid_shift_socket_pair[0], &arg_uid_shift, sizeof(arg_uid_shift), MSG_NOSIGNAL);
if (l < 0) {
r = log_error_errno(errno, "Failed to send UID shift: %m");
goto finish;
}
if (l != sizeof(arg_uid_shift)) {
log_error("Short write while writing UID shift.");
r = -EIO;
goto finish;
}
}
}
/* Wait for the outer child. */
r = wait_for_terminate_and_warn("namespace helper", pid, NULL);
if (r < 0)
@@ -3504,24 +3779,13 @@ int main(int argc, char *argv[]) {
log_debug("Init process invoked as PID " PID_FMT, pid);
if (arg_userns) {
if (arg_userns_mode != USER_NAMESPACE_NO) {
if (!barrier_place_and_sync(&barrier)) { /* #1 */
log_error("Child died too early.");
r = -ESRCH;
goto finish;
}
l = recv(uid_shift_socket_pair[0], &arg_uid_shift, sizeof(arg_uid_shift), 0);
if (l < 0) {
r = log_error_errno(errno, "Failed to read UID shift: %m");
goto finish;
}
if (l != sizeof(arg_uid_shift)) {
log_error("Short read while reading UID shift.");
r = EIO;
goto finish;
}
r = setup_uid_map(pid);
if (r < 0)
goto finish;
@@ -3619,6 +3883,10 @@ int main(int argc, char *argv[]) {
goto finish;
}
/* At this point we have made use of the UID we picked, and thus nss-mymachines will make them appear
* in getpwuid(), thus we can release the /etc/passwd lock. */
etc_passwd_lock = safe_close(etc_passwd_lock);
sd_notifyf(false,
"READY=1\n"
"STATUS=Container running.\n"