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nspawn: optionally fix up OS tree uid/gids for userns

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This adds a new --private-userns-chown switch that may be used in combination
with --private-userns. If it is passed a recursive chmod() operation is run on
the OS tree, fixing all file owner UID/GIDs to the right ranges. This should
make user namespacing pretty workable, as the OS trees don't need to be
prepared manually anymore.
This commit is contained in:
Lennart Poettering 2016-04-20 22:53:39 +02:00
parent 6402d5c628
commit 7336138eed
6 changed files with 560 additions and 2 deletions
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1
.gitignore vendored
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@ -240,6 +240,7 @@
/test-ns
/test-nss
/test-parse-util
/test-patch-uid
/test-path
/test-path-lookup
/test-path-util

13
Makefile.am
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@ -3021,6 +3021,8 @@ systemd_nspawn_SOURCES = \
src/nspawn/nspawn-setuid.h \
src/nspawn/nspawn-stub-pid1.c \
src/nspawn/nspawn-stub-pid1.h \
src/nspawn/nspawn-patch-uid.c \
src/nspawn/nspawn-patch-uid.h \
src/core/mount-setup.c \
src/core/mount-setup.h \
src/core/loopback-setup.c \
@ -3048,6 +3050,17 @@ systemd_nspawn_LDADD += \
libfirewall.la
endif
test_patch_uid_SOURCES = \
src/nspawn/nspawn-patch-uid.c \
src/nspawn/nspawn-patch-uid.h \
src/nspawn/test-patch-uid.c
test_patch_uid_LDADD = \
libshared.la
manual_tests += \
test-patch-uid
# ------------------------------------------------------------------------------
systemd_run_SOURCES = \
src/run/run.c

417
src/nspawn/nspawn-patch-uid.c Normal file
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@ -0,0 +1,417 @@
/***
This file is part of systemd.
Copyright 2016 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 <fcntl.h>
#ifdef HAVE_ACL
#include <sys/acl.h>
#endif
#include <sys/stat.h>
#include <unistd.h>
#include "acl-util.h"
#include "dirent-util.h"
#include "fd-util.h"
#include "nspawn-patch-uid.h"
#include "stdio-util.h"
#include "string-util.h"
#include "strv.h"
#include "user-util.h"
#ifdef HAVE_ACL
static int get_acl(int fd, const char *name, acl_type_t type, acl_t *ret) {
char procfs_path[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
acl_t acl;
assert(fd >= 0);
assert(ret);
if (name) {
_cleanup_close_ int child_fd = -1;
child_fd = openat(fd, name, O_PATH|O_CLOEXEC|O_NOFOLLOW);
if (child_fd < 0)
return -errno;
xsprintf(procfs_path, "/proc/self/fd/%i", child_fd);
acl = acl_get_file(procfs_path, type);
} else if (type == ACL_TYPE_ACCESS)
acl = acl_get_fd(fd);
else {
xsprintf(procfs_path, "/proc/self/fd/%i", fd);
acl = acl_get_file(procfs_path, type);
}
if (!acl)
return -errno;
*ret = acl;
return 0;
}
static int set_acl(int fd, const char *name, acl_type_t type, acl_t acl) {
char procfs_path[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
int r;
assert(fd >= 0);
assert(acl);
if (name) {
_cleanup_close_ int child_fd = -1;
child_fd = openat(fd, name, O_PATH|O_CLOEXEC|O_NOFOLLOW);
if (child_fd < 0)
return -errno;
xsprintf(procfs_path, "/proc/self/fd/%i", child_fd);
r = acl_set_file(procfs_path, type, acl);
} else if (type == ACL_TYPE_ACCESS)
r = acl_set_fd(fd, acl);
else {
xsprintf(procfs_path, "/proc/self/fd/%i", fd);
r = acl_set_file(procfs_path, type, acl);
}
if (r < 0)
return -errno;
return 0;
}
static int shift_acl(acl_t acl, uid_t shift, acl_t *ret) {
_cleanup_(acl_freep) acl_t copy = NULL;
acl_entry_t i;
int r;
assert(acl);
assert(ret);
r = acl_get_entry(acl, ACL_FIRST_ENTRY, &i);
if (r < 0)
return -errno;
while (r > 0) {
uid_t *old_uid, new_uid;
bool modify = false;
acl_tag_t tag;
if (acl_get_tag_type(i, &tag) < 0)
return -errno;
if (IN_SET(tag, ACL_USER, ACL_GROUP)) {
/* We don't distuingish here between uid_t and gid_t, let's make sure the compiler checks that
* this is actually OK */
assert_cc(sizeof(uid_t) == sizeof(gid_t));
old_uid = acl_get_qualifier(i);
if (!old_uid)
return -errno;
new_uid = shift | (*old_uid & UINT32_C(0xFFFF));
if (!uid_is_valid(new_uid))
return -EINVAL;
modify = new_uid != *old_uid;
if (modify && !copy) {
int n;
/* There's no copy of the ACL yet? if so, let's create one, and start the loop from the
* beginning, so that we copy all entries, starting from the first, this time. */
n = acl_entries(acl);
if (n < 0)
return -errno;
copy = acl_init(n);
if (!copy)
return -errno;
/* Seek back to the beginning */
r = acl_get_entry(acl, ACL_FIRST_ENTRY, &i);
if (r < 0)
return -errno;
continue;
}
}
if (copy) {
acl_entry_t new_entry;
if (acl_create_entry(&copy, &new_entry) < 0)
return -errno;
if (acl_copy_entry(new_entry, i) < 0)
return -errno;
if (modify)
if (acl_set_qualifier(new_entry, &new_uid) < 0)
return -errno;
}
r = acl_get_entry(acl, ACL_NEXT_ENTRY, &i);
if (r < 0)
return -errno;
}
*ret = copy;
copy = NULL;
return !!*ret;
}
static int patch_acls(int fd, const char *name, const struct stat *st, uid_t shift) {
_cleanup_(acl_freep) acl_t acl = NULL, shifted = NULL;
bool changed = false;
int r;
assert(fd >= 0);
assert(st);
/* ACLs are not supported on symlinks, there's no point in trying */
if (S_ISLNK(st->st_mode))
return 0;
r = get_acl(fd, name, ACL_TYPE_ACCESS, &acl);
if (r == -EOPNOTSUPP)
return 0;
if (r < 0)
return r;
r = shift_acl(acl, shift, &shifted);
if (r < 0)
return r;
if (r > 0) {
r = set_acl(fd, name, ACL_TYPE_ACCESS, shifted);
if (r < 0)
return r;
changed = true;
}
if (S_ISDIR(st->st_mode)) {
acl_free(acl);
acl_free(shifted);
acl = shifted = NULL;
r = get_acl(fd, name, ACL_TYPE_DEFAULT, &acl);
if (r < 0)
return r;
r = shift_acl(acl, shift, &shifted);
if (r < 0)
return r;
if (r > 0) {
r = set_acl(fd, name, ACL_TYPE_DEFAULT, shifted);
if (r < 0)
return r;
changed = true;
}
}
return changed;
}
#else
static int patch_acls(int fd, const char *name, const struct stat *st, uid_t shift) {
return 0;
}
#endif
static int patch_fd(int fd, const char *name, const struct stat *st, uid_t shift) {
uid_t new_uid;
gid_t new_gid;
bool changed = false;
int r;
assert(fd >= 0);
assert(st);
new_uid = shift | (st->st_uid & UINT32_C(0xFFFF));
new_gid = (gid_t) shift | (st->st_gid & UINT32_C(0xFFFF));
if (!uid_is_valid(new_uid) || !gid_is_valid(new_gid))
return -EINVAL;
if (st->st_uid != new_uid || st->st_gid != new_gid) {
if (name)
r = fchownat(fd, name, new_uid, new_gid, AT_SYMLINK_NOFOLLOW);
else
r = fchown(fd, new_uid, new_gid);
if (r < 0)
return -errno;
/* The Linux kernel alters the mode in some cases of chown(). Let's undo this. */
if (name && !S_ISLNK(st->st_mode))
r = fchmodat(fd, name, st->st_mode, 0);
else
r = fchmod(fd, st->st_mode);
if (r < 0)
return -errno;
changed = true;
}
r = patch_acls(fd, name, st, shift);
if (r < 0)
return r;
return r > 0 || changed;
}
static int recurse_fd(int fd, bool donate_fd, const struct stat *st, uid_t shift) {
bool changed = false;
int r;
assert(fd >= 0);
r = patch_fd(fd, NULL, st, shift);
if (r < 0)
goto finish;
if (S_ISDIR(st->st_mode)) {
_cleanup_closedir_ DIR *d = NULL;
struct dirent *de;
if (!donate_fd) {
int copy;
copy = fcntl(fd, F_DUPFD_CLOEXEC, 3);
if (copy < 0)
return -errno;
fd = copy;
donate_fd = true;
}
d = fdopendir(fd);
if (!d) {
r = -errno;
goto finish;
}
fd = -1;
FOREACH_DIRENT_ALL(de, d, r = -errno; goto finish) {
struct stat fst;
if (STR_IN_SET(de->d_name, ".", ".."))
continue;
if (fstatat(dirfd(d), de->d_name, &fst, AT_SYMLINK_NOFOLLOW) < 0) {
r = -errno;
goto finish;
}
if (S_ISDIR(fst.st_mode)) {
int subdir_fd;
subdir_fd = openat(dirfd(d), de->d_name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME);
if (subdir_fd < 0) {
r = -errno;
goto finish;
}
r = recurse_fd(subdir_fd, true, &fst, shift);
if (r < 0)
goto finish;
if (r > 0)
changed = true;
} else {
r = patch_fd(dirfd(d), de->d_name, &fst, shift);
if (r < 0)
goto finish;
if (r > 0)
changed = true;
}
}
}
r = changed;
finish:
if (donate_fd)
safe_close(fd);
return r;
}
static int fd_patch_uid_internal(int fd, bool donate_fd, uid_t shift, uid_t range) {
struct stat st;
int r;
assert(fd >= 0);
/* Recursively adjusts the UID/GIDs of all files of a directory tree. This is used to automatically fix up an
* OS tree to the used user namespace UID range. Note that this automatic adjustment only works for UID ranges
* following the concept that the upper 16bit of a UID identify the container, and the lower 16bit are the actual
* UID within the container. */
if ((shift & 0xFFFF) != 0) {
/* We only support containers where the shift starts at a 2^16 boundary */
r = -EOPNOTSUPP;
goto finish;
}
if (range != 0x10000) {
/* We only support containers with 16bit UID ranges for the patching logic */
r = -EOPNOTSUPP;
goto finish;
}
if (fstat(fd, &st) < 0) {
r = -errno;
goto finish;
}
if ((uint32_t) st.st_uid >> 16 != (uint32_t) st.st_gid >> 16) {
/* We only support containers where the uid/gid container ID match */
r = -EBADE;
goto finish;
}
/* Try to detect if the range is already right. Of course, this a pretty drastic optimization, as we assume
* that if the top-level dir has the right upper 16bit assigned, then everything below will have too... */
if (((uint32_t) (st.st_uid ^ shift) >> 16) == 0)
return 0;
return recurse_fd(fd, donate_fd, &st, shift);
finish:
if (donate_fd)
safe_close(fd);
return r;
}
int fd_patch_uid(int fd, uid_t shift, uid_t range) {
return fd_patch_uid_internal(fd, false, shift, range);
}
int path_patch_uid(const char *path, uid_t shift, uid_t range) {
int fd;
fd = open(path, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME);
if (fd < 0)
return -errno;
return fd_patch_uid_internal(fd, true, shift, range);
}

23
src/nspawn/nspawn-patch-uid.h Normal file
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@ -0,0 +1,23 @@
/***
This file is part of systemd.
Copyright 2016 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 <sys/types.h>
int fd_patch_uid(int fd, uid_t shift, uid_t range);
int path_patch_uid(const char *path, uid_t shift, uid_t range);

47
src/nspawn/nspawn.c
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@ -75,6 +75,7 @@
#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"
@ -175,6 +176,7 @@ static ExposePort *arg_expose_ports = NULL;
static char **arg_property = NULL;
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;
@ -204,6 +206,7 @@ static void help(void) {
" --property=NAME=VALUE Set scope unit property\n"
" --private-users[=UIDBASE[:NUIDS]]\n"
" Run within user namespace\n"
" --private-user-chown Adjust OS tree file ownership for private user range\n"
" --private-network Disable network in container\n"
" --network-interface=INTERFACE\n"
" Assign an existing network interface to the\n"
@ -349,6 +352,7 @@ 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 +396,7 @@ 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 },
@ -825,6 +830,10 @@ static int parse_argv(int argc, char *argv[]) {
arg_userns = true;
break;
case ARG_PRIVATE_USERS_CHOWN:
arg_userns_chown = true;
break;
case ARG_KILL_SIGNAL:
arg_kill_signal = signal_from_string_try_harder(optarg);
if (arg_kill_signal < 0) {
@ -933,8 +942,15 @@ 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 && access("/proc/self/uid_map", F_OK) < 0) {
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);
@ -2218,6 +2234,29 @@ 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 || !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,
@ -2763,6 +2802,10 @@ static int outer_child(
if (mount(directory, directory, NULL, MS_BIND|MS_REC, NULL) < 0)
return log_error_errno(errno, "Failed to make bind mount: %m");
r = recursive_chown(directory, arg_uid_shift, arg_uid_range);
if (r < 0)
return r;
r = setup_volatile(directory, arg_volatile_mode, arg_userns, arg_uid_shift, arg_uid_range, arg_selinux_context);
if (r < 0)
return r;

61
src/nspawn/test-patch-uid.c Normal file
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@ -0,0 +1,61 @@
/***
This file is part of systemd.
Copyright 2016 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 <stdlib.h>
#include "log.h"
#include "nspawn-patch-uid.h"
#include "user-util.h"
#include "util.h"
int main(int argc, char *argv[]) {
uid_t shift, range;
int r;
log_set_max_level(LOG_DEBUG);
log_parse_environment();
log_open();
if (argc != 4) {
log_error("Expected PATH SHIFT RANGE parameters.");
return EXIT_FAILURE;
}
r = parse_uid(argv[2], &shift);
if (r < 0) {
log_error_errno(r, "Failed to parse UID shift %s.", argv[2]);
return EXIT_FAILURE;
}
r = parse_gid(argv[3], &range);
if (r < 0) {
log_error_errno(r, "Failed to parse UID range %s.", argv[3]);
return EXIT_FAILURE;
}
r = path_patch_uid(argv[1], shift, range);
if (r < 0) {
log_error_errno(r, "Failed to patch directory tree: %m");
return EXIT_FAILURE;
}
log_info("Changed: %s", yes_no(r));
return EXIT_SUCCESS;
}