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Merge pull request #29529 from yuwata/core-namespace-check-priv

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core/namespace: check if we have enough privilege
This commit is contained in:
Luca Boccassi 2023-10-26 14:27:56 +01:00 committed by GitHub
commit e34836aa59
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3 changed files with 91 additions and 66 deletions
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147
src/core/namespace.c
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@ -973,6 +973,26 @@ static char *settle_runtime_dir(RuntimeScope scope) {
return runtime_dir;
}
static int create_temporary_mount_point(RuntimeScope scope, char **ret) {
_cleanup_free_ char *runtime_dir = NULL, *temporary_mount = NULL;
assert(ret);
runtime_dir = settle_runtime_dir(scope);
if (!runtime_dir)
return log_oom_debug();
temporary_mount = path_join(runtime_dir, "systemd/namespace-XXXXXX");
if (!temporary_mount)
return log_oom_debug();
if (!mkdtemp(temporary_mount))
return log_debug_errno(errno, "Failed to create temporary directory '%s': %m", temporary_mount);
*ret = TAKE_PTR(temporary_mount);
return 0;
}
static int mount_private_dev(MountEntry *m, RuntimeScope scope) {
static const char devnodes[] =
"/dev/null\0"
@ -982,23 +1002,16 @@ static int mount_private_dev(MountEntry *m, RuntimeScope scope) {
"/dev/urandom\0"
"/dev/tty\0";
_cleanup_free_ char *runtime_dir = NULL, *temporary_mount = NULL;
_cleanup_free_ char *temporary_mount = NULL;
const char *dev = NULL, *devpts = NULL, *devshm = NULL, *devhugepages = NULL, *devmqueue = NULL, *devlog = NULL, *devptmx = NULL;
bool can_mknod = true;
int r;
assert(m);
runtime_dir = settle_runtime_dir(scope);
if (!runtime_dir)
return log_oom_debug();
temporary_mount = path_join(runtime_dir, "systemd/namespace-dev-XXXXXX");
if (!temporary_mount)
return log_oom_debug();
if (!mkdtemp(temporary_mount))
return log_debug_errno(errno, "Failed to create temporary directory '%s': %m", temporary_mount);
r = create_temporary_mount_point(scope, &temporary_mount);
if (r < 0)
return r;
dev = strjoina(temporary_mount, "/dev");
(void) mkdir(dev, 0755);
@ -1146,37 +1159,77 @@ static int mount_bind_sysfs(const MountEntry *m) {
return mount_nofollow_verbose(LOG_DEBUG, "/sys", mount_entry_path(m), NULL, MS_BIND|MS_REC, NULL);
}
static int mount_private_sysfs(const MountEntry *m) {
const char *entry_path = mount_entry_path(ASSERT_PTR(m));
int r, n;
static int mount_private_apivfs(
const char *fstype,
const char *entry_path,
const char *bind_source,
const char *opts,
RuntimeScope scope) {
_cleanup_(rmdir_and_freep) char *temporary_mount = NULL;
int r;
assert(fstype);
assert(entry_path);
assert(bind_source);
(void) mkdir_p_label(entry_path, 0755);
n = umount_recursive(entry_path, 0);
/* First, check if we have enough privileges to mount a new instance. Note, a new sysfs instance
* cannot be mounted on an already existing mount. Let's use a temporary place. */
r = create_temporary_mount_point(scope, &temporary_mount);
if (r < 0)
return r;
r = mount_nofollow_verbose(LOG_DEBUG, "sysfs", entry_path, "sysfs", MS_NOSUID|MS_NOEXEC|MS_NODEV, NULL);
r = mount_nofollow_verbose(LOG_DEBUG, fstype, temporary_mount, fstype, MS_NOSUID|MS_NOEXEC|MS_NODEV, opts);
if (r == -EINVAL && opts)
/* If this failed with EINVAL then this likely means the textual hidepid= stuff for procfs is
* not supported by the kernel, and thus the per-instance hidepid= neither, which means we
* really don't want to use it, since it would affect our host's /proc mount. Hence let's
* gracefully fallback to a classic, unrestricted version. */
r = mount_nofollow_verbose(LOG_DEBUG, fstype, temporary_mount, fstype, MS_NOSUID|MS_NOEXEC|MS_NODEV, /* opts = */ NULL);
if (ERRNO_IS_NEG_PRIVILEGE(r)) {
/* When we do not have enough privileges to mount sysfs, fall back to use existing /sys. */
/* When we do not have enough privileges to mount a new instance, fall back to use an
* existing mount. */
if (n > 0)
/* /sys or some of sub-mounts are umounted in the above. Refuse incomplete tree.
* Propagate the original error code returned by mount() in the above. */
return r;
r = path_is_mount_point(entry_path, /* root = */ NULL, /* flags = */ 0);
if (r < 0)
return log_debug_errno(r, "Unable to determine whether '%s' is already mounted: %m", entry_path);
if (r > 0)
return 0; /* Use the current mount as is. */
return mount_bind_sysfs(m);
/* We lack permissions to mount a new instance, and it is not already mounted. But we can
* access the host's, so as a final fallback bind-mount it to the destination, as most likely
* we are inside a user manager in an unprivileged user namespace. */
return mount_nofollow_verbose(LOG_DEBUG, bind_source, entry_path, /* fstype = */ NULL, MS_BIND|MS_REC, /* opts = */ NULL);
} else if (r < 0)
return r;
/* We mounted a new instance now. Let's bind mount the children over now. */
(void) bind_mount_submounts("/sys", entry_path);
/* OK. We have a new mount instance. Let's clear an existing mount and its submounts. */
r = umount_recursive(entry_path, /* flags = */ 0);
if (r < 0)
log_debug_errno(r, "Failed to unmount directories below '%s', ignoring: %m", entry_path);
/* Then, move the new mount instance. */
r = mount_nofollow_verbose(LOG_DEBUG, temporary_mount, entry_path, /* fstype = */ NULL, MS_MOVE, /* opts = */ NULL);
if (r < 0)
return r;
/* We mounted a new instance now. Let's bind mount the children over now. This matters for nspawn
* where a bunch of files are overmounted, in particular the boot id. */
(void) bind_mount_submounts(bind_source, entry_path);
return 0;
}
static int mount_private_sysfs(const MountEntry *m, const NamespaceParameters *p) {
assert(m);
assert(p);
return mount_private_apivfs("sysfs", mount_entry_path(m), "/sys", /* opts = */ NULL, p->runtime_scope);
}
static int mount_procfs(const MountEntry *m, const NamespaceParameters *p) {
_cleanup_free_ char *opts = NULL;
const char *entry_path;
int r, n;
assert(m);
assert(p);
@ -1212,49 +1265,11 @@ static int mount_procfs(const MountEntry *m, const NamespaceParameters *p) {
return -ENOMEM;
}
entry_path = mount_entry_path(m);
(void) mkdir_p_label(entry_path, 0755);
/* Mount a new instance, so that we get the one that matches our user namespace, if we are running in
* one. i.e we don't reuse existing mounts here under any condition, we want a new instance owned by
* our user namespace and with our hidepid= settings applied. Hence, let's get rid of everything
* mounted on /proc/ first. */
n = umount_recursive(entry_path, 0);
r = mount_nofollow_verbose(LOG_DEBUG, "proc", entry_path, "proc", MS_NOSUID|MS_NOEXEC|MS_NODEV, opts);
if (r == -EINVAL && opts)
/* If this failed with EINVAL then this likely means the textual hidepid= stuff is
* not supported by the kernel, and thus the per-instance hidepid= neither, which
* means we really don't want to use it, since it would affect our host's /proc
* mount. Hence let's gracefully fallback to a classic, unrestricted version. */
r = mount_nofollow_verbose(LOG_DEBUG, "proc", entry_path, "proc", MS_NOSUID|MS_NOEXEC|MS_NODEV, NULL);
if (ERRNO_IS_NEG_PRIVILEGE(r)) {
/* When we do not have enough privileges to mount /proc, fall back to use existing /proc. */
if (n > 0)
/* /proc or some of sub-mounts are umounted in the above. Refuse incomplete tree.
* Propagate the original error code returned by mount() in the above. */
return r;
r = path_is_mount_point(entry_path, NULL, 0);
if (r < 0)
return log_debug_errno(r, "Unable to determine whether /proc is already mounted: %m");
if (r > 0)
return 0;
/* We lack permissions to mount a new instance of /proc, and it is not already mounted. But
* we can access the host's, so as a final fallback bind-mount it to the destination, as most
* likely we are inside a user manager in an unprivileged user namespace. */
return mount_nofollow_verbose(LOG_DEBUG, "/proc", entry_path, NULL, MS_BIND|MS_REC, NULL);
} else if (r < 0)
return r;
/* We mounted a new instance now. Let's bind mount the children over now. This matters for nspawn
* where a bunch of files are overmounted, in particular the boot id */
(void) bind_mount_submounts("/proc", entry_path);
return 0;
return mount_private_apivfs("proc", mount_entry_path(m), "/proc", opts, p->runtime_scope);
}
static int mount_tmpfs(const MountEntry *m) {
@ -1593,7 +1608,7 @@ static int apply_one_mount(
return mount_bind_dev(m);
case PRIVATE_SYSFS:
return mount_private_sysfs(m);
return mount_private_sysfs(m, p);
case BIND_SYSFS:
return mount_bind_sysfs(m);

3
test/TEST-07-PID1/test.sh
View File

@ -4,6 +4,9 @@ set -e
TEST_DESCRIPTION="Tests for core PID1 functionality"
# for testing PrivateNetwork=yes
NSPAWN_ARGUMENTS="--capability=CAP_NET_ADMIN"
# shellcheck source=test/test-functions
. "${TEST_BASE_DIR:?}/test-functions"

7
test/units/testsuite-07.private-network.sh Executable file
View File

@ -0,0 +1,7 @@
#!/usr/bin/env bash
# SPDX-License-Identifier: LGPL-2.1-or-later
set -eux
set -o pipefail
# For issue https://github.com/systemd/systemd/issues/29526
systemd-run -p PrivateNetwork=yes --wait /bin/true