From 10e421f70889a672f984785393051e0471c0aeb2 Mon Sep 17 00:00:00 2001

From: Daan De Meyer <daan.j.demeyer@gmail.com>

Date: Mon, 9 Sep 2024 12:25:28 +0200

Subject: [PATCH] core: Add support for PrivateUsers=identity

This configures an indentity mapping similar to

systemd-nspawn --private-users=identity.

(cherry picked from commit fa693fdc7e17618958c505af4b2f39ecd1c3363e)

---

 man/org.freedesktop.systemd1.xml         | 24 ++++++++++

 man/systemd.exec.xml                     | 35 ++++++++++-----

 src/core/dbus-execute.c                  | 57 ++++++++++++++++++++++--

 src/core/exec-invoke.c                   | 56 +++++++++++++++--------

 src/core/execute-serialize.c             |  9 ++--

 src/core/execute.c                       |  2 +-

 src/core/execute.h                       |  2 +-

 src/core/load-fragment-gperf.gperf.in    |  2 +-

 src/core/load-fragment.c                 |  1 +

 src/core/load-fragment.h                 |  1 +

 src/core/namespace.c                     |  8 ++++

 src/core/namespace.h                     | 11 +++++

 src/shared/bus-unit-util.c               |  1 +

 test/units/TEST-07-PID1.private-users.sh | 12 +++++

 14 files changed, 179 insertions(+), 42 deletions(-)

 create mode 100755 test/units/TEST-07-PID1.private-users.sh

diff --git a/man/org.freedesktop.systemd1.xml b/man/org.freedesktop.systemd1.xml

index b0b45097e30a3..ce0757cf9cfa2 100644

--- a/man/org.freedesktop.systemd1.xml

+++ b/man/org.freedesktop.systemd1.xml

@@ -3221,6 +3221,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateUsers = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

+      readonly s PrivateUsersEx = '...';

+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateMounts = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateIPC = ...;

@@ -3832,6 +3834,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {

+    

+

@@ -4516,6 +4520,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateUsers"/>

+    <variablelist class="dbus-property" generated="True" extra-ref="PrivateUsersEx"/>

+

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateMounts"/>

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateIPC"/>

@@ -5338,6 +5344,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateUsers = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

+      readonly s PrivateUsersEx = '...';

+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateMounts = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateIPC = ...;

@@ -5961,6 +5969,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {

+    

+

@@ -6625,6 +6635,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateUsers"/>

+    <variablelist class="dbus-property" generated="True" extra-ref="PrivateUsersEx"/>

+

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateMounts"/>

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateIPC"/>

@@ -7311,6 +7323,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateUsers = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

+      readonly s PrivateUsersEx = '...';

+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateMounts = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateIPC = ...;

@@ -7860,6 +7874,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {

+    

+

@@ -8436,6 +8452,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateUsers"/>

+    <variablelist class="dbus-property" generated="True" extra-ref="PrivateUsersEx"/>

+

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateMounts"/>

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateIPC"/>

@@ -9245,6 +9263,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateUsers = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

+      readonly s PrivateUsersEx = '...';

+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateMounts = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b PrivateIPC = ...;

@@ -9780,6 +9800,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {

+    

+

@@ -10342,6 +10364,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateUsers"/>

+    <variablelist class="dbus-property" generated="True" extra-ref="PrivateUsersEx"/>

+

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateMounts"/>

     <variablelist class="dbus-property" generated="True" extra-ref="PrivateIPC"/>

diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml

index 21527f756d669..3cdb7ff70a09b 100644

--- a/man/systemd.exec.xml

+++ b/man/systemd.exec.xml

@@ -1941,18 +1941,29 @@ BindReadOnlyPaths=/var/lib/systemd</programlisting>

       <varlistentry>

         <term><varname>PrivateUsers=</varname></term>

-        <listitem><para>Takes a boolean argument. If true, sets up a new user namespace for the executed processes and

-        configures a minimal user and group mapping, that maps the <literal>root</literal> user and group as well as

-        the unit's own user and group to themselves and everything else to the <literal>nobody</literal> user and

-        group. This is useful to securely detach the user and group databases used by the unit from the rest of the

-        system, and thus to create an effective sandbox environment. All files, directories, processes, IPC objects and

-        other resources owned by users/groups not equaling <literal>root</literal> or the unit's own will stay visible

-        from within the unit but appear owned by the <literal>nobody</literal> user and group. If this mode is enabled,

-        all unit processes are run without privileges in the host user namespace (regardless if the unit's own

-        user/group is <literal>root</literal> or not). Specifically this means that the process will have zero process

-        capabilities on the host's user namespace, but full capabilities within the service's user namespace. Settings

-        such as <varname>CapabilityBoundingSet=</varname> will affect only the latter, and there's no way to acquire

-        additional capabilities in the host's user namespace. Defaults to off.</para>

+        <listitem><para>Takes a boolean argument or one of <literal>self</literal> or

+        <literal>identity</literal>. Defaults to off. If enabled, sets up a new user namespace for the

+        executed processes and configures a user and group mapping. If set to a true value or

+        <literal>self</literal>, a minimal user and group mapping is configured that maps the

+        <literal>root</literal> user and group as well as the unit's own user and group to themselves and

+        everything else to the <literal>nobody</literal> user and group. This is useful to securely detach

+        the user and group databases used by the unit from the rest of the system, and thus to create an

+        effective sandbox environment. All files, directories, processes, IPC objects and other resources

+        owned by users/groups not equaling <literal>root</literal> or the unit's own will stay visible from

+        within the unit but appear owned by the <literal>nobody</literal> user and group. </para>

+

+        <para>If the parameter is <literal>identity</literal>, user namespacing is set up with an identity

+        mapping for the first 65536 UIDs/GIDs. Any UIDs/GIDs above 65536 will be mapped to the

+        <literal>nobody</literal> user and group, respectively. While this does not provide UID/GID isolation,

+        since all UIDs/GIDs are chosen identically it does provide process capability isolation, and hence is

+        often a good choice if proper user namespacing with distinct UID maps is not appropriate.</para>

+

+        <para>If this mode is enabled, all unit processes are run without privileges in the host user

+        namespace (regardless if the unit's own user/group is <literal>root</literal> or not). Specifically

+        this means that the process will have zero process capabilities on the host's user namespace, but

+        full capabilities within the service's user namespace. Settings such as

+        <varname>CapabilityBoundingSet=</varname> will affect only the latter, and there's no way to acquire

+        additional capabilities in the host's user namespace.</para>

         <para>When this setting is set up by a per-user instance of the service manager, the mapping of the

         <literal>root</literal> user and group to itself is omitted (unless the user manager is root).

diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c

index b0d9402e53ca7..1aeba38df60a6 100644

--- a/src/core/dbus-execute.c

+++ b/src/core/dbus-execute.c

@@ -58,6 +58,7 @@ static BUS_DEFINE_PROPERTY_GET(property_get_mount_apivfs, "b", ExecContext, exec

 static BUS_DEFINE_PROPERTY_GET2(property_get_ioprio_class, "i", ExecContext, exec_context_get_effective_ioprio, ioprio_prio_class);

 static BUS_DEFINE_PROPERTY_GET2(property_get_ioprio_priority, "i", ExecContext, exec_context_get_effective_ioprio, ioprio_prio_data);

 static BUS_DEFINE_PROPERTY_GET_GLOBAL(property_get_empty_string, "s", NULL);

+static BUS_DEFINE_PROPERTY_GET_REF(property_get_private_users_ex, "s", PrivateUsers, private_users_to_string);

 static BUS_DEFINE_PROPERTY_GET_REF(property_get_syslog_level, "i", int, LOG_PRI);

 static BUS_DEFINE_PROPERTY_GET_REF(property_get_syslog_facility, "i", int, LOG_FAC);

 static BUS_DEFINE_PROPERTY_GET(property_get_cpu_affinity_from_numa, "b", ExecContext, exec_context_get_cpu_affinity_from_numa);

@@ -943,6 +944,21 @@ static int property_get_image_policy(

         return sd_bus_message_append(reply, "s", s);

 }

+static int property_get_private_users(

+                sd_bus *bus,

+                const char *path,

+                const char *interface,

+                const char *property,

+                sd_bus_message *reply,

+                void *userdata,

+                sd_bus_error *error) {

+

+        PrivateUsers *p = ASSERT_PTR(userdata);

+        int b = *p != PRIVATE_USERS_OFF;

+

+        return sd_bus_message_append_basic(reply, 'b', &b);

+}

+

 const sd_bus_vtable bus_exec_vtable[] = {

         SD_BUS_VTABLE_START(0),

         SD_BUS_PROPERTY("Environment", "as", NULL, offsetof(ExecContext, environment), SD_BUS_VTABLE_PROPERTY_CONST),

@@ -1063,7 +1079,8 @@ const sd_bus_vtable bus_exec_vtable[] = {

         SD_BUS_PROPERTY("ProtectKernelLogs", "b", bus_property_get_bool, offsetof(ExecContext, protect_kernel_logs), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("ProtectControlGroups", "b", bus_property_get_bool, offsetof(ExecContext, protect_control_groups), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("PrivateNetwork", "b", bus_property_get_bool, offsetof(ExecContext, private_network), SD_BUS_VTABLE_PROPERTY_CONST),

-        SD_BUS_PROPERTY("PrivateUsers", "b", bus_property_get_bool, offsetof(ExecContext, private_users), SD_BUS_VTABLE_PROPERTY_CONST),

+        SD_BUS_PROPERTY("PrivateUsers", "b", property_get_private_users, offsetof(ExecContext, private_users), SD_BUS_VTABLE_PROPERTY_CONST),

+        SD_BUS_PROPERTY("PrivateUsersEx", "s", property_get_private_users_ex, offsetof(ExecContext, private_users), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("PrivateMounts", "b", bus_property_get_tristate, offsetof(ExecContext, private_mounts), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("PrivateIPC", "b", bus_property_get_bool, offsetof(ExecContext, private_ipc), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("ProtectHome", "s", property_get_protect_home, offsetof(ExecContext, protect_home), SD_BUS_VTABLE_PROPERTY_CONST),

@@ -1738,6 +1755,41 @@ int bus_exec_context_set_transient_property(

         if (streq(name, "PrivateTmp"))

                 return bus_set_transient_bool(u, name, &c->private_tmp, message, flags, error);

+        if (streq(name, "PrivateUsers")) {

+                int v;

+

+                r = sd_bus_message_read(message, "b", &v);

+                if (r < 0)

+                        return r;

+

+                if (!UNIT_WRITE_FLAGS_NOOP(flags)) {

+                        c->private_users = v ? PRIVATE_USERS_SELF : PRIVATE_USERS_OFF;

+                        (void) unit_write_settingf(u, flags, name, "%s=%s", name, yes_no(v));

+                }

+

+                return 1;

+

+        } else if (streq(name, "PrivateUsersEx")) {

+                const char *s;

+                PrivateUsers t;

+

+                r = sd_bus_message_read(message, "s", &s);

+                if (r < 0)

+                        return r;

+

+                t = private_users_from_string(s);

+                if (t < 0)

+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid %s setting: %s", name, s);

+

+                if (!UNIT_WRITE_FLAGS_NOOP(flags)) {

+                        c->private_users = t;

+                        (void) unit_write_settingf(u, flags, name, "PrivateUsers=%s",

+                                                   private_users_to_string(c->private_users));

+                }

+

+                return 1;

+        }

+

         if (streq(name, "PrivateDevices"))

                 return bus_set_transient_bool(u, name, &c->private_devices, message, flags, error);

@@ -1753,9 +1805,6 @@ int bus_exec_context_set_transient_property(

         if (streq(name, "PrivateIPC"))

                 return bus_set_transient_bool(u, name, &c->private_ipc, message, flags, error);

-        if (streq(name, "PrivateUsers"))

-                return bus_set_transient_bool(u, name, &c->private_users, message, flags, error);

-

         if (streq(name, "NoNewPrivileges"))

                 return bus_set_transient_bool(u, name, &c->no_new_privileges, message, flags, error);

diff --git a/src/core/exec-invoke.c b/src/core/exec-invoke.c

index 5850a595f0475..1f4a9923df7e0 100644

--- a/src/core/exec-invoke.c

+++ b/src/core/exec-invoke.c

@@ -2080,7 +2080,7 @@ static int build_pass_environment(const ExecContext *c, char ***ret) {

         return 0;

 }

-static int setup_private_users(uid_t ouid, gid_t ogid, uid_t uid, gid_t gid) {

+static int setup_private_users(PrivateUsers private_users, uid_t ouid, gid_t ogid, uid_t uid, gid_t gid) {

         _cleanup_free_ char *uid_map = NULL, *gid_map = NULL;

         _cleanup_close_pair_ int errno_pipe[2] = EBADF_PAIR;

         _cleanup_close_ int unshare_ready_fd = -EBADF;

@@ -2099,33 +2099,48 @@ static int setup_private_users(uid_t ouid, gid_t ogid, uid_t uid, gid_t gid) {

          * For unprivileged users (i.e. without capabilities), the root to root mapping is excluded. As such, it

          * does not need CAP_SETUID to write the single line mapping to itself. */

+        if (private_users == PRIVATE_USERS_OFF)

+                return 0;

+

+        if (private_users == PRIVATE_USERS_IDENTITY) {

+                uid_map = strdup("0 0 65536\n");

+                if (!uid_map)

+                        return -ENOMEM;

         /* Can only set up multiple mappings with CAP_SETUID. */

-        if (have_effective_cap(CAP_SETUID) > 0 && uid != ouid && uid_is_valid(uid))

+        } else if (have_effective_cap(CAP_SETUID) > 0 && uid != ouid && uid_is_valid(uid)) {

                 r = asprintf(&uid_map,

                              UID_FMT " " UID_FMT " 1\n"     /* Map $OUID → $OUID */

                              UID_FMT " " UID_FMT " 1\n",    /* Map $UID → $UID */

                              ouid, ouid, uid, uid);

-        else

+                if (r < 0)

+                        return -ENOMEM;

+        } else {

                 r = asprintf(&uid_map,

                              UID_FMT " " UID_FMT " 1\n",    /* Map $OUID → $OUID */

                              ouid, ouid);

+                if (r < 0)

+                        return -ENOMEM;

+        }

-        if (r < 0)

-                return -ENOMEM;

-

+        if (private_users == PRIVATE_USERS_IDENTITY) {

+                gid_map = strdup("0 0 65536\n");

+                if (!gid_map)

+                        return -ENOMEM;

         /* Can only set up multiple mappings with CAP_SETGID. */

-        if (have_effective_cap(CAP_SETGID) > 0 && gid != ogid && gid_is_valid(gid))

+        } else if (have_effective_cap(CAP_SETGID) > 0 && gid != ogid && gid_is_valid(gid)) {

                 r = asprintf(&gid_map,

                              GID_FMT " " GID_FMT " 1\n"     /* Map $OGID → $OGID */

                              GID_FMT " " GID_FMT " 1\n",    /* Map $GID → $GID */

                              ogid, ogid, gid, gid);

-        else

+                if (r < 0)

+                        return -ENOMEM;

+        } else {

                 r = asprintf(&gid_map,

                              GID_FMT " " GID_FMT " 1\n",    /* Map $OGID -> $OGID */

                              ogid, ogid);

-

-        if (r < 0)

-                return -ENOMEM;

+                if (r < 0)

+                        return -ENOMEM;

+        }

         /* Create a communication channel so that the parent can tell the child when it finished creating the user

          * namespace. */

@@ -2236,7 +2251,7 @@ static int setup_private_users(uid_t ouid, gid_t ogid, uid_t uid, gid_t gid) {

         if (r != EXIT_SUCCESS) /* If something strange happened with the child, let's consider this fatal, too */

                 return -EIO;

-        return 0;

+        return 1;

 }

 static int create_many_symlinks(const char *root, const char *source, char **symlinks) {

@@ -3865,7 +3880,7 @@ static bool exec_context_need_unprivileged_private_users(

         if (params->runtime_scope != RUNTIME_SCOPE_USER)

                 return false;

-        return context->private_users ||

+        return context->private_users != PRIVATE_USERS_OFF ||

                context->private_tmp ||

                context->private_devices ||

                context->private_network ||

@@ -4720,18 +4735,23 @@ int exec_invoke(

                 /* If we're unprivileged, set up the user namespace first to enable use of the other namespaces.

                  * Users with CAP_SYS_ADMIN can set up user namespaces last because they will be able to

                  * set up all of the other namespaces (i.e. network, mount, UTS) without a user namespace. */

+                PrivateUsers pu = context->private_users;

+                if (pu == PRIVATE_USERS_OFF)

+                        pu = PRIVATE_USERS_SELF;

-                r = setup_private_users(saved_uid, saved_gid, uid, gid);

+                r = setup_private_users(pu, saved_uid, saved_gid, uid, gid);

                 /* If it was requested explicitly and we can't set it up, fail early. Otherwise, continue and let

                  * the actual requested operations fail (or silently continue). */

-                if (r < 0 && context->private_users) {

+                if (r < 0 && context->private_users != PRIVATE_USERS_OFF) {

                         *exit_status = EXIT_USER;

                         return log_exec_error_errno(context, params, r, "Failed to set up user namespacing for unprivileged user: %m");

                 }

                 if (r < 0)

                         log_exec_info_errno(context, params, r, "Failed to set up user namespacing for unprivileged user, ignoring: %m");

-                else

+                else {

+                        assert(r > 0);

                         userns_set_up = true;

+                }

         }

         if (exec_needs_network_namespace(context) && runtime && runtime->shared && runtime->shared->netns_storage_socket[0] >= 0) {

@@ -4844,8 +4864,8 @@ int exec_invoke(

          * case of mount namespaces being less privileged when the mount point list is copied from a

          * different user namespace). */

-        if (needs_sandboxing && context->private_users && !userns_set_up) {

-                r = setup_private_users(saved_uid, saved_gid, uid, gid);

+        if (needs_sandboxing && !userns_set_up) {

+                r = setup_private_users(context->private_users, saved_uid, saved_gid, uid, gid);

                 if (r < 0) {

                         *exit_status = EXIT_USER;

                         return log_exec_error_errno(context, params, r, "Failed to set up user namespacing: %m");

diff --git a/src/core/execute-serialize.c b/src/core/execute-serialize.c

index 41b31e9ae3f21..867a74419da98 100644

--- a/src/core/execute-serialize.c

+++ b/src/core/execute-serialize.c

@@ -1880,7 +1880,7 @@ static int exec_context_serialize(const ExecContext *c, FILE *f) {

         if (r < 0)

                 return r;

-        r = serialize_bool_elide(f, "exec-context-private-users", c->private_users);

+        r = serialize_item(f, "exec-context-private-users", private_users_to_string(c->private_users));

         if (r < 0)

                 return r;

@@ -2772,10 +2772,9 @@ static int exec_context_deserialize(ExecContext *c, FILE *f) {

                                 return r;

                         c->private_network = r;

                 } else if ((val = startswith(l, "exec-context-private-users="))) {

-                        r = parse_boolean(val);

-                        if (r < 0)

-                                return r;

-                        c->private_users = r;

+                        c->private_users = private_users_from_string(val);

+                        if (c->private_users < 0)

+                                return -EINVAL;

                 } else if ((val = startswith(l, "exec-context-private-ipc="))) {

                         r = parse_boolean(val);

                         if (r < 0)

diff --git a/src/core/execute.c b/src/core/execute.c

index f74665fcd7b9a..c2241803b763a 100644

--- a/src/core/execute.c

+++ b/src/core/execute.c

@@ -973,7 +973,7 @@ void exec_context_dump(const ExecContext *c, FILE* f, const char *prefix) {

                 prefix, yes_no(c->protect_clock),

                 prefix, yes_no(c->protect_control_groups),

                 prefix, yes_no(c->private_network),

-                prefix, yes_no(c->private_users),

+                prefix, private_users_to_string(c->private_users),

                 prefix, protect_home_to_string(c->protect_home),

                 prefix, protect_system_to_string(c->protect_system),

                 prefix, yes_no(exec_context_get_effective_mount_apivfs(c)),

diff --git a/src/core/execute.h b/src/core/execute.h

index 107ae2524387c..603feac0d6027 100644

--- a/src/core/execute.h

+++ b/src/core/execute.h

@@ -317,7 +317,7 @@ struct ExecContext {

         bool private_tmp;

         bool private_network;

         bool private_devices;

-        bool private_users;

+        PrivateUsers private_users;

         bool private_ipc;

         bool protect_kernel_tunables;

         bool protect_kernel_modules;

diff --git a/src/core/load-fragment-gperf.gperf.in b/src/core/load-fragment-gperf.gperf.in

index df219d86dfeaa..213b36ec05eee 100644

--- a/src/core/load-fragment-gperf.gperf.in

+++ b/src/core/load-fragment-gperf.gperf.in

@@ -130,7 +130,7 @@

 {{type}}.IPCNamespacePath,                 config_parse_unit_path_printf,               0,                                  offsetof({{type}}, exec_context.ipc_namespace_path)

 {{type}}.LogNamespace,                     config_parse_log_namespace,                  0,                                  offsetof({{type}}, exec_context)

 {{type}}.PrivateNetwork,                   config_parse_bool,                           0,                                  offsetof({{type}}, exec_context.private_network)

-{{type}}.PrivateUsers,                     config_parse_bool,                           0,                                  offsetof({{type}}, exec_context.private_users)

+{{type}}.PrivateUsers,                     config_parse_private_users,                  0,                                  offsetof({{type}}, exec_context.private_users)

 {{type}}.PrivateMounts,                    config_parse_tristate,                       0,                                  offsetof({{type}}, exec_context.private_mounts)

 {{type}}.PrivateIPC,                       config_parse_bool,                           0,                                  offsetof({{type}}, exec_context.private_ipc)

 {{type}}.ProtectSystem,                    config_parse_protect_system,                 0,                                  offsetof({{type}}, exec_context.protect_system)

diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c

index a1a116a439774..23b5a66742da7 100644

--- a/src/core/load-fragment.c

+++ b/src/core/load-fragment.c

@@ -132,6 +132,7 @@ DEFINE_CONFIG_PARSE_ENUM(config_parse_collect_mode, collect_mode, CollectMode, "

 DEFINE_CONFIG_PARSE_ENUM(config_parse_device_policy, cgroup_device_policy, CGroupDevicePolicy, "Failed to parse device policy");

 DEFINE_CONFIG_PARSE_ENUM(config_parse_exec_keyring_mode, exec_keyring_mode, ExecKeyringMode, "Failed to parse keyring mode");

 DEFINE_CONFIG_PARSE_ENUM(config_parse_protect_proc, protect_proc, ProtectProc, "Failed to parse /proc/ protection mode");

+DEFINE_CONFIG_PARSE_ENUM(config_parse_private_users, private_users, PrivateUsers, "Failed to parse private users mode");

 DEFINE_CONFIG_PARSE_ENUM(config_parse_proc_subset, proc_subset, ProcSubset, "Failed to parse /proc/ subset mode");

 DEFINE_CONFIG_PARSE_ENUM(config_parse_exec_utmp_mode, exec_utmp_mode, ExecUtmpMode, "Failed to parse utmp mode");

 DEFINE_CONFIG_PARSE_ENUM(config_parse_job_mode, job_mode, JobMode, "Failed to parse job mode");

diff --git a/src/core/load-fragment.h b/src/core/load-fragment.h

index 005b91510608f..b6741c9207ab0 100644

--- a/src/core/load-fragment.h

+++ b/src/core/load-fragment.h

@@ -113,6 +113,7 @@ CONFIG_PARSER_PROTOTYPE(config_parse_import_credential);

 CONFIG_PARSER_PROTOTYPE(config_parse_set_status);

 CONFIG_PARSER_PROTOTYPE(config_parse_namespace_path_strv);

 CONFIG_PARSER_PROTOTYPE(config_parse_temporary_filesystems);

+CONFIG_PARSER_PROTOTYPE(config_parse_private_users);

 CONFIG_PARSER_PROTOTYPE(config_parse_cpu_quota);

 CONFIG_PARSER_PROTOTYPE(config_parse_allowed_cpuset);

 CONFIG_PARSER_PROTOTYPE(config_parse_protect_home);

diff --git a/src/core/namespace.c b/src/core/namespace.c

index b92bb012eee31..052a4452c12b7 100644

--- a/src/core/namespace.c

+++ b/src/core/namespace.c

@@ -3080,3 +3080,11 @@ static const char* const proc_subset_table[_PROC_SUBSET_MAX] = {

 };

 DEFINE_STRING_TABLE_LOOKUP(proc_subset, ProcSubset);

+

+static const char* const private_users_table[_PRIVATE_USERS_MAX] = {

+        [PRIVATE_USERS_OFF]      = "off",

+        [PRIVATE_USERS_SELF]     = "self",

+        [PRIVATE_USERS_IDENTITY] = "identity",

+};

+

+DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(private_users, PrivateUsers, PRIVATE_USERS_SELF);

diff --git a/src/core/namespace.h b/src/core/namespace.h

index 921716bf3ec93..d10d7f440ad8b 100644

--- a/src/core/namespace.h

+++ b/src/core/namespace.h

@@ -53,6 +53,14 @@ typedef enum ProcSubset {

         _PROC_SUBSET_INVALID = -EINVAL,

 } ProcSubset;

+typedef enum PrivateUsers {

+        PRIVATE_USERS_OFF,

+        PRIVATE_USERS_SELF,

+        PRIVATE_USERS_IDENTITY,

+        _PRIVATE_USERS_MAX,

+        _PRIVATE_USERS_INVALID = -EINVAL,

+} PrivateUsers;

+

 struct BindMount {

         char *source;

         char *destination;

@@ -184,6 +192,9 @@ ProtectProc protect_proc_from_string(const char *s) _pure_;

 const char* proc_subset_to_string(ProcSubset i) _const_;

 ProcSubset proc_subset_from_string(const char *s) _pure_;

+const char* private_users_to_string(PrivateUsers i) _const_;

+PrivateUsers private_users_from_string(const char *s) _pure_;

+

 void bind_mount_free_many(BindMount *b, size_t n);

 int bind_mount_add(BindMount **b, size_t *n, const BindMount *item);

diff --git a/src/shared/bus-unit-util.c b/src/shared/bus-unit-util.c

index da83422524fa4..ff24ac5dd40dc 100644

--- a/src/shared/bus-unit-util.c

+++ b/src/shared/bus-unit-util.c

@@ -1037,6 +1037,7 @@ static int bus_append_execute_property(sd_bus_message *m, const char *field, con

                               "SyslogIdentifier",

                               "ProtectSystem",

                               "ProtectHome",

+                              "PrivateUsersEx",

                               "SELinuxContext",

                               "RootImage",

                               "RootVerity",

diff --git a/test/units/TEST-07-PID1.private-users.sh b/test/units/TEST-07-PID1.private-users.sh

new file mode 100755

index 0000000000000..2475b5d365d59

--- /dev/null

+++ b/test/units/TEST-07-PID1.private-users.sh

@@ -0,0 +1,12 @@

+#!/usr/bin/env bash

+# SPDX-License-Identifier: LGPL-2.1-or-later

+# shellcheck disable=SC2016

+set -eux

+set -o pipefail

+

+systemd-run -p PrivateUsers=yes --wait bash -c 'test "$(cat /proc/self/uid_map)" == "         0          0          1"'

+systemd-run -p PrivateUsers=yes --wait bash -c 'test "$(cat /proc/self/gid_map)" == "         0          0          1"'

+systemd-run -p PrivateUsersEx=self --wait bash -c 'test "$(cat /proc/self/uid_map)" == "         0          0          1"'

+systemd-run -p PrivateUsersEx=self --wait bash -c 'test "$(cat /proc/self/gid_map)" == "         0          0          1"'

+systemd-run -p PrivateUsersEx=identity --wait bash -c 'test "$(cat /proc/self/uid_map)" == "         0          0      65536"'

+systemd-run -p PrivateUsersEx=identity --wait bash -c 'test "$(cat /proc/self/gid_map)" == "         0          0      65536"'