man: document the new RestrictSUIDSGID= setting

(cherry picked from commit 7445db6eb70e8d5989f481d0c5a08ace7047ae5b)
Related: #1687512

2 files changed, 30 insertions, 12 deletions

diff --git a/doc/TRANSIENT-SETTINGS.md b/doc/TRANSIENT-SETTINGS.md
index 0ea444b133..c2b5c0dcce 100644
--- a/doc/TRANSIENT-SETTINGS.md
+++ b/doc/TRANSIENT-SETTINGS.md
@@ -149,6 +149,7 @@ All execution-related settings are available for transient units.
 ✓ MemoryDenyWriteExecute=
 ✓ RestrictNamespaces=
 ✓ RestrictRealtime=
+✓ RestrictSUIDSGID=
 ✓ RestrictAddressFamilies=
 ✓ LockPersonality=
 ✓ LimitCPU=
diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index 87fb8b34f4..45ed1864f8 100644
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -348,18 +348,19 @@ CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
       <varlistentry>
         <term><varname>NoNewPrivileges=</varname></term>
 
-        <listitem><para>Takes a boolean argument. If true, ensures that the service process and all its children can
-        never gain new privileges through <function>execve()</function> (e.g. via setuid or setgid bits, or filesystem
-        capabilities). This is the simplest and most effective way to ensure that a process and its children can never
-        elevate privileges again. Defaults to false, but certain settings override this and ignore the value of this
-        setting.  This is the case when <varname>SystemCallFilter=</varname>,
-        <varname>SystemCallArchitectures=</varname>, <varname>RestrictAddressFamilies=</varname>,
-        <varname>RestrictNamespaces=</varname>, <varname>PrivateDevices=</varname>,
-        <varname>ProtectKernelTunables=</varname>, <varname>ProtectKernelModules=</varname>,
-        <varname>MemoryDenyWriteExecute=</varname>, <varname>RestrictRealtime=</varname>, or
-        <varname>LockPersonality=</varname> are specified. Note that even if this setting is overridden by them,
-        <command>systemctl show</command> shows the original value of this setting. Also see
-        <ulink url="https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">No New Privileges
+        <listitem><para>Takes a boolean argument. If true, ensures that the service process and all its
+        children can never gain new privileges through <function>execve()</function> (e.g. via setuid or
+        setgid bits, or filesystem capabilities). This is the simplest and most effective way to ensure that
+        a process and its children can never elevate privileges again. Defaults to false, but certain
+        settings override this and ignore the value of this setting.  This is the case when
+        <varname>SystemCallFilter=</varname>, <varname>SystemCallArchitectures=</varname>,
+        <varname>RestrictAddressFamilies=</varname>, <varname>RestrictNamespaces=</varname>,
+        <varname>PrivateDevices=</varname>, <varname>ProtectKernelTunables=</varname>,
+        <varname>ProtectKernelModules=</varname>, <varname>MemoryDenyWriteExecute=</varname>,
+        <varname>RestrictRealtime=</varname>, <varname>RestrictSUIDSGID=</varname> or
+        <varname>LockPersonality=</varname> are specified. Note that even if this setting is overridden by
+        them, <command>systemctl show</command> shows the original value of this setting. Also see <ulink
+        url="https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">No New Privileges
         Flag</ulink>.  </para></listitem>
       </varlistentry>
 
@@ -1275,6 +1276,22 @@ RestrictNamespaces=~cgroup net</programlisting>
       </varlistentry>
 
       <varlistentry>
+        <term><varname>RestrictSUIDSGID=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If set, any attempts to set the set-user-ID (SUID) or
+        set-group-ID (SGID) bits on files or directories will be denied (for details on these bits see
+        <citerefentry
+        project='man-pages'><refentrytitle>inode</refentrytitle><manvolnum>7</manvolnum></citerefentry>). If
+        running in user mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant>
+        capability (e.g. setting <varname>User=</varname>), <varname>NoNewPrivileges=yes</varname> is
+        implied. As the SUID/SGID bits are mechanisms to elevate privileges, and allows users to acquire the
+        identity of other users, it is recommended to restrict creation of SUID/SGID files to the few
+        programs that actually require them. Note that this restricts marking of any type of file system
+        object with these bits, including both regular files and directories (where the SGID is a different
+        meaning than for files, see documentation). Defaults to off.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><varname>RemoveIPC=</varname></term>
 
         <listitem><para>Takes a boolean parameter. If set, all System V and POSIX IPC objects owned by the user and