core:sandbox: Add ProtectKernelModules= option

This is useful to turn off explicit module load and unload operations on modular
kernels. This option removes CAP_SYS_MODULE from the capability bounding set for
the unit, and installs a system call filter to block module system calls.

This option will not prevent the kernel from loading modules using the module
auto-load feature which is a system wide operation.

1 files changed, 17 insertions, 0 deletions

diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index 986985ad35..3bea4976b3 100644
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -1405,6 +1405,23 @@
       </varlistentry>
 
       <varlistentry>
+        <term><varname>ProtectKernelModules=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If true, explicit module loading will
+        be denied. This allows to turn off module load and unload operations on modular
+        kernels. It is recomended to turn this on for most services that do not need special
+        file systems or extra kernel modules to work. Default to off. Enabling this option
+        removes <constant>CAP_SYS_MODULE</constant> from the capability bounding set for
+        the unit, and installs a system call filter to block module system calls.
+        Note that limited automatic module loading due to user configuration or kernel
+        mapping tables might still happen as side effect of requested user operations,
+        both privileged and unprivileged. To disable module auto-load feature please see
+        <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        <constant>kernel.modules_disabled</constant> mechanism and
+        <filename>/proc/sys/kernel/modules_disabled</filename> documentation.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><varname>Personality=</varname></term>
 
         <listitem><para>Controls which kernel architecture <citerefentry