pam_namespace: secure tmp-inst directories

When using polyinstantiation for /tmp and/or /var/tmp, pam_namespace
creates subdirectories with fixed name tmp-inst. These paths should be
secured as early as possible to avoid that somehow these directories
could created and controlled by for example a malicious user or
service.

Ship a systemd service, which creates the directories early in
boot sequence with correct permissions and ownership.

Closes #111.

Signed-off-by: Topi Miettinen <toiwoton@gmail.com>

1 files changed, 62 insertions, 0 deletions

diff --git a/modules/pam_namespace/pam_namespace_helper.8.xml b/modules/pam_namespace/pam_namespace_helper.8.xml
new file mode 100644
index 00000000..2f5adbed
--- /dev/null
+++ b/modules/pam_namespace/pam_namespace_helper.8.xml
@@ -0,0 +1,62 @@
+<?xml version="1.0" encoding='UTF-8'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+	"http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">
+
+<refentry id="pam_namespace_helper">
+
+  <refmeta>
+    <refentrytitle>pam_namespace_helper</refentrytitle>
+    <manvolnum>8</manvolnum>
+    <refmiscinfo class="sectdesc">Linux-PAM Manual</refmiscinfo>
+  </refmeta>
+
+  <refnamediv id="pam_namespace_helper-name">
+    <refname>pam_namespace_helper</refname>
+    <refpurpose>Helper binary that creates home directories</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <cmdsynopsis id="pam_namespace_helper-cmdsynopsis">
+      <command>pam_namespace_helper</command>
+    </cmdsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1 id="pam_namespace_helper-description">
+
+    <title>DESCRIPTION</title>
+
+    <para>
+      <emphasis>pam_namespace_helper</emphasis> is a helper program
+      for the <emphasis>pam_namespace</emphasis> module that sets up a
+      private namespace for a session with polyinstantiated
+      directories. The helper ensures that the namespace mount points
+      exist before they are started to be used for the
+      polyinstantiated directories. Mount points for home directories
+      (lines with $HOME) are not created.
+    </para>
+
+    <para>
+      <emphasis>pam_namespace_helper</emphasis> should be run by
+      systemd at system startup. It should also be run by the
+      administrator after defining the polyinstantiated directories
+      but before enabling them.
+    </para>
+  </refsect1>
+
+  <refsect1 id='pam_namespace_helper-see_also'>
+    <title>SEE ALSO</title>
+    <para>
+      <citerefentry>
+	<refentrytitle>pam_namespace</refentrytitle><manvolnum>8</manvolnum>
+      </citerefentry>
+    </para>
+  </refsect1>
+
+  <refsect1 id='pam_namespace_helper-author'>
+    <title>AUTHOR</title>
+      <para>
+        Written by Topi Miettinen.
+      </para>
+  </refsect1>
+
+</refentry>