You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
97 lines
3.6 KiB
97 lines
3.6 KiB
15 years ago
|
<chapter id="security">
|
||
|
|
<title>&kppp; and security issues</title>
|
||
|
|
|
||
|
|
<para>This section is mainly for superusers (<systemitem>root</systemitem>)
|
||
|
|
people with high security demands, or simply technically interested people. It
|
||
|
|
is not necessary to read this if you only use &Linux; at home for yourself,
|
||
|
|
although you may learn a thing or two in any case.</para>
|
||
|
|
|
||
|
|
<sect1 id="security-restricting-access">
|
||
|
|
<title>Restricting access to &kppp;</title>
|
||
|
|
|
||
|
|
<para>A system administrator might want to restrict access as to who is allowed
|
||
|
|
to use &kppp;. There are two ways to accomplish this.</para>
|
||
|
|
|
||
|
|
<sect2 id="security-group-permissions">
|
||
|
|
<title>Restricting access with group permissions</title>
|
||
|
|
|
||
|
|
<para>Create a new group (you might want to name it
|
||
|
|
<systemitem>dialout</systemitem> or similar), and put every user that should be
|
||
|
|
allowed to use &kppp; into that group. Then type at the prompt:</para>
|
||
|
|
|
||
|
|
<screen><prompt>#</prompt> <userinput><command>chown</command> <option>root.dialout</option> <filename>/opt/kde/bin/kppp</filename></userinput>
|
||
|
|
<prompt>#</prompt> <userinput><command>chmod</command> <option>4750</option> <filename>/opt/kde/bin/kppp</filename></userinput>
|
||
|
|
</screen>
|
||
|
|
|
||
|
|
<para>This assumes that &kde; was installed in <filename class="directory">
|
||
|
|
/opt/kde/</filename> and that your new group is named
|
||
|
|
<systemitem>dialout</systemitem>.</para>
|
||
|
|
|
||
|
|
</sect2>
|
||
|
|
|
||
|
|
<sect2 id="security-kppps-way">
|
||
|
|
<title>Restricting access &kppp;'s way</title>
|
||
|
|
|
||
|
|
<para>Before doing anything, &kppp; checks if there is a file named
|
||
|
|
<filename>/etc/kppp.allow</filename>. If such a file exists, only users named in
|
||
|
|
this file are allowed to dial out. This file must be readable by everyone (but
|
||
|
|
of course <emphasis>NOT</emphasis> writable.) Only login names are recognized,
|
||
|
|
so you cannot use <acronym>UID</acronym>'s in this file. Here is a short
|
||
|
|
example:</para>
|
||
|
|
|
||
|
|
<screen>
|
||
|
|
# /etc/kppp.allow
|
||
|
|
# comment lines like this are ignored
|
||
|
|
# as well as empty lines
|
||
|
|
|
||
|
|
fred
|
||
|
|
karl
|
||
|
|
daisy
|
||
|
|
</screen>
|
||
|
|
|
||
|
|
<para>In the example above, only the users <systemitem>fred</systemitem>,
|
||
|
|
<systemitem>karl</systemitem> and <systemitem>daisy</systemitem> are allowed to
|
||
|
|
dial out, as well as every user with a <acronym>UID</acronym> of 0 (so you don't
|
||
|
|
have to explicitly list root in the file).</para>
|
||
|
|
|
||
|
|
</sect2>
|
||
|
|
|
||
|
|
</sect1>
|
||
|
|
|
||
|
|
<sect1 id="security-why-suid">
|
||
|
|
<title>&kppp; has the <acronym>SUID</acronym> bit on? What about
|
||
|
|
security?</title>
|
||
|
|
|
||
|
|
<para>It's virtually impossible to write a dialer without the
|
||
|
|
<acronym>SUID</acronym> bit that is both safe and easy to use for inexperienced
|
||
|
|
users. &kppp; addresses the security issues with the following strategy.</para>
|
||
|
|
|
||
|
|
<itemizedlist>
|
||
|
|
<listitem>
|
||
|
|
<para>Immediately after the program starts, &kppp; forks.</para>
|
||
|
|
</listitem>
|
||
|
|
<listitem>
|
||
|
|
<para>The master process, which handles all the <acronym>GUI</acronym> operations
|
||
|
|
(such as user interaction), drops the <acronym>SUID</acronym> state after the
|
||
|
|
fork, and runs with normal user privileges.</para>
|
||
|
|
</listitem>
|
||
|
|
<listitem>
|
||
|
|
<para>The slave process keeps its privileges, and is responsible for all
|
||
|
|
actions that need <systemitem>root</systemitem> privileges. To
|
||
|
|
keep this part safe, no &kde; or &Qt; library calls are used here, just simple
|
||
|
|
library calls. The source code for this process is short (around 500 lines) and
|
||
|
|
well documented, so it's easy for you to check it for security holes.</para>
|
||
|
|
</listitem>
|
||
|
|
<listitem>
|
||
|
|
<para>Master and slave processes communicate with standard &UNIX;
|
||
|
|
<acronym>IPC</acronym>.</para>
|
||
|
|
</listitem>
|
||
|
|
</itemizedlist>
|
||
|
|
|
||
|
|
<para>Special thanks to Harri Porten for writing this excellent piece of code.
|
||
|
|
It was thought to be impossible, but he managed it within a week.</para>
|
||
|
|
|
||
|
|
</sect1>
|
||
|
|
|
||
|
|
</chapter>
|