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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>4.2. Choice of a service name</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"><link rel="home" href="Linux-PAM_ADG.html" title="The Linux-PAM Application Developers' Guide"><link rel="up" href="adg-security.html" title="Chapter 4.  Security issues of Linux-PAM"><link rel="prev" href="adg-security-library-calls.html" title="4.1. Care about standard library calls"><link rel="next" href="adg-security-conv-function.html" title="4.3. The conversation function"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">4.2. Choice of a service name</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="adg-security-library-calls.html">Prev</a> </td><th width="60%" align="center">Chapter 4. 
      Security issues of <span class="emphasis"><em>Linux-PAM</em></span>
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        When picking the <span class="emphasis"><em>service-name</em></span> that
        corresponds to the first entry in the
        <span class="emphasis"><em>Linux-PAM</em></span> configuration file,
        the application programmer should <span class="emphasis"><em>avoid</em></span>
        the temptation of choosing something related to
        <code class="varname">argv[0]</code>. It is a trivial matter for any user
        to invoke any application on a system under a different name and
        this should not be permitted to cause a security breach.
      </p><p>
        In general, this is always the right advice if the program is
        setuid, or otherwise more privileged than the user that invokes
        it. In some cases, avoiding this advice is convenient, but as an
        author of such an application, you should consider well the ways
        in which your program will be installed and used. (Its often the
        case that programs are not intended to be setuid, but end up
        being installed that way for convenience. If your program falls
        into this category, don't fall into the trap of making this mistake.)
      </p><p>
        To invoke some <span class="emphasis"><em>target</em></span> application by
        another name, the user may symbolically link the target application
        with the desired name. To be precise all the user need do is,
        <span class="command"><strong>ln -s /target/application ./preferred_name</strong></span>
        and then run <span class="command"><strong>./preferred_name</strong></span>.
      </p><p>
        By studying the <span class="emphasis"><em>Linux-PAM</em></span>
        configuration file(s), an attacker can choose the
        <span class="command"><strong>preferred_name</strong></span> to be that of a service enjoying
        minimal protection; for example a game which uses
        <span class="emphasis"><em>Linux-PAM</em></span> to restrict access to
        certain hours of the day.  If the service-name were to be linked
        to the filename under which the service was invoked, it
        is clear that the user is effectively in the position of
        dictating which authentication scheme the service uses. Needless
        to say, this is not a secure situation.
      </p><p>
        The conclusion is that the application developer should carefully
        define the service-name of an application. The safest thing is to
        make it a single hard-wired name.
      </p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="adg-security-library-calls.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="adg-security.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="adg-security-conv-function.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">4.1. Care about standard library calls </td><td width="20%" align="center"><a accesskey="h" href="Linux-PAM_ADG.html">Home</a></td><td width="40%" align="right" valign="top"> 4.3. The conversation function</td></tr></table></div></body></html>