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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>4.1. Care about standard library calls</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.html" title="Chapter 4. Security issues of Linux-PAM"><link rel="next" href="adg-security-service-name.html" title="4.2. Choice of a service name"></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">4.1. Care about standard library calls</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="adg-security.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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In general, writers of authorization-granting applications should
assume that each module is likely to call any or
<span class="emphasis"><em>all</em></span> 'libc' functions. For 'libc' functions
that return pointers to static/dynamically allocated structures
(ie. the library allocates the memory and the user is not expected
to '<code class="function">free()</code>' it) any module call to this
function is likely to corrupt a pointer previously
obtained by the application. The application programmer should
either re-call such a 'libc' function after a call to the
<span class="emphasis"><em>Linux-PAM</em></span> library, or copy the
structure contents to some safe area of memory before passing
control to the <span class="emphasis"><em>Linux-PAM</em></span> library.
</p><p>
Two important function classes that fall into this category are
<span class="citerefentry"><span class="refentrytitle">getpwnam</span>(3)</span> and <span class="citerefentry"><span class="refentrytitle">syslog</span>(3)</span>.
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