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Code Editor : mwg-expected-by-module-item.html

<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>2.1.  Getting and setting PAM_ITEMs and data</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="Linux-PAM_MWG.html" title="The Linux-PAM Module Writers' Guide"><link rel="up" href="mwg-expected-by-module.html" title="Chapter 2. What can be expected by the module"><link rel="prev" href="mwg-expected-by-module.html" title="Chapter 2. What can be expected by the module"><link rel="next" href="mwg-expected-by-module-other.html" title="2.2.  Other functions provided by libpam"></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">2.1. 
        Getting and setting <span class="emphasis"><em>PAM_ITEM</em></span>s and
        <span class="emphasis"><em>data</em></span>
      </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="mwg-expected-by-module.html">Prev</a> </td><th width="60%" align="center">Chapter 2. What can be expected by the module</th><td width="20%" align="right"> <a accesskey="n" href="mwg-expected-by-module-other.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="mwg-expected-by-module-item"></a>2.1. 
        Getting and setting <span class="emphasis"><em>PAM_ITEM</em></span>s and
        <span class="emphasis"><em>data</em></span>
      </h2></div></div></div><p>
        First, we cover what the module should expect from the
        <span class="emphasis"><em>Linux-PAM</em></span> library and a
        <span class="emphasis"><em>Linux-PAM</em></span> aware application.
        Essentially this is the <code class="filename">libpam.*</code> library.
      </p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="mwg-pam_set_data"></a>2.1.1. Set module internal data</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_modules.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">pam_set_data</b>(</code></td><td><var class="pdparam">pamh</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">module_data_name</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">data</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">(*cleanup)(pam_handle_t *pamh, void *data, int error_status)</var><code>)</code>;</td><td> </td></tr></table><div class="paramdef-list"><code>pam_handle_t *<var class="pdparam">pamh</var></code>;<br><code>const char *<var class="pdparam">module_data_name</var></code>;<br><code>void *<var class="pdparam">data</var></code>;<br><code>void <var class="pdparam">(*cleanup)(pam_handle_t *pamh, void *data, int error_status)</var></code>;</div><div class="funcprototype-spacer"> </div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_set_data-description"></a>2.1.1.1. DESCRIPTION</h4></div></div></div><p>
      The <code class="function">pam_set_data</code> function associates a pointer
      to an object with the (hopefully) unique string
      <span class="emphasis"><em>module_data_name</em></span> in the PAM context specified
      by the <span class="emphasis"><em>pamh</em></span> argument.
    </p><p>
      PAM modules may be dynamically loadable objects. In general such files
      should not contain <span class="emphasis"><em>static</em></span> variables. This function
      and its counterpart
      <span class="citerefentry"><span class="refentrytitle">pam_get_data</span>(3)</span>,
      provide a mechanism for a module to associate some data with
      the handle <span class="emphasis"><em>pamh</em></span>. Typically a module will call the
      <code class="function">pam_set_data</code> function to register some data
       under a (hopefully) unique <span class="emphasis"><em>module_data_name</em></span>.
       The data is available for use by other modules too but
       <span class="emphasis"><em>not</em></span> by an application. Since this functions
       stores only a pointer to the <span class="emphasis"><em>data</em></span>, the module
       should not modify or free the content of it.
    </p><p>
      The function <code class="function">cleanup()</code> is associated with the
      <span class="emphasis"><em>data</em></span> and, if non-NULL, it is called when this
      data is over-written or following a call to
      <span class="citerefentry"><span class="refentrytitle">pam_end</span>(3)</span>.
    </p><p>
      The <span class="emphasis"><em>error_status</em></span> argument is used to indicate
      to the module the sort of action it is to take in cleaning this data
      item. As an example, Kerberos creates a ticket file during the
      authentication phase, this file might be associated with a data item.
      When
      <span class="citerefentry"><span class="refentrytitle">pam_end</span>(3)</span>
      is called by the module, the <span class="emphasis"><em>error_status</em></span>
      carries the return value of the
      <span class="citerefentry"><span class="refentrytitle">pam_authenticate</span>(3)</span>
     or other <span class="emphasis"><em>libpam</em></span> function as appropriate. Based
     on this value the Kerberos module may choose to delete the ticket file
     (<span class="emphasis"><em>authentication failure</em></span>) or leave it in place.
   </p><p>
     The <span class="emphasis"><em>error_status</em></span> may have been logically
     OR'd with either of the following two values:
   </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_DATA_REPLACE</span></dt><dd><p>
            When a data item is being replaced (through a second call to
            <code class="function">pam_set_data</code>) this mask is used.
            Otherwise, the call is assumed to be from
            <span class="citerefentry"><span class="refentrytitle">pam_end</span>(3)</span>.
          </p></dd><dt><span class="term">PAM_DATA_SILENT</span></dt><dd><p>
            Which indicates that the process would prefer to perform the
            <code class="function">cleanup()</code> quietly. That is, discourages
            logging/messages to the user.
          </p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_set_data-return_values"></a>2.1.1.2. RETURN VALUES</h4></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_BUF_ERR</span></dt><dd><p>
              Memory buffer error.
          </p></dd><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
             Data was successful stored.
          </p></dd><dt><span class="term">PAM_SYSTEM_ERR</span></dt><dd><p>
             A NULL pointer was submitted as PAM handle or the
             function was called by an application.
          </p></dd></dl></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="mwg-pam_get_data"></a>2.1.2. Get module internal data</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_modules.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">pam_get_data</b>(</code></td><td><var class="pdparam">pamh</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">module_data_name</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">data</var><code>)</code>;</td><td> </td></tr></table><div class="paramdef-list"><code>const pam_handle_t *<var class="pdparam">pamh</var></code>;<br><code>const char *<var class="pdparam">module_data_name</var></code>;<br><code>const void **<var class="pdparam">data</var></code>;</div><div class="funcprototype-spacer"> </div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_get_data-description"></a>2.1.2.1. DESCRIPTION</h4></div></div></div><p>
      This function together with the
      <span class="citerefentry"><span class="refentrytitle">pam_set_data</span>(3)</span> function
      is useful to manage module-specific data meaningful only to
      the calling PAM module.
    </p><p>
      The <code class="function">pam_get_data</code> function looks up the
      object associated with the (hopefully) unique string
      <span class="emphasis"><em>module_data_name</em></span> in the PAM context
      specified by the <span class="emphasis"><em>pamh</em></span> argument.
      A successful call to
      <code class="function">pam_get_data</code> will result in
      <span class="emphasis"><em>data</em></span> pointing to the object. Note,
      this data is <span class="emphasis"><em>not</em></span> a copy and should be
      treated as <span class="emphasis"><em>constant</em></span> by the module.
    </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_get_data-return_values"></a>2.1.2.2. RETURN VALUES</h4></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
             Data was successful retrieved.
          </p></dd><dt><span class="term">PAM_SYSTEM_ERR</span></dt><dd><p>
             A NULL pointer was submitted as PAM handle or the
             function was called by an application.
          </p></dd><dt><span class="term">PAM_NO_MODULE_DATA</span></dt><dd><p>
              Module data not found or there is an entry, but it has
              the value NULL.
          </p></dd></dl></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="mwg-pam_set_item"></a>2.1.3. Setting PAM items</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_modules.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">pam_set_item</b>(</code></td><td><var class="pdparam">pamh</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">item_type</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">item</var><code>)</code>;</td><td> </td></tr></table><div class="paramdef-list"><code>pam_handle_t *<var class="pdparam">pamh</var></code>;<br><code>int <var class="pdparam">item_type</var></code>;<br><code>const void *<var class="pdparam">item</var></code>;</div><div class="funcprototype-spacer"> </div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_set_item-description"></a>2.1.3.1. DESCRIPTION</h4></div></div></div><p>
      The <code class="function">pam_set_item</code> function allows applications
      and PAM service modules to access and to update PAM informations
      of <span class="emphasis"><em>item_type</em></span>. For this a copy
      of the object pointed to by the <span class="emphasis"><em>item</em></span> argument
      is created. The following <span class="emphasis"><em>item_type</em></span>s are
      supported:
   </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_SERVICE</span></dt><dd><p>
            The service name (which identifies that PAM stack that
            the PAM functions will use to authenticate the program).
          </p></dd><dt><span class="term">PAM_USER</span></dt><dd><p>
            The username of the entity under whose identity service
            will be given. That is, following authentication,
            <span class="emphasis"><em>PAM_USER</em></span> identifies the local entity
            that gets to use the service. Note, this value can be mapped
            from something (eg., "anonymous") to something else (eg.
            "guest119") by any module in the PAM stack. As such an
            application should consult the value of
            <span class="emphasis"><em>PAM_USER</em></span> after each call to a PAM function.
          </p></dd><dt><span class="term">PAM_USER_PROMPT</span></dt><dd><p>
            The string used when prompting for a user's name. The default
            value for this string is a localized version of "login: ".
          </p></dd><dt><span class="term">PAM_TTY</span></dt><dd><p>
            The terminal name: prefixed by <code class="filename">/dev/</code> if
            it is a device file; for graphical, X-based, applications the
            value for this item should be the
            <span class="emphasis"><em>$DISPLAY</em></span> variable.
          </p></dd><dt><span class="term">PAM_RUSER</span></dt><dd><p>
            The requesting user name: local name for a locally
            requesting user or a remote user name for a remote
            requesting user.
          </p><p>
            Generally an application or module will attempt to supply
            the value that is most strongly authenticated (a local account
            before a remote one. The level of trust in this value is
            embodied in the actual authentication stack associated with
            the application, so it is ultimately at the discretion of the
            system administrator.
          </p><p>
            <span class="emphasis"><em>PAM_RUSER@PAM_RHOST</em></span> should always identify
             the requesting user. In some cases,
             <span class="emphasis"><em>PAM_RUSER</em></span> may be NULL. In such situations,
             it is unclear who the requesting entity is.
          </p></dd><dt><span class="term">PAM_RHOST</span></dt><dd><p>
            The requesting hostname (the hostname of the machine from
            which the <span class="emphasis"><em>PAM_RUSER</em></span> entity is requesting
            service). That is <span class="emphasis"><em>PAM_RUSER@PAM_RHOST</em></span>
            does identify the requesting user. In some applications,
            <span class="emphasis"><em>PAM_RHOST</em></span> may be NULL. In such situations,
            it is unclear where the authentication request is originating
            from.
          </p></dd><dt><span class="term">PAM_AUTHTOK</span></dt><dd><p>
            The authentication token (often a password). This token
            should be ignored by all module functions besides
            <span class="citerefentry"><span class="refentrytitle">pam_sm_authenticate</span>(3)</span> and
            <span class="citerefentry"><span class="refentrytitle">pam_sm_chauthtok</span>(3)</span>.
            In the former function it is used to pass the most recent
            authentication token from one stacked module to another. In
            the latter function the token is used for another purpose.
            It contains the currently active authentication token.
          </p></dd><dt><span class="term">PAM_OLDAUTHTOK</span></dt><dd><p>
            The old authentication token. This token should be ignored
            by all module functions except
            <span class="citerefentry"><span class="refentrytitle">pam_sm_chauthtok</span>(3)</span>.
          </p></dd><dt><span class="term">PAM_CONV</span></dt><dd><p>
            The pam_conv structure. See
            <span class="citerefentry"><span class="refentrytitle">pam_conv</span>(3)</span>.
          </p></dd></dl></div><p>
     The following additional items are specific to Linux-PAM and should not be used in
     portable applications:
   </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_FAIL_DELAY</span></dt><dd><p>
            A function pointer to redirect centrally managed
            failure delays. See
            <span class="citerefentry"><span class="refentrytitle">pam_fail_delay</span>(3)</span>.
          </p></dd><dt><span class="term">PAM_XDISPLAY</span></dt><dd><p>
            The name of the X display.  For graphical, X-based applications the
	    value for this item should be the <span class="emphasis"><em>$DISPLAY</em></span>
	    variable.  This value may be used independently of
	    <span class="emphasis"><em>PAM_TTY</em></span> for passing the
	    name of the display.
          </p></dd><dt><span class="term">PAM_XAUTHDATA</span></dt><dd><p>
            A pointer to a structure containing the X authentication data
	    required to make a connection to the display specified by
	    <span class="emphasis"><em>PAM_XDISPLAY</em></span>, if such information is
	    necessary.  See
            <span class="citerefentry"><span class="refentrytitle">pam_xauth_data</span>(3)</span>.
          </p></dd><dt><span class="term">PAM_AUTHTOK_TYPE</span></dt><dd><p>
            The default action is for the module to use the
            following prompts when requesting passwords:
            "New UNIX password: " and "Retype UNIX password: ".
            The example word <span class="emphasis"><em>UNIX</em></span> can
            be replaced with this item, by default it is empty.
            This item is used by <span class="citerefentry"><span class="refentrytitle">pam_get_authtok</span>(3)</span>.
          </p></dd></dl></div><p>
      For all <span class="emphasis"><em>item_type</em></span>s, other than PAM_CONV and
      PAM_FAIL_DELAY, <span class="emphasis"><em>item</em></span> is a pointer to a &lt;NUL&gt;
      terminated character string. In the case of PAM_CONV,
      <span class="emphasis"><em>item</em></span> points to an initialized
      <span class="emphasis"><em>pam_conv</em></span> structure. In the case of
      PAM_FAIL_DELAY, <span class="emphasis"><em>item</em></span> is a function pointer:
      <code class="function">void (*delay_fn)(int retval, unsigned usec_delay, void *appdata_ptr)</code>
    </p><p>
      Both, PAM_AUTHTOK and PAM_OLDAUTHTOK, will be reseted before
      returning to the application. Which means an application is not
      able to access the authentication tokens.
    </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_set_item-return_values"></a>2.1.3.2. RETURN VALUES</h4></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_BAD_ITEM</span></dt><dd><p>
             The application attempted to set an undefined or inaccessible
             item.
          </p></dd><dt><span class="term">PAM_BUF_ERR</span></dt><dd><p>
              Memory buffer error.
          </p></dd><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
             Data was successful updated.
          </p></dd><dt><span class="term">PAM_SYSTEM_ERR</span></dt><dd><p>
             The <span class="emphasis"><em>pam_handle_t</em></span> passed as first
             argument was invalid.
          </p></dd></dl></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="mwg-pam_get_item"></a>2.1.4. Getting PAM items</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_modules.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">pam_get_item</b>(</code></td><td><var class="pdparam">pamh</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">item_type</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">item</var><code>)</code>;</td><td> </td></tr></table><div class="paramdef-list"><code>const pam_handle_t *<var class="pdparam">pamh</var></code>;<br><code>int <var class="pdparam">item_type</var></code>;<br><code>const void **<var class="pdparam">item</var></code>;</div><div class="funcprototype-spacer"> </div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_get_item-description"></a>2.1.4.1. DESCRIPTION</h4></div></div></div><p>
      The <code class="function">pam_get_item</code> function allows applications
      and PAM service modules to access and retrieve PAM informations
      of <span class="emphasis"><em>item_type</em></span>. Upon successful return,
      <span class="emphasis"><em>item</em></span> contains a pointer to the value of the
      corresponding item. Note, this is a pointer to the
      <span class="emphasis"><em>actual</em></span> data and should
      <span class="emphasis"><em>not</em></span> be <span class="emphasis"><em>free()</em></span>'ed or
      over-written! The following values are supported for
      <span class="emphasis"><em>item_type</em></span>:
   </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_SERVICE</span></dt><dd><p>
            The service name (which identifies that PAM stack that
            the PAM functions will use to authenticate the program).
          </p></dd><dt><span class="term">PAM_USER</span></dt><dd><p>
            The username of the entity under whose identity service
            will be given. That is, following authentication,
            <span class="emphasis"><em>PAM_USER</em></span> identifies the local entity
            that gets to use the service. Note, this value can be mapped
            from something (eg., "anonymous") to something else (eg.
            "guest119") by any module in the PAM stack. As such an
            application should consult the value of
            <span class="emphasis"><em>PAM_USER</em></span> after each call to a PAM function.
          </p></dd><dt><span class="term">PAM_USER_PROMPT</span></dt><dd><p>
            The string used when prompting for a user's name. The default
            value for this string is a localized version of "login: ".
          </p></dd><dt><span class="term">PAM_TTY</span></dt><dd><p>
            The terminal name: prefixed by <code class="filename">/dev/</code> if
            it is a device file; for graphical, X-based, applications the
            value for this item should be the
            <span class="emphasis"><em>$DISPLAY</em></span> variable.
          </p></dd><dt><span class="term">PAM_RUSER</span></dt><dd><p>
            The requesting user name: local name for a locally
            requesting user or a remote user name for a remote
            requesting user.
          </p><p>
            Generally an application or module will attempt to supply
            the value that is most strongly authenticated (a local account
            before a remote one. The level of trust in this value is
            embodied in the actual authentication stack associated with
            the application, so it is ultimately at the discretion of the
            system administrator.
          </p><p>
            <span class="emphasis"><em>PAM_RUSER@PAM_RHOST</em></span> should always identify
             the requesting user. In some cases,
             <span class="emphasis"><em>PAM_RUSER</em></span> may be NULL. In such situations,
             it is unclear who the requesting entity is.
          </p></dd><dt><span class="term">PAM_RHOST</span></dt><dd><p>
            The requesting hostname (the hostname of the machine from
            which the <span class="emphasis"><em>PAM_RUSER</em></span> entity is requesting
            service). That is <span class="emphasis"><em>PAM_RUSER@PAM_RHOST</em></span>
            does identify the requesting user. In some applications,
            <span class="emphasis"><em>PAM_RHOST</em></span> may be NULL. In such situations,
            it is unclear where the authentication request is originating
            from.
          </p></dd><dt><span class="term">PAM_AUTHTOK</span></dt><dd><p>
            The authentication token (often a password). This token
            should be ignored by all module functions besides
            <span class="citerefentry"><span class="refentrytitle">pam_sm_authenticate</span>(3)</span> and
            <span class="citerefentry"><span class="refentrytitle">pam_sm_chauthtok</span>(3)</span>.
            In the former function it is used to pass the most recent
            authentication token from one stacked module to another. In
            the latter function the token is used for another purpose.
            It contains the currently active authentication token.
          </p></dd><dt><span class="term">PAM_OLDAUTHTOK</span></dt><dd><p>
            The old authentication token. This token should be ignored
            by all module functions except
            <span class="citerefentry"><span class="refentrytitle">pam_sm_chauthtok</span>(3)</span>.
          </p></dd><dt><span class="term">PAM_CONV</span></dt><dd><p>
            The pam_conv structure. See
            <span class="citerefentry"><span class="refentrytitle">pam_conv</span>(3)</span>.
          </p></dd></dl></div><p>
     The following additional items are specific to Linux-PAM and should not be used in
     portable applications:
   </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_FAIL_DELAY</span></dt><dd><p>
            A function pointer to redirect centrally managed
            failure delays. See
            <span class="citerefentry"><span class="refentrytitle">pam_fail_delay</span>(3)</span>.
          </p></dd><dt><span class="term">PAM_XDISPLAY</span></dt><dd><p>
            The name of the X display.  For graphical, X-based applications the
	    value for this item should be the <span class="emphasis"><em>$DISPLAY</em></span>
	    variable.  This value may be used independently of
	    <span class="emphasis"><em>PAM_TTY</em></span> for passing the
	    name of the display.
          </p></dd><dt><span class="term">PAM_XAUTHDATA</span></dt><dd><p>
            A pointer to a structure containing the X authentication data
	    required to make a connection to the display specified by
	    <span class="emphasis"><em>PAM_XDISPLAY</em></span>, if such information is
	    necessary.  See
            <span class="citerefentry"><span class="refentrytitle">pam_xauth_data</span>(3)</span>.
          </p></dd><dt><span class="term">PAM_AUTHTOK_TYPE</span></dt><dd><p>
            The default action is for the module to use the
            following prompts when requesting passwords:
            "New UNIX password: " and "Retype UNIX password: ".
            The example word <span class="emphasis"><em>UNIX</em></span> can
            be replaced with this item, by default it is empty.
            This item is used by <span class="citerefentry"><span class="refentrytitle">pam_get_authtok</span>(3)</span>.
          </p></dd></dl></div><p>
      If a service module wishes to obtain the name of the user,
      it should not use this function, but instead perform a call to
      <span class="citerefentry"><span class="refentrytitle">pam_get_user</span>(3)</span>.
    </p><p>
      Only a service module is privileged to read the
      authentication tokens, PAM_AUTHTOK and PAM_OLDAUTHTOK.
    </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_get_item-return_values"></a>2.1.4.2. RETURN VALUES</h4></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_BAD_ITEM</span></dt><dd><p>
             The application attempted to set an undefined or inaccessible
             item.
          </p></dd><dt><span class="term">PAM_BUF_ERR</span></dt><dd><p>
              Memory buffer error.
          </p></dd><dt><span class="term">PAM_PERM_DENIED</span></dt><dd><p>
             The value of <span class="emphasis"><em>item</em></span> was NULL.
          </p></dd><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
             Data was successful updated.
          </p></dd><dt><span class="term">PAM_SYSTEM_ERR</span></dt><dd><p>
             The <span class="emphasis"><em>pam_handle_t</em></span> passed as first
             argument was invalid.
          </p></dd></dl></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="mwg-pam_get_user"></a>2.1.5. Get user name</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_modules.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">pam_get_user</b>(</code></td><td><var class="pdparam">pamh</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">user</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">prompt</var><code>)</code>;</td><td> </td></tr></table><div class="paramdef-list"><code>const pam_handle_t *<var class="pdparam">pamh</var></code>;<br><code>const char **<var class="pdparam">user</var></code>;<br><code>const char *<var class="pdparam">prompt</var></code>;</div><div class="funcprototype-spacer"> </div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_get_user-description"></a>2.1.5.1. DESCRIPTION</h4></div></div></div><p>
      The <code class="function">pam_get_user</code> function returns the
      name of the user specified by
      <span class="citerefentry"><span class="refentrytitle">pam_start</span>(3)</span>. If no user was specified it what
      <code class="function">pam_get_item (pamh, PAM_USER, ... );</code> would
      have returned. If this is NULL it obtains the username via the
      <span class="citerefentry"><span class="refentrytitle">pam_conv</span>(3)</span> mechanism, it prompts the user with the first
      non-NULL string in the following list:
    </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
          The <span class="emphasis"><em>prompt</em></span> argument passed to the function.
        </p></li><li class="listitem"><p>
          What is returned by pam_get_item (pamh, PAM_USER_PROMPT, ... );
        </p></li><li class="listitem"><p>
          The default prompt: "login: "
        </p></li></ul></div><p>
      By whatever means the username is obtained, a pointer to it is
      returned as the contents of <span class="emphasis"><em>*user</em></span>. Note,
      this memory should <span class="emphasis"><em>not</em></span> be
      <span class="emphasis"><em>free()</em></span>'d or <span class="emphasis"><em>modified</em></span>
      by the module.
    </p><p>
      This function sets the <span class="emphasis"><em>PAM_USER</em></span> item
      associated with the
      <span class="citerefentry"><span class="refentrytitle">pam_set_item</span>(3)</span> and
      <span class="citerefentry"><span class="refentrytitle">pam_get_item</span>(3)</span> functions.
    </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_get_user-return_values"></a>2.1.5.2. RETURN VALUES</h4></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
             User name was successful retrieved.
          </p></dd><dt><span class="term">PAM_SYSTEM_ERR</span></dt><dd><p>
             A NULL pointer was submitted.
          </p></dd><dt><span class="term">PAM_CONV_ERR</span></dt><dd><p>
             The conversation method supplied by the
             application failed to obtain the username.
          </p></dd></dl></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="mwg-pam_conv"></a>2.1.6. The conversation function</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_appl.h&gt;</pre></div><pre class="programlisting">
struct pam_message {
    int msg_style;
    const char *msg;
};

struct pam_response {
    char *resp;
    int resp_retcode;
};

struct pam_conv {
    int (*conv)(int num_msg, const struct pam_message **msg,
                struct pam_response **resp, void *appdata_ptr);
    void *appdata_ptr;
};
  </pre><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_conv-description"></a>2.1.6.1. DESCRIPTION</h4></div></div></div><p>
      The PAM library uses an application-defined callback to allow
      a direct communication between a loaded module and the application.
      This callback is specified by the
      <span class="emphasis"><em>struct pam_conv</em></span> passed to
      <span class="citerefentry"><span class="refentrytitle">pam_start</span>(3)</span>
      at the start of the transaction.
    </p><p>
      When a module calls the referenced conv() function, the argument
      <span class="emphasis"><em>appdata_ptr</em></span> is set to the second element of
      this structure.
    </p><p>
      The other arguments of a call to conv() concern the information
      exchanged by module and application. That is to say,
      <span class="emphasis"><em>num_msg</em></span> holds the length of the array of
      pointers, <span class="emphasis"><em>msg</em></span>. After a successful return, the
      pointer <span class="emphasis"><em>resp</em></span> points to an array of pam_response
      structures, holding the application supplied text. The
      <span class="emphasis"><em>resp_retcode</em></span> member of this struct is unused and
      should be set to zero. It is the caller's responsibility to release
      both, this array and the responses themselves, using
      <span class="citerefentry"><span class="refentrytitle">free</span>(3)</span>. Note, <span class="emphasis"><em>*resp</em></span> is a
      <span class="emphasis"><em>struct pam_response</em></span> array and not an array of
      pointers.
    </p><p>
      The number of responses is always equal to the
      <span class="emphasis"><em>num_msg</em></span> conversation function argument.
      This does require that the response array is
      <span class="citerefentry"><span class="refentrytitle">free</span>(3)</span>'d after
      every call to the conversation function.  The index of the
      responses corresponds directly to the prompt index in the
      pam_message array.
    </p><p>
      On failure, the conversation function should release any resources
      it has allocated, and return one of the predefined PAM error codes.
    </p><p>
      Each message can have one of four types, specified by the
      <span class="emphasis"><em>msg_style</em></span> member of
      <span class="emphasis"><em>struct pam_message</em></span>:
    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_PROMPT_ECHO_OFF</span></dt><dd><p>
             Obtain a string without echoing any text.
          </p></dd><dt><span class="term">PAM_PROMPT_ECHO_ON</span></dt><dd><p>
            Obtain a string whilst echoing text.
          </p></dd><dt><span class="term">PAM_ERROR_MSG</span></dt><dd><p>
            Display an error message.
          </p></dd><dt><span class="term">PAM_TEXT_INFO</span></dt><dd><p>
            Display some text.
          </p></dd></dl></div><p>
      The point of having an array of messages is that it becomes possible
      to pass a number of things to the application in a single call from
      the module. It can also be convenient for the application that related
      things come at once: a windows based application can then present a
      single form with many messages/prompts on at once.
    </p><p>
      In passing, it is worth noting that there is a descrepency between
      the way Linux-PAM handles the const struct pam_message **msg
      conversation function argument from the way that Solaris' PAM
      (and derivitives, known to include HP/UX, are there others?) does.
      Linux-PAM interprets the msg argument as entirely equivalent to the
      following prototype
  const struct pam_message *msg[] (which, in spirit, is consistent with
  the commonly used prototypes for argv argument to the familiar main()
  function: char **argv; and char *argv[]). Said another way Linux-PAM
  interprets the msg argument as a pointer to an array of num_msg read
  only 'struct pam_message' pointers.  Solaris' PAM implementation
  interprets this argument as a pointer to a pointer to an array of
  num_msg pam_message structures.  Fortunately, perhaps, for most
  module/application developers when num_msg has a value of one these
  two definitions are entirely equivalent. Unfortunately, casually
  raising this number to two has led to unanticipated compatibility
  problems.
    </p><p>
  For what its worth the two known module writer work-arounds for trying
  to maintain source level compatibility with both PAM implementations
  are:
    </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
          never call the conversation function with num_msg greater than one.
        </p></li><li class="listitem"><p>
          set up msg as doubly referenced so both types of conversation
          function can find the messages. That is, make
        </p><pre class="programlisting">
       msg[n] = &amp; (( *msg )[n])
       </pre></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mwg-pam_conv-return_values"></a>2.1.6.2. RETURN VALUES</h4></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_BUF_ERR</span></dt><dd><p>
             Memory buffer error.
          </p></dd><dt><span class="term">PAM_CONV_ERR</span></dt><dd><p>
             Conversation failure. The application should not set
             <span class="emphasis"><em>*resp</em></span>.
          </p></dd><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
             Success.
          </p></dd></dl></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="adg-pam_putenv"></a>2.1.7. Set or change PAM environment variable</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_appl.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">pam_putenv</b>(</code></td><td><var class="pdparam">pamh</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">name_value</var><code>)</code>;</td><td> </td></tr></table><div class="paramdef-list"><code>pam_handle_t *<var class="pdparam">pamh</var></code>;<br><code>const char *<var class="pdparam">name_value</var></code>;</div><div class="funcprototype-spacer"> </div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="adg-pam_putenv-description"></a>2.1.7.1. DESCRIPTION</h4></div></div></div><p>
      The <code class="function">pam_putenv</code> function is used to
      add or change the value of PAM environment variables as
      associated with the <span class="emphasis"><em>pamh</em></span> handle.
    </p><p>
      The <span class="emphasis"><em>pamh</em></span> argument is an authentication
      handle obtained by a prior call to pam_start().
      The <span class="emphasis"><em>name_value</em></span> argument is a single NUL
      terminated string of one of the following forms:
    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">NAME=value of variable</span></dt><dd><p>
             In this case the environment variable of the given NAME
             is set to the indicated value:
             <span class="emphasis"><em>value of variable</em></span>. If this variable
             is already known, it is overwritten. Otherwise it is added
             to the PAM environment.
          </p></dd><dt><span class="term">NAME=</span></dt><dd><p>
            This function sets the variable to an empty value. It is
            listed separately to indicate that this is the correct way
            to achieve such a setting.
          </p></dd><dt><span class="term">NAME</span></dt><dd><p>
            Without an '=' the <code class="function">pam_putenv</code>() function
            will delete the
            corresponding variable from the PAM environment.
          </p></dd></dl></div><p>
      <code class="function">pam_putenv</code>() operates on a copy of
      <span class="emphasis"><em>name_value</em></span>, which means in contrast to
      <span class="citerefentry"><span class="refentrytitle">putenv</span>(3)</span>, the application is responsible to free the data.
    </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="adg-pam_putenv-return_values"></a>2.1.7.2. RETURN VALUES</h4></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_PERM_DENIED</span></dt><dd><p>
             Argument <span class="emphasis"><em>name_value</em></span> given is a NULL pointer.
          </p></dd><dt><span class="term">PAM_BAD_ITEM</span></dt><dd><p>
             Variable requested (for deletion) is not currently set.
          </p></dd><dt><span class="term">PAM_ABORT</span></dt><dd><p>
             The <span class="emphasis"><em>pamh</em></span> handle is corrupt.
          </p></dd><dt><span class="term">PAM_BUF_ERR</span></dt><dd><p>
             Memory buffer error.
          </p></dd><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
             The environment variable was successfully updated.
          </p></dd></dl></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="adg-pam_getenv"></a>2.1.8. Get a PAM environment variable</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_appl.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">const char *<b class="fsfunc">pam_getenv</b>(</code></td><td><var class="pdparam">pamh</var>, </td><td> </td></tr><tr><td> </td><td><var class="pdparam">name</var><code>)</code>;</td><td> </td></tr></table><div class="paramdef-list"><code>pam_handle_t *<var class="pdparam">pamh</var></code>;<br><code>const char *<var class="pdparam">name</var></code>;</div><div class="funcprototype-spacer"> </div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="adg-pam_getenv-description"></a>2.1.8.1. DESCRIPTION</h4></div></div></div><p>
      The <code class="function">pam_getenv</code> function searches the
      PAM environment list as associated with the handle
      <span class="emphasis"><em>pamh</em></span> for an item that matches the string
      pointed to by <span class="emphasis"><em>name</em></span> and returns a pointer
      to the value of the environment variable. The application is
      not allowed to free the data.
    </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="adg-pam_getenv-return_values"></a>2.1.8.2. RETURN VALUES</h4></div></div></div><p>
      The <code class="function">pam_getenv</code> function returns NULL
      on failure.
    </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="adg-pam_getenvlist"></a>2.1.9. Getting the PAM environment</h3></div></div></div><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;security/pam_appl.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">char **<b class="fsfunc">pam_getenvlist</b>(</code></td><td><var class="pdparam">pamh</var><code>)</code>;</td><td> </td></tr></table><div class="paramdef-list"><code>pam_handle_t *<var class="pdparam">pamh</var></code>;</div><div class="funcprototype-spacer"> </div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="adg-pam_getenvlist-description"></a>2.1.9.1. DESCRIPTION</h4></div></div></div><p>
      The <code class="function">pam_getenvlist</code> function returns a complete
      copy of the PAM environment as associated with the handle
      <span class="emphasis"><em>pamh</em></span>. The PAM environment variables
      represent the contents of the regular environment variables of the
      authenticated user when service is granted.
    </p><p>
      The format of the memory is a malloc()'d array of char pointers,
      the last element of which is set to NULL. Each of the non-NULL
      entries in this array point to a NUL terminated and malloc()'d
      char string of the form: "<span class="emphasis"><em>name=value</em></span>".
    </p><p>
      It should be noted that this memory will never be free()'d by
      libpam. Once obtained by a call to
      <code class="function">pam_getenvlist</code>, it is the responsibility of
      the calling application to free() this memory.
    </p><p>
      It is by design, and not a coincidence, that the format and contents
      of the returned array matches that required for the third argument of
      the
      <span class="citerefentry"><span class="refentrytitle">execle</span>(3)</span> function call.
    </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="adg-pam_getenvlist-return_values"></a>2.1.9.2. RETURN VALUES</h4></div></div></div><p>
      The <code class="function">pam_getenvlist</code> function returns NULL
      on failure.
    </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="mwg-expected-by-module.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="mwg-expected-by-module.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="mwg-expected-by-module-other.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 2. What can be expected by the module </td><td width="20%" align="center"><a accesskey="h" href="Linux-PAM_MWG.html">Home</a></td><td width="40%" align="right" valign="top"> 2.2. 
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