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<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 <security/pam_modules.h></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 <security/pam_modules.h></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 <security/pam_modules.h></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 <NUL> 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 <security/pam_modules.h></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 <security/pam_modules.h></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 <security/pam_appl.h></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] = & (( *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 <security/pam_appl.h></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 <security/pam_appl.h></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 <security/pam_appl.h></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. Other functions provided by <code class="filename">libpam</code> </td></tr></table></div></body></html>