summaryrefslogtreecommitdiff
path: root/doc/man/pam_conv.3.xml
blob: 0098ff942e9dcf93d73f5d0ba9c53db0466235ef (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
                   "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">
<refentry id='pam_conv'>
  <refmeta>
    <refentrytitle>pam_conv</refentrytitle>
    <manvolnum>3</manvolnum>
    <refmiscinfo class='setdesc'>Linux-PAM Manual</refmiscinfo>
  </refmeta>

  <refnamediv id="pam_conv-name">
    <refname>pam_conv</refname>
    <refpurpose>PAM conversation function</refpurpose>
  </refnamediv>

<!-- body begins here -->

  <refsynopsisdiv>
    <funcsynopsis id="pam_conv-synopsis">
      <funcsynopsisinfo>#include &lt;security/pam_appl.h&gt;</funcsynopsisinfo>
    </funcsynopsis>
    <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;
};
    </programlisting>
  </refsynopsisdiv>

  <refsect1 id='pam_conv-description'>
    <title>DESCRIPTION</title>
    <para>
      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
      <emphasis>struct pam_conv</emphasis> passed to
      <citerefentry>
        <refentrytitle>pam_start</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>
      at the start of the transaction.
    </para>
    <para>
      When a module calls the referenced conv() function, the argument
      <emphasis>appdata_ptr</emphasis> is set to the second element of
      this structure.
    </para>
    <para>
      The other arguments of a call to conv() concern the information
      exchanged by module and application. That is to say,
      <emphasis>num_msg</emphasis> holds the length of the array of
      pointers, <emphasis>msg</emphasis>. After a successful return, the
      pointer <emphasis>resp</emphasis> points to an array of pam_response
      structures, holding the application supplied text. The
      <emphasis>resp_retcode</emphasis> 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
      <citerefentry>
        <refentrytitle>free</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>. Note, <emphasis>*resp</emphasis> is a
      <emphasis>struct pam_response</emphasis> array and not an array of
      pointers.
    </para>
    <para>
      The number of responses is always equal to the
      <emphasis>num_msg</emphasis> conversation function argument.
      This does require that the response array is
      <citerefentry>
        <refentrytitle>free</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>'d after
      every call to the conversation function.  The index of the
      responses corresponds directly to the prompt index in the
      pam_message array.
    </para>
    <para>
      On failure, the conversation function should release any resources
      it has allocated, and return one of the predefined PAM error codes.
    </para>
    <para>
      Each message can have one of four types, specified by the
      <emphasis>msg_style</emphasis> member of
      <emphasis>struct pam_message</emphasis>:
    </para>
    <variablelist>
      <varlistentry>
        <term>PAM_PROMPT_ECHO_OFF</term>
        <listitem>
           <para>
             Obtain a string without echoing any text.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_PROMPT_ECHO_ON</term>
        <listitem>
          <para>
            Obtain a string whilst echoing text.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_ERROR_MSG</term>
        <listitem>
          <para>
            Display an error message.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_TEXT_INFO</term>
        <listitem>
          <para>
            Display some text.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
    <para>
      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.
    </para>
    <para>
      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.
    </para>
    <para>
  For what its worth the two known module writer work-arounds for trying
  to maintain source level compatibility with both PAM implementations
  are:
    </para>
   <itemizedlist>
      <listitem>
        <para>
          never call the conversation function with num_msg greater than one.
        </para>
      </listitem>
      <listitem>
        <para>
          set up msg as doubly referenced so both types of conversation
          function can find the messages. That is, make
        </para>
        <programlisting>
       msg[n] = &amp; (( *msg )[n])
       </programlisting>
      </listitem>
    </itemizedlist>
  </refsect1>

  <refsect1 id="pam_conv-return_values">
    <title>RETURN VALUES</title>
    <variablelist>
      <varlistentry>
        <term>PAM_BUF_ERR</term>
        <listitem>
           <para>
             Memory buffer error.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_CONV_ERR</term>
        <listitem>
           <para>
             Conversation failure. The application should not set
             <emphasis>*resp</emphasis>.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_SUCCESS</term>
        <listitem>
           <para>
             Success.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1 id='pam_conv-see_also'>
    <title>SEE ALSO</title>
    <para>
      <citerefentry>
        <refentrytitle>pam_start</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>,
      <citerefentry>
        <refentrytitle>pam_set_item</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>,
      <citerefentry>
        <refentrytitle>pam_get_item</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>,
      <citerefentry>
        <refentrytitle>pam_strerror</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>,
      <citerefentry>
        <refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum>
      </citerefentry>
    </para>
  </refsect1>
</refentry>