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<H2><A NAME="libpam-misc-section"></A> <A NAME="s5">5. A library of miscellaneous helper functions</A></H2>
<P>To aid the work of the application developer a library of
miscellaneous functions is provided. It is called <CODE>libpam_misc</CODE>,
and contains functions for allocating memory (securely), a text based
conversation function, and routines for enhancing the standard
PAM-environment variable support.
<P>
<H2><A NAME="ss5.1">5.1 Requirements</A>
</H2>
<P>The functions, structures and macros, made available by this library
can be defined by including <CODE><security/pam_misc.h></CODE>. It
should be noted that this library is specific to <B>Linux-PAM</B> and is
not referred to in the defining DCE-RFC (see
<A HREF="pam_appl-10.html#bibliography">the bibliography</A>) below.
<P>
<H2><A NAME="ss5.2">5.2 Functions supplied</A>
</H2>
<H3>Safe string duplication</H3>
<P>
<BLOCKQUOTE><CODE>
<PRE>
extern char *xstrdup(const char *s)
</PRE>
</CODE></BLOCKQUOTE>
Return a duplicate copy of the <CODE>NUL</CODE> terminated string,
<CODE>s</CODE>. <CODE>NULL</CODE> is returned if there is insufficient memory
available for the duplicate or if <CODE>s=NULL</CODE>.
<P>
<H3>A text based conversation function</H3>
<P>
<BLOCKQUOTE><CODE>
<PRE>
extern int misc_conv(int num_msg, const struct pam_message **msgm,
struct pam_response **response, void *appdata_ptr);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<P>This is a function that will prompt the user with the appropriate
comments and obtain the appropriate inputs as directed by
authentication modules.
<P>
<P>In addition to simply slotting into the appropriate <CODE>struct
pam_conv</CODE>, this function provides some time-out facilities. The
function exports five variables that can be used by an application
programmer to limit the amount of time this conversation function will
spend waiting for the user to type something.
<P>
<P>The five variables are as follows:
<DL>
<DT><B><CODE>extern time_t pam_misc_conv_warn_time;</CODE></B><DD><P>This variable contains the <EM>time</EM> (as returned by <CODE>time()</CODE>) that
the user should be first warned that the clock is ticking. By default
it has the value <CODE>0</CODE>, which indicates that no such warning will be
given. The application may set its value to sometime in the future,
but this should be done prior to passing control to the <B>Linux-PAM</B>
library.
<P>
<DT><B><CODE>extern const char *pam_misc_conv_warn_line;</CODE></B><DD><P>Used in conjuction with <CODE>pam_misc_conv_warn_time</CODE>, this variable is
a pointer to the string that will be displayed when it becomes time to
warn the user that the timeout is approaching. Its default value is
``..\a.Time is running out...\n'', but this can be changed
by the application prior to passing control to <B>Linux-PAM</B>.
<P>
<DT><B><CODE>extern time_t pam_misc_conv_die_time;</CODE></B><DD><P>This variable contains the <EM>time</EM> (as returned by <CODE>time()</CODE>) that
the conversation will time out. By default it has the value <CODE>0</CODE>,
which indicates that the conversation function will not timeout. The
application may set its value to sometime in the future, this should
be done prior to passing control to the <B>Linux-PAM</B> library.
<P>
<DT><B><CODE>extern const char *pam_misc_conv_die_line;</CODE></B><DD><P>Used in conjuction with <CODE>pam_misc_conv_die_time</CODE>, this variable is
a pointer to the string that will be displayed when the conversation
times out. Its default value is ``..\a.Sorry, your time is
up!\n'', but this can be changed by the application prior to
passing control to <B>Linux-PAM</B>.
<P>
<DT><B><CODE>extern int pam_misc_conv_died;</CODE></B><DD><P>Following a return from the <B>Linux-PAM</B> libraray, the value of this
variable indicates whether the conversation has timed out. A value of
<CODE>1</CODE> indicates the time-out occurred.
<P>
<DT><B><CODE>extern int (*pam_binary_handler_fn)(const union pam_u_packet_p send,
union pam_u_packet_p *receive);</CODE></B><DD><P>This function pointer is initialized to <CODE>NULL</CODE> but can be filled
with a function that provides machine-machine (hidden) message
exchange. It is intended for use with hidden authentication protocols
such as RSA or Diffie-Hellman key exchanges. (This is still under
development.)
<P>
</DL>
<P>
<H3>Transcribing an environment to that of Linux-PAM</H3>
<P>
<BLOCKQUOTE><CODE>
<PRE>
extern int pam_misc_paste_env(pam_handle_t *pamh,
const char * const * user_env);
</PRE>
</CODE></BLOCKQUOTE>
<P>This function takes the supplied list of environment pointers and
<EM>uploads</EM> its contents to the <B>Linux-PAM</B> environment. Success
is indicated by <CODE>PAM_SUCCESS</CODE>.
<P>
<H3>Saving the Linux-PAM environment for later use</H3>
<P>
<BLOCKQUOTE><CODE>
<PRE>
extern char **pam_misc_copy_env(pam_handle_t *pamh);
</PRE>
</CODE></BLOCKQUOTE>
<P>This function returns a pointer to a list of environment variables
that are a direct copy of the <B>Linux-PAM</B> environment. The memory
associated with these variables are the responsibility of the
application and should be liberated with a call to
<CODE>pam_misc_drop_env()</CODE>.
<P>
<H3>Liberating a locally saved environment</H3>
<P>
<BLOCKQUOTE><CODE>
<PRE>
extern char **pam_misc_drop_env(char **env);
</PRE>
</CODE></BLOCKQUOTE>
<P>This function is defined to complement the <CODE>pam_misc_copy_env()</CODE>
function. It liberates the memory associated with <CODE>env</CODE>,
<EM>overwriting</EM> with <CODE>0</CODE> all memory before <CODE>free()</CODE>ing it.
<P>
<H3>BSD like Linux-PAM environment variable setting</H3>
<P>
<BLOCKQUOTE><CODE>
<PRE>
extern int pam_misc_setenv(pam_handle_t *pamh, const char *name,
const char *value, int readonly);
</PRE>
</CODE></BLOCKQUOTE>
<P>This function performs a task equivalent to <CODE>pam_putenv()</CODE>, its
syntax is, however, more like the BSD style function; <CODE>setenv()</CODE>.
The <CODE>name</CODE> and <CODE>value</CODE> are concatenated with an ``<CODE>=</CODE>'' to
form a <CODE>name_value</CODE> and passed to <CODE>pam_putenv()</CODE>. If, however,
the <B>Linux-PAM</B> variable is already set, the replacement will only
be applied if the last argument, <CODE>readonly</CODE>, is zero.
<P>
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