path: root/src/tls.c

/*************************************************
*     Exim - an Internet mail transport agent    *
*************************************************/

/* Copyright (c) University of Cambridge 1995 - 2018 */
/* See the file NOTICE for conditions of use and distribution. */

/* This module provides TLS (aka SSL) support for Exim. The code for OpenSSL is
based on a patch that was originally contributed by Steve Haslam. It was
adapted from stunnel, a GPL program by Michal Trojnara. The code for GNU TLS is
based on a patch contributed by Nikos Mavrogiannopoulos. Because these packages
are so very different, the functions for each are kept in separate files. The
relevant file is #included as required, after any any common functions.

No cryptographic code is included in Exim. All this module does is to call
functions from the OpenSSL or GNU TLS libraries. */


#include "exim.h"
#include "transports/smtp.h"

#if defined(MACRO_PREDEF) && defined(SUPPORT_TLS)
# ifndef USE_GNUTLS
#  include "macro_predef.h"
#  include "tls-openssl.c"
# endif
#endif

#ifndef MACRO_PREDEF

/* This module is compiled only when it is specifically requested in the
build-time configuration. However, some compilers don't like compiling empty
modules, so keep them happy with a dummy when skipping the rest. Make it
reference itself to stop picky compilers complaining that it is unused, and put
in a dummy argument to stop even pickier compilers complaining about infinite
loops. */

#ifndef SUPPORT_TLS
static void dummy(int x) { dummy(x-1); }
#else

/* Static variables that are used for buffering data by both sets of
functions and the common functions below.

We're moving away from this; GnuTLS is already using a state, which
can switch, so we can do TLS callouts during ACLs. */

static const int ssl_xfer_buffer_size = 4096;
#ifndef USE_GNUTLS
static uschar *ssl_xfer_buffer = NULL;
static int ssl_xfer_buffer_lwm = 0;
static int ssl_xfer_buffer_hwm = 0;
static int ssl_xfer_eof = FALSE;
static BOOL ssl_xfer_error = FALSE;
#endif

uschar *tls_channelbinding_b64 = NULL;


/*************************************************
*       Expand string; give error on failure     *
*************************************************/

/* If expansion is forced to fail, set the result NULL and return TRUE.
Other failures return FALSE. For a server, an SMTP response is given.

Arguments:
  s         the string to expand; if NULL just return TRUE
  name      name of string being expanded (for error)
  result    where to put the result

Returns:    TRUE if OK; result may still be NULL after forced failure
*/

static BOOL
expand_check(const uschar *s, const uschar *name, uschar **result, uschar ** errstr)
{
if (!s)
  *result = NULL;
else if (  !(*result = expand_string(US s)) /* need to clean up const more */
	&& !f.expand_string_forcedfail
	)
  {
  *errstr = US"Internal error";
  log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
    expand_string_message);
  return FALSE;
  }
return TRUE;
}


/*************************************************
*        Timezone environment flipping           *
*************************************************/

static uschar *
to_tz(uschar * tz)
{
uschar * old = US getenv("TZ");
(void) setenv("TZ", CCS tz, 1);
tzset();
return old;
}

static void
restore_tz(uschar * tz)
{
if (tz)
  (void) setenv("TZ", CCS tz, 1);
else
  (void) os_unsetenv(US"TZ");
tzset();
}

/*************************************************
*        Many functions are package-specific     *
*************************************************/

#ifdef USE_GNUTLS
# include "tls-gnu.c"
# include "tlscert-gnu.c"

# define ssl_xfer_buffer (state_server.xfer_buffer)
# define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
# define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
# define ssl_xfer_eof (state_server.xfer_eof)
# define ssl_xfer_error (state_server.xfer_error)

#else
# include "tls-openssl.c"
# include "tlscert-openssl.c"
#endif



/*************************************************
*           TLS version of ungetc                *
*************************************************/

/* Puts a character back in the input buffer. Only ever
called once.
Only used by the server-side TLS.

Arguments:
  ch           the character

Returns:       the character
*/

int
tls_ungetc(int ch)
{
ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
return ch;
}



/*************************************************
*           TLS version of feof                  *
*************************************************/

/* Tests for a previous EOF
Only used by the server-side TLS.

Arguments:     none
Returns:       non-zero if the eof flag is set
*/

int
tls_feof(void)
{
return (int)ssl_xfer_eof;
}



/*************************************************
*              TLS version of ferror             *
*************************************************/

/* Tests for a previous read error, and returns with errno
restored to what it was when the error was detected.
Only used by the server-side TLS.

>>>>> Hmm. Errno not handled yet. Where do we get it from?  >>>>>

Arguments:     none
Returns:       non-zero if the error flag is set
*/

int
tls_ferror(void)
{
return (int)ssl_xfer_error;
}


/*************************************************
*           TLS version of smtp_buffered         *
*************************************************/

/* Tests for unused chars in the TLS input buffer.
Only used by the server-side TLS.

Arguments:     none
Returns:       TRUE/FALSE
*/

BOOL
tls_smtp_buffered(void)
{
return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
}


#endif  /* SUPPORT_TLS */

void
tls_modify_variables(tls_support * dest_tsp)
{
modify_variable(US"tls_bits",                 &dest_tsp->bits);
modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
modify_variable(US"tls_cipher",               &dest_tsp->cipher);
modify_variable(US"tls_peerdn",               &dest_tsp->peerdn);
#if defined(SUPPORT_TLS) && !defined(USE_GNUTLS)
modify_variable(US"tls_sni",                  &dest_tsp->sni);
#endif
}


#ifdef SUPPORT_TLS
/************************************************
*	TLS certificate name operations         *
************************************************/

/* Convert an rfc4514 DN to an exim comma-sep list.
Backslashed commas need to be replaced by doublecomma
for Exim's list quoting.  We modify the given string
inplace.
*/

static void
dn_to_list(uschar * dn)
{
uschar * cp;
for (cp = dn; *cp; cp++)
  if (cp[0] == '\\' && cp[1] == ',')
    *cp++ = ',';
}


/* Extract fields of a given type from an RFC4514-
format Distinguished Name.  Return an Exim list.
NOTE: We modify the supplied dn string during operation.

Arguments:
	dn	Distinguished Name string
	mod	list containing optional output list-sep and
		field selector match, comma-separated
Return:
	allocated string with list of matching fields,
	field type stripped
*/

uschar *
tls_field_from_dn(uschar * dn, const uschar * mod)
{
int insep = ',';
uschar outsep = '\n';
uschar * ele;
uschar * match = NULL;
int len;
gstring * list = NULL;

while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
  if (ele[0] != '>')
    match = ele;	/* field tag to match */
  else if (ele[1])
    outsep = ele[1];	/* nondefault output separator */

dn_to_list(dn);
insep = ',';
len = match ? Ustrlen(match) : -1;
while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
  if (  !match
     || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
     )
    list = string_append_listele(list, outsep, ele+len+1);
return string_from_gstring(list);
}


/* Compare a domain name with a possibly-wildcarded name. Wildcards
are restricted to a single one, as the first element of patterns
having at least three dot-separated elements.  Case-independent.
Return TRUE for a match
*/
static BOOL
is_name_match(const uschar * name, const uschar * pat)
{
uschar * cp;
return *pat == '*'		/* possible wildcard match */
  ?    *++pat == '.'		/* starts star, dot              */
    && !Ustrchr(++pat, '*')	/* has no more stars             */
    && Ustrchr(pat, '.')	/* and has another dot.          */
    && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
    && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
  :    !Ustrchr(pat+1, '*')
    && strcmpic(name, pat) == 0;
}

/* Compare a list of names with the dnsname elements
of the Subject Alternate Name, if any, and the
Subject otherwise.

Arguments:
	namelist names to compare
	cert	 certificate

Returns:
	TRUE/FALSE
*/

BOOL
tls_is_name_for_cert(const uschar * namelist, void * cert)
{
uschar * altnames = tls_cert_subject_altname(cert, US"dns");
uschar * subjdn;
uschar * certname;
int cmp_sep = 0;
uschar * cmpname;

if ((altnames = tls_cert_subject_altname(cert, US"dns")))
  {
  int alt_sep = '\n';
  while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
    {
    const uschar * an = altnames;
    while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
      if (is_name_match(cmpname, certname))
	return TRUE;
    }
  }

else if ((subjdn = tls_cert_subject(cert, NULL)))
  {
  int sn_sep = ',';

  dn_to_list(subjdn);
  while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
    {
    const uschar * sn = subjdn;
    while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
      if (  *certname++ == 'C'
	 && *certname++ == 'N'
	 && *certname++ == '='
	 && is_name_match(cmpname, certname)
	 )
	return TRUE;
    }
  }
return FALSE;
}
#endif	/*SUPPORT_TLS*/
#endif	/*!MACRO_PREDEF*/

/* vi: aw ai sw=2
*/
/* End of tls.c */