src/src/tls.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2012 */
   6 /* See the file NOTICE for conditions of use and distribution. */
   7
   8 /* This module provides TLS (aka SSL) support for Exim. The code for OpenSSL is
   9 based on a patch that was originally contributed by Steve Haslam. It was
  10 adapted from stunnel, a GPL program by Michal Trojnara. The code for GNU TLS is
  11 based on a patch contributed by Nikos Mavroyanopoulos. Because these packages
  12 are so very different, the functions for each are kept in separate files. The
  13 relevant file is #included as required, after any any common functions.
  14
  15 No cryptographic code is included in Exim. All this module does is to call
  16 functions from the OpenSSL or GNU TLS libraries. */
  17
  18
  19 #include "exim.h"
  20 #include "transports/smtp.h"
  21
  22 /* This module is compiled only when it is specifically requested in the
  23 build-time configuration. However, some compilers don't like compiling empty
  24 modules, so keep them happy with a dummy when skipping the rest. Make it
  25 reference itself to stop picky compilers complaining that it is unused, and put
  26 in a dummy argument to stop even pickier compilers complaining about infinite
  27 loops. */
  28
  29 #ifndef SUPPORT_TLS
  30 static void dummy(int x) { dummy(x-1); }
  31 #else
  32
  33 /* Static variables that are used for buffering data by both sets of
  34 functions and the common functions below.
  35
  36 We're moving away from this; GnuTLS is already using a state, which
  37 can switch, so we can do TLS callouts during ACLs. */
  38
  39 static const int ssl_xfer_buffer_size = 4096;
  40 #ifndef USE_GNUTLS
  41 static uschar *ssl_xfer_buffer = NULL;
  42 static int ssl_xfer_buffer_lwm = 0;
  43 static int ssl_xfer_buffer_hwm = 0;
  44 static int ssl_xfer_eof = 0;
  45 static int ssl_xfer_error = 0;
  46 #endif
  47
  48 uschar *tls_channelbinding_b64 = NULL;
  49
  50
  51 /*************************************************
  52 *       Expand string; give error on failure     *
  53 *************************************************/
  54
  55 /* If expansion is forced to fail, set the result NULL and return TRUE.
  56 Other failures return FALSE. For a server, an SMTP response is given.
  57
  58 Arguments:
  59   s         the string to expand; if NULL just return TRUE
  60   name      name of string being expanded (for error)
  61   result    where to put the result
  62
  63 Returns:    TRUE if OK; result may still be NULL after forced failure
  64 */
  65
  66 static BOOL
  67 expand_check(const uschar *s, const uschar *name, uschar **result)
  68 {
  69 if (s == NULL) *result = NULL; else
  70   {
  71   *result = expand_string(US s); /* need to clean up const some more */
  72   if (*result == NULL && !expand_string_forcedfail)
  73     {
  74     log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
  75       expand_string_message);
  76     return FALSE;
  77     }
  78   }
  79 return TRUE;
  80 }
  81
  82
  83 /*************************************************
  84 *        Many functions are package-specific     *
  85 *************************************************/
  86
  87 #ifdef USE_GNUTLS
  88 #include "tls-gnu.c"
  89 #include "tlscert-gnu.c"
  90
  91 #define ssl_xfer_buffer (state_server.xfer_buffer)
  92 #define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
  93 #define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
  94 #define ssl_xfer_eof (state_server.xfer_eof)
  95 #define ssl_xfer_error (state_server.xfer_error)
  96
  97 #else
  98 #include "tls-openssl.c"
  99 #include "tlscert-openssl.c"
 100 #endif
 101
 102
 103
 104 /*************************************************
 105 *           TLS version of ungetc                *
 106 *************************************************/
 107
 108 /* Puts a character back in the input buffer. Only ever
 109 called once.
 110 Only used by the server-side TLS.
 111
 112 Arguments:
 113   ch           the character
 114
 115 Returns:       the character
 116 */
 117
 118 int
 119 tls_ungetc(int ch)
 120 {
 121 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
 122 return ch;
 123 }
 124
 125
 126
 127 /*************************************************
 128 *           TLS version of feof                  *
 129 *************************************************/
 130
 131 /* Tests for a previous EOF
 132 Only used by the server-side TLS.
 133
 134 Arguments:     none
 135 Returns:       non-zero if the eof flag is set
 136 */
 137
 138 int
 139 tls_feof(void)
 140 {
 141 return ssl_xfer_eof;
 142 }
 143
 144
 145
 146 /*************************************************
 147 *              TLS version of ferror             *
 148 *************************************************/
 149
 150 /* Tests for a previous read error, and returns with errno
 151 restored to what it was when the error was detected.
 152 Only used by the server-side TLS.
 153
 154 >>>>> Hmm. Errno not handled yet. Where do we get it from?  >>>>>
 155
 156 Arguments:     none
 157 Returns:       non-zero if the error flag is set
 158 */
 159
 160 int
 161 tls_ferror(void)
 162 {
 163 return ssl_xfer_error;
 164 }
 165
 166
 167 /*************************************************
 168 *           TLS version of smtp_buffered         *
 169 *************************************************/
 170
 171 /* Tests for unused chars in the TLS input buffer.
 172 Only used by the server-side TLS.
 173
 174 Arguments:     none
 175 Returns:       TRUE/FALSE
 176 */
 177
 178 BOOL
 179 tls_smtp_buffered(void)
 180 {
 181 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
 182 }
 183
 184
 185 #endif  /* SUPPORT_TLS */
 186
 187 void
 188 tls_modify_variables(tls_support * dest_tsp)
 189 {
 190 modify_variable(US"tls_bits",                 &dest_tsp->bits);
 191 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
 192 modify_variable(US"tls_cipher",               &dest_tsp->cipher);
 193 modify_variable(US"tls_peerdn",               &dest_tsp->peerdn);
 194 #if defined(SUPPORT_TLS) && !defined(USE_GNUTLS)
 195 modify_variable(US"tls_sni",                  &dest_tsp->sni);
 196 #endif
 197 }
 198
 199
 200 #ifdef SUPPORT_TLS
 201 /************************************************
 202 *       TLS certificate name operations         *
 203 ************************************************/
 204
 205 /* Convert an rfc4514 DN to an exim comma-sep list.
 206 Backslashed commas need to be replaced by doublecomma
 207 for Exim's list quoting.  We modify the given string
 208 inplace.
 209 */
 210
 211 static void
 212 dn_to_list(uschar * dn)
 213 {
 214 uschar * cp;
 215 for (cp = dn; *cp; cp++)
 216   if (cp[0] == '\\' && cp[1] == ',')
 217     *cp++ = ',';
 218 }
 219
 220
 221 /* Extract fields of a given type from an RFC4514-
 222 format Distinguished Name.  Return an Exim list.
 223 NOTE: We modify the supplied dn string during operation.
 224
 225 Arguments:
 226         dn      Distinguished Name string
 227         mod     string containing optional list-sep and
 228                 field selector match, comma-separated
 229 Return:
 230         allocated string with list of matching fields,
 231         field type stripped
 232 */
 233
 234 uschar *
 235 tls_field_from_dn(uschar * dn, uschar * mod)
 236 {
 237 int insep = ',';
 238 uschar outsep = '\n';
 239 uschar * ele;
 240 uschar * match = NULL;
 241 int len;
 242 uschar * list = NULL;
 243
 244 while (ele = string_nextinlist(&mod, &insep, NULL, 0))
 245   if (ele[0] != '>')
 246     match = ele;        /* field tag to match */
 247   else if (ele[1])
 248     outsep = ele[1];    /* nondefault separator */
 249
 250 dn_to_list(dn);
 251 insep = ',';
 252 len = Ustrlen(match);
 253 while (ele = string_nextinlist(&dn, &insep, NULL, 0))
 254   if (Ustrncmp(ele, match, len) == 0 && ele[len] == '=')
 255     list = string_append_listele(list, outsep, ele+len+1);
 256 return list;
 257 }
 258
 259
 260 # ifdef EXPERIMENTAL_CERTNAMES
 261 /* Compare a domain name with a possibly-wildcarded name. Wildcards
 262 are restricted to a single one, as the first element of patterns
 263 having at least three dot-separated elements.  Case-independent.
 264 Return TRUE for a match
 265 */
 266 static BOOL
 267 is_name_match(const uschar * name, const uschar * pat)
 268 {
 269 uschar * cp;
 270 return *pat == '*'              /* possible wildcard match */
 271   ?    *++pat == '.'            /* starts star, dot              */
 272     && !Ustrchr(++pat, '*')     /* has no more stars             */
 273     && Ustrchr(pat, '.')        /* and has another dot.          */
 274     && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
 275     && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
 276   :    !Ustrchr(pat+1, '*')
 277     && strcmpic(name, pat) == 0;
 278 }
 279
 280 /* Compare a list of names with the dnsname elements
 281 of the Subject Alternate Name, if any, and the
 282 Subject otherwise.
 283
 284 Arguments:
 285         namelist names to compare
 286         cert     certificate
 287
 288 Returns:
 289         TRUE/FALSE
 290 */
 291
 292 BOOL
 293 tls_is_name_for_cert(uschar * namelist, void * cert)
 294 {
 295 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
 296 uschar * subjdn;
 297 uschar * certname;
 298 int cmp_sep = 0;
 299 uschar * cmpname;
 300
 301 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
 302   {
 303   int alt_sep = '\n';
 304   while (cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0))
 305     {
 306     uschar * an = altnames;
 307     while (certname = string_nextinlist(&an, &alt_sep, NULL, 0))
 308       if (is_name_match(cmpname, certname))
 309         return TRUE;
 310     }
 311   }
 312
 313 else if ((subjdn = tls_cert_subject(cert, NULL)))
 314   {
 315   int sn_sep = ',';
 316   uschar * sn;
 317
 318   dn_to_list(subjdn);
 319   while (cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0))
 320     {
 321     uschar * sn = subjdn;
 322     while (certname = string_nextinlist(&sn, &sn_sep, NULL, 0))
 323       if (  *certname++ == 'C'
 324          && *certname++ == 'N'
 325          && *certname++ == '='
 326          && is_name_match(cmpname, certname)
 327          )
 328         return TRUE;
 329     }
 330   }
 331 return FALSE;
 332 }
 333 # endif /*EXPERIMENTAL_CERTNAMES*/
 334 #endif  /*SUPPORY_TLS*/
 335
 336 /* vi: aw ai sw=2
 337 */
 338 /* End of tls.c */