src/src/tls.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2018 */
   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 Mavrogiannopoulos. 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 = FALSE;
  45 static BOOL ssl_xfer_error = FALSE;
  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, uschar ** errstr)
  68 {
  69 if (!s)
  70   *result = NULL;
  71 else if (  !(*result = expand_string(US s)) /* need to clean up const more */
  72         && !expand_string_forcedfail
  73         )
  74   {
  75   *errstr = US"Internal error";
  76   log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
  77     expand_string_message);
  78   return FALSE;
  79   }
  80 return TRUE;
  81 }
  82
  83
  84 /*************************************************
  85 *        Timezone environment flipping           *
  86 *************************************************/
  87
  88 static uschar *
  89 to_tz(uschar * tz)
  90 {
  91 uschar * old = US getenv("TZ");
  92 (void) setenv("TZ", CCS tz, 1);
  93 tzset();
  94 return old;
  95 }
  96
  97 static void
  98 restore_tz(uschar * tz)
  99 {
 100 if (tz)
 101   (void) setenv("TZ", CCS tz, 1);
 102 else
 103   (void) os_unsetenv(US"TZ");
 104 tzset();
 105 }
 106
 107 /*************************************************
 108 *        Many functions are package-specific     *
 109 *************************************************/
 110
 111 #ifdef USE_GNUTLS
 112 # include "tls-gnu.c"
 113 # include "tlscert-gnu.c"
 114
 115 # define ssl_xfer_buffer (state_server.xfer_buffer)
 116 # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
 117 # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
 118 # define ssl_xfer_eof (state_server.xfer_eof)
 119 # define ssl_xfer_error (state_server.xfer_error)
 120
 121 #else
 122 # include "tls-openssl.c"
 123 # include "tlscert-openssl.c"
 124 #endif
 125
 126
 127
 128 /*************************************************
 129 *           TLS version of ungetc                *
 130 *************************************************/
 131
 132 /* Puts a character back in the input buffer. Only ever
 133 called once.
 134 Only used by the server-side TLS.
 135
 136 Arguments:
 137   ch           the character
 138
 139 Returns:       the character
 140 */
 141
 142 int
 143 tls_ungetc(int ch)
 144 {
 145 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
 146 return ch;
 147 }
 148
 149
 150
 151 /*************************************************
 152 *           TLS version of feof                  *
 153 *************************************************/
 154
 155 /* Tests for a previous EOF
 156 Only used by the server-side TLS.
 157
 158 Arguments:     none
 159 Returns:       non-zero if the eof flag is set
 160 */
 161
 162 int
 163 tls_feof(void)
 164 {
 165 return (int)ssl_xfer_eof;
 166 }
 167
 168
 169
 170 /*************************************************
 171 *              TLS version of ferror             *
 172 *************************************************/
 173
 174 /* Tests for a previous read error, and returns with errno
 175 restored to what it was when the error was detected.
 176 Only used by the server-side TLS.
 177
 178 >>>>> Hmm. Errno not handled yet. Where do we get it from?  >>>>>
 179
 180 Arguments:     none
 181 Returns:       non-zero if the error flag is set
 182 */
 183
 184 int
 185 tls_ferror(void)
 186 {
 187 return (int)ssl_xfer_error;
 188 }
 189
 190
 191 /*************************************************
 192 *           TLS version of smtp_buffered         *
 193 *************************************************/
 194
 195 /* Tests for unused chars in the TLS input buffer.
 196 Only used by the server-side TLS.
 197
 198 Arguments:     none
 199 Returns:       TRUE/FALSE
 200 */
 201
 202 BOOL
 203 tls_smtp_buffered(void)
 204 {
 205 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
 206 }
 207
 208
 209 #endif  /* SUPPORT_TLS */
 210
 211 void
 212 tls_modify_variables(tls_support * dest_tsp)
 213 {
 214 modify_variable(US"tls_bits",                 &dest_tsp->bits);
 215 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
 216 modify_variable(US"tls_cipher",               &dest_tsp->cipher);
 217 modify_variable(US"tls_peerdn",               &dest_tsp->peerdn);
 218 #if defined(SUPPORT_TLS) && !defined(USE_GNUTLS)
 219 modify_variable(US"tls_sni",                  &dest_tsp->sni);
 220 #endif
 221 }
 222
 223
 224 #ifdef SUPPORT_TLS
 225 /************************************************
 226 *       TLS certificate name operations         *
 227 ************************************************/
 228
 229 /* Convert an rfc4514 DN to an exim comma-sep list.
 230 Backslashed commas need to be replaced by doublecomma
 231 for Exim's list quoting.  We modify the given string
 232 inplace.
 233 */
 234
 235 static void
 236 dn_to_list(uschar * dn)
 237 {
 238 uschar * cp;
 239 for (cp = dn; *cp; cp++)
 240   if (cp[0] == '\\' && cp[1] == ',')
 241     *cp++ = ',';
 242 }
 243
 244
 245 /* Extract fields of a given type from an RFC4514-
 246 format Distinguished Name.  Return an Exim list.
 247 NOTE: We modify the supplied dn string during operation.
 248
 249 Arguments:
 250         dn      Distinguished Name string
 251         mod     list containing optional output list-sep and
 252                 field selector match, comma-separated
 253 Return:
 254         allocated string with list of matching fields,
 255         field type stripped
 256 */
 257
 258 uschar *
 259 tls_field_from_dn(uschar * dn, const uschar * mod)
 260 {
 261 int insep = ',';
 262 uschar outsep = '\n';
 263 uschar * ele;
 264 uschar * match = NULL;
 265 int len;
 266 gstring * list = NULL;
 267
 268 while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
 269   if (ele[0] != '>')
 270     match = ele;        /* field tag to match */
 271   else if (ele[1])
 272     outsep = ele[1];    /* nondefault output separator */
 273
 274 dn_to_list(dn);
 275 insep = ',';
 276 len = match ? Ustrlen(match) : -1;
 277 while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
 278   if (  !match
 279      || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
 280      )
 281     list = string_append_listele(list, outsep, ele+len+1);
 282 return string_from_gstring(list);
 283 }
 284
 285
 286 /* Compare a domain name with a possibly-wildcarded name. Wildcards
 287 are restricted to a single one, as the first element of patterns
 288 having at least three dot-separated elements.  Case-independent.
 289 Return TRUE for a match
 290 */
 291 static BOOL
 292 is_name_match(const uschar * name, const uschar * pat)
 293 {
 294 uschar * cp;
 295 return *pat == '*'              /* possible wildcard match */
 296   ?    *++pat == '.'            /* starts star, dot              */
 297     && !Ustrchr(++pat, '*')     /* has no more stars             */
 298     && Ustrchr(pat, '.')        /* and has another dot.          */
 299     && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
 300     && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
 301   :    !Ustrchr(pat+1, '*')
 302     && strcmpic(name, pat) == 0;
 303 }
 304
 305 /* Compare a list of names with the dnsname elements
 306 of the Subject Alternate Name, if any, and the
 307 Subject otherwise.
 308
 309 Arguments:
 310         namelist names to compare
 311         cert     certificate
 312
 313 Returns:
 314         TRUE/FALSE
 315 */
 316
 317 BOOL
 318 tls_is_name_for_cert(const uschar * namelist, void * cert)
 319 {
 320 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
 321 uschar * subjdn;
 322 uschar * certname;
 323 int cmp_sep = 0;
 324 uschar * cmpname;
 325
 326 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
 327   {
 328   int alt_sep = '\n';
 329   while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
 330     {
 331     const uschar * an = altnames;
 332     while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
 333       if (is_name_match(cmpname, certname))
 334         return TRUE;
 335     }
 336   }
 337
 338 else if ((subjdn = tls_cert_subject(cert, NULL)))
 339   {
 340   int sn_sep = ',';
 341
 342   dn_to_list(subjdn);
 343   while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
 344     {
 345     const uschar * sn = subjdn;
 346     while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
 347       if (  *certname++ == 'C'
 348          && *certname++ == 'N'
 349          && *certname++ == '='
 350          && is_name_match(cmpname, certname)
 351          )
 352         return TRUE;
 353     }
 354   }
 355 return FALSE;
 356 }
 357 #endif  /*SUPPORT_TLS*/
 358
 359 /* vi: aw ai sw=2
 360 */
 361 /* End of tls.c */