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 #if defined(MACRO_PREDEF) && !defined(DISABLE_TLS)
  23 # include "macro_predef.h"
  24 # ifdef USE_GNUTLS
  25 #  include "tls-gnu.c"
  26 # else
  27 #  include "tls-openssl.c"
  28 # endif
  29 #endif
  30
  31 #ifndef MACRO_PREDEF
  32
  33 /* This module is compiled only when it is specifically requested in the
  34 build-time configuration. However, some compilers don't like compiling empty
  35 modules, so keep them happy with a dummy when skipping the rest. Make it
  36 reference itself to stop picky compilers complaining that it is unused, and put
  37 in a dummy argument to stop even pickier compilers complaining about infinite
  38 loops. */
  39
  40 #ifdef DISABLE_TLS
  41 static void dummy(int x) { dummy(x-1); }
  42 #else
  43
  44 /* Static variables that are used for buffering data by both sets of
  45 functions and the common functions below.
  46
  47 We're moving away from this; GnuTLS is already using a state, which
  48 can switch, so we can do TLS callouts during ACLs. */
  49
  50 static const int ssl_xfer_buffer_size = 4096;
  51 #ifndef USE_GNUTLS
  52 static uschar *ssl_xfer_buffer = NULL;
  53 static int ssl_xfer_buffer_lwm = 0;
  54 static int ssl_xfer_buffer_hwm = 0;
  55 static int ssl_xfer_eof = FALSE;
  56 static BOOL ssl_xfer_error = FALSE;
  57 #endif
  58
  59 uschar *tls_channelbinding_b64 = NULL;
  60
  61
  62 /*************************************************
  63 *       Expand string; give error on failure     *
  64 *************************************************/
  65
  66 /* If expansion is forced to fail, set the result NULL and return TRUE.
  67 Other failures return FALSE. For a server, an SMTP response is given.
  68
  69 Arguments:
  70   s         the string to expand; if NULL just return TRUE
  71   name      name of string being expanded (for error)
  72   result    where to put the result
  73
  74 Returns:    TRUE if OK; result may still be NULL after forced failure
  75 */
  76
  77 static BOOL
  78 expand_check(const uschar *s, const uschar *name, uschar **result, uschar ** errstr)
  79 {
  80 if (!s)
  81   *result = NULL;
  82 else if (  !(*result = expand_string(US s)) /* need to clean up const more */
  83         && !f.expand_string_forcedfail
  84         )
  85   {
  86   *errstr = US"Internal error";
  87   log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
  88     expand_string_message);
  89   return FALSE;
  90   }
  91 return TRUE;
  92 }
  93
  94
  95 /*************************************************
  96 *        Timezone environment flipping           *
  97 *************************************************/
  98
  99 static uschar *
 100 to_tz(uschar * tz)
 101 {
 102 uschar * old = US getenv("TZ");
 103 (void) setenv("TZ", CCS tz, 1);
 104 tzset();
 105 return old;
 106 }
 107
 108 static void
 109 restore_tz(uschar * tz)
 110 {
 111 if (tz)
 112   (void) setenv("TZ", CCS tz, 1);
 113 else
 114   (void) os_unsetenv(US"TZ");
 115 tzset();
 116 }
 117
 118 /*************************************************
 119 *        Many functions are package-specific     *
 120 *************************************************/
 121
 122 #ifdef USE_GNUTLS
 123 # include "tls-gnu.c"
 124 # include "tlscert-gnu.c"
 125
 126 # define ssl_xfer_buffer (state_server.xfer_buffer)
 127 # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
 128 # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
 129 # define ssl_xfer_eof (state_server.xfer_eof)
 130 # define ssl_xfer_error (state_server.xfer_error)
 131
 132 #else
 133 # include "tls-openssl.c"
 134 # include "tlscert-openssl.c"
 135 #endif
 136
 137
 138
 139 /*************************************************
 140 *           TLS version of ungetc                *
 141 *************************************************/
 142
 143 /* Puts a character back in the input buffer. Only ever
 144 called once.
 145 Only used by the server-side TLS.
 146
 147 Arguments:
 148   ch           the character
 149
 150 Returns:       the character
 151 */
 152
 153 int
 154 tls_ungetc(int ch)
 155 {
 156 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
 157 return ch;
 158 }
 159
 160
 161
 162 /*************************************************
 163 *           TLS version of feof                  *
 164 *************************************************/
 165
 166 /* Tests for a previous EOF
 167 Only used by the server-side TLS.
 168
 169 Arguments:     none
 170 Returns:       non-zero if the eof flag is set
 171 */
 172
 173 int
 174 tls_feof(void)
 175 {
 176 return (int)ssl_xfer_eof;
 177 }
 178
 179
 180
 181 /*************************************************
 182 *              TLS version of ferror             *
 183 *************************************************/
 184
 185 /* Tests for a previous read error, and returns with errno
 186 restored to what it was when the error was detected.
 187 Only used by the server-side TLS.
 188
 189 >>>>> Hmm. Errno not handled yet. Where do we get it from?  >>>>>
 190
 191 Arguments:     none
 192 Returns:       non-zero if the error flag is set
 193 */
 194
 195 int
 196 tls_ferror(void)
 197 {
 198 return (int)ssl_xfer_error;
 199 }
 200
 201
 202 /*************************************************
 203 *           TLS version of smtp_buffered         *
 204 *************************************************/
 205
 206 /* Tests for unused chars in the TLS input buffer.
 207 Only used by the server-side TLS.
 208
 209 Arguments:     none
 210 Returns:       TRUE/FALSE
 211 */
 212
 213 BOOL
 214 tls_smtp_buffered(void)
 215 {
 216 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
 217 }
 218
 219
 220 #endif  /*DISABLE_TLS*/
 221
 222 void
 223 tls_modify_variables(tls_support * dest_tsp)
 224 {
 225 modify_variable(US"tls_bits",                 &dest_tsp->bits);
 226 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
 227 modify_variable(US"tls_cipher",               &dest_tsp->cipher);
 228 modify_variable(US"tls_peerdn",               &dest_tsp->peerdn);
 229 #if !defined(DISABLE_TLS) && !defined(USE_GNUTLS)
 230 modify_variable(US"tls_sni",                  &dest_tsp->sni);
 231 #endif
 232 }
 233
 234
 235 #ifndef DISABLE_TLS
 236 /************************************************
 237 *       TLS certificate name operations         *
 238 ************************************************/
 239
 240 /* Convert an rfc4514 DN to an exim comma-sep list.
 241 Backslashed commas need to be replaced by doublecomma
 242 for Exim's list quoting.  We modify the given string
 243 inplace.
 244 */
 245
 246 static void
 247 dn_to_list(uschar * dn)
 248 {
 249 for (uschar * cp = dn; *cp; cp++)
 250   if (cp[0] == '\\' && cp[1] == ',')
 251     *cp++ = ',';
 252 }
 253
 254
 255 /* Extract fields of a given type from an RFC4514-
 256 format Distinguished Name.  Return an Exim list.
 257 NOTE: We modify the supplied dn string during operation.
 258
 259 Arguments:
 260         dn      Distinguished Name string
 261         mod     list containing optional output list-sep and
 262                 field selector match, comma-separated
 263 Return:
 264         allocated string with list of matching fields,
 265         field type stripped
 266 */
 267
 268 uschar *
 269 tls_field_from_dn(uschar * dn, const uschar * mod)
 270 {
 271 int insep = ',';
 272 uschar outsep = '\n';
 273 uschar * ele;
 274 uschar * match = NULL;
 275 int len;
 276 gstring * list = NULL;
 277
 278 while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
 279   if (ele[0] != '>')
 280     match = ele;        /* field tag to match */
 281   else if (ele[1])
 282     outsep = ele[1];    /* nondefault output separator */
 283
 284 dn_to_list(dn);
 285 insep = ',';
 286 len = match ? Ustrlen(match) : -1;
 287 while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
 288   if (  !match
 289      || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
 290      )
 291     list = string_append_listele(list, outsep, ele+len+1);
 292 return string_from_gstring(list);
 293 }
 294
 295
 296 /* Compare a domain name with a possibly-wildcarded name. Wildcards
 297 are restricted to a single one, as the first element of patterns
 298 having at least three dot-separated elements.  Case-independent.
 299 Return TRUE for a match
 300 */
 301 static BOOL
 302 is_name_match(const uschar * name, const uschar * pat)
 303 {
 304 uschar * cp;
 305 return *pat == '*'              /* possible wildcard match */
 306   ?    *++pat == '.'            /* starts star, dot              */
 307     && !Ustrchr(++pat, '*')     /* has no more stars             */
 308     && Ustrchr(pat, '.')        /* and has another dot.          */
 309     && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
 310     && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
 311   :    !Ustrchr(pat+1, '*')
 312     && strcmpic(name, pat) == 0;
 313 }
 314
 315 /* Compare a list of names with the dnsname elements
 316 of the Subject Alternate Name, if any, and the
 317 Subject otherwise.
 318
 319 Arguments:
 320         namelist names to compare
 321         cert     certificate
 322
 323 Returns:
 324         TRUE/FALSE
 325 */
 326
 327 BOOL
 328 tls_is_name_for_cert(const uschar * namelist, void * cert)
 329 {
 330 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
 331 uschar * subjdn;
 332 uschar * certname;
 333 int cmp_sep = 0;
 334 uschar * cmpname;
 335
 336 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
 337   {
 338   int alt_sep = '\n';
 339   while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
 340     {
 341     const uschar * an = altnames;
 342     while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
 343       if (is_name_match(cmpname, certname))
 344         return TRUE;
 345     }
 346   }
 347
 348 else if ((subjdn = tls_cert_subject(cert, NULL)))
 349   {
 350   int sn_sep = ',';
 351
 352   dn_to_list(subjdn);
 353   while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
 354     {
 355     const uschar * sn = subjdn;
 356     while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
 357       if (  *certname++ == 'C'
 358          && *certname++ == 'N'
 359          && *certname++ == '='
 360          && is_name_match(cmpname, certname)
 361          )
 362         return TRUE;
 363     }
 364   }
 365 return FALSE;
 366 }
 367 #endif  /*!DISABLE_TLS*/
 368 #endif  /*!MACRO_PREDEF*/
 369
 370 /* vi: aw ai sw=2
 371 */
 372 /* End of tls.c */