src/src/dkim.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 /* Code for DKIM support. Other DKIM relevant code is in
   9    receive.c, transport.c and transports/smtp.c */
  10
  11 #include "exim.h"
  12
  13 #ifndef DISABLE_DKIM
  14
  15 # include "pdkim/pdkim.h"
  16
  17 # ifdef MACRO_PREDEF
  18 #  include "macro_predef.h"
  19
  20 void
  21 params_dkim(void)
  22 {
  23 builtin_macro_create_var(US"_DKIM_SIGN_HEADERS", US PDKIM_DEFAULT_SIGN_HEADERS);
  24 }
  25 # else  /*!MACRO_PREDEF*/
  26
  27
  28
  29 pdkim_ctx dkim_sign_ctx;
  30
  31 int dkim_verify_oldpool;
  32 pdkim_ctx *dkim_verify_ctx = NULL;
  33 pdkim_signature *dkim_signatures = NULL;
  34 pdkim_signature *dkim_cur_sig = NULL;
  35 static const uschar * dkim_collect_error = NULL;
  36
  37
  38
  39 /*XXX the caller only uses the first record if we return multiple.
  40 */
  41
  42 uschar *
  43 dkim_exim_query_dns_txt(uschar * name)
  44 {
  45 dns_answer dnsa;
  46 dns_scan dnss;
  47 dns_record *rr;
  48 gstring * g = NULL;
  49
  50 lookup_dnssec_authenticated = NULL;
  51 if (dns_lookup(&dnsa, name, T_TXT, NULL) != DNS_SUCCEED)
  52   return NULL;  /*XXX better error detail?  logging? */
  53
  54 /* Search for TXT record */
  55
  56 for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
  57      rr;
  58      rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
  59   if (rr->type == T_TXT)
  60     {
  61     int rr_offset = 0;
  62
  63     /* Copy record content to the answer buffer */
  64
  65     while (rr_offset < rr->size)
  66       {
  67       uschar len = rr->data[rr_offset++];
  68
  69       g = string_catn(g, US(rr->data + rr_offset), len);
  70       if (g->ptr >= PDKIM_DNS_TXT_MAX_RECLEN)
  71         goto bad;
  72
  73       rr_offset += len;
  74       }
  75
  76     /* check if this looks like a DKIM record */
  77     if (Ustrncmp(g->s, "v=", 2) != 0 || strncasecmp(CS g->s, "v=dkim", 6) == 0)
  78       {
  79       gstring_reset_unused(g);
  80       return string_from_gstring(g);
  81       }
  82
  83     if (g) g->ptr = 0;          /* overwrite previous record */
  84     }
  85
  86 bad:
  87 if (g) store_reset(g);
  88 return NULL;    /*XXX better error detail?  logging? */
  89 }
  90
  91
  92 void
  93 dkim_exim_init(void)
  94 {
  95 pdkim_init();
  96 }
  97
  98
  99
 100 void
 101 dkim_exim_verify_init(BOOL dot_stuffing)
 102 {
 103 /* There is a store-reset between header & body reception
 104 so cannot use the main pool. Any allocs done by Exim
 105 memory-handling must use the perm pool. */
 106
 107 dkim_verify_oldpool = store_pool;
 108 store_pool = POOL_PERM;
 109
 110 /* Free previous context if there is one */
 111
 112 if (dkim_verify_ctx)
 113   pdkim_free_ctx(dkim_verify_ctx);
 114
 115 /* Create new context */
 116
 117 dkim_verify_ctx = pdkim_init_verify(&dkim_exim_query_dns_txt, dot_stuffing);
 118 dkim_collect_input = !!dkim_verify_ctx;
 119 dkim_collect_error = NULL;
 120
 121 /* Start feed up with any cached data */
 122 receive_get_cache();
 123
 124 store_pool = dkim_verify_oldpool;
 125 }
 126
 127
 128 void
 129 dkim_exim_verify_feed(uschar * data, int len)
 130 {
 131 int rc;
 132
 133 store_pool = POOL_PERM;
 134 if (  dkim_collect_input
 135    && (rc = pdkim_feed(dkim_verify_ctx, data, len)) != PDKIM_OK)
 136   {
 137   dkim_collect_error = pdkim_errstr(rc);
 138   log_write(0, LOG_MAIN,
 139              "DKIM: validation error: %.100s", dkim_collect_error);
 140   dkim_collect_input = FALSE;
 141   }
 142 store_pool = dkim_verify_oldpool;
 143 }
 144
 145
 146 /* Log the result for the given signature */
 147 static void
 148 dkim_exim_verify_log_sig(pdkim_signature * sig)
 149 {
 150 gstring * logmsg;
 151 uschar * s;
 152
 153 if (!sig) return;
 154
 155 /* Remember the domain for the first pass result */
 156
 157 if (  !dkim_verify_overall
 158    && dkim_verify_status
 159       ? Ustrcmp(dkim_verify_status, US"pass") == 0
 160       : sig->verify_status == PDKIM_VERIFY_PASS
 161    )
 162   dkim_verify_overall = string_copy(sig->domain);
 163
 164 /* Rewrite the sig result if the ACL overrode it.  This is only
 165 needed because the DMARC code (sigh) peeks at the dkim sigs.
 166 Mark the sig for this having been done. */
 167
 168 if (  dkim_verify_status
 169    && (  dkim_verify_status != dkim_exim_expand_query(DKIM_VERIFY_STATUS)
 170       || dkim_verify_reason != dkim_exim_expand_query(DKIM_VERIFY_REASON)
 171    )  )
 172   {                     /* overridden by ACL */
 173   sig->verify_ext_status = -1;
 174   if (Ustrcmp(dkim_verify_status, US"fail") == 0)
 175     sig->verify_status = PDKIM_VERIFY_POLICY | PDKIM_VERIFY_FAIL;
 176   else if (Ustrcmp(dkim_verify_status, US"invalid") == 0)
 177     sig->verify_status = PDKIM_VERIFY_POLICY | PDKIM_VERIFY_INVALID;
 178   else if (Ustrcmp(dkim_verify_status, US"none") == 0)
 179     sig->verify_status = PDKIM_VERIFY_POLICY | PDKIM_VERIFY_NONE;
 180   else if (Ustrcmp(dkim_verify_status, US"pass") == 0)
 181     sig->verify_status = PDKIM_VERIFY_POLICY | PDKIM_VERIFY_PASS;
 182   else
 183     sig->verify_status = -1;
 184   }
 185
 186 if (!LOGGING(dkim_verbose)) return;
 187
 188
 189 logmsg = string_catn(NULL, US"DKIM: ", 6);
 190 if (!(s = sig->domain)) s = US"<UNSET>";
 191 logmsg = string_append(logmsg, 2, "d=", s);
 192 if (!(s = sig->selector)) s = US"<UNSET>";
 193 logmsg = string_append(logmsg, 2, " s=", s);
 194 logmsg = string_append(logmsg, 7,
 195   " c=", sig->canon_headers == PDKIM_CANON_SIMPLE ? "simple" : "relaxed",
 196   "/",   sig->canon_body    == PDKIM_CANON_SIMPLE ? "simple" : "relaxed",
 197   " a=", dkim_sig_to_a_tag(sig),
 198 string_sprintf(" b=" SIZE_T_FMT,
 199                 (int)sig->sighash.len > -1 ? sig->sighash.len * 8 : 0));
 200 if ((s= sig->identity)) logmsg = string_append(logmsg, 2, " i=", s);
 201 if (sig->created > 0) logmsg = string_cat(logmsg,
 202                               string_sprintf(" t=%lu", sig->created));
 203 if (sig->expires > 0) logmsg = string_cat(logmsg,
 204                               string_sprintf(" x=%lu", sig->expires));
 205 if (sig->bodylength > -1) logmsg = string_cat(logmsg,
 206                               string_sprintf(" l=%lu", sig->bodylength));
 207
 208 if (sig->verify_status & PDKIM_VERIFY_POLICY)
 209   logmsg = string_append(logmsg, 5,
 210             US" [", dkim_verify_status, US" - ", dkim_verify_reason, US"]");
 211 else
 212   switch (sig->verify_status)
 213     {
 214     case PDKIM_VERIFY_NONE:
 215       logmsg = string_cat(logmsg, US" [not verified]");
 216       break;
 217
 218     case PDKIM_VERIFY_INVALID:
 219       logmsg = string_cat(logmsg, US" [invalid - ");
 220       switch (sig->verify_ext_status)
 221         {
 222         case PDKIM_VERIFY_INVALID_PUBKEY_UNAVAILABLE:
 223           logmsg = string_cat(logmsg,
 224                         US"public key record (currently?) unavailable]");
 225           break;
 226
 227         case PDKIM_VERIFY_INVALID_BUFFER_SIZE:
 228           logmsg = string_cat(logmsg, US"overlong public key record]");
 229           break;
 230
 231         case PDKIM_VERIFY_INVALID_PUBKEY_DNSRECORD:
 232         case PDKIM_VERIFY_INVALID_PUBKEY_IMPORT:
 233           logmsg = string_cat(logmsg, US"syntax error in public key record]");
 234           break;
 235
 236         case PDKIM_VERIFY_INVALID_SIGNATURE_ERROR:
 237           logmsg = string_cat(logmsg, US"signature tag missing or invalid]");
 238           break;
 239
 240         case PDKIM_VERIFY_INVALID_DKIM_VERSION:
 241           logmsg = string_cat(logmsg, US"unsupported DKIM version]");
 242           break;
 243
 244         default:
 245           logmsg = string_cat(logmsg, US"unspecified problem]");
 246         }
 247       break;
 248
 249     case PDKIM_VERIFY_FAIL:
 250       logmsg = string_cat(logmsg, US" [verification failed - ");
 251       switch (sig->verify_ext_status)
 252         {
 253         case PDKIM_VERIFY_FAIL_BODY:
 254           logmsg = string_cat(logmsg,
 255                US"body hash mismatch (body probably modified in transit)]");
 256           break;
 257
 258         case PDKIM_VERIFY_FAIL_MESSAGE:
 259           logmsg = string_cat(logmsg,
 260                 US"signature did not verify "
 261                 "(headers probably modified in transit)]");
 262           break;
 263
 264         default:
 265           logmsg = string_cat(logmsg, US"unspecified reason]");
 266         }
 267       break;
 268
 269     case PDKIM_VERIFY_PASS:
 270       logmsg = string_cat(logmsg, US" [verification succeeded]");
 271       break;
 272     }
 273
 274 log_write(0, LOG_MAIN, "%s", string_from_gstring(logmsg));
 275 return;
 276 }
 277
 278
 279 /* Log a line for each signature */
 280 void
 281 dkim_exim_verify_log_all(void)
 282 {
 283 pdkim_signature * sig;
 284 for (sig = dkim_signatures; sig; sig = sig->next) dkim_exim_verify_log_sig(sig);
 285 }
 286
 287
 288 void
 289 dkim_exim_verify_finish(void)
 290 {
 291 pdkim_signature * sig;
 292 int rc;
 293 gstring * g = NULL;
 294 const uschar * errstr = NULL;
 295
 296 store_pool = POOL_PERM;
 297
 298 /* Delete eventual previous signature chain */
 299
 300 dkim_signers = NULL;
 301 dkim_signatures = NULL;
 302
 303 if (dkim_collect_error)
 304   {
 305   log_write(0, LOG_MAIN,
 306       "DKIM: Error during validation, disabling signature verification: %.100s",
 307       dkim_collect_error);
 308   dkim_disable_verify = TRUE;
 309   goto out;
 310   }
 311
 312 dkim_collect_input = FALSE;
 313
 314 /* Finish DKIM operation and fetch link to signatures chain */
 315
 316 rc = pdkim_feed_finish(dkim_verify_ctx, &dkim_signatures, &errstr);
 317 if (rc != PDKIM_OK && errstr)
 318   log_write(0, LOG_MAIN, "DKIM: validation error: %s", errstr);
 319
 320 /* Build a colon-separated list of signing domains (and identities, if present) in dkim_signers */
 321
 322 for (sig = dkim_signatures; sig; sig = sig->next)
 323   {
 324   if (sig->domain)   g = string_append_listele(g, ':', sig->domain);
 325   if (sig->identity) g = string_append_listele(g, ':', sig->identity);
 326   }
 327
 328 if (g) dkim_signers = g->s;
 329
 330 out:
 331 store_pool = dkim_verify_oldpool;
 332 }
 333
 334
 335
 336 /* Args as per dkim_exim_acl_run() below */
 337 static int
 338 dkim_acl_call(uschar * id, gstring ** res_ptr,
 339   uschar ** user_msgptr, uschar ** log_msgptr)
 340 {
 341 int rc;
 342 DEBUG(D_receive)
 343   debug_printf("calling acl_smtp_dkim for dkim_cur_signer='%s'\n", id);
 344
 345 rc = acl_check(ACL_WHERE_DKIM, NULL, acl_smtp_dkim, user_msgptr, log_msgptr);
 346 dkim_exim_verify_log_sig(dkim_cur_sig);
 347 *res_ptr = string_append_listele(*res_ptr, ':', dkim_verify_status);
 348 return rc;
 349 }
 350
 351
 352
 353 /* For the given identity, run the DKIM ACL once for each matching signature.
 354
 355 Arguments
 356  id             Identity to look for in dkim signatures
 357  res_ptr        ptr to growable string-list of status results,
 358                 appended to per ACL run
 359  user_msgptr    where to put a user error (for SMTP response)
 360  log_msgptr     where to put a logging message (not for SMTP response)
 361
 362 Returns:       OK         access is granted by an ACCEPT verb
 363                DISCARD    access is granted by a DISCARD verb
 364                FAIL       access is denied
 365                FAIL_DROP  access is denied; drop the connection
 366                DEFER      can't tell at the moment
 367                ERROR      disaster
 368 */
 369
 370 int
 371 dkim_exim_acl_run(uschar * id, gstring ** res_ptr,
 372   uschar ** user_msgptr, uschar ** log_msgptr)
 373 {
 374 pdkim_signature * sig;
 375 uschar * cmp_val;
 376 int rc = -1;
 377
 378 dkim_verify_status = US"none";
 379 dkim_verify_reason = US"";
 380 dkim_cur_signer = id;
 381
 382 if (dkim_disable_verify || !id || !dkim_verify_ctx)
 383   return OK;
 384
 385 /* Find signatures to run ACL on */
 386
 387 for (sig = dkim_signatures; sig; sig = sig->next)
 388   if (  (cmp_val = Ustrchr(id, '@') != NULL ? US sig->identity : US sig->domain)
 389      && strcmpic(cmp_val, id) == 0
 390      )
 391     {
 392     /* The "dkim_domain" and "dkim_selector" expansion variables have
 393     related globals, since they are used in the signing code too.
 394     Instead of inventing separate names for verification, we set
 395     them here. This is easy since a domain and selector is guaranteed
 396     to be in a signature. The other dkim_* expansion items are
 397     dynamically fetched from dkim_cur_sig at expansion time (see
 398     function below). */
 399
 400     dkim_cur_sig = sig;
 401     dkim_signing_domain = US sig->domain;
 402     dkim_signing_selector = US sig->selector;
 403     dkim_key_length = sig->sighash.len * 8;
 404
 405     /* These two return static strings, so we can compare the addr
 406     later to see if the ACL overwrote them.  Check that when logging */
 407
 408     dkim_verify_status = dkim_exim_expand_query(DKIM_VERIFY_STATUS);
 409     dkim_verify_reason = dkim_exim_expand_query(DKIM_VERIFY_REASON);
 410
 411     if ((rc = dkim_acl_call(id, res_ptr, user_msgptr, log_msgptr)) != OK)
 412       return rc;
 413     }
 414
 415 if (rc != -1)
 416   return rc;
 417
 418 /* No matching sig found.  Call ACL once anyway. */
 419
 420 dkim_cur_sig = NULL;
 421 return dkim_acl_call(id, res_ptr, user_msgptr, log_msgptr);
 422 }
 423
 424
 425 static uschar *
 426 dkim_exim_expand_defaults(int what)
 427 {
 428 switch (what)
 429   {
 430   case DKIM_ALGO:               return US"";
 431   case DKIM_BODYLENGTH:         return US"9999999999999";
 432   case DKIM_CANON_BODY:         return US"";
 433   case DKIM_CANON_HEADERS:      return US"";
 434   case DKIM_COPIEDHEADERS:      return US"";
 435   case DKIM_CREATED:            return US"0";
 436   case DKIM_EXPIRES:            return US"9999999999999";
 437   case DKIM_HEADERNAMES:        return US"";
 438   case DKIM_IDENTITY:           return US"";
 439   case DKIM_KEY_GRANULARITY:    return US"*";
 440   case DKIM_KEY_SRVTYPE:        return US"*";
 441   case DKIM_KEY_NOTES:          return US"";
 442   case DKIM_KEY_TESTING:        return US"0";
 443   case DKIM_NOSUBDOMAINS:       return US"0";
 444   case DKIM_VERIFY_STATUS:      return US"none";
 445   case DKIM_VERIFY_REASON:      return US"";
 446   default:                      return US"";
 447   }
 448 }
 449
 450
 451 uschar *
 452 dkim_exim_expand_query(int what)
 453 {
 454 if (!dkim_verify_ctx || dkim_disable_verify || !dkim_cur_sig)
 455   return dkim_exim_expand_defaults(what);
 456
 457 switch (what)
 458   {
 459   case DKIM_ALGO:
 460     return dkim_sig_to_a_tag(dkim_cur_sig);
 461
 462   case DKIM_BODYLENGTH:
 463     return dkim_cur_sig->bodylength >= 0
 464       ? string_sprintf("%ld", dkim_cur_sig->bodylength)
 465       : dkim_exim_expand_defaults(what);
 466
 467   case DKIM_CANON_BODY:
 468     switch (dkim_cur_sig->canon_body)
 469       {
 470       case PDKIM_CANON_RELAXED: return US"relaxed";
 471       case PDKIM_CANON_SIMPLE:
 472       default:                  return US"simple";
 473       }
 474
 475   case DKIM_CANON_HEADERS:
 476     switch (dkim_cur_sig->canon_headers)
 477       {
 478       case PDKIM_CANON_RELAXED: return US"relaxed";
 479       case PDKIM_CANON_SIMPLE:
 480       default:                  return US"simple";
 481       }
 482
 483   case DKIM_COPIEDHEADERS:
 484     return dkim_cur_sig->copiedheaders
 485       ? US dkim_cur_sig->copiedheaders : dkim_exim_expand_defaults(what);
 486
 487   case DKIM_CREATED:
 488     return dkim_cur_sig->created > 0
 489       ? string_sprintf("%lu", dkim_cur_sig->created)
 490       : dkim_exim_expand_defaults(what);
 491
 492   case DKIM_EXPIRES:
 493     return dkim_cur_sig->expires > 0
 494       ? string_sprintf("%lu", dkim_cur_sig->expires)
 495       : dkim_exim_expand_defaults(what);
 496
 497   case DKIM_HEADERNAMES:
 498     return dkim_cur_sig->headernames
 499       ? dkim_cur_sig->headernames : dkim_exim_expand_defaults(what);
 500
 501   case DKIM_IDENTITY:
 502     return dkim_cur_sig->identity
 503       ? US dkim_cur_sig->identity : dkim_exim_expand_defaults(what);
 504
 505   case DKIM_KEY_GRANULARITY:
 506     return dkim_cur_sig->pubkey
 507       ? dkim_cur_sig->pubkey->granularity
 508       ? US dkim_cur_sig->pubkey->granularity
 509       : dkim_exim_expand_defaults(what)
 510       : dkim_exim_expand_defaults(what);
 511
 512   case DKIM_KEY_SRVTYPE:
 513     return dkim_cur_sig->pubkey
 514       ? dkim_cur_sig->pubkey->srvtype
 515       ? US dkim_cur_sig->pubkey->srvtype
 516       : dkim_exim_expand_defaults(what)
 517       : dkim_exim_expand_defaults(what);
 518
 519   case DKIM_KEY_NOTES:
 520     return dkim_cur_sig->pubkey
 521       ? dkim_cur_sig->pubkey->notes
 522       ? US dkim_cur_sig->pubkey->notes
 523       : dkim_exim_expand_defaults(what)
 524       : dkim_exim_expand_defaults(what);
 525
 526   case DKIM_KEY_TESTING:
 527     return dkim_cur_sig->pubkey
 528       ? dkim_cur_sig->pubkey->testing
 529       ? US"1"
 530       : dkim_exim_expand_defaults(what)
 531       : dkim_exim_expand_defaults(what);
 532
 533   case DKIM_NOSUBDOMAINS:
 534     return dkim_cur_sig->pubkey
 535       ? dkim_cur_sig->pubkey->no_subdomaining
 536       ? US"1"
 537       : dkim_exim_expand_defaults(what)
 538       : dkim_exim_expand_defaults(what);
 539
 540   case DKIM_VERIFY_STATUS:
 541     switch (dkim_cur_sig->verify_status)
 542       {
 543       case PDKIM_VERIFY_INVALID:        return US"invalid";
 544       case PDKIM_VERIFY_FAIL:           return US"fail";
 545       case PDKIM_VERIFY_PASS:           return US"pass";
 546       case PDKIM_VERIFY_NONE:
 547       default:                          return US"none";
 548       }
 549
 550   case DKIM_VERIFY_REASON:
 551     switch (dkim_cur_sig->verify_ext_status)
 552       {
 553       case PDKIM_VERIFY_INVALID_PUBKEY_UNAVAILABLE:
 554                                                 return US"pubkey_unavailable";
 555       case PDKIM_VERIFY_INVALID_PUBKEY_DNSRECORD:return US"pubkey_dns_syntax";
 556       case PDKIM_VERIFY_INVALID_PUBKEY_IMPORT:  return US"pubkey_der_syntax";
 557       case PDKIM_VERIFY_FAIL_BODY:              return US"bodyhash_mismatch";
 558       case PDKIM_VERIFY_FAIL_MESSAGE:           return US"signature_incorrect";
 559       }
 560
 561   default:
 562     return US"";
 563   }
 564 }
 565
 566
 567 void
 568 dkim_exim_sign_init(void)
 569 {
 570 int old_pool = store_pool;
 571 store_pool = POOL_MAIN;
 572 pdkim_init_context(&dkim_sign_ctx, FALSE, &dkim_exim_query_dns_txt);
 573 store_pool = old_pool;
 574 }
 575
 576
 577 /* Generate signatures for the given file.
 578 If a prefix is given, prepend it to the file for the calculations.
 579
 580 Return:
 581   NULL:         error; error string written
 582   string:       signature header(s), or a zero-length string (not an error)
 583 */
 584
 585 gstring *
 586 dkim_exim_sign(int fd, off_t off, uschar * prefix,
 587   struct ob_dkim * dkim, const uschar ** errstr)
 588 {
 589 const uschar * dkim_domain = NULL;
 590 int sep = 0;
 591 gstring * seen_doms = NULL;
 592 pdkim_signature * sig;
 593 gstring * sigbuf;
 594 int pdkim_rc;
 595 int sread;
 596 uschar buf[4096];
 597 int save_errno = 0;
 598 int old_pool = store_pool;
 599 uschar * errwhen;
 600 const uschar * s;
 601
 602 if (dkim->dot_stuffed)
 603   dkim_sign_ctx.flags |= PDKIM_DOT_TERM;
 604
 605 store_pool = POOL_MAIN;
 606
 607 if ((s = dkim->dkim_domain) && !(dkim_domain = expand_cstring(s)))
 608   /* expansion error, do not send message. */
 609   { errwhen = US"dkim_domain"; goto expand_bad; }
 610
 611 /* Set $dkim_domain expansion variable to each unique domain in list. */
 612
 613 if (dkim_domain)
 614   while ((dkim_signing_domain = string_nextinlist(&dkim_domain, &sep, NULL, 0)))
 615   {
 616   const uschar * dkim_sel;
 617   int sel_sep = 0;
 618
 619   if (dkim_signing_domain[0] == '\0')
 620     continue;
 621
 622   /* Only sign once for each domain, no matter how often it
 623   appears in the expanded list. */
 624
 625   if (match_isinlist(dkim_signing_domain, CUSS &seen_doms,
 626       0, NULL, NULL, MCL_STRING, TRUE, NULL) == OK)
 627     continue;
 628
 629   seen_doms = string_append_listele(seen_doms, ':', dkim_signing_domain);
 630
 631   /* Set $dkim_selector expansion variable to each selector in list,
 632   for this domain. */
 633
 634   if (!(dkim_sel = expand_string(dkim->dkim_selector)))
 635     { errwhen = US"dkim_selector"; goto expand_bad; }
 636
 637   while ((dkim_signing_selector = string_nextinlist(&dkim_sel, &sel_sep,
 638           NULL, 0)))
 639     {
 640     uschar * dkim_canon_expanded;
 641     int pdkim_canon;
 642     uschar * dkim_sign_headers_expanded = NULL;
 643     uschar * dkim_private_key_expanded;
 644     uschar * dkim_hash_expanded;
 645     uschar * dkim_identity_expanded = NULL;
 646
 647     /* Get canonicalization to use */
 648
 649     dkim_canon_expanded = dkim->dkim_canon
 650       ? expand_string(dkim->dkim_canon) : US"relaxed";
 651     if (!dkim_canon_expanded)   /* expansion error, do not send message. */
 652       { errwhen = US"dkim_canon"; goto expand_bad; }
 653
 654     if (Ustrcmp(dkim_canon_expanded, "relaxed") == 0)
 655       pdkim_canon = PDKIM_CANON_RELAXED;
 656     else if (Ustrcmp(dkim_canon_expanded, "simple") == 0)
 657       pdkim_canon = PDKIM_CANON_SIMPLE;
 658     else
 659       {
 660       log_write(0, LOG_MAIN,
 661                  "DKIM: unknown canonicalization method '%s', defaulting to 'relaxed'.\n",
 662                  dkim_canon_expanded);
 663       pdkim_canon = PDKIM_CANON_RELAXED;
 664       }
 665
 666     if (  dkim->dkim_sign_headers
 667        && !(dkim_sign_headers_expanded = expand_string(dkim->dkim_sign_headers)))
 668       { errwhen = US"dkim_sign_header"; goto expand_bad; }
 669     /* else pass NULL, which means default header list */
 670
 671     /* Get private key to use. */
 672
 673     if (!(dkim_private_key_expanded = expand_string(dkim->dkim_private_key)))
 674       { errwhen = US"dkim_private_key"; goto expand_bad; }
 675
 676     if (  Ustrlen(dkim_private_key_expanded) == 0
 677        || Ustrcmp(dkim_private_key_expanded, "0") == 0
 678        || Ustrcmp(dkim_private_key_expanded, "false") == 0
 679        )
 680       continue;         /* don't sign, but no error */
 681
 682     if (  dkim_private_key_expanded[0] == '/'
 683        && !(dkim_private_key_expanded =
 684              expand_file_big_buffer(dkim_private_key_expanded)))
 685       goto bad;
 686
 687     if (!(dkim_hash_expanded = expand_string(dkim->dkim_hash)))
 688       { errwhen = US"dkim_hash"; goto expand_bad; }
 689
 690     if (dkim->dkim_identity)
 691       if (!(dkim_identity_expanded = expand_string(dkim->dkim_identity)))
 692         { errwhen = US"dkim_identity"; goto expand_bad; }
 693       else if (!*dkim_identity_expanded)
 694         dkim_identity_expanded = NULL;
 695
 696     if (!(sig = pdkim_init_sign(&dkim_sign_ctx, dkim_signing_domain,
 697                           dkim_signing_selector,
 698                           dkim_private_key_expanded,
 699                           dkim_hash_expanded,
 700                           errstr
 701                           )))
 702       goto bad;
 703     dkim_private_key_expanded[0] = '\0';
 704
 705     pdkim_set_optional(sig,
 706                         CS dkim_sign_headers_expanded,
 707                         CS dkim_identity_expanded,
 708                         pdkim_canon,
 709                         pdkim_canon, -1, 0, 0);
 710
 711     if (!pdkim_set_sig_bodyhash(&dkim_sign_ctx, sig))
 712       goto bad;
 713
 714     if (!dkim_sign_ctx.sig)             /* link sig to context chain */
 715       dkim_sign_ctx.sig = sig;
 716     else
 717       {
 718       pdkim_signature * n = dkim_sign_ctx.sig;
 719       while (n->next) n = n->next;
 720       n->next = sig;
 721       }
 722     }
 723   }
 724
 725 /* We may need to carry on with the data-feed even if there are no DKIM sigs to
 726 produce, if some other package (eg. ARC) is signing. */
 727
 728 if (!dkim_sign_ctx.sig && !dkim->force_bodyhash)
 729   {
 730   DEBUG(D_transport) debug_printf("DKIM: no viable signatures to use\n");
 731   sigbuf = string_get(1);       /* return a zero-len string */
 732   }
 733 else
 734   {
 735   if (prefix && (pdkim_rc = pdkim_feed(&dkim_sign_ctx, prefix, Ustrlen(prefix))) != PDKIM_OK)
 736     goto pk_bad;
 737
 738   if (lseek(fd, off, SEEK_SET) < 0)
 739     sread = -1;
 740   else
 741     while ((sread = read(fd, &buf, sizeof(buf))) > 0)
 742       if ((pdkim_rc = pdkim_feed(&dkim_sign_ctx, buf, sread)) != PDKIM_OK)
 743         goto pk_bad;
 744
 745   /* Handle failed read above. */
 746   if (sread == -1)
 747     {
 748     debug_printf("DKIM: Error reading -K file.\n");
 749     save_errno = errno;
 750     goto bad;
 751     }
 752
 753   /* Build string of headers, one per signature */
 754
 755   if ((pdkim_rc = pdkim_feed_finish(&dkim_sign_ctx, &sig, errstr)) != PDKIM_OK)
 756     goto pk_bad;
 757
 758   if (!sig)
 759     {
 760     DEBUG(D_transport) debug_printf("DKIM: no signatures to use\n");
 761     sigbuf = string_get(1);     /* return a zero-len string */
 762     }
 763   else for (sigbuf = NULL; sig; sig = sig->next)
 764     sigbuf = string_append(sigbuf, 2, US sig->signature_header, US"\r\n");
 765   }
 766
 767 CLEANUP:
 768   (void) string_from_gstring(sigbuf);
 769   store_pool = old_pool;
 770   errno = save_errno;
 771   return sigbuf;
 772
 773 pk_bad:
 774   log_write(0, LOG_MAIN|LOG_PANIC,
 775                 "DKIM: signing failed: %.100s", pdkim_errstr(pdkim_rc));
 776 bad:
 777   sigbuf = NULL;
 778   goto CLEANUP;
 779
 780 expand_bad:
 781   log_write(0, LOG_MAIN | LOG_PANIC, "failed to expand %s: %s",
 782               errwhen, expand_string_message);
 783   goto bad;
 784 }
 785
 786
 787
 788
 789 gstring *
 790 authres_dkim(gstring * g)
 791 {
 792 pdkim_signature * sig;
 793 int start = 0;          /* compiler quietening */
 794
 795 DEBUG(D_acl) start = g->ptr;
 796
 797 for (sig = dkim_signatures; sig; sig = sig->next)
 798   {
 799   g = string_catn(g, US";\n\tdkim=", 8);
 800
 801   if (sig->verify_status & PDKIM_VERIFY_POLICY)
 802     g = string_append(g, 5,
 803       US"policy (", dkim_verify_status, US" - ", dkim_verify_reason, US")");
 804   else switch(sig->verify_status)
 805     {
 806     case PDKIM_VERIFY_NONE:    g = string_cat(g, US"none"); break;
 807     case PDKIM_VERIFY_INVALID:
 808       switch (sig->verify_ext_status)
 809         {
 810         case PDKIM_VERIFY_INVALID_PUBKEY_UNAVAILABLE:
 811           g = string_cat(g, US"tmperror (pubkey unavailable)\n\t\t"); break;
 812         case PDKIM_VERIFY_INVALID_BUFFER_SIZE:
 813           g = string_cat(g, US"permerror (overlong public key record)\n\t\t"); break;
 814         case PDKIM_VERIFY_INVALID_PUBKEY_DNSRECORD:
 815         case PDKIM_VERIFY_INVALID_PUBKEY_IMPORT:
 816           g = string_cat(g, US"neutral (syntax error in public key record)\n\t\t");
 817           break;
 818         case PDKIM_VERIFY_INVALID_SIGNATURE_ERROR:
 819           g = string_cat(g, US"neutral (signature tag missing or invalid)\n\t\t");
 820           break;
 821         case PDKIM_VERIFY_INVALID_DKIM_VERSION:
 822           g = string_cat(g, US"neutral (unsupported DKIM version)\n\t\t");
 823           break;
 824         default:
 825           g = string_cat(g, US"permerror (unspecified problem)\n\t\t"); break;
 826         }
 827       break;
 828     case PDKIM_VERIFY_FAIL:
 829       switch (sig->verify_ext_status)
 830         {
 831         case PDKIM_VERIFY_FAIL_BODY:
 832           g = string_cat(g,
 833             US"fail (body hash mismatch; body probably modified in transit)\n\t\t");
 834           break;
 835         case PDKIM_VERIFY_FAIL_MESSAGE:
 836           g = string_cat(g,
 837             US"fail (signature did not verify; headers probably modified in transit)\n\t\t");
 838           break;
 839         default:
 840           g = string_cat(g, US"fail (unspecified reason)\n\t\t");
 841           break;
 842         }
 843       break;
 844     case PDKIM_VERIFY_PASS:    g = string_cat(g, US"pass"); break;
 845     default:                   g = string_cat(g, US"permerror"); break;
 846     }
 847   if (sig->domain)   g = string_append(g, 2, US" header.d=", sig->domain);
 848   if (sig->identity) g = string_append(g, 2, US" header.i=", sig->identity);
 849   if (sig->selector) g = string_append(g, 2, US" header.s=", sig->selector);
 850   g = string_append(g, 2, US" header.a=", dkim_sig_to_a_tag(sig));
 851   }
 852
 853 DEBUG(D_acl)
 854   if (g->ptr == start)
 855     debug_printf("DKIM: no authres\n");
 856   else
 857     debug_printf("DKIM: authres '%.*s'\n", g->ptr - start - 3, g->s + start + 3);
 858 return g;
 859 }
 860
 861
 862 # endif /*!MACRO_PREDEF*/
 863 #endif  /*!DISABLE_DKIM*/