| 1 | /* $Cambridge: exim/src/src/dkim-exim.c,v 1.2 2007/10/09 14:10:34 tom Exp $ */ |
| 2 | |
| 3 | /************************************************* |
| 4 | * Exim - an Internet mail transport agent * |
| 5 | *************************************************/ |
| 6 | |
| 7 | /* Copyright (c) University of Cambridge 1995 - 2007 */ |
| 8 | /* See the file NOTICE for conditions of use and distribution. */ |
| 9 | |
| 10 | /* Code for DKIM support. Other DKIM relevant code is in |
| 11 | receive.c, transport.c and transports/smtp.c */ |
| 12 | |
| 13 | #include "exim.h" |
| 14 | |
| 15 | #ifdef EXPERIMENTAL_DKIM |
| 16 | |
| 17 | /* Globals related to the DKIM reference library. */ |
| 18 | DKIMContext *dkim_context = NULL; |
| 19 | DKIMSignOptions *dkim_sign_options = NULL; |
| 20 | DKIMVerifyOptions *dkim_verify_options = NULL; |
| 21 | int dkim_verify_result = DKIM_NEUTRAL; |
| 22 | int dkim_internal_status = DKIM_SUCCESS; |
| 23 | |
| 24 | /* Global char buffer for getc/ungetc functions. We need |
| 25 | to accumulate some chars to be able to match EOD and |
| 26 | doubled SMTP dots. Those must not be fed to the validation |
| 27 | engine. */ |
| 28 | int dkimbuff[6] = {256,256,256,256,256,256}; |
| 29 | |
| 30 | /* receive_getc() wrapper that feeds DKIM while Exim reads |
| 31 | the message. */ |
| 32 | int dkim_receive_getc(void) { |
| 33 | int i; |
| 34 | |
| 35 | #ifdef EXPERIMENTAL_DOMAINKEYS |
| 36 | int c = dk_receive_getc(); |
| 37 | #else |
| 38 | int c = receive_getc(); |
| 39 | #endif |
| 40 | |
| 41 | if ((dkim_context != NULL) && |
| 42 | (dkim_internal_status == DKIM_SUCCESS)) { |
| 43 | /* Send oldest byte */ |
| 44 | if (dkimbuff[0] < 256) { |
| 45 | DKIMVerifyProcess(dkim_context,(char *)&dkimbuff[0],1); |
| 46 | /* debug_printf("%c",(int)dkimbuff[0]); */ |
| 47 | } |
| 48 | /* rotate buffer */ |
| 49 | for (i=0;i<5;i++) dkimbuff[i]=dkimbuff[i+1]; |
| 50 | dkimbuff[5]=c; |
| 51 | /* look for our candidate patterns */ |
| 52 | if ( (dkimbuff[1] == '\r') && |
| 53 | (dkimbuff[2] == '\n') && |
| 54 | (dkimbuff[3] == '.') && |
| 55 | (dkimbuff[4] == '\r') && |
| 56 | (dkimbuff[5] == '\n') ) { |
| 57 | /* End of DATA */ |
| 58 | dkimbuff[1] = 256; |
| 59 | dkimbuff[2] = 256; |
| 60 | dkimbuff[3] = 256; |
| 61 | dkimbuff[4] = 256; |
| 62 | dkimbuff[5] = 256; |
| 63 | } |
| 64 | if ( (dkimbuff[2] == '\r') && |
| 65 | (dkimbuff[3] == '\n') && |
| 66 | (dkimbuff[4] == '.') && |
| 67 | (dkimbuff[5] == '.') ) { |
| 68 | /* doubled dot, skip this char */ |
| 69 | dkimbuff[5] = 256; |
| 70 | } |
| 71 | } |
| 72 | |
| 73 | return c; |
| 74 | } |
| 75 | |
| 76 | /* When exim puts a char back in the fd, we |
| 77 | must rotate our buffer back. */ |
| 78 | int dkim_receive_ungetc(int c) { |
| 79 | |
| 80 | if ((dkim_context != NULL) && |
| 81 | (dkim_internal_status == DKIM_SUCCESS)) { |
| 82 | int i; |
| 83 | /* rotate buffer back */ |
| 84 | for (i=5;i>0;i--) dkimbuff[i]=dkimbuff[i-1]; |
| 85 | dkimbuff[0]=256; |
| 86 | } |
| 87 | |
| 88 | #ifdef EXPERIMENTAL_DOMAINKEYS |
| 89 | return dk_receive_ungetc(c); |
| 90 | #else |
| 91 | return receive_ungetc(c); |
| 92 | #endif |
| 93 | } |
| 94 | |
| 95 | |
| 96 | void dkim_exim_verify_init(void) { |
| 97 | int old_pool = store_pool; |
| 98 | |
| 99 | /* Bail out unless we got perfect conditions */ |
| 100 | if (!(smtp_input && |
| 101 | !smtp_batched_input && |
| 102 | dkim_do_verify)) { |
| 103 | return; |
| 104 | } |
| 105 | |
| 106 | store_pool = POOL_PERM; |
| 107 | |
| 108 | dkim_context = NULL; |
| 109 | dkim_verify_options = NULL; |
| 110 | |
| 111 | dkim_context = store_get(sizeof(DKIMContext)); |
| 112 | dkim_verify_options = store_get(sizeof(DKIMVerifyOptions)); |
| 113 | |
| 114 | if (!dkim_context || |
| 115 | !dkim_verify_options) { |
| 116 | debug_printf("DKIM: Can't allocate memory for verifying.\n"); |
| 117 | dkim_context = NULL; |
| 118 | } |
| 119 | |
| 120 | memset(dkim_context,0,sizeof(DKIMContext)); |
| 121 | memset(dkim_verify_options,0,sizeof(DKIMVerifyOptions)); |
| 122 | |
| 123 | dkim_verify_options->nHonorBodyLengthTag = 1; /* Honor the l= tag */ |
| 124 | dkim_verify_options->nCheckPolicy = 1; /* Fetch sender's policy */ |
| 125 | dkim_verify_options->nSubjectRequired = 1; /* Do not require Subject header inclusion */ |
| 126 | |
| 127 | dkim_verify_options->pfnSelectorCallback = NULL; |
| 128 | dkim_verify_options->pfnPolicyCallback = NULL; |
| 129 | |
| 130 | dkim_status_wrap( DKIMVerifyInit(dkim_context, dkim_verify_options), |
| 131 | "error calling DKIMVerifyInit()" ); |
| 132 | |
| 133 | if (dkim_internal_status != DKIM_SUCCESS) { |
| 134 | /* Invalidate context */ |
| 135 | dkim_context = NULL; |
| 136 | } |
| 137 | |
| 138 | store_pool = old_pool; |
| 139 | } |
| 140 | |
| 141 | |
| 142 | void dkim_exim_verify_finish(void) { |
| 143 | int i; |
| 144 | int old_pool = store_pool; |
| 145 | |
| 146 | if (!dkim_do_verify || |
| 147 | (!(smtp_input && !smtp_batched_input)) || |
| 148 | (dkim_context == NULL) || |
| 149 | (dkim_internal_status != DKIM_SUCCESS)) return; |
| 150 | |
| 151 | store_pool = POOL_PERM; |
| 152 | |
| 153 | /* Flush eventual remaining input chars */ |
| 154 | for (i=0;i<6;i++) |
| 155 | if (dkimbuff[i] < 256) |
| 156 | DKIMVerifyProcess(dkim_context,(char *)&dkimbuff[i],1); |
| 157 | |
| 158 | /* Fetch global result. Can be one of: |
| 159 | DKIM_SUCCESS |
| 160 | DKIM_PARTIAL_SUCCESS |
| 161 | DKIM_NEUTRAL |
| 162 | DKIM_FAIL |
| 163 | */ |
| 164 | dkim_verify_result = DKIMVerifyResults(dkim_context); |
| 165 | |
| 166 | store_pool = old_pool; |
| 167 | } |
| 168 | |
| 169 | |
| 170 | /* Lookup result for a given domain (or identity) */ |
| 171 | int dkim_exim_verify_result(uschar *domain, uschar **result, uschar **error) { |
| 172 | int sig_count = 0; |
| 173 | int i,rc; |
| 174 | char policy[512]; |
| 175 | DKIMVerifyDetails *dkim_verify_details = NULL; |
| 176 | |
| 177 | if (!dkim_do_verify || |
| 178 | (!(smtp_input && !smtp_batched_input)) || |
| 179 | (dkim_context == NULL) || |
| 180 | (dkim_internal_status != DKIM_SUCCESS)) { |
| 181 | rc = DKIM_EXIM_UNVERIFIED; |
| 182 | goto YIELD; |
| 183 | } |
| 184 | |
| 185 | DKIMVerifyGetDetails(dkim_context, |
| 186 | &sig_count, |
| 187 | &dkim_verify_details, |
| 188 | policy); |
| 189 | |
| 190 | |
| 191 | rc = DKIM_EXIM_UNSIGNED; |
| 192 | |
| 193 | debug_printf("DKIM: We have %d signature(s)\n",sig_count); |
| 194 | for (i=0;i<sig_count;i++) { |
| 195 | debug_printf( "DKIM: [%d] ", i + 1 ); |
| 196 | if (!dkim_verify_details[i].Domain) { |
| 197 | debug_printf("parse error (no domain)\n"); |
| 198 | continue; |
| 199 | } |
| 200 | |
| 201 | if (dkim_verify_details[i].nResult >= 0) { |
| 202 | debug_printf( "GOOD d=%s i=%s\n", |
| 203 | dkim_verify_details[i].Domain, |
| 204 | dkim_verify_details[i].IdentityDomain ); |
| 205 | } |
| 206 | else { |
| 207 | debug_printf( "FAIL d=%s i=%s c=%d\n", |
| 208 | dkim_verify_details[i].Domain, |
| 209 | dkim_verify_details[i].IdentityDomain, |
| 210 | dkim_verify_details[i].nResult |
| 211 | ); |
| 212 | |
| 213 | } |
| 214 | |
| 215 | if ( (strcmpic(domain,dkim_verify_details[i].Domain) == 0) || |
| 216 | (strcmpic(domain,dkim_verify_details[i].IdentityDomain) == 0) ) { |
| 217 | if (dkim_verify_details[i].nResult >= 0) { |
| 218 | rc = DKIM_EXIM_GOOD; |
| 219 | /* TODO: Add From: domain check */ |
| 220 | } |
| 221 | else { |
| 222 | /* Return DEFER for temp. error types */ |
| 223 | if (dkim_verify_details[i].nResult == DKIM_SELECTOR_DNS_TEMP_FAILURE) { |
| 224 | rc = DKIM_EXIM_DEFER; |
| 225 | } |
| 226 | else { |
| 227 | rc = DKIM_EXIM_FAIL; |
| 228 | } |
| 229 | } |
| 230 | } |
| 231 | } |
| 232 | |
| 233 | YIELD: |
| 234 | switch (rc) { |
| 235 | case DKIM_EXIM_FAIL: |
| 236 | *result = "bad"; |
| 237 | break; |
| 238 | case DKIM_EXIM_DEFER: |
| 239 | *result = "defer"; |
| 240 | break; |
| 241 | case DKIM_EXIM_UNVERIFIED: |
| 242 | *result = "unverified"; |
| 243 | break; |
| 244 | case DKIM_EXIM_UNSIGNED: |
| 245 | *result = "unsigned"; |
| 246 | break; |
| 247 | case DKIM_EXIM_GOOD: |
| 248 | *result = "good"; |
| 249 | break; |
| 250 | } |
| 251 | |
| 252 | return rc; |
| 253 | } |
| 254 | |
| 255 | |
| 256 | |
| 257 | uschar *dkim_exim_sign_headers = NULL; |
| 258 | int dkim_exim_header_callback(const char* header) { |
| 259 | int sep = 0; |
| 260 | uschar *hdr_ptr = dkim_exim_sign_headers; |
| 261 | uschar *hdr_itr = NULL; |
| 262 | uschar hdr_buf[512]; |
| 263 | uschar *hdr_name = string_copy(US header); |
| 264 | char *colon_pos = strchr(hdr_name,':'); |
| 265 | |
| 266 | if (colon_pos == NULL) return 0; |
| 267 | *colon_pos = '\0'; |
| 268 | |
| 269 | debug_printf("DKIM: header '%s' ",hdr_name); |
| 270 | while ((hdr_itr = string_nextinlist(&hdr_ptr, &sep, |
| 271 | hdr_buf, |
| 272 | sizeof(hdr_buf))) != NULL) { |
| 273 | if (strcmpic((uschar *)hdr_name,hdr_itr) == 0) { |
| 274 | debug_printf("included in signature.\n"); |
| 275 | return 1; |
| 276 | } |
| 277 | } |
| 278 | debug_printf("NOT included in signature.\n"); |
| 279 | return 0; |
| 280 | } |
| 281 | |
| 282 | uschar *dkim_exim_sign(int dkim_fd, |
| 283 | uschar *dkim_private_key, |
| 284 | uschar *dkim_domain, |
| 285 | uschar *dkim_selector, |
| 286 | uschar *dkim_canon, |
| 287 | uschar *dkim_sign_headers) { |
| 288 | |
| 289 | uschar *rc = NULL; |
| 290 | char buf[4096]; |
| 291 | int seen_lf = 0; |
| 292 | int seen_lfdot = 0; |
| 293 | int save_errno = 0; |
| 294 | int sread; |
| 295 | char *signature; |
| 296 | int old_pool = store_pool; |
| 297 | store_pool = POOL_PERM; |
| 298 | |
| 299 | dkim_context = NULL; |
| 300 | dkim_sign_options = NULL; |
| 301 | |
| 302 | dkim_context = store_get(sizeof(DKIMContext)); |
| 303 | dkim_sign_options = store_get(sizeof(DKIMSignOptions)); |
| 304 | |
| 305 | memset(dkim_sign_options,0,sizeof(DKIMSignOptions)); |
| 306 | memset(dkim_context,0,sizeof(DKIMContext)); |
| 307 | |
| 308 | dkim_sign_options->nIncludeBodyLengthTag = 0; |
| 309 | dkim_sign_options->nIncludeCopiedHeaders = 0; |
| 310 | dkim_sign_options->nHash = DKIM_HASH_SHA256; |
| 311 | dkim_sign_options->nIncludeTimeStamp = 0; |
| 312 | dkim_sign_options->nIncludeQueryMethod = 0; |
| 313 | dkim_sign_options->pfnHeaderCallback = dkim_exim_header_callback; |
| 314 | dkim_sign_options->nIncludeBodyHash = DKIM_BODYHASH_IETF_1; |
| 315 | |
| 316 | |
| 317 | dkim_domain = expand_string(dkim_domain); |
| 318 | if (dkim_domain == NULL) { |
| 319 | /* expansion error, do not send message. */ |
| 320 | log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand " |
| 321 | "dkim_domain: %s", expand_string_message); |
| 322 | rc = NULL; |
| 323 | goto CLEANUP; |
| 324 | } |
| 325 | /* Set up $dkim_domain expansion variable. */ |
| 326 | dkim_signing_domain = dkim_domain; |
| 327 | Ustrncpy((uschar *)dkim_sign_options->szDomain,dkim_domain,255); |
| 328 | |
| 329 | |
| 330 | /* Get selector to use. */ |
| 331 | dkim_selector = expand_string(dkim_selector); |
| 332 | if (dkim_selector == NULL) { |
| 333 | log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand " |
| 334 | "dkim_selector: %s", expand_string_message); |
| 335 | rc = NULL; |
| 336 | goto CLEANUP; |
| 337 | } |
| 338 | /* Set up $dkim_selector expansion variable. */ |
| 339 | dkim_signing_selector = dkim_selector; |
| 340 | Ustrncpy((uschar *)dkim_sign_options->szSelector,dkim_selector,79); |
| 341 | |
| 342 | /* Expand provided options */ |
| 343 | dkim_canon = expand_string(dkim_canon?dkim_canon:US"relaxed"); |
| 344 | if (dkim_canon == NULL) { |
| 345 | /* expansion error, do not send message. */ |
| 346 | log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand " |
| 347 | "dkim_canon: %s", expand_string_message); |
| 348 | rc = NULL; |
| 349 | goto CLEANUP; |
| 350 | } |
| 351 | if (Ustrcmp(dkim_canon, "relaxed") == 0) |
| 352 | dkim_sign_options->nCanon = DKIM_SIGN_RELAXED; |
| 353 | else if (Ustrcmp(dkim_canon, "simple") == 0) |
| 354 | dkim_sign_options->nCanon = DKIM_SIGN_SIMPLE; |
| 355 | else { |
| 356 | log_write(0, LOG_MAIN, "DKIM: unknown canonicalization method '%s', defaulting to 'relaxed'.\n",dkim_canon); |
| 357 | dkim_sign_options->nCanon = DKIM_SIGN_RELAXED; |
| 358 | } |
| 359 | |
| 360 | /* Expand signing headers once */ |
| 361 | if (dkim_sign_headers != NULL) { |
| 362 | dkim_sign_headers = expand_string(dkim_sign_headers); |
| 363 | if (dkim_sign_headers == NULL) { |
| 364 | log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand " |
| 365 | "dkim_sign_headers: %s", expand_string_message); |
| 366 | rc = NULL; |
| 367 | goto CLEANUP; |
| 368 | } |
| 369 | } |
| 370 | |
| 371 | if (dkim_sign_headers == NULL) { |
| 372 | /* Use RFC defaults */ |
| 373 | dkim_sign_headers = US"from:sender:reply-to:subject:date:" |
| 374 | "message-id:to:cc:mime-version:content-type:" |
| 375 | "content-transfer-encoding:content-id:" |
| 376 | "content-description:resent-date:resent-from:" |
| 377 | "resent-sender:resent-to:resent-cc:resent-message-id:" |
| 378 | "in-reply-to:references:" |
| 379 | "list-id:list-help:list-unsubscribe:" |
| 380 | "list-subscribe:list-post:list-owner:list-archive"; |
| 381 | } |
| 382 | dkim_exim_sign_headers = dkim_sign_headers; |
| 383 | |
| 384 | /* Get private key to use. */ |
| 385 | dkim_private_key = expand_string(dkim_private_key); |
| 386 | if (dkim_private_key == NULL) { |
| 387 | log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand " |
| 388 | "dkim_private_key: %s", expand_string_message); |
| 389 | rc = NULL; |
| 390 | goto CLEANUP; |
| 391 | } |
| 392 | |
| 393 | if ( (Ustrlen(dkim_private_key) == 0) || |
| 394 | (Ustrcmp(dkim_private_key,"0") == 0) || |
| 395 | (Ustrcmp(dkim_private_key,"false") == 0) ) { |
| 396 | /* don't sign, but no error */ |
| 397 | rc = US""; |
| 398 | goto CLEANUP; |
| 399 | } |
| 400 | |
| 401 | if (dkim_private_key[0] == '/') { |
| 402 | int privkey_fd = 0; |
| 403 | /* Looks like a filename, load the private key. */ |
| 404 | memset(big_buffer,0,big_buffer_size); |
| 405 | privkey_fd = open(CS dkim_private_key,O_RDONLY); |
| 406 | (void)read(privkey_fd,big_buffer,16383); |
| 407 | (void)close(privkey_fd); |
| 408 | dkim_private_key = big_buffer; |
| 409 | } |
| 410 | |
| 411 | /* Initialize signing context. */ |
| 412 | dkim_status_wrap( DKIMSignInit(dkim_context, dkim_sign_options), |
| 413 | "error calling DKIMSignInit()" ); |
| 414 | |
| 415 | if (dkim_internal_status != DKIM_SUCCESS) { |
| 416 | /* Invalidate context */ |
| 417 | dkim_context = NULL; |
| 418 | goto CLEANUP; |
| 419 | } |
| 420 | |
| 421 | while((sread = read(dkim_fd,&buf,4096)) > 0) { |
| 422 | int pos = 0; |
| 423 | char c; |
| 424 | |
| 425 | while (pos < sread) { |
| 426 | c = buf[pos++]; |
| 427 | |
| 428 | if ((c == '.') && seen_lfdot) { |
| 429 | /* escaped dot, write "\n.", continue */ |
| 430 | dkim_internal_status = DKIMSignProcess(dkim_context,"\n.",2); |
| 431 | seen_lf = 0; |
| 432 | seen_lfdot = 0; |
| 433 | continue; |
| 434 | } |
| 435 | |
| 436 | if (seen_lfdot) { |
| 437 | /* EOM, write "\n" and break */ |
| 438 | dkim_internal_status = DKIMSignProcess(dkim_context,"\n",1); |
| 439 | break; |
| 440 | } |
| 441 | |
| 442 | if ((c == '.') && seen_lf) { |
| 443 | seen_lfdot = 1; |
| 444 | continue; |
| 445 | } |
| 446 | |
| 447 | if (seen_lf) { |
| 448 | /* normal lf, just send it */ |
| 449 | dkim_internal_status = DKIMSignProcess(dkim_context,"\n",1); |
| 450 | seen_lf = 0; |
| 451 | } |
| 452 | |
| 453 | if (c == '\n') { |
| 454 | seen_lf = 1; |
| 455 | continue; |
| 456 | } |
| 457 | |
| 458 | /* write the char */ |
| 459 | dkim_internal_status = DKIMSignProcess(dkim_context,&c,1); |
| 460 | } |
| 461 | } |
| 462 | |
| 463 | /* Handle failed read above. */ |
| 464 | if (sread == -1) { |
| 465 | debug_printf("DKIM: Error reading -K file.\n"); |
| 466 | save_errno = errno; |
| 467 | rc = NULL; |
| 468 | goto CLEANUP; |
| 469 | } |
| 470 | |
| 471 | if (!dkim_status_wrap(dkim_internal_status, |
| 472 | "error while processing message data")) { |
| 473 | rc = NULL; |
| 474 | goto CLEANUP; |
| 475 | } |
| 476 | |
| 477 | if (!dkim_status_wrap( DKIMSignGetSig2( dkim_context, dkim_private_key, &signature ), |
| 478 | "error while signing message" ) ) { |
| 479 | rc = NULL; |
| 480 | goto CLEANUP; |
| 481 | } |
| 482 | |
| 483 | log_write(0, LOG_MAIN, "Message signed with DKIM: %s\n",signature); |
| 484 | |
| 485 | rc = store_get(strlen(signature)+3); |
| 486 | Ustrcpy(rc,US signature); |
| 487 | Ustrcat(rc,US"\r\n"); |
| 488 | |
| 489 | CLEANUP: |
| 490 | if (dkim_context != NULL) { |
| 491 | dkim_context = NULL; |
| 492 | } |
| 493 | store_pool = old_pool; |
| 494 | errno = save_errno; |
| 495 | return rc; |
| 496 | } |
| 497 | |
| 498 | unsigned int dkim_status_wrap(int stat, uschar *text) { |
| 499 | char *p = DKIMGetErrorString(stat); |
| 500 | |
| 501 | if (stat != DKIM_SUCCESS) { |
| 502 | debug_printf("DKIM: %s",text?text:US""); |
| 503 | if (p) debug_printf(" (%s)",p); |
| 504 | debug_printf("\n"); |
| 505 | } |
| 506 | dkim_internal_status = stat; |
| 507 | return (dkim_internal_status==DKIM_SUCCESS)?1:0; |
| 508 | } |
| 509 | |
| 510 | #endif |