1/*++ 2/* NAME 3/* postscreen_dnsbl 3 4/* SUMMARY 5/* postscreen DNSBL support 6/* SYNOPSIS 7/* #include <postscreen.h> 8/* 9/* void psc_dnsbl_init(void) 10/* 11/* int psc_dnsbl_request(client_addr, callback, context) 12/* char *client_addr; 13/* void (*callback)(int, char *); 14/* char *context; 15/* 16/* int psc_dnsbl_retrieve(client_addr, dnsbl_name, dnsbl_index) 17/* char *client_addr; 18/* const char **dnsbl_name; 19/* int dnsbl_index; 20/* DESCRIPTION 21/* This module implements preliminary support for DNSBL lookups. 22/* Multiple requests for the same information are handled with 23/* reference counts. 24/* 25/* psc_dnsbl_init() initializes this module, and must be called 26/* once before any of the other functions in this module. 27/* 28/* psc_dnsbl_request() requests a blocklist score for the 29/* specified client IP address and increments the reference 30/* count. The request completes in the background. The client 31/* IP address must be in inet_ntop(3) output format. The 32/* callback argument specifies a function that is called when 33/* the requested result is available. The context is passed 34/* on to the callback function. The callback should ignore its 35/* first argument (it exists for compatibility with Postfix 36/* generic event infrastructure). 37/* The result value is the index for the psc_dnsbl_retrieve() 38/* call. 39/* 40/* psc_dnsbl_retrieve() retrieves the result score requested with 41/* psc_dnsbl_request() and decrements the reference count. It 42/* is an error to retrieve a score without requesting it first. 43/* LICENSE 44/* .ad 45/* .fi 46/* The Secure Mailer license must be distributed with this software. 47/* AUTHOR(S) 48/* Wietse Venema 49/* IBM T.J. Watson Research 50/* P.O. Box 704 51/* Yorktown Heights, NY 10598, USA 52/*--*/ 53 54/* System library. */ 55 56#include <sys_defs.h> 57#include <sys/socket.h> /* AF_INET */ 58#include <netinet/in.h> /* inet_pton() */ 59#include <arpa/inet.h> /* inet_pton() */ 60#include <stdio.h> /* sscanf */ 61 62/* Utility library. */ 63 64#include <msg.h> 65#include <mymalloc.h> 66#include <argv.h> 67#include <htable.h> 68#include <events.h> 69#include <vstream.h> 70#include <connect.h> 71#include <split_at.h> 72#include <valid_hostname.h> 73#include <ip_match.h> 74#include <myaddrinfo.h> 75#include <stringops.h> 76 77/* Global library. */ 78 79#include <mail_params.h> 80#include <mail_proto.h> 81 82/* Application-specific. */ 83 84#include <postscreen.h> 85 86 /* 87 * Talking to the DNSBLOG service. 88 */ 89#define DNSBLOG_TIMEOUT 10 90static char *psc_dnsbl_service; 91 92 /* 93 * Per-DNSBL filters and weights. 94 * 95 * The postscreen_dnsbl_sites parameter specifies zero or more DNSBL domains. 96 * We provide multiple access methods, one for quick iteration when sending 97 * queries to all DNSBL servers, and one for quick location when receiving a 98 * reply from one DNSBL server. 99 * 100 * Each DNSBL domain can be specified more than once, each time with a 101 * different (filter, weight) pair. We group (filter, weight) pairs in a 102 * linked list under their DNSBL domain name. The list head has a reference 103 * to a "safe name" for the DNSBL, in case the name includes a password. 104 */ 105static HTABLE *dnsbl_site_cache; /* indexed by DNSBNL domain */ 106static HTABLE_INFO **dnsbl_site_list; /* flattened cache */ 107 108typedef struct { 109 const char *safe_dnsbl; /* from postscreen_dnsbl_reply_map */ 110 struct PSC_DNSBL_SITE *first; /* list of (filter, weight) tuples */ 111} PSC_DNSBL_HEAD; 112 113typedef struct PSC_DNSBL_SITE { 114 char *filter; /* printable filter (default: null) */ 115 char *byte_codes; /* encoded filter (default: null) */ 116 int weight; /* reply weight (default: 1) */ 117 struct PSC_DNSBL_SITE *next; /* linked list */ 118} PSC_DNSBL_SITE; 119 120 /* 121 * Per-client DNSBL scores. 122 * 123 * Some SMTP clients make parallel connections. This can trigger parallel 124 * blocklist score requests when the pre-handshake delays of the connections 125 * overlap. 126 * 127 * We combine requests for the same score under the client IP address in a 128 * single reference-counted entry. The reference count goes up with each 129 * request for a score, and it goes down with each score retrieval. Each 130 * score has one or more requestors that need to be notified when the result 131 * is ready, so that postscreen can terminate a pre-handshake delay when all 132 * pre-handshake tests are completed. 133 */ 134static HTABLE *dnsbl_score_cache; /* indexed by client address */ 135 136typedef struct { 137 void (*callback) (int, char *); /* generic call-back routine */ 138 char *context; /* generic call-back argument */ 139} PSC_CALL_BACK_ENTRY; 140 141typedef struct { 142 const char *dnsbl_name; /* DNSBL with largest contribution */ 143 int dnsbl_weight; /* weight of largest contribution */ 144 int total; /* combined blocklist score */ 145 int refcount; /* score reference count */ 146 int pending_lookups; /* nr of DNS requests in flight */ 147 int request_id; /* duplicate suppression */ 148 /* Call-back table support. */ 149 int index; /* next table index */ 150 int limit; /* last valid index */ 151 PSC_CALL_BACK_ENTRY table[1]; /* actually a bunch */ 152} PSC_DNSBL_SCORE; 153 154#define PSC_CALL_BACK_INIT(sp) do { \ 155 (sp)->limit = 0; \ 156 (sp)->index = 0; \ 157 } while (0) 158 159#define PSC_CALL_BACK_INDEX_OF_LAST(sp) ((sp)->index - 1) 160 161#define PSC_CALL_BACK_CANCEL(sp, idx) do { \ 162 PSC_CALL_BACK_ENTRY *_cb_; \ 163 if ((idx) < 0 || (idx) >= (sp)->index) \ 164 msg_panic("%s: index %d must be >= 0 and < %d", \ 165 myname, (idx), (sp)->index); \ 166 _cb_ = (sp)->table + (idx); \ 167 event_cancel_timer(_cb_->callback, _cb_->context); \ 168 _cb_->callback = 0; \ 169 _cb_->context = 0; \ 170 } while (0) 171 172#define PSC_CALL_BACK_EXTEND(hp, sp) do { \ 173 if ((sp)->index >= (sp)->limit) { \ 174 int _count_ = ((sp)->limit ? (sp)->limit * 2 : 5); \ 175 (hp)->value = myrealloc((char *) (sp), sizeof(*(sp)) + \ 176 _count_ * sizeof((sp)->table)); \ 177 (sp) = (PSC_DNSBL_SCORE *) (hp)->value; \ 178 (sp)->limit = _count_; \ 179 } \ 180 } while (0) 181 182#define PSC_CALL_BACK_ENTER(sp, fn, ctx) do { \ 183 PSC_CALL_BACK_ENTRY *_cb_ = (sp)->table + (sp)->index++; \ 184 _cb_->callback = (fn); \ 185 _cb_->context = (ctx); \ 186 } while (0) 187 188#define PSC_CALL_BACK_NOTIFY(sp, ev) do { \ 189 PSC_CALL_BACK_ENTRY *_cb_; \ 190 for (_cb_ = (sp)->table; _cb_ < (sp)->table + (sp)->index; _cb_++) \ 191 if (_cb_->callback != 0) \ 192 _cb_->callback((ev), _cb_->context); \ 193 } while (0) 194 195#define PSC_NULL_EVENT (0) 196 197 /* 198 * Per-request state. 199 * 200 * This implementation stores the client IP address and DNSBL domain in the 201 * DNSBLOG query/reply stream. This simplifies code, and allows the DNSBLOG 202 * server to produce more informative logging. 203 */ 204static VSTRING *reply_client; /* client address in DNSBLOG reply */ 205static VSTRING *reply_dnsbl; /* domain in DNSBLOG reply */ 206static VSTRING *reply_addr; /* adress list in DNSBLOG reply */ 207 208/* psc_dnsbl_add_site - add DNSBL site information */ 209 210static void psc_dnsbl_add_site(const char *site) 211{ 212 const char *myname = "psc_dnsbl_add_site"; 213 char *saved_site = mystrdup(site); 214 VSTRING *byte_codes = 0; 215 PSC_DNSBL_HEAD *head; 216 PSC_DNSBL_SITE *new_site; 217 char junk; 218 const char *weight_text; 219 char *pattern_text; 220 int weight; 221 HTABLE_INFO *ht; 222 char *parse_err; 223 224 /* 225 * Parse the required DNSBL domain name, the optional reply filter and 226 * the optional reply weight factor. 227 */ 228#define DO_GRIPE 1 229 230 /* Negative weight means whitelist. */ 231 if ((weight_text = split_at(saved_site, '*')) != 0) { 232 if (sscanf(weight_text, "%d%c", &weight, &junk) != 1) 233 msg_fatal("bad DNSBL weight factor \"%s\" in \"%s\"", 234 weight_text, site); 235 } else { 236 weight = 1; 237 } 238 /* Reply filter. */ 239 if ((pattern_text = split_at(saved_site, '=')) != 0) { 240 byte_codes = vstring_alloc(100); 241 if ((parse_err = ip_match_parse(byte_codes, pattern_text)) != 0) 242 msg_fatal("bad DNSBL filter syntax: %s", parse_err); 243 } 244 if (valid_hostname(saved_site, DO_GRIPE) == 0) 245 msg_fatal("bad DNSBL domain name \"%s\" in \"%s\"", 246 saved_site, site); 247 248 if (msg_verbose > 1) 249 msg_info("%s: \"%s\" -> domain=\"%s\" pattern=\"%s\" weight=%d", 250 myname, site, saved_site, pattern_text ? pattern_text : 251 "null", weight); 252 253 /* 254 * Look up or create the (filter, weight) list head for this DNSBL domain 255 * name. 256 */ 257 if ((head = (PSC_DNSBL_HEAD *) 258 htable_find(dnsbl_site_cache, saved_site)) == 0) { 259 head = (PSC_DNSBL_HEAD *) mymalloc(sizeof(*head)); 260 ht = htable_enter(dnsbl_site_cache, saved_site, (char *) head); 261 /* Translate the DNSBL name into a safe name if available. */ 262 if (psc_dnsbl_reply == 0 263 || (head->safe_dnsbl = dict_get(psc_dnsbl_reply, saved_site)) == 0) 264 head->safe_dnsbl = ht->key; 265 if (psc_dnsbl_reply && psc_dnsbl_reply->error) 266 msg_fatal("%s:%s lookup error", psc_dnsbl_reply->type, 267 psc_dnsbl_reply->name); 268 head->first = 0; 269 } 270 271 /* 272 * Append the new (filter, weight) node to the list for this DNSBL domain 273 * name. 274 */ 275 new_site = (PSC_DNSBL_SITE *) mymalloc(sizeof(*new_site)); 276 new_site->filter = (pattern_text ? mystrdup(pattern_text) : 0); 277 new_site->byte_codes = (byte_codes ? ip_match_save(byte_codes) : 0); 278 new_site->weight = weight; 279 new_site->next = head->first; 280 head->first = new_site; 281 282 myfree(saved_site); 283 if (byte_codes) 284 vstring_free(byte_codes); 285} 286 287/* psc_dnsbl_match - match DNSBL reply filter */ 288 289static int psc_dnsbl_match(const char *filter, ARGV *reply) 290{ 291 char addr_buf[MAI_HOSTADDR_STRSIZE]; 292 char **cpp; 293 294 /* 295 * Run the replies through the pattern-matching engine. 296 */ 297 for (cpp = reply->argv; *cpp != 0; cpp++) { 298 if (inet_pton(AF_INET, *cpp, addr_buf) != 1) 299 msg_warn("address conversion error for %s -- ignoring this reply", 300 *cpp); 301 if (ip_match_execute(filter, addr_buf)) 302 return (1); 303 } 304 return (0); 305} 306 307/* psc_dnsbl_retrieve - retrieve blocklist score, decrement reference count */ 308 309int psc_dnsbl_retrieve(const char *client_addr, const char **dnsbl_name, 310 int dnsbl_index) 311{ 312 const char *myname = "psc_dnsbl_retrieve"; 313 PSC_DNSBL_SCORE *score; 314 int result_score; 315 316 /* 317 * Sanity check. 318 */ 319 if ((score = (PSC_DNSBL_SCORE *) 320 htable_find(dnsbl_score_cache, client_addr)) == 0) 321 msg_panic("%s: no blocklist score for %s", myname, client_addr); 322 323 /* 324 * Disable callbacks. 325 */ 326 PSC_CALL_BACK_CANCEL(score, dnsbl_index); 327 328 /* 329 * Reads are destructive. 330 */ 331 result_score = score->total; 332 *dnsbl_name = score->dnsbl_name; 333 score->refcount -= 1; 334 if (score->refcount < 1) { 335 if (msg_verbose > 1) 336 msg_info("%s: delete blocklist score for %s", myname, client_addr); 337 htable_delete(dnsbl_score_cache, client_addr, myfree); 338 } 339 return (result_score); 340} 341 342/* psc_dnsbl_receive - receive DNSBL reply, update blocklist score */ 343 344static void psc_dnsbl_receive(int event, char *context) 345{ 346 const char *myname = "psc_dnsbl_receive"; 347 VSTREAM *stream = (VSTREAM *) context; 348 PSC_DNSBL_SCORE *score; 349 PSC_DNSBL_HEAD *head; 350 PSC_DNSBL_SITE *site; 351 ARGV *reply_argv; 352 int request_id; 353 354 PSC_CLEAR_EVENT_REQUEST(vstream_fileno(stream), psc_dnsbl_receive, context); 355 356 /* 357 * Receive the DNSBL lookup result. 358 * 359 * This is preliminary code to explore the field. Later, DNSBL lookup will 360 * be handled by an UDP-based DNS client that is built directly into some 361 * Postfix daemon. 362 * 363 * Don't bother looking up the blocklist score when the client IP address is 364 * not listed at the DNSBL. 365 * 366 * Don't panic when the blocklist score no longer exists. It may be deleted 367 * when the client triggers a "drop" action after pregreet, when the 368 * client does not pregreet and the DNSBL reply arrives late, or when the 369 * client triggers a "drop" action after hanging up. 370 */ 371 if (event == EVENT_READ 372 && attr_scan(stream, 373 ATTR_FLAG_STRICT, 374 ATTR_TYPE_STR, MAIL_ATTR_RBL_DOMAIN, reply_dnsbl, 375 ATTR_TYPE_STR, MAIL_ATTR_ACT_CLIENT_ADDR, reply_client, 376 ATTR_TYPE_INT, MAIL_ATTR_LABEL, &request_id, 377 ATTR_TYPE_STR, MAIL_ATTR_RBL_ADDR, reply_addr, 378 ATTR_TYPE_END) == 4 379 && (score = (PSC_DNSBL_SCORE *) 380 htable_find(dnsbl_score_cache, STR(reply_client))) != 0 381 && score->request_id == request_id) { 382 383 /* 384 * Run this response past all applicable DNSBL filters and update the 385 * blocklist score for this client IP address. 386 * 387 * Don't panic when the DNSBL domain name is not found. The DNSBLOG 388 * server may be messed up. 389 */ 390 if (msg_verbose > 1) 391 msg_info("%s: client=\"%s\" score=%d domain=\"%s\" reply=\"%s\"", 392 myname, STR(reply_client), score->total, 393 STR(reply_dnsbl), STR(reply_addr)); 394 if (*STR(reply_addr) != 0) { 395 head = (PSC_DNSBL_HEAD *) 396 htable_find(dnsbl_site_cache, STR(reply_dnsbl)); 397 site = (head ? head->first : (PSC_DNSBL_SITE *) 0); 398 for (reply_argv = 0; site != 0; site = site->next) { 399 if (site->byte_codes == 0 400 || psc_dnsbl_match(site->byte_codes, reply_argv ? reply_argv : 401 (reply_argv = argv_split(STR(reply_addr), " ")))) { 402 if (score->dnsbl_name == 0 403 || score->dnsbl_weight < site->weight) { 404 score->dnsbl_name = head->safe_dnsbl; 405 score->dnsbl_weight = site->weight; 406 } 407 score->total += site->weight; 408 if (msg_verbose > 1) 409 msg_info("%s: filter=\"%s\" weight=%d score=%d", 410 myname, site->filter ? site->filter : "null", 411 site->weight, score->total); 412 } 413 } 414 if (reply_argv != 0) 415 argv_free(reply_argv); 416 } 417 418 /* 419 * Notify the requestor(s) that the result is ready to be picked up. 420 * If this call isn't made, clients have to sit out the entire 421 * pre-handshake delay. 422 */ 423 score->pending_lookups -= 1; 424 if (score->pending_lookups == 0) 425 PSC_CALL_BACK_NOTIFY(score, PSC_NULL_EVENT); 426 } else if (event == EVENT_TIME) { 427 msg_warn("dnsblog reply timeout %ds for %s", 428 DNSBLOG_TIMEOUT, (char *) vstream_context(stream)); 429 } 430 /* Here, score may be a null pointer. */ 431 vstream_fclose(stream); 432} 433 434/* psc_dnsbl_request - send dnsbl query, increment reference count */ 435 436int psc_dnsbl_request(const char *client_addr, 437 void (*callback) (int, char *), 438 char *context) 439{ 440 const char *myname = "psc_dnsbl_request"; 441 int fd; 442 VSTREAM *stream; 443 HTABLE_INFO **ht; 444 PSC_DNSBL_SCORE *score; 445 HTABLE_INFO *hash_node; 446 static int request_count; 447 448 /* 449 * Some spambots make several connections at nearly the same time, 450 * causing their pregreet delays to overlap. Such connections can share 451 * the efforts of DNSBL lookup. 452 * 453 * We store a reference-counted DNSBL score under its client IP address. We 454 * increment the reference count with each score request, and decrement 455 * the reference count with each score retrieval. 456 * 457 * Do not notify the requestor NOW when the DNS replies are already in. 458 * Reason: we must not make a backwards call while we are still in the 459 * middle of executing the corresponding forward call. Instead we create 460 * a zero-delay timer request and call the notification function from 461 * there. 462 * 463 * psc_dnsbl_request() could instead return a result value to indicate that 464 * the DNSBL score is already available, but that would complicate the 465 * caller with two different notification code paths: one asynchronous 466 * code path via the callback invocation, and one synchronous code path 467 * via the psc_dnsbl_request() result value. That would be a source of 468 * future bugs. 469 */ 470 if ((hash_node = htable_locate(dnsbl_score_cache, client_addr)) != 0) { 471 score = (PSC_DNSBL_SCORE *) hash_node->value; 472 score->refcount += 1; 473 PSC_CALL_BACK_EXTEND(hash_node, score); 474 PSC_CALL_BACK_ENTER(score, callback, context); 475 if (msg_verbose > 1) 476 msg_info("%s: reuse blocklist score for %s refcount=%d pending=%d", 477 myname, client_addr, score->refcount, 478 score->pending_lookups); 479 if (score->pending_lookups == 0) 480 event_request_timer(callback, context, EVENT_NULL_DELAY); 481 return (PSC_CALL_BACK_INDEX_OF_LAST(score)); 482 } 483 if (msg_verbose > 1) 484 msg_info("%s: create blocklist score for %s", myname, client_addr); 485 score = (PSC_DNSBL_SCORE *) mymalloc(sizeof(*score)); 486 score->request_id = request_count++; 487 score->dnsbl_name = 0; 488 score->dnsbl_weight = 0; 489 score->total = 0; 490 score->refcount = 1; 491 score->pending_lookups = 0; 492 PSC_CALL_BACK_INIT(score); 493 PSC_CALL_BACK_ENTER(score, callback, context); 494 (void) htable_enter(dnsbl_score_cache, client_addr, (char *) score); 495 496 /* 497 * Send a query to all DNSBL servers. Later, DNSBL lookup will be done 498 * with an UDP-based DNS client that is built directly into Postfix code. 499 * We therefore do not optimize the maximum out of this temporary 500 * implementation. 501 */ 502 for (ht = dnsbl_site_list; *ht; ht++) { 503 if ((fd = LOCAL_CONNECT(psc_dnsbl_service, NON_BLOCKING, 1)) < 0) { 504 msg_warn("%s: connect to %s service: %m", 505 myname, psc_dnsbl_service); 506 continue; 507 } 508 stream = vstream_fdopen(fd, O_RDWR); 509 vstream_control(stream, 510 VSTREAM_CTL_CONTEXT, ht[0]->key, 511 VSTREAM_CTL_END); 512 attr_print(stream, ATTR_FLAG_NONE, 513 ATTR_TYPE_STR, MAIL_ATTR_RBL_DOMAIN, ht[0]->key, 514 ATTR_TYPE_STR, MAIL_ATTR_ACT_CLIENT_ADDR, client_addr, 515 ATTR_TYPE_INT, MAIL_ATTR_LABEL, score->request_id, 516 ATTR_TYPE_END); 517 if (vstream_fflush(stream) != 0) { 518 msg_warn("%s: error sending to %s service: %m", 519 myname, psc_dnsbl_service); 520 vstream_fclose(stream); 521 continue; 522 } 523 PSC_READ_EVENT_REQUEST(vstream_fileno(stream), psc_dnsbl_receive, 524 (char *) stream, DNSBLOG_TIMEOUT); 525 score->pending_lookups += 1; 526 } 527 return (PSC_CALL_BACK_INDEX_OF_LAST(score)); 528} 529 530/* psc_dnsbl_init - initialize */ 531 532void psc_dnsbl_init(void) 533{ 534 const char *myname = "psc_dnsbl_init"; 535 ARGV *dnsbl_site = argv_split(var_psc_dnsbl_sites, ", \t\r\n"); 536 char **cpp; 537 538 /* 539 * Sanity check. 540 */ 541 if (dnsbl_site_cache != 0) 542 msg_panic("%s: called more than once", myname); 543 544 /* 545 * pre-compute the DNSBLOG socket name. 546 */ 547 psc_dnsbl_service = concatenate(MAIL_CLASS_PRIVATE, "/", 548 var_dnsblog_service, (char *) 0); 549 550 /* 551 * Prepare for quick iteration when sending out queries to all DNSBL 552 * servers, and for quick lookup when a reply arrives from a specific 553 * DNSBL server. 554 */ 555 dnsbl_site_cache = htable_create(13); 556 for (cpp = dnsbl_site->argv; *cpp; cpp++) 557 psc_dnsbl_add_site(*cpp); 558 argv_free(dnsbl_site); 559 dnsbl_site_list = htable_list(dnsbl_site_cache); 560 561 /* 562 * The per-client blocklist score. 563 */ 564 dnsbl_score_cache = htable_create(13); 565 566 /* 567 * Space for ad-hoc DNSBLOG server request/reply parameters. 568 */ 569 reply_client = vstring_alloc(100); 570 reply_dnsbl = vstring_alloc(100); 571 reply_addr = vstring_alloc(100); 572} 573