1 /*
2 * iterator/iter_scrub.c - scrubbing, normalization, sanitization of DNS msgs.
3 *
4 * Copyright (c) 2007, NLnet Labs. All rights reserved.
5 *
6 * This software is open source.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 *
12 * Redistributions of source code must retain the above copyright notice,
13 * this list of conditions and the following disclaimer.
14 *
15 * Redistributions in binary form must reproduce the above copyright notice,
16 * this list of conditions and the following disclaimer in the documentation
17 * and/or other materials provided with the distribution.
18 *
19 * Neither the name of the NLNET LABS nor the names of its contributors may
20 * be used to endorse or promote products derived from this software without
21 * specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
24 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
25 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
26 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
27 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
28 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
29 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
30 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
31 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
32 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
33 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
34 */
35
36 /**
37 * \file
38 *
39 * This file has routine(s) for cleaning up incoming DNS messages from
40 * possible useless or malicious junk in it.
41 */
42 #include "config.h"
43 #include "iterator/iter_scrub.h"
44 #include "iterator/iterator.h"
45 #include "iterator/iter_priv.h"
46 #include "services/cache/rrset.h"
47 #include "util/log.h"
48 #include "util/net_help.h"
49 #include "util/regional.h"
50 #include "util/config_file.h"
51 #include "util/module.h"
52 #include "util/data/msgparse.h"
53 #include "util/data/dname.h"
54 #include "util/data/msgreply.h"
55 #include "util/alloc.h"
56 #include "sldns/sbuffer.h"
57
58 /** RRset flag used during scrubbing. The RRset is OK. */
59 #define RRSET_SCRUB_OK 0x80
60
61 /** remove rrset, update loop variables */
62 static void
remove_rrset(const char * str,sldns_buffer * pkt,struct msg_parse * msg,struct rrset_parse * prev,struct rrset_parse ** rrset)63 remove_rrset(const char* str, sldns_buffer* pkt, struct msg_parse* msg,
64 struct rrset_parse* prev, struct rrset_parse** rrset)
65 {
66 if(verbosity >= VERB_QUERY && str
67 && (*rrset)->dname_len <= LDNS_MAX_DOMAINLEN) {
68 uint8_t buf[LDNS_MAX_DOMAINLEN+1];
69 dname_pkt_copy(pkt, buf, (*rrset)->dname);
70 log_nametypeclass(VERB_QUERY, str, buf,
71 (*rrset)->type, ntohs((*rrset)->rrset_class));
72 }
73 if(prev)
74 prev->rrset_all_next = (*rrset)->rrset_all_next;
75 else msg->rrset_first = (*rrset)->rrset_all_next;
76 if(msg->rrset_last == *rrset)
77 msg->rrset_last = prev;
78 msg->rrset_count --;
79 switch((*rrset)->section) {
80 case LDNS_SECTION_ANSWER: msg->an_rrsets--; break;
81 case LDNS_SECTION_AUTHORITY: msg->ns_rrsets--; break;
82 case LDNS_SECTION_ADDITIONAL: msg->ar_rrsets--; break;
83 default: log_assert(0);
84 }
85 msgparse_bucket_remove(msg, *rrset);
86 *rrset = (*rrset)->rrset_all_next;
87 }
88
89 /** return true if rr type has additional names in it */
90 static int
has_additional(uint16_t t)91 has_additional(uint16_t t)
92 {
93 switch(t) {
94 case LDNS_RR_TYPE_MB:
95 case LDNS_RR_TYPE_MD:
96 case LDNS_RR_TYPE_MF:
97 case LDNS_RR_TYPE_NS:
98 case LDNS_RR_TYPE_MX:
99 case LDNS_RR_TYPE_KX:
100 case LDNS_RR_TYPE_SRV:
101 return 1;
102 case LDNS_RR_TYPE_NAPTR:
103 /* TODO: NAPTR not supported, glue stripped off */
104 return 0;
105 }
106 return 0;
107 }
108
109 /** get additional name from rrset RR, return false if no name present */
110 static int
get_additional_name(struct rrset_parse * rrset,struct rr_parse * rr,uint8_t ** nm,size_t * nmlen,sldns_buffer * pkt)111 get_additional_name(struct rrset_parse* rrset, struct rr_parse* rr,
112 uint8_t** nm, size_t* nmlen, sldns_buffer* pkt)
113 {
114 size_t offset = 0;
115 size_t len, oldpos;
116 switch(rrset->type) {
117 case LDNS_RR_TYPE_MB:
118 case LDNS_RR_TYPE_MD:
119 case LDNS_RR_TYPE_MF:
120 case LDNS_RR_TYPE_NS:
121 offset = 0;
122 break;
123 case LDNS_RR_TYPE_MX:
124 case LDNS_RR_TYPE_KX:
125 offset = 2;
126 break;
127 case LDNS_RR_TYPE_SRV:
128 offset = 6;
129 break;
130 case LDNS_RR_TYPE_NAPTR:
131 /* TODO: NAPTR not supported, glue stripped off */
132 return 0;
133 default:
134 return 0;
135 }
136 len = sldns_read_uint16(rr->ttl_data+sizeof(uint32_t));
137 if(len < offset+1)
138 return 0; /* rdata field too small */
139 *nm = rr->ttl_data+sizeof(uint32_t)+sizeof(uint16_t)+offset;
140 oldpos = sldns_buffer_position(pkt);
141 sldns_buffer_set_position(pkt, (size_t)(*nm - sldns_buffer_begin(pkt)));
142 *nmlen = pkt_dname_len(pkt);
143 sldns_buffer_set_position(pkt, oldpos);
144 if(*nmlen == 0)
145 return 0;
146 return 1;
147 }
148
149 /** Place mark on rrsets in additional section they are OK */
150 static void
mark_additional_rrset(sldns_buffer * pkt,struct msg_parse * msg,struct rrset_parse * rrset)151 mark_additional_rrset(sldns_buffer* pkt, struct msg_parse* msg,
152 struct rrset_parse* rrset)
153 {
154 /* Mark A and AAAA for NS as appropriate additional section info. */
155 uint8_t* nm = NULL;
156 size_t nmlen = 0;
157 struct rr_parse* rr;
158
159 if(!has_additional(rrset->type))
160 return;
161 for(rr = rrset->rr_first; rr; rr = rr->next) {
162 if(get_additional_name(rrset, rr, &nm, &nmlen, pkt)) {
163 /* mark A */
164 hashvalue_type h = pkt_hash_rrset(pkt, nm,
165 LDNS_RR_TYPE_A, rrset->rrset_class, 0);
166 struct rrset_parse* r = msgparse_hashtable_lookup(
167 msg, pkt, h, 0, nm, nmlen,
168 LDNS_RR_TYPE_A, rrset->rrset_class);
169 if(r && r->section == LDNS_SECTION_ADDITIONAL) {
170 r->flags |= RRSET_SCRUB_OK;
171 }
172
173 /* mark AAAA */
174 h = pkt_hash_rrset(pkt, nm, LDNS_RR_TYPE_AAAA,
175 rrset->rrset_class, 0);
176 r = msgparse_hashtable_lookup(msg, pkt, h, 0, nm,
177 nmlen, LDNS_RR_TYPE_AAAA, rrset->rrset_class);
178 if(r && r->section == LDNS_SECTION_ADDITIONAL) {
179 r->flags |= RRSET_SCRUB_OK;
180 }
181 }
182 }
183 }
184
185 /** Get target name of a CNAME */
186 static int
parse_get_cname_target(struct rrset_parse * rrset,uint8_t ** sname,size_t * snamelen,sldns_buffer * pkt)187 parse_get_cname_target(struct rrset_parse* rrset, uint8_t** sname,
188 size_t* snamelen, sldns_buffer* pkt)
189 {
190 size_t oldpos, dlen;
191 if(rrset->rr_count != 1) {
192 struct rr_parse* sig;
193 verbose(VERB_ALGO, "Found CNAME rrset with "
194 "size > 1: %u", (unsigned)rrset->rr_count);
195 /* use the first CNAME! */
196 rrset->rr_count = 1;
197 rrset->size = rrset->rr_first->size;
198 for(sig=rrset->rrsig_first; sig; sig=sig->next)
199 rrset->size += sig->size;
200 rrset->rr_last = rrset->rr_first;
201 rrset->rr_first->next = NULL;
202 }
203 if(rrset->rr_first->size < sizeof(uint16_t)+1)
204 return 0; /* CNAME rdata too small */
205 *sname = rrset->rr_first->ttl_data + sizeof(uint32_t)
206 + sizeof(uint16_t); /* skip ttl, rdatalen */
207 *snamelen = rrset->rr_first->size - sizeof(uint16_t);
208
209 if(rrset->rr_first->outside_packet) {
210 if(!dname_valid(*sname, *snamelen))
211 return 0;
212 return 1;
213 }
214 oldpos = sldns_buffer_position(pkt);
215 sldns_buffer_set_position(pkt, (size_t)(*sname - sldns_buffer_begin(pkt)));
216 dlen = pkt_dname_len(pkt);
217 sldns_buffer_set_position(pkt, oldpos);
218 if(dlen == 0)
219 return 0; /* parse fail on the rdata name */
220 *snamelen = dlen;
221 return 1;
222 }
223
224 /** Synthesize CNAME from DNAME, false if too long */
225 static int
synth_cname(uint8_t * qname,size_t qnamelen,struct rrset_parse * dname_rrset,uint8_t * alias,size_t * aliaslen,sldns_buffer * pkt)226 synth_cname(uint8_t* qname, size_t qnamelen, struct rrset_parse* dname_rrset,
227 uint8_t* alias, size_t* aliaslen, sldns_buffer* pkt)
228 {
229 /* we already know that sname is a strict subdomain of DNAME owner */
230 uint8_t* dtarg = NULL;
231 size_t dtarglen;
232 if(!parse_get_cname_target(dname_rrset, &dtarg, &dtarglen, pkt))
233 return 0;
234 if(qnamelen <= dname_rrset->dname_len)
235 return 0;
236 if(qnamelen == 0)
237 return 0;
238 log_assert(qnamelen > dname_rrset->dname_len);
239 /* DNAME from com. to net. with qname example.com. -> example.net. */
240 /* so: \3com\0 to \3net\0 and qname \7example\3com\0 */
241 *aliaslen = qnamelen + dtarglen - dname_rrset->dname_len;
242 if(*aliaslen > LDNS_MAX_DOMAINLEN)
243 return 0; /* should have been RCODE YXDOMAIN */
244 /* decompress dnames into buffer, we know it fits */
245 dname_pkt_copy(pkt, alias, qname);
246 dname_pkt_copy(pkt, alias+(qnamelen-dname_rrset->dname_len), dtarg);
247 return 1;
248 }
249
250 /** synthesize a CNAME rrset */
251 static struct rrset_parse*
synth_cname_rrset(uint8_t ** sname,size_t * snamelen,uint8_t * alias,size_t aliaslen,struct regional * region,struct msg_parse * msg,struct rrset_parse * rrset,struct rrset_parse * prev,struct rrset_parse * nx,sldns_buffer * pkt)252 synth_cname_rrset(uint8_t** sname, size_t* snamelen, uint8_t* alias,
253 size_t aliaslen, struct regional* region, struct msg_parse* msg,
254 struct rrset_parse* rrset, struct rrset_parse* prev,
255 struct rrset_parse* nx, sldns_buffer* pkt)
256 {
257 struct rrset_parse* cn = (struct rrset_parse*)regional_alloc(region,
258 sizeof(struct rrset_parse));
259 if(!cn)
260 return NULL;
261 memset(cn, 0, sizeof(*cn));
262 cn->rr_first = (struct rr_parse*)regional_alloc(region,
263 sizeof(struct rr_parse));
264 if(!cn->rr_first)
265 return NULL;
266 cn->rr_last = cn->rr_first;
267 /* CNAME from sname to alias */
268 cn->dname = (uint8_t*)regional_alloc(region, *snamelen);
269 if(!cn->dname)
270 return NULL;
271 dname_pkt_copy(pkt, cn->dname, *sname);
272 cn->dname_len = *snamelen;
273 cn->type = LDNS_RR_TYPE_CNAME;
274 cn->section = rrset->section;
275 cn->rrset_class = rrset->rrset_class;
276 cn->rr_count = 1;
277 cn->size = sizeof(uint16_t) + aliaslen;
278 cn->hash=pkt_hash_rrset(pkt, cn->dname, cn->type, cn->rrset_class, 0);
279 /* allocate TTL + rdatalen + uncompressed dname */
280 memset(cn->rr_first, 0, sizeof(struct rr_parse));
281 cn->rr_first->outside_packet = 1;
282 cn->rr_first->ttl_data = (uint8_t*)regional_alloc(region,
283 sizeof(uint32_t)+sizeof(uint16_t)+aliaslen);
284 if(!cn->rr_first->ttl_data)
285 return NULL;
286 memmove(cn->rr_first->ttl_data, rrset->rr_first->ttl_data,
287 sizeof(uint32_t)); /* RFC6672: synth CNAME TTL == DNAME TTL */
288 sldns_write_uint16(cn->rr_first->ttl_data+4, aliaslen);
289 memmove(cn->rr_first->ttl_data+6, alias, aliaslen);
290 cn->rr_first->size = sizeof(uint16_t)+aliaslen;
291
292 /* link it in */
293 cn->rrset_all_next = nx;
294 if(prev)
295 prev->rrset_all_next = cn;
296 else msg->rrset_first = cn;
297 if(nx == NULL)
298 msg->rrset_last = cn;
299 msg->rrset_count ++;
300 msg->an_rrsets++;
301 /* it is not inserted in the msg hashtable. */
302
303 *sname = cn->rr_first->ttl_data + sizeof(uint32_t)+sizeof(uint16_t);
304 *snamelen = aliaslen;
305 return cn;
306 }
307
308 /** check if DNAME applies to a name */
309 static int
pkt_strict_sub(sldns_buffer * pkt,uint8_t * sname,uint8_t * dr)310 pkt_strict_sub(sldns_buffer* pkt, uint8_t* sname, uint8_t* dr)
311 {
312 uint8_t buf1[LDNS_MAX_DOMAINLEN+1];
313 uint8_t buf2[LDNS_MAX_DOMAINLEN+1];
314 /* decompress names */
315 dname_pkt_copy(pkt, buf1, sname);
316 dname_pkt_copy(pkt, buf2, dr);
317 return dname_strict_subdomain_c(buf1, buf2);
318 }
319
320 /** check subdomain with decompression */
321 static int
pkt_sub(sldns_buffer * pkt,uint8_t * comprname,uint8_t * zone)322 pkt_sub(sldns_buffer* pkt, uint8_t* comprname, uint8_t* zone)
323 {
324 uint8_t buf[LDNS_MAX_DOMAINLEN+1];
325 dname_pkt_copy(pkt, buf, comprname);
326 return dname_subdomain_c(buf, zone);
327 }
328
329 /** check subdomain with decompression, compressed is parent */
330 static int
sub_of_pkt(sldns_buffer * pkt,uint8_t * zone,uint8_t * comprname)331 sub_of_pkt(sldns_buffer* pkt, uint8_t* zone, uint8_t* comprname)
332 {
333 uint8_t buf[LDNS_MAX_DOMAINLEN+1];
334 dname_pkt_copy(pkt, buf, comprname);
335 return dname_subdomain_c(zone, buf);
336 }
337
338 /** Check if there are SOA records in the authority section (negative) */
339 static int
soa_in_auth(struct msg_parse * msg)340 soa_in_auth(struct msg_parse* msg)
341 {
342 struct rrset_parse* rrset;
343 for(rrset = msg->rrset_first; rrset; rrset = rrset->rrset_all_next)
344 if(rrset->type == LDNS_RR_TYPE_SOA &&
345 rrset->section == LDNS_SECTION_AUTHORITY)
346 return 1;
347 return 0;
348 }
349
350 /** Check if type is allowed in the authority section */
351 static int
type_allowed_in_authority_section(uint16_t tp)352 type_allowed_in_authority_section(uint16_t tp)
353 {
354 if(tp == LDNS_RR_TYPE_SOA || tp == LDNS_RR_TYPE_NS ||
355 tp == LDNS_RR_TYPE_DS || tp == LDNS_RR_TYPE_NSEC ||
356 tp == LDNS_RR_TYPE_NSEC3)
357 return 1;
358 return 0;
359 }
360
361 /** Check if type is allowed in the additional section */
362 static int
type_allowed_in_additional_section(uint16_t tp)363 type_allowed_in_additional_section(uint16_t tp)
364 {
365 if(tp == LDNS_RR_TYPE_A || tp == LDNS_RR_TYPE_AAAA)
366 return 1;
367 return 0;
368 }
369
370 /**
371 * This routine normalizes a response. This includes removing "irrelevant"
372 * records from the answer and additional sections and (re)synthesizing
373 * CNAMEs from DNAMEs, if present.
374 *
375 * @param pkt: packet.
376 * @param msg: msg to normalize.
377 * @param qinfo: original query.
378 * @param region: where to allocate synthesized CNAMEs.
379 * @param env: module env with config options.
380 * @return 0 on error.
381 */
382 static int
scrub_normalize(sldns_buffer * pkt,struct msg_parse * msg,struct query_info * qinfo,struct regional * region,struct module_env * env)383 scrub_normalize(sldns_buffer* pkt, struct msg_parse* msg,
384 struct query_info* qinfo, struct regional* region,
385 struct module_env* env)
386 {
387 uint8_t* sname = qinfo->qname;
388 size_t snamelen = qinfo->qname_len;
389 struct rrset_parse* rrset, *prev, *nsset=NULL;
390
391 if(FLAGS_GET_RCODE(msg->flags) != LDNS_RCODE_NOERROR &&
392 FLAGS_GET_RCODE(msg->flags) != LDNS_RCODE_NXDOMAIN)
393 return 1;
394
395 /* For the ANSWER section, remove all "irrelevant" records and add
396 * synthesized CNAMEs from DNAMEs
397 * This will strip out-of-order CNAMEs as well. */
398
399 /* walk through the parse packet rrset list, keep track of previous
400 * for insert and delete ease, and examine every RRset */
401 prev = NULL;
402 rrset = msg->rrset_first;
403 while(rrset && rrset->section == LDNS_SECTION_ANSWER) {
404 if(rrset->type == LDNS_RR_TYPE_DNAME &&
405 pkt_strict_sub(pkt, sname, rrset->dname)) {
406 /* check if next rrset is correct CNAME. else,
407 * synthesize a CNAME */
408 struct rrset_parse* nx = rrset->rrset_all_next;
409 uint8_t alias[LDNS_MAX_DOMAINLEN+1];
410 size_t aliaslen = 0;
411 if(rrset->rr_count != 1) {
412 verbose(VERB_ALGO, "Found DNAME rrset with "
413 "size > 1: %u",
414 (unsigned)rrset->rr_count);
415 return 0;
416 }
417 if(!synth_cname(sname, snamelen, rrset, alias,
418 &aliaslen, pkt)) {
419 verbose(VERB_ALGO, "synthesized CNAME "
420 "too long");
421 return 0;
422 }
423 if(nx && nx->type == LDNS_RR_TYPE_CNAME &&
424 dname_pkt_compare(pkt, sname, nx->dname) == 0) {
425 /* check next cname */
426 uint8_t* t = NULL;
427 size_t tlen = 0;
428 if(!parse_get_cname_target(nx, &t, &tlen, pkt))
429 return 0;
430 if(dname_pkt_compare(pkt, alias, t) == 0) {
431 /* it's OK and better capitalized */
432 prev = rrset;
433 rrset = nx;
434 continue;
435 }
436 /* synth ourselves */
437 }
438 /* synth a CNAME rrset */
439 prev = synth_cname_rrset(&sname, &snamelen, alias,
440 aliaslen, region, msg, rrset, rrset, nx, pkt);
441 if(!prev) {
442 log_err("out of memory synthesizing CNAME");
443 return 0;
444 }
445 /* FIXME: resolve the conflict between synthesized
446 * CNAME ttls and the cache. */
447 rrset = nx;
448 continue;
449
450 }
451
452 /* The only records in the ANSWER section not allowed to */
453 if(dname_pkt_compare(pkt, sname, rrset->dname) != 0) {
454 remove_rrset("normalize: removing irrelevant RRset:",
455 pkt, msg, prev, &rrset);
456 continue;
457 }
458
459 /* Follow the CNAME chain. */
460 if(rrset->type == LDNS_RR_TYPE_CNAME) {
461 struct rrset_parse* nx = rrset->rrset_all_next;
462 uint8_t* oldsname = sname;
463 /* see if the next one is a DNAME, if so, swap them */
464 if(nx && nx->section == LDNS_SECTION_ANSWER &&
465 nx->type == LDNS_RR_TYPE_DNAME &&
466 nx->rr_count == 1 &&
467 pkt_strict_sub(pkt, sname, nx->dname)) {
468 /* there is a DNAME after this CNAME, it
469 * is in the ANSWER section, and the DNAME
470 * applies to the name we cover */
471 /* check if the alias of the DNAME equals
472 * this CNAME */
473 uint8_t alias[LDNS_MAX_DOMAINLEN+1];
474 size_t aliaslen = 0;
475 uint8_t* t = NULL;
476 size_t tlen = 0;
477 if(synth_cname(sname, snamelen, nx, alias,
478 &aliaslen, pkt) &&
479 parse_get_cname_target(rrset, &t, &tlen, pkt) &&
480 dname_pkt_compare(pkt, alias, t) == 0) {
481 /* the synthesized CNAME equals the
482 * current CNAME. This CNAME is the
483 * one that the DNAME creates, and this
484 * CNAME is better capitalised */
485 verbose(VERB_ALGO, "normalize: re-order of DNAME and its CNAME");
486 if(prev) prev->rrset_all_next = nx;
487 else msg->rrset_first = nx;
488 if(nx->rrset_all_next == NULL)
489 msg->rrset_last = rrset;
490 rrset->rrset_all_next =
491 nx->rrset_all_next;
492 nx->rrset_all_next = rrset;
493 /* prev = nx; unused, enable if there
494 * is other rrset removal code after
495 * this */
496 }
497 }
498
499 /* move to next name in CNAME chain */
500 if(!parse_get_cname_target(rrset, &sname, &snamelen, pkt))
501 return 0;
502 prev = rrset;
503 rrset = rrset->rrset_all_next;
504 /* in CNAME ANY response, can have data after CNAME */
505 if(qinfo->qtype == LDNS_RR_TYPE_ANY) {
506 while(rrset && rrset->section ==
507 LDNS_SECTION_ANSWER &&
508 dname_pkt_compare(pkt, oldsname,
509 rrset->dname) == 0) {
510 prev = rrset;
511 rrset = rrset->rrset_all_next;
512 }
513 }
514 continue;
515 }
516
517 /* Otherwise, make sure that the RRset matches the qtype. */
518 if(qinfo->qtype != LDNS_RR_TYPE_ANY &&
519 qinfo->qtype != rrset->type) {
520 remove_rrset("normalize: removing irrelevant RRset:",
521 pkt, msg, prev, &rrset);
522 continue;
523 }
524
525 /* Mark the additional names from relevant rrset as OK. */
526 /* only for RRsets that match the query name, other ones
527 * will be removed by sanitize, so no additional for them */
528 if(dname_pkt_compare(pkt, qinfo->qname, rrset->dname) == 0)
529 mark_additional_rrset(pkt, msg, rrset);
530
531 prev = rrset;
532 rrset = rrset->rrset_all_next;
533 }
534
535 /* Mark additional names from AUTHORITY */
536 while(rrset && rrset->section == LDNS_SECTION_AUTHORITY) {
537 /* protect internals of recursor by making sure to del these */
538 if(rrset->type==LDNS_RR_TYPE_DNAME ||
539 rrset->type==LDNS_RR_TYPE_CNAME ||
540 rrset->type==LDNS_RR_TYPE_A ||
541 rrset->type==LDNS_RR_TYPE_AAAA) {
542 remove_rrset("normalize: removing irrelevant "
543 "RRset:", pkt, msg, prev, &rrset);
544 continue;
545 }
546 /* Allowed list of types in the authority section */
547 if(env->cfg->harden_unknown_additional &&
548 !type_allowed_in_authority_section(rrset->type)) {
549 remove_rrset("normalize: removing irrelevant "
550 "RRset:", pkt, msg, prev, &rrset);
551 continue;
552 }
553 /* only one NS set allowed in authority section */
554 if(rrset->type==LDNS_RR_TYPE_NS) {
555 /* NS set must be pertinent to the query */
556 if(!sub_of_pkt(pkt, qinfo->qname, rrset->dname)) {
557 remove_rrset("normalize: removing irrelevant "
558 "RRset:", pkt, msg, prev, &rrset);
559 continue;
560 }
561 /* we don't want NS sets for NXDOMAIN answers,
562 * because they could contain poisonous contents,
563 * from. eg. fragmentation attacks, inserted after
564 * long RRSIGs in the packet get to the packet
565 * border and such */
566 /* also for NODATA answers */
567 if(FLAGS_GET_RCODE(msg->flags) == LDNS_RCODE_NXDOMAIN ||
568 (FLAGS_GET_RCODE(msg->flags) == LDNS_RCODE_NOERROR
569 && soa_in_auth(msg) && msg->an_rrsets == 0)) {
570 remove_rrset("normalize: removing irrelevant "
571 "RRset:", pkt, msg, prev, &rrset);
572 continue;
573 }
574 if(nsset == NULL) {
575 nsset = rrset;
576 } else {
577 remove_rrset("normalize: removing irrelevant "
578 "RRset:", pkt, msg, prev, &rrset);
579 continue;
580 }
581 }
582 /* if this is type DS and we query for type DS we just got
583 * a referral answer for our type DS query, fix packet */
584 if(rrset->type==LDNS_RR_TYPE_DS &&
585 qinfo->qtype == LDNS_RR_TYPE_DS &&
586 dname_pkt_compare(pkt, qinfo->qname, rrset->dname) == 0) {
587 rrset->section = LDNS_SECTION_ANSWER;
588 msg->ancount = rrset->rr_count + rrset->rrsig_count;
589 msg->nscount = 0;
590 msg->arcount = 0;
591 msg->an_rrsets = 1;
592 msg->ns_rrsets = 0;
593 msg->ar_rrsets = 0;
594 msg->rrset_count = 1;
595 msg->rrset_first = rrset;
596 msg->rrset_last = rrset;
597 rrset->rrset_all_next = NULL;
598 return 1;
599 }
600 mark_additional_rrset(pkt, msg, rrset);
601 prev = rrset;
602 rrset = rrset->rrset_all_next;
603 }
604
605 /* For each record in the additional section, remove it if it is an
606 * address record and not in the collection of additional names
607 * found in ANSWER and AUTHORITY. */
608 /* These records have not been marked OK previously */
609 while(rrset && rrset->section == LDNS_SECTION_ADDITIONAL) {
610 if(rrset->type==LDNS_RR_TYPE_A ||
611 rrset->type==LDNS_RR_TYPE_AAAA)
612 {
613 if((rrset->flags & RRSET_SCRUB_OK)) {
614 /* remove flag to clean up flags variable */
615 rrset->flags &= ~RRSET_SCRUB_OK;
616 } else {
617 remove_rrset("normalize: removing irrelevant "
618 "RRset:", pkt, msg, prev, &rrset);
619 continue;
620 }
621 }
622 /* protect internals of recursor by making sure to del these */
623 if(rrset->type==LDNS_RR_TYPE_DNAME ||
624 rrset->type==LDNS_RR_TYPE_CNAME ||
625 rrset->type==LDNS_RR_TYPE_NS) {
626 remove_rrset("normalize: removing irrelevant "
627 "RRset:", pkt, msg, prev, &rrset);
628 continue;
629 }
630 /* Allowed list of types in the additional section */
631 if(env->cfg->harden_unknown_additional &&
632 !type_allowed_in_additional_section(rrset->type)) {
633 remove_rrset("normalize: removing irrelevant "
634 "RRset:", pkt, msg, prev, &rrset);
635 continue;
636 }
637 prev = rrset;
638 rrset = rrset->rrset_all_next;
639 }
640
641 return 1;
642 }
643
644 /**
645 * Store potential poison in the cache (only if hardening disabled).
646 * The rrset is stored in the cache but removed from the message.
647 * So that it will be used for infrastructure purposes, but not be
648 * returned to the client.
649 * @param pkt: packet
650 * @param msg: message parsed
651 * @param env: environment with cache
652 * @param rrset: to store.
653 */
654 static void
store_rrset(sldns_buffer * pkt,struct msg_parse * msg,struct module_env * env,struct rrset_parse * rrset)655 store_rrset(sldns_buffer* pkt, struct msg_parse* msg, struct module_env* env,
656 struct rrset_parse* rrset)
657 {
658 struct ub_packed_rrset_key* k;
659 struct packed_rrset_data* d;
660 struct rrset_ref ref;
661 time_t now = *env->now;
662
663 k = alloc_special_obtain(env->alloc);
664 if(!k)
665 return;
666 k->entry.data = NULL;
667 if(!parse_copy_decompress_rrset(pkt, msg, rrset, NULL, k)) {
668 alloc_special_release(env->alloc, k);
669 return;
670 }
671 d = (struct packed_rrset_data*)k->entry.data;
672 packed_rrset_ttl_add(d, now);
673 ref.key = k;
674 ref.id = k->id;
675 /*ignore ret: it was in the cache, ref updated */
676 (void)rrset_cache_update(env->rrset_cache, &ref, env->alloc, now);
677 }
678
679 /**
680 * Check if right hand name in NSEC is within zone
681 * @param pkt: the packet buffer for decompression.
682 * @param rrset: the NSEC rrset
683 * @param zonename: the zone name.
684 * @return true if BAD.
685 */
sanitize_nsec_is_overreach(sldns_buffer * pkt,struct rrset_parse * rrset,uint8_t * zonename)686 static int sanitize_nsec_is_overreach(sldns_buffer* pkt,
687 struct rrset_parse* rrset, uint8_t* zonename)
688 {
689 struct rr_parse* rr;
690 uint8_t* rhs;
691 size_t len;
692 log_assert(rrset->type == LDNS_RR_TYPE_NSEC);
693 for(rr = rrset->rr_first; rr; rr = rr->next) {
694 size_t pos = sldns_buffer_position(pkt);
695 size_t rhspos;
696 rhs = rr->ttl_data+4+2;
697 len = sldns_read_uint16(rr->ttl_data+4);
698 rhspos = rhs-sldns_buffer_begin(pkt);
699 sldns_buffer_set_position(pkt, rhspos);
700 if(pkt_dname_len(pkt) == 0) {
701 /* malformed */
702 sldns_buffer_set_position(pkt, pos);
703 return 1;
704 }
705 if(sldns_buffer_position(pkt)-rhspos > len) {
706 /* outside of rdata boundaries */
707 sldns_buffer_set_position(pkt, pos);
708 return 1;
709 }
710 sldns_buffer_set_position(pkt, pos);
711 if(!pkt_sub(pkt, rhs, zonename)) {
712 /* overreaching */
713 return 1;
714 }
715 }
716 /* all NSEC RRs OK */
717 return 0;
718 }
719
720 /** Remove individual RRs, if the length is wrong. Returns true if the RRset
721 * has been removed. */
722 static int
scrub_sanitize_rr_length(sldns_buffer * pkt,struct msg_parse * msg,struct rrset_parse * prev,struct rrset_parse ** rrset,int * added_ede,struct module_qstate * qstate)723 scrub_sanitize_rr_length(sldns_buffer* pkt, struct msg_parse* msg,
724 struct rrset_parse* prev, struct rrset_parse** rrset, int* added_ede,
725 struct module_qstate* qstate)
726 {
727 struct rr_parse* rr, *rr_prev = NULL;
728 for(rr = (*rrset)->rr_first; rr; rr = rr->next) {
729
730 /* Sanity check for length of records
731 * An A record should be 6 bytes only
732 * (2 bytes for length and 4 for IPv4 addr)*/
733 if((*rrset)->type == LDNS_RR_TYPE_A && rr->size != 6 ) {
734 if(!*added_ede) {
735 *added_ede = 1;
736 errinf_ede(qstate, "sanitize: records of inappropriate length have been removed.",
737 LDNS_EDE_OTHER);
738 }
739 if(msgparse_rrset_remove_rr("sanitize: removing type A RR of inappropriate length:",
740 pkt, *rrset, rr_prev, rr, NULL, 0)) {
741 remove_rrset("sanitize: removing type A RRset of inappropriate length:",
742 pkt, msg, prev, rrset);
743 return 1;
744 }
745 continue;
746 }
747
748 /* Sanity check for length of records
749 * An AAAA record should be 18 bytes only
750 * (2 bytes for length and 16 for IPv6 addr)*/
751 if((*rrset)->type == LDNS_RR_TYPE_AAAA && rr->size != 18 ) {
752 if(!*added_ede) {
753 *added_ede = 1;
754 errinf_ede(qstate, "sanitize: records of inappropriate length have been removed.",
755 LDNS_EDE_OTHER);
756 }
757 if(msgparse_rrset_remove_rr("sanitize: removing type AAAA RR of inappropriate length:",
758 pkt, *rrset, rr_prev, rr, NULL, 0)) {
759 remove_rrset("sanitize: removing type AAAA RRset of inappropriate length:",
760 pkt, msg, prev, rrset);
761 return 1;
762 }
763 continue;
764 }
765 rr_prev = rr;
766 }
767 return 0;
768 }
769
770 /**
771 * Given a response event, remove suspect RRsets from the response.
772 * "Suspect" rrsets are potentially poison. Note that this routine expects
773 * the response to be in a "normalized" state -- that is, all "irrelevant"
774 * RRsets have already been removed, CNAMEs are in order, etc.
775 *
776 * @param pkt: packet.
777 * @param msg: msg to normalize.
778 * @param qinfo: the question originally asked.
779 * @param zonename: name of server zone.
780 * @param env: module environment with config and cache.
781 * @param ie: iterator environment with private address data.
782 * @param qstate: for setting errinf for EDE error messages.
783 * @return 0 on error.
784 */
785 static int
scrub_sanitize(sldns_buffer * pkt,struct msg_parse * msg,struct query_info * qinfo,uint8_t * zonename,struct module_env * env,struct iter_env * ie,struct module_qstate * qstate)786 scrub_sanitize(sldns_buffer* pkt, struct msg_parse* msg,
787 struct query_info* qinfo, uint8_t* zonename, struct module_env* env,
788 struct iter_env* ie, struct module_qstate* qstate)
789 {
790 int del_addi = 0; /* if additional-holding rrsets are deleted, we
791 do not trust the normalized additional-A-AAAA any more */
792 int added_rrlen_ede = 0;
793 struct rrset_parse* rrset, *prev;
794 prev = NULL;
795 rrset = msg->rrset_first;
796
797 /* the first DNAME is allowed to stay. It needs checking before
798 * it can be used from the cache. After normalization, an initial
799 * DNAME will have a correctly synthesized CNAME after it. */
800 if(rrset && rrset->type == LDNS_RR_TYPE_DNAME &&
801 rrset->section == LDNS_SECTION_ANSWER &&
802 pkt_strict_sub(pkt, qinfo->qname, rrset->dname) &&
803 pkt_sub(pkt, rrset->dname, zonename)) {
804 prev = rrset; /* DNAME allowed to stay in answer section */
805 rrset = rrset->rrset_all_next;
806 }
807
808 /* remove all records from the answer section that are
809 * not the same domain name as the query domain name.
810 * The answer section should contain rrsets with the same name
811 * as the question. For DNAMEs a CNAME has been synthesized.
812 * Wildcards have the query name in answer section.
813 * ANY queries get query name in answer section.
814 * Remainders of CNAME chains are cut off and resolved by iterator. */
815 while(rrset && rrset->section == LDNS_SECTION_ANSWER) {
816 if(dname_pkt_compare(pkt, qinfo->qname, rrset->dname) != 0) {
817 if(has_additional(rrset->type)) del_addi = 1;
818 remove_rrset("sanitize: removing extraneous answer "
819 "RRset:", pkt, msg, prev, &rrset);
820 continue;
821 }
822 prev = rrset;
823 rrset = rrset->rrset_all_next;
824 }
825
826 /* At this point, we brutally remove ALL rrsets that aren't
827 * children of the originating zone. The idea here is that,
828 * as far as we know, the server that we contacted is ONLY
829 * authoritative for the originating zone. It, of course, MAY
830 * be authoritative for any other zones, and of course, MAY
831 * NOT be authoritative for some subdomains of the originating
832 * zone. */
833 prev = NULL;
834 rrset = msg->rrset_first;
835 while(rrset) {
836
837 /* Sanity check for length of records */
838 if(rrset->type == LDNS_RR_TYPE_A ||
839 rrset->type == LDNS_RR_TYPE_AAAA) {
840 if(scrub_sanitize_rr_length(pkt, msg, prev, &rrset,
841 &added_rrlen_ede, qstate))
842 continue;
843 }
844
845 /* remove private addresses */
846 if( (rrset->type == LDNS_RR_TYPE_A ||
847 rrset->type == LDNS_RR_TYPE_AAAA)) {
848
849 /* do not set servfail since this leads to too
850 * many drops of other people using rfc1918 space */
851 /* also do not remove entire rrset, unless all records
852 * in it are bad */
853 if(priv_rrset_bad(ie->priv, pkt, rrset)) {
854 remove_rrset(NULL, pkt, msg, prev, &rrset);
855 continue;
856 }
857 }
858
859 /* skip DNAME records -- they will always be followed by a
860 * synthesized CNAME, which will be relevant.
861 * FIXME: should this do something differently with DNAME
862 * rrsets NOT in Section.ANSWER? */
863 /* But since DNAME records are also subdomains of the zone,
864 * same check can be used */
865
866 if(!pkt_sub(pkt, rrset->dname, zonename)) {
867 if(msg->an_rrsets == 0 &&
868 rrset->type == LDNS_RR_TYPE_NS &&
869 rrset->section == LDNS_SECTION_AUTHORITY &&
870 FLAGS_GET_RCODE(msg->flags) ==
871 LDNS_RCODE_NOERROR && !soa_in_auth(msg) &&
872 sub_of_pkt(pkt, zonename, rrset->dname)) {
873 /* noerror, nodata and this NS rrset is above
874 * the zone. This is LAME!
875 * Leave in the NS for lame classification. */
876 /* remove everything from the additional
877 * (we dont want its glue that was approved
878 * during the normalize action) */
879 del_addi = 1;
880 } else if(!env->cfg->harden_glue && (
881 rrset->type == LDNS_RR_TYPE_A ||
882 rrset->type == LDNS_RR_TYPE_AAAA)) {
883 /* store in cache! Since it is relevant
884 * (from normalize) it will be picked up
885 * from the cache to be used later */
886 store_rrset(pkt, msg, env, rrset);
887 remove_rrset("sanitize: storing potential "
888 "poison RRset:", pkt, msg, prev, &rrset);
889 continue;
890 } else {
891 if(has_additional(rrset->type)) del_addi = 1;
892 remove_rrset("sanitize: removing potential "
893 "poison RRset:", pkt, msg, prev, &rrset);
894 continue;
895 }
896 }
897 if(del_addi && rrset->section == LDNS_SECTION_ADDITIONAL) {
898 remove_rrset("sanitize: removing potential "
899 "poison reference RRset:", pkt, msg, prev, &rrset);
900 continue;
901 }
902 /* check if right hand side of NSEC is within zone */
903 if(rrset->type == LDNS_RR_TYPE_NSEC &&
904 sanitize_nsec_is_overreach(pkt, rrset, zonename)) {
905 remove_rrset("sanitize: removing overreaching NSEC "
906 "RRset:", pkt, msg, prev, &rrset);
907 continue;
908 }
909 prev = rrset;
910 rrset = rrset->rrset_all_next;
911 }
912 return 1;
913 }
914
915 int
scrub_message(sldns_buffer * pkt,struct msg_parse * msg,struct query_info * qinfo,uint8_t * zonename,struct regional * region,struct module_env * env,struct module_qstate * qstate,struct iter_env * ie)916 scrub_message(sldns_buffer* pkt, struct msg_parse* msg,
917 struct query_info* qinfo, uint8_t* zonename, struct regional* region,
918 struct module_env* env, struct module_qstate* qstate,
919 struct iter_env* ie)
920 {
921 /* basic sanity checks */
922 log_nametypeclass(VERB_ALGO, "scrub for", zonename, LDNS_RR_TYPE_NS,
923 qinfo->qclass);
924 if(msg->qdcount > 1)
925 return 0;
926 if( !(msg->flags&BIT_QR) )
927 return 0;
928 msg->flags &= ~(BIT_AD|BIT_Z); /* force off bit AD and Z */
929
930 /* make sure that a query is echoed back when NOERROR or NXDOMAIN */
931 /* this is not required for basic operation but is a forgery
932 * resistance (security) feature */
933 if((FLAGS_GET_RCODE(msg->flags) == LDNS_RCODE_NOERROR ||
934 FLAGS_GET_RCODE(msg->flags) == LDNS_RCODE_NXDOMAIN) &&
935 msg->qdcount == 0)
936 return 0;
937
938 /* if a query is echoed back, make sure it is correct. Otherwise,
939 * this may be not a reply to our query. */
940 if(msg->qdcount == 1) {
941 if(dname_pkt_compare(pkt, msg->qname, qinfo->qname) != 0)
942 return 0;
943 if(msg->qtype != qinfo->qtype || msg->qclass != qinfo->qclass)
944 return 0;
945 }
946
947 /* normalize the response, this cleans up the additional. */
948 if(!scrub_normalize(pkt, msg, qinfo, region, env))
949 return 0;
950 /* delete all out-of-zone information */
951 if(!scrub_sanitize(pkt, msg, qinfo, zonename, env, ie, qstate))
952 return 0;
953 return 1;
954 }
955