a0e2184bddc513bec500b644ce11ba51b6f2a49c
[exim.git] / src / src / arc.c
1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
4 /* Experimental ARC support for Exim
5 Copyright (c) Jeremy Harris 2018
6 License: GPL
7 */
8
9 #include "exim.h"
10 #ifdef EXPERIMENTAL_ARC
11 # if !defined SUPPORT_SPF
12 # error SPF must also be enabled for ARC
13 # elif defined DISABLE_DKIM
14 # error DKIM must also be enabled for ARC
15 # else
16
17 # include "functions.h"
18 # include "pdkim/pdkim.h"
19 # include "pdkim/signing.h"
20
21 extern pdkim_ctx * dkim_verify_ctx;
22 extern pdkim_ctx dkim_sign_ctx;
23
24 /******************************************************************************/
25
26 typedef struct hdr_rlist {
27 struct hdr_rlist * prev;
28 BOOL used;
29 header_line * h;
30 } hdr_rlist;
31
32 typedef struct arc_line {
33 header_line * complete; /* including the header name; nul-term */
34 uschar * relaxed;
35
36 /* identified tag contents */
37 /*XXX t= for AS? */
38 blob i;
39 blob cv;
40 blob a;
41 blob b;
42 blob bh;
43 blob d;
44 blob h;
45 blob s;
46 blob c;
47 blob l;
48
49 /* tag content sub-portions */
50 blob a_algo;
51 blob a_hash;
52
53 blob c_head;
54 blob c_body;
55
56 /* modified copy of b= field in line */
57 blob rawsig_no_b_val;
58 } arc_line;
59
60 typedef struct arc_set {
61 struct arc_set * next;
62 struct arc_set * prev;
63
64 unsigned instance;
65 arc_line * hdr_aar;
66 arc_line * hdr_ams;
67 arc_line * hdr_as;
68
69 const uschar * ams_verify_done;
70 BOOL ams_verify_passed;
71 } arc_set;
72
73 typedef struct arc_ctx {
74 arc_set * arcset_chain;
75 arc_set * arcset_chain_last;
76 } arc_ctx;
77
78 #define ARC_HDR_AAR US"ARC-Authentication-Results:"
79 #define ARC_HDRLEN_AAR 27
80 #define ARC_HDR_AMS US"ARC-Message-Signature:"
81 #define ARC_HDRLEN_AMS 22
82 #define ARC_HDR_AS US"ARC-Seal:"
83 #define ARC_HDRLEN_AS 9
84 #define HDR_AR US"Authentication-Results:"
85 #define HDRLEN_AR 23
86
87 static hdr_rlist * headers_rlist;
88 static arc_ctx arc_sign_ctx = { NULL };
89
90
91 /******************************************************************************/
92
93
94 /* Get the instance number from the header.
95 Return 0 on error */
96 static unsigned
97 arc_instance_from_hdr(const arc_line * al)
98 {
99 const uschar * s = al->i.data;
100 if (!s || !al->i.len) return 0;
101 return (unsigned) atoi(CCS s);
102 }
103
104
105 static uschar *
106 skip_fws(uschar * s)
107 {
108 uschar c = *s;
109 while (c && (c == ' ' || c == '\t' || c == '\n' || c == '\r')) c = *++s;
110 return s;
111 }
112
113
114 /* Locate instance struct on chain, inserting a new one if
115 needed. The chain is in increasing-instance-number order
116 by the "next" link, and we have a "prev" link also.
117 */
118
119 static arc_set *
120 arc_find_set(arc_ctx * ctx, unsigned i)
121 {
122 arc_set ** pas, * as, * next, * prev;
123
124 for (pas = &ctx->arcset_chain, prev = NULL, next = ctx->arcset_chain;
125 as = *pas; pas = &as->next)
126 {
127 if (as->instance > i) break;
128 if (as->instance == i)
129 {
130 DEBUG(D_acl) debug_printf("ARC: existing instance %u\n", i);
131 return as;
132 }
133 next = as->next;
134 prev = as;
135 }
136
137 DEBUG(D_acl) debug_printf("ARC: new instance %u\n", i);
138 *pas = as = store_get(sizeof(arc_set));
139 memset(as, 0, sizeof(arc_set));
140 as->next = next;
141 as->prev = prev;
142 as->instance = i;
143 if (next)
144 next->prev = as;
145 else
146 ctx->arcset_chain_last = as;
147 return as;
148 }
149
150
151
152 /* Insert a tag content into the line structure.
153 Note this is a reference to existing data, not a copy.
154 Check for already-seen tag.
155 The string-pointer is on the '=' for entry. Update it past the
156 content (to the ;) on return;
157 */
158
159 static uschar *
160 arc_insert_tagvalue(arc_line * al, unsigned loff, uschar ** ss)
161 {
162 uschar * s = *ss;
163 uschar c = *++s;
164 blob * b = (blob *)(US al + loff);
165 size_t len = 0;
166
167 /* [FWS] tag-value [FWS] */
168
169 if (b->data) return US"fail";
170 s = skip_fws(s); /* FWS */
171
172 b->data = s;
173 while ((c = *s) && c != ';') { len++; s++; }
174 *ss = s;
175 while (len && ((c = s[-1]) == ' ' || c == '\t' || c == '\n' || c == '\r'))
176 { s--; len--; } /* FWS */
177 b->len = len;
178 return NULL;
179 }
180
181
182 /* Inspect a header line, noting known tag fields.
183 Check for duplicates. */
184
185 static uschar *
186 arc_parse_line(arc_line * al, header_line * h, unsigned off, BOOL instance_only)
187 {
188 uschar * s = h->text + off;
189 uschar * r = NULL; /* compiler-quietening */
190 uschar c;
191
192 al->complete = h;
193
194 if (!instance_only)
195 {
196 al->rawsig_no_b_val.data = store_get(h->slen + 1);
197 memcpy(al->rawsig_no_b_val.data, h->text, off); /* copy the header name blind */
198 r = al->rawsig_no_b_val.data + off;
199 al->rawsig_no_b_val.len = off;
200 }
201
202 /* tag-list = tag-spec *( ";" tag-spec ) [ ";" ] */
203
204 while ((c = *s))
205 {
206 char tagchar;
207 uschar * t;
208 unsigned i = 0;
209 uschar * fieldstart = s;
210 uschar * bstart = NULL, * bend;
211
212 /* tag-spec = [FWS] tag-name [FWS] "=" [FWS] tag-value [FWS] */
213
214 s = skip_fws(s); /* FWS */
215 if (!*s) break;
216 /* debug_printf("%s: consider '%s'\n", __FUNCTION__, s); */
217 tagchar = *s++;
218 s = skip_fws(s); /* FWS */
219 if (!*s) break;
220
221 if (!instance_only || tagchar == 'i') switch (tagchar)
222 {
223 case 'a': /* a= AMS algorithm */
224 {
225 if (*s != '=') return US"no 'a' value";
226 if (arc_insert_tagvalue(al, offsetof(arc_line, a), &s)) return US"a tag dup";
227
228 /* substructure: algo-hash (eg. rsa-sha256) */
229
230 t = al->a_algo.data = al->a.data;
231 while (*t != '-')
232 if (!*t++ || ++i > al->a.len) return US"no '-' in 'a' value";
233 al->a_algo.len = i;
234 if (*t++ != '-') return US"no '-' in 'a' value";
235 al->a_hash.data = t;
236 al->a_hash.len = al->a.len - i - 1;
237 }
238 break;
239 case 'b':
240 {
241 gstring * g = NULL;
242
243 switch (*s)
244 {
245 case '=': /* b= AMS signature */
246 if (al->b.data) return US"already b data";
247 bstart = s+1;
248
249 /* The signature can have FWS inserted in the content;
250 make a stripped copy */
251
252 while ((c = *++s) && c != ';')
253 if (c != ' ' && c != '\t' && c != '\n' && c != '\r')
254 g = string_catn(g, s, 1);
255 al->b.data = string_from_gstring(g);
256 al->b.len = g->ptr;
257 gstring_reset_unused(g);
258 bend = s;
259 break;
260 case 'h': /* bh= AMS body hash */
261 s = skip_fws(++s); /* FWS */
262 if (*s != '=') return US"no bh value";
263 if (al->bh.data) return US"already bh data";
264
265 /* The bodyhash can have FWS inserted in the content;
266 make a stripped copy */
267
268 while ((c = *++s) && c != ';')
269 if (c != ' ' && c != '\t' && c != '\n' && c != '\r')
270 g = string_catn(g, s, 1);
271 al->bh.data = string_from_gstring(g);
272 al->bh.len = g->ptr;
273 gstring_reset_unused(g);
274 break;
275 default:
276 return US"b? tag";
277 }
278 }
279 break;
280 case 'c':
281 switch (*s)
282 {
283 case '=': /* c= AMS canonicalisation */
284 if (arc_insert_tagvalue(al, offsetof(arc_line, c), &s)) return US"c tag dup";
285
286 /* substructure: head/body (eg. relaxed/simple)) */
287
288 t = al->c_head.data = al->c.data;
289 while (isalpha(*t))
290 if (!*t++ || ++i > al->a.len) break;
291 al->c_head.len = i;
292 if (*t++ == '/') /* /body is optional */
293 {
294 al->c_body.data = t;
295 al->c_body.len = al->c.len - i - 1;
296 }
297 else
298 {
299 al->c_body.data = US"simple";
300 al->c_body.len = 6;
301 }
302 break;
303 case 'v': /* cv= AS validity */
304 if (*++s != '=') return US"cv tag val";
305 if (arc_insert_tagvalue(al, offsetof(arc_line, cv), &s)) return US"cv tag dup";
306 break;
307 default:
308 return US"c? tag";
309 }
310 break;
311 case 'd': /* d= AMS domain */
312 if (*s != '=') return US"d tag val";
313 if (arc_insert_tagvalue(al, offsetof(arc_line, d), &s)) return US"d tag dup";
314 break;
315 case 'h': /* h= AMS headers */
316 if (*s != '=') return US"h tag val";
317 if (arc_insert_tagvalue(al, offsetof(arc_line, h), &s)) return US"h tag dup";
318 break;
319 case 'i': /* i= ARC set instance */
320 if (*s != '=') return US"i tag val";
321 if (arc_insert_tagvalue(al, offsetof(arc_line, i), &s)) return US"i tag dup";
322 if (instance_only) goto done;
323 break;
324 case 'l': /* l= bodylength */
325 if (*s != '=') return US"l tag val";
326 if (arc_insert_tagvalue(al, offsetof(arc_line, l), &s)) return US"l tag dup";
327 break;
328 case 's': /* s= AMS selector */
329 if (*s != '=') return US"s tag val";
330 if (arc_insert_tagvalue(al, offsetof(arc_line, s), &s)) return US"s tag dup";
331 break;
332 }
333
334 while ((c = *s) && c != ';') s++;
335 if (c) s++; /* ; after tag-spec */
336
337 /* for all but the b= tag, copy the field including FWS. For the b=,
338 drop the tag content. */
339
340 if (!instance_only)
341 if (bstart)
342 {
343 size_t n = bstart - fieldstart;
344 memcpy(r, fieldstart, n); /* FWS "b=" */
345 r += n;
346 al->rawsig_no_b_val.len += n;
347 n = s - bend;
348 memcpy(r, bend, n); /* FWS ";" */
349 r += n;
350 al->rawsig_no_b_val.len += n;
351 }
352 else
353 {
354 size_t n = s - fieldstart;
355 memcpy(r, fieldstart, n);
356 r += n;
357 al->rawsig_no_b_val.len += n;
358 }
359 }
360
361 if (!instance_only)
362 *r = '\0';
363
364 done:
365 /* debug_printf("%s: finshed\n", __FUNCTION__); */
366 return NULL;
367 }
368
369
370 /* Insert one header line in the correct set of the chain,
371 adding instances as needed and checking for duplicate lines.
372 */
373
374 static uschar *
375 arc_insert_hdr(arc_ctx * ctx, header_line * h, unsigned off, unsigned hoff,
376 BOOL instance_only)
377 {
378 int i;
379 arc_set * as;
380 arc_line * al = store_get(sizeof(arc_line)), ** alp;
381 uschar * e;
382
383 memset(al, 0, sizeof(arc_line));
384
385 if ((e = arc_parse_line(al, h, off, instance_only)))
386 {
387 DEBUG(D_acl) if (e) debug_printf("ARC: %s\n", e);
388 return US"line parse";
389 }
390 if (!(i = arc_instance_from_hdr(al))) return US"instance find";
391 if (!(as = arc_find_set(ctx, i))) return US"set find";
392 if (*(alp = (arc_line **)(US as + hoff))) return US"dup hdr";
393
394 *alp = al;
395 return NULL;
396 }
397
398
399
400
401 static const uschar *
402 arc_try_header(arc_ctx * ctx, header_line * h, BOOL instance_only)
403 {
404 const uschar * e;
405
406 /*debug_printf("consider hdr '%s'\n", h->text);*/
407 if (strncmpic(ARC_HDR_AAR, h->text, ARC_HDRLEN_AAR) == 0)
408 {
409 DEBUG(D_acl)
410 {
411 int len = h->slen;
412 uschar * s;
413 for (s = h->text + h->slen; s[-1] == '\r' || s[-1] == '\n'; )
414 s--, len--;
415 debug_printf("ARC: found AAR: %.*s\n", len, h->text);
416 }
417 if ((e = arc_insert_hdr(ctx, h, ARC_HDRLEN_AAR, offsetof(arc_set, hdr_aar),
418 TRUE)))
419 {
420 DEBUG(D_acl) debug_printf("inserting AAR: %s\n", e);
421 return US"inserting AAR";
422 }
423 }
424 else if (strncmpic(ARC_HDR_AMS, h->text, ARC_HDRLEN_AMS) == 0)
425 {
426 arc_line * ams;
427
428 DEBUG(D_acl)
429 {
430 int len = h->slen;
431 uschar * s;
432 for (s = h->text + h->slen; s[-1] == '\r' || s[-1] == '\n'; )
433 s--, len--;
434 debug_printf("ARC: found AMS: %.*s\n", len, h->text);
435 }
436 if ((e = arc_insert_hdr(ctx, h, ARC_HDRLEN_AMS, offsetof(arc_set, hdr_ams),
437 instance_only)))
438 {
439 DEBUG(D_acl) debug_printf("inserting AMS: %s\n", e);
440 return US"inserting AMS";
441 }
442
443 /* defaults */
444 /*XXX dubious selection of ams here */
445 ams = ctx->arcset_chain->hdr_ams;
446 if (!ams->c.data)
447 {
448 ams->c_head.data = US"simple"; ams->c_head.len = 6;
449 ams->c_body = ams->c_head;
450 }
451 }
452 else if (strncmpic(ARC_HDR_AS, h->text, ARC_HDRLEN_AS) == 0)
453 {
454 DEBUG(D_acl)
455 {
456 int len = h->slen;
457 uschar * s;
458 for (s = h->text + h->slen; s[-1] == '\r' || s[-1] == '\n'; )
459 s--, len--;
460 debug_printf("ARC: found AS: %.*s\n", len, h->text);
461 }
462 if ((e = arc_insert_hdr(ctx, h, ARC_HDRLEN_AS, offsetof(arc_set, hdr_as),
463 instance_only)))
464 {
465 DEBUG(D_acl) debug_printf("inserting AS: %s\n", e);
466 return US"inserting AS";
467 }
468 }
469 return NULL;
470 }
471
472
473
474 /* Gather the chain of arc sets from the headers.
475 Check for duplicates while that is done. Also build the
476 reverse-order headers list;
477
478 Return: ARC state if determined, eg. by lack of any ARC chain.
479 */
480
481 static const uschar *
482 arc_vfy_collect_hdrs(arc_ctx * ctx)
483 {
484 header_line * h;
485 hdr_rlist * r = NULL, * rprev = NULL;
486 const uschar * e;
487
488 DEBUG(D_acl) debug_printf("ARC: collecting arc sets\n");
489 for (h = header_list; h; h = h->next)
490 {
491 r = store_get(sizeof(hdr_rlist));
492 r->prev = rprev;
493 r->used = FALSE;
494 r->h = h;
495 rprev = r;
496
497 if ((e = arc_try_header(ctx, h, FALSE)))
498 {
499 arc_state_reason = string_sprintf("collecting headers: %s", e);
500 return US"fail";
501 }
502 }
503 headers_rlist = r;
504
505 if (!ctx->arcset_chain) return US"none";
506 return NULL;
507 }
508
509
510 static BOOL
511 arc_cv_match(arc_line * al, const uschar * s)
512 {
513 return Ustrncmp(s, al->cv.data, al->cv.len) == 0;
514 }
515
516 /******************************************************************************/
517
518 /* Return the hash of headers from the message that the AMS claims it
519 signed.
520 */
521
522 static void
523 arc_get_verify_hhash(arc_ctx * ctx, arc_line * ams, blob * hhash)
524 {
525 const uschar * headernames = string_copyn(ams->h.data, ams->h.len);
526 const uschar * hn;
527 int sep = ':';
528 hdr_rlist * r;
529 BOOL relaxed = Ustrncmp(US"relaxed", ams->c_head.data, ams->c_head.len) == 0;
530 int hashtype = pdkim_hashname_to_hashtype(
531 ams->a_hash.data, ams->a_hash.len);
532 hctx hhash_ctx;
533 const uschar * s;
534 int len;
535
536 if (!exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
537 {
538 DEBUG(D_acl)
539 debug_printf("ARC: hash setup error, possibly nonhandled hashtype\n");
540 return;
541 }
542
543 /* For each headername in the list from the AMS (walking in order)
544 walk the message headers in reverse order, adding to the hash any
545 found for the first time. For that last point, maintain used-marks
546 on the list of message headers. */
547
548 DEBUG(D_acl) debug_printf("ARC: AMS header data for verification:\n");
549
550 for (r = headers_rlist; r; r = r->prev)
551 r->used = FALSE;
552 while ((hn = string_nextinlist(&headernames, &sep, NULL, 0)))
553 for (r = headers_rlist; r; r = r->prev)
554 if ( !r->used
555 && strncasecmp(CCS (s = r->h->text), CCS hn, Ustrlen(hn)) == 0
556 )
557 {
558 if (relaxed) s = pdkim_relax_header_n(s, r->h->slen, TRUE);
559
560 len = Ustrlen(s);
561 DEBUG(D_acl) pdkim_quoteprint(s, len);
562 exim_sha_update(&hhash_ctx, s, Ustrlen(s));
563 r->used = TRUE;
564 break;
565 }
566
567 /* Finally add in the signature header (with the b= tag stripped); no CRLF */
568
569 s = ams->rawsig_no_b_val.data, len = ams->rawsig_no_b_val.len;
570 if (relaxed)
571 len = Ustrlen(s = pdkim_relax_header_n(s, len, FALSE));
572 DEBUG(D_acl) pdkim_quoteprint(s, len);
573 exim_sha_update(&hhash_ctx, s, len);
574
575 exim_sha_finish(&hhash_ctx, hhash);
576 DEBUG(D_acl)
577 { debug_printf("ARC: header hash: "); pdkim_hexprint(hhash->data, hhash->len); }
578 return;
579 }
580
581
582
583
584 static pdkim_pubkey *
585 arc_line_to_pubkey(arc_line * al)
586 {
587 uschar * dns_txt;
588 pdkim_pubkey * p;
589
590 if (!(dns_txt = dkim_exim_query_dns_txt(string_sprintf("%.*s._domainkey.%.*s",
591 al->s.len, al->s.data, al->d.len, al->d.data))))
592 {
593 DEBUG(D_acl) debug_printf("pubkey dns lookup fail\n");
594 return NULL;
595 }
596
597 if ( !(p = pdkim_parse_pubkey_record(dns_txt))
598 || (Ustrcmp(p->srvtype, "*") != 0 && Ustrcmp(p->srvtype, "email") != 0)
599 )
600 {
601 DEBUG(D_acl) debug_printf("pubkey dns lookup format error\n");
602 return NULL;
603 }
604
605 /* If the pubkey limits use to specified hashes, reject unusable
606 signatures. XXX should we have looked for multiple dns records? */
607
608 if (p->hashes)
609 {
610 const uschar * list = p->hashes, * ele;
611 int sep = ':';
612
613 while ((ele = string_nextinlist(&list, &sep, NULL, 0)))
614 if (Ustrncmp(ele, al->a_hash.data, al->a_hash.len) == 0) break;
615 if (!ele)
616 {
617 DEBUG(D_acl) debug_printf("pubkey h=%s vs sig a=%.*s\n",
618 p->hashes, (int)al->a.len, al->a.data);
619 return NULL;
620 }
621 }
622 return p;
623 }
624
625
626
627
628 static pdkim_bodyhash *
629 arc_ams_setup_vfy_bodyhash(arc_line * ams)
630 {
631 int canon_head, canon_body;
632 long bodylen;
633
634 pdkim_cstring_to_canons(ams->c.data, ams->c.len, &canon_head, &canon_body);
635 bodylen = ams->l.data
636 ? strtol(CS string_copyn(ams->l.data, ams->l.len), NULL, 10) : -1;
637
638 return pdkim_set_bodyhash(dkim_verify_ctx,
639 pdkim_hashname_to_hashtype(ams->a_hash.data, ams->a_hash.len),
640 canon_body,
641 bodylen);
642 }
643
644
645
646 /* Verify an AMS. This is a DKIM-sig header, but with an ARC i= tag
647 and without a DKIM v= tag.
648 */
649
650 static const uschar *
651 arc_ams_verify(arc_ctx * ctx, arc_set * as)
652 {
653 arc_line * ams = as->hdr_ams;
654 pdkim_bodyhash * b;
655 pdkim_pubkey * p;
656 blob sighash;
657 blob hhash;
658 ev_ctx vctx;
659 int hashtype;
660 const uschar * errstr;
661
662 as->ams_verify_done = US"in-progress";
663
664 /* Check the AMS has all the required tags:
665 "a=" algorithm
666 "b=" signature
667 "bh=" body hash
668 "d=" domain (for key lookup)
669 "h=" headers (included in signature)
670 "s=" key-selector (for key lookup)
671 */
672 if ( !ams->a.data || !ams->b.data || !ams->bh.data || !ams->d.data
673 || !ams->h.data || !ams->s.data)
674 {
675 as->ams_verify_done = arc_state_reason = US"required tag missing";
676 return US"fail";
677 }
678
679
680 /* The bodyhash should have been created earlier, and the dkim code should
681 have managed calculating it during message input. Find the reference to it. */
682
683 if (!(b = arc_ams_setup_vfy_bodyhash(ams)))
684 {
685 as->ams_verify_done = arc_state_reason = US"internal hash setup error";
686 return US"fail";
687 }
688
689 DEBUG(D_acl)
690 {
691 debug_printf("ARC i=%d AMS Body bytes hashed: %lu\n"
692 " Body %.*s computed: ",
693 as->instance, b->signed_body_bytes,
694 (int)ams->a_hash.len, ams->a_hash.data);
695 pdkim_hexprint(CUS b->bh.data, b->bh.len);
696 }
697
698 /* We know the bh-tag blob is of a nul-term string, so safe as a string */
699
700 if ( !ams->bh.data
701 || (pdkim_decode_base64(ams->bh.data, &sighash), sighash.len != b->bh.len)
702 || memcmp(sighash.data, b->bh.data, b->bh.len) != 0
703 )
704 {
705 DEBUG(D_acl)
706 {
707 debug_printf("ARC i=%d AMS Body hash from headers: ", as->instance);
708 pdkim_hexprint(sighash.data, sighash.len);
709 debug_printf("ARC i=%d AMS Body hash did NOT match\n", as->instance);
710 }
711 return as->ams_verify_done = arc_state_reason = US"AMS body hash miscompare";
712 }
713
714 DEBUG(D_acl) debug_printf("ARC i=%d AMS Body hash compared OK\n", as->instance);
715
716 /* Get the public key from DNS */
717
718 if (!(p = arc_line_to_pubkey(ams)))
719 return as->ams_verify_done = arc_state_reason = US"pubkey problem";
720
721 /* We know the b-tag blob is of a nul-term string, so safe as a string */
722 pdkim_decode_base64(ams->b.data, &sighash);
723
724 arc_get_verify_hhash(ctx, ams, &hhash);
725
726 /* Setup the interface to the signing library */
727
728 if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx)))
729 {
730 DEBUG(D_acl) debug_printf("ARC verify init: %s\n", errstr);
731 as->ams_verify_done = arc_state_reason = US"internal sigverify init error";
732 return US"fail";
733 }
734
735 hashtype = pdkim_hashname_to_hashtype(ams->a_hash.data, ams->a_hash.len);
736
737 if ((errstr = exim_dkim_verify(&vctx,
738 pdkim_hashes[hashtype].exim_hashmethod, &hhash, &sighash)))
739 {
740 DEBUG(D_acl) debug_printf("ARC i=%d AMS verify %s\n", as->instance, errstr);
741 return as->ams_verify_done = arc_state_reason = US"AMS sig nonverify";
742 }
743
744 DEBUG(D_acl) debug_printf("ARC i=%d AMS verify pass\n", as->instance);
745 as->ams_verify_passed = TRUE;
746 return NULL;
747 }
748
749
750
751 /* Check the sets are instance-continuous and that all
752 members are present. Check that no arc_seals are "fail".
753 Set the highest instance number global.
754 Verify the latest AMS.
755 */
756 static uschar *
757 arc_headers_check(arc_ctx * ctx)
758 {
759 arc_set * as;
760 int inst;
761 BOOL ams_fail_found = FALSE;
762 uschar * ret = NULL;
763
764 if (!(as = ctx->arcset_chain))
765 return US"none";
766
767 for(inst = 0; as; as = as->next)
768 {
769 if ( as->instance != ++inst
770 || !as->hdr_aar || !as->hdr_ams || !as->hdr_as
771 || arc_cv_match(as->hdr_as, US"fail")
772 )
773 {
774 arc_state_reason = string_sprintf("i=%d fail"
775 " (cv, sequence or missing header)", as->instance);
776 DEBUG(D_acl) debug_printf("ARC %s\n", arc_state_reason);
777 ret = US"fail";
778 }
779
780 /* Evaluate the oldest-pass AMS validation while we're here.
781 It does not affect the AS chain validation but is reported as
782 auxilary info. */
783
784 if (!ams_fail_found)
785 if (arc_ams_verify(ctx, as))
786 ams_fail_found = TRUE;
787 else
788 arc_oldest_pass = inst;
789 arc_state_reason = NULL;
790 }
791
792 arc_received = ctx->arcset_chain_last;
793 arc_received_instance = inst;
794 if (ret)
795 return ret;
796
797 /* We can skip the latest-AMS validation, if we already did it. */
798
799 as = ctx->arcset_chain_last;
800 if (as->ams_verify_done && !as->ams_verify_passed)
801 {
802 arc_state_reason = as->ams_verify_done;
803 return US"fail";
804 }
805 if (!!arc_ams_verify(ctx, as))
806 return US"fail";
807
808 return NULL;
809 }
810
811
812 /******************************************************************************/
813 static const uschar *
814 arc_seal_verify(arc_ctx * ctx, arc_set * as)
815 {
816 arc_line * hdr_as = as->hdr_as;
817 arc_set * as2;
818 int hashtype;
819 hctx hhash_ctx;
820 blob hhash_computed;
821 blob sighash;
822 ev_ctx vctx;
823 pdkim_pubkey * p;
824 const uschar * errstr;
825
826 DEBUG(D_acl) debug_printf("ARC: AS vfy i=%d\n", as->instance);
827 /*
828 1. If the value of the "cv" tag on that seal is "fail", the
829 chain state is "fail" and the algorithm stops here. (This
830 step SHOULD be skipped if the earlier step (2.1) was
831 performed) [it was]
832
833 2. In Boolean nomenclature: if ((i == 1 && cv != "none") or (cv
834 == "none" && i != 1)) then the chain state is "fail" and the
835 algorithm stops here (note that the ordering of the logic is
836 structured for short-circuit evaluation).
837 */
838
839 if ( as->instance == 1 && !arc_cv_match(hdr_as, US"none")
840 || arc_cv_match(hdr_as, US"none") && as->instance != 1
841 )
842 {
843 arc_state_reason = US"seal cv state";
844 return US"fail";
845 }
846
847 /*
848 3. Initialize a hash function corresponding to the "a" tag of
849 the ARC-Seal.
850 */
851
852 hashtype = pdkim_hashname_to_hashtype(hdr_as->a_hash.data, hdr_as->a_hash.len);
853
854 if (!exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
855 {
856 DEBUG(D_acl)
857 debug_printf("ARC: hash setup error, possibly nonhandled hashtype\n");
858 arc_state_reason = US"seal hash setup error";
859 return US"fail";
860 }
861
862 /*
863 4. Compute the canonicalized form of the ARC header fields, in
864 the order described in Section 5.4.2, using the "relaxed"
865 header canonicalization defined in Section 3.4.2 of
866 [RFC6376]. Pass the canonicalized result to the hash
867 function.
868
869 Headers are CRLF-separated, but the last one is not crlf-terminated.
870 */
871
872 DEBUG(D_acl) debug_printf("ARC: AS header data for verification:\n");
873 for (as2 = ctx->arcset_chain;
874 as2 && as2->instance <= as->instance;
875 as2 = as2->next)
876 {
877 arc_line * al;
878 uschar * s;
879 int len;
880
881 al = as2->hdr_aar;
882 if (!(s = al->relaxed))
883 al->relaxed = s = pdkim_relax_header_n(al->complete->text,
884 al->complete->slen, TRUE);
885 len = Ustrlen(s);
886 DEBUG(D_acl) pdkim_quoteprint(s, len);
887 exim_sha_update(&hhash_ctx, s, len);
888
889 al = as2->hdr_ams;
890 if (!(s = al->relaxed))
891 al->relaxed = s = pdkim_relax_header_n(al->complete->text,
892 al->complete->slen, TRUE);
893 len = Ustrlen(s);
894 DEBUG(D_acl) pdkim_quoteprint(s, len);
895 exim_sha_update(&hhash_ctx, s, len);
896
897 al = as2->hdr_as;
898 if (as2->instance == as->instance)
899 s = pdkim_relax_header_n(al->rawsig_no_b_val.data,
900 al->rawsig_no_b_val.len, FALSE);
901 else if (!(s = al->relaxed))
902 al->relaxed = s = pdkim_relax_header_n(al->complete->text,
903 al->complete->slen, TRUE);
904 len = Ustrlen(s);
905 DEBUG(D_acl) pdkim_quoteprint(s, len);
906 exim_sha_update(&hhash_ctx, s, len);
907 }
908
909 /*
910 5. Retrieve the final digest from the hash function.
911 */
912
913 exim_sha_finish(&hhash_ctx, &hhash_computed);
914 DEBUG(D_acl)
915 {
916 debug_printf("ARC i=%d AS Header %.*s computed: ",
917 as->instance, (int)hdr_as->a_hash.len, hdr_as->a_hash.data);
918 pdkim_hexprint(hhash_computed.data, hhash_computed.len);
919 }
920
921
922 /*
923 6. Retrieve the public key identified by the "s" and "d" tags in
924 the ARC-Seal, as described in Section 4.1.6.
925 */
926
927 if (!(p = arc_line_to_pubkey(hdr_as)))
928 return US"pubkey problem";
929
930 /*
931 7. Determine whether the signature portion ("b" tag) of the ARC-
932 Seal and the digest computed above are valid according to the
933 public key. (See also Section Section 8.4 for failure case
934 handling)
935
936 8. If the signature is not valid, the chain state is "fail" and
937 the algorithm stops here.
938 */
939
940 /* We know the b-tag blob is of a nul-term string, so safe as a string */
941 pdkim_decode_base64(hdr_as->b.data, &sighash);
942
943 if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx)))
944 {
945 DEBUG(D_acl) debug_printf("ARC verify init: %s\n", errstr);
946 return US"fail";
947 }
948
949 hashtype = pdkim_hashname_to_hashtype(hdr_as->a_hash.data, hdr_as->a_hash.len);
950
951 if ((errstr = exim_dkim_verify(&vctx,
952 pdkim_hashes[hashtype].exim_hashmethod,
953 &hhash_computed, &sighash)))
954 {
955 DEBUG(D_acl)
956 debug_printf("ARC i=%d AS headers verify: %s\n", as->instance, errstr);
957 arc_state_reason = US"seal sigverify error";
958 return US"fail";
959 }
960
961 DEBUG(D_acl) debug_printf("ARC: AS vfy i=%d pass\n", as->instance);
962 return NULL;
963 }
964
965
966 static const uschar *
967 arc_verify_seals(arc_ctx * ctx)
968 {
969 arc_set * as = ctx->arcset_chain;
970
971 if (!as)
972 return US"none";
973
974 while (as)
975 {
976 if (arc_seal_verify(ctx, as)) return US"fail";
977 as = as->next;
978 }
979 DEBUG(D_acl) debug_printf("ARC: AS vfy overall pass\n");
980 return NULL;
981 }
982 /******************************************************************************/
983
984 /* Do ARC verification. Called from DATA ACL, on a verify = arc
985 condition. No arguments; we are checking globals.
986
987 Return: The ARC state, or NULL on error.
988 */
989
990 const uschar *
991 acl_verify_arc(void)
992 {
993 arc_ctx ctx = { NULL };
994 const uschar * res;
995
996 /* AS evaluation, per
997 https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-10#section-6
998 */
999 /* 1. Collect all ARC sets currently on the message. If there were
1000 none, the ARC state is "none" and the algorithm stops here.
1001 */
1002
1003 if ((res = arc_vfy_collect_hdrs(&ctx)))
1004 goto out;
1005
1006 /* 2. If the form of any ARC set is invalid (e.g., does not contain
1007 exactly one of each of the three ARC-specific header fields),
1008 then the chain state is "fail" and the algorithm stops here.
1009
1010 1. To avoid the overhead of unnecessary computation and delay
1011 from crypto and DNS operations, the cv value for all ARC-
1012 Seal(s) MAY be checked at this point. If any of the values
1013 are "fail", then the overall state of the chain is "fail" and
1014 the algorithm stops here.
1015
1016 3. Conduct verification of the ARC-Message-Signature header field
1017 bearing the highest instance number. If this verification fails,
1018 then the chain state is "fail" and the algorithm stops here.
1019 */
1020
1021 if ((res = arc_headers_check(&ctx)))
1022 goto out;
1023
1024 /* 4. For each ARC-Seal from the "N"th instance to the first, apply the
1025 following logic:
1026
1027 1. If the value of the "cv" tag on that seal is "fail", the
1028 chain state is "fail" and the algorithm stops here. (This
1029 step SHOULD be skipped if the earlier step (2.1) was
1030 performed)
1031
1032 2. In Boolean nomenclature: if ((i == 1 && cv != "none") or (cv
1033 == "none" && i != 1)) then the chain state is "fail" and the
1034 algorithm stops here (note that the ordering of the logic is
1035 structured for short-circuit evaluation).
1036
1037 3. Initialize a hash function corresponding to the "a" tag of
1038 the ARC-Seal.
1039
1040 4. Compute the canonicalized form of the ARC header fields, in
1041 the order described in Section 5.4.2, using the "relaxed"
1042 header canonicalization defined in Section 3.4.2 of
1043 [RFC6376]. Pass the canonicalized result to the hash
1044 function.
1045
1046 5. Retrieve the final digest from the hash function.
1047
1048 6. Retrieve the public key identified by the "s" and "d" tags in
1049 the ARC-Seal, as described in Section 4.1.6.
1050
1051 7. Determine whether the signature portion ("b" tag) of the ARC-
1052 Seal and the digest computed above are valid according to the
1053 public key. (See also Section Section 8.4 for failure case
1054 handling)
1055
1056 8. If the signature is not valid, the chain state is "fail" and
1057 the algorithm stops here.
1058
1059 5. If all seals pass validation, then the chain state is "pass", and
1060 the algorithm is complete.
1061 */
1062
1063 if ((res = arc_verify_seals(&ctx)))
1064 goto out;
1065
1066 res = US"pass";
1067
1068 out:
1069 return res;
1070 }
1071
1072 /******************************************************************************/
1073
1074 /* Prepend the header to the rlist */
1075
1076 static hdr_rlist *
1077 arc_rlist_entry(hdr_rlist * list, const uschar * s, int len)
1078 {
1079 hdr_rlist * r = store_get(sizeof(hdr_rlist) + sizeof(header_line));
1080 header_line * h = r->h = (header_line *)(r+1);
1081
1082 r->prev = list;
1083 r->used = FALSE;
1084 h->next = NULL;
1085 h->type = 0;
1086 h->slen = len;
1087 h->text = US s;
1088
1089 /* This works for either NL or CRLF lines; also nul-termination */
1090 while (*++s)
1091 if (*s == '\n' && s[1] != '\t' && s[1] != ' ') break;
1092 s++; /* move past end of line */
1093
1094 return r;
1095 }
1096
1097
1098 /* Walk the given headers strings identifying each header, and construct
1099 a reverse-order list. Also parse ARC-chain headers and build the chain
1100 struct, retaining pointers into the string.
1101 */
1102
1103 static hdr_rlist *
1104 arc_sign_scan_headers(arc_ctx * ctx, gstring * sigheaders)
1105 {
1106 const uschar * s;
1107 hdr_rlist * rheaders = NULL;
1108
1109 s = sigheaders ? sigheaders->s : NULL;
1110 if (s) while (*s)
1111 {
1112 const uschar * s2 = s;
1113
1114 /* This works for either NL or CRLF lines; also nul-termination */
1115 while (*++s2)
1116 if (*s2 == '\n' && s2[1] != '\t' && s2[1] != ' ') break;
1117 s2++; /* move past end of line */
1118
1119 rheaders = arc_rlist_entry(rheaders, s, s2 - s);
1120 s = s2;
1121 }
1122 return rheaders;
1123 }
1124
1125
1126
1127 /* Return the A-R content, without identity, with line-ending and
1128 NUL termination. */
1129
1130 static BOOL
1131 arc_sign_find_ar(header_line * headers, const uschar * identity, blob * ret)
1132 {
1133 header_line * h;
1134 int ilen = Ustrlen(identity);
1135
1136 ret->data = NULL;
1137 for(h = headers; h; h = h->next)
1138 {
1139 uschar * s = h->text, c;
1140 int len = h->slen;
1141
1142 if (Ustrncmp(s, HDR_AR, HDRLEN_AR) != 0) continue;
1143 s += HDRLEN_AR, len -= HDRLEN_AR; /* header name */
1144 while ( len > 0
1145 && (c = *s) && (c == ' ' || c == '\t' || c == '\r' || c == '\n'))
1146 s++, len--; /* FWS */
1147 if (Ustrncmp(s, identity, ilen) != 0) continue;
1148 s += ilen; len -= ilen; /* identity */
1149 if (len <= 0) continue;
1150 if ((c = *s) && c == ';') s++, len--; /* identity terminator */
1151 while ( len > 0
1152 && (c = *s) && (c == ' ' || c == '\t' || c == '\r' || c == '\n'))
1153 s++, len--; /* FWS */
1154 if (len <= 0) continue;
1155 ret->data = s;
1156 ret->len = len;
1157 return TRUE;
1158 }
1159 return FALSE;
1160 }
1161
1162
1163
1164 /* Append a constructed AAR including CRLF. Add it to the arc_ctx too. */
1165
1166 static gstring *
1167 arc_sign_append_aar(gstring * g, arc_ctx * ctx,
1168 const uschar * identity, int instance, blob * ar)
1169 {
1170 int aar_off = g ? g->ptr : 0;
1171 arc_set * as = store_get(sizeof(arc_set) + sizeof(arc_line) + sizeof(header_line));
1172 arc_line * al = (arc_line *)(as+1);
1173 header_line * h = (header_line *)(al+1);
1174
1175 g = string_catn(g, ARC_HDR_AAR, ARC_HDRLEN_AAR);
1176 g = string_cat(g, string_sprintf(" i=%d; %s;\r\n\t", instance, identity));
1177 g = string_catn(g, US ar->data, ar->len);
1178
1179 h->slen = g->ptr - aar_off;
1180 h->text = g->s + aar_off;
1181 al->complete = h;
1182 as->next = NULL;
1183 as->prev = ctx->arcset_chain_last;
1184 as->instance = instance;
1185 as->hdr_aar = al;
1186 if (instance == 1)
1187 ctx->arcset_chain = as;
1188 else
1189 ctx->arcset_chain_last->next = as;
1190 ctx->arcset_chain_last = as;
1191
1192 DEBUG(D_transport) debug_printf("ARC: AAR '%.*s'\n", h->slen - 2, h->text);
1193 return g;
1194 }
1195
1196
1197
1198 static BOOL
1199 arc_sig_from_pseudoheader(gstring * hdata, int hashtype, const uschar * privkey,
1200 blob * sig, const uschar * why)
1201 {
1202 hashmethod hm = /*sig->keytype == KEYTYPE_ED25519*/ FALSE
1203 ? HASH_SHA2_512 : pdkim_hashes[hashtype].exim_hashmethod;
1204 blob hhash;
1205 es_ctx sctx;
1206 const uschar * errstr;
1207
1208 DEBUG(D_transport)
1209 {
1210 hctx hhash_ctx;
1211 debug_printf("ARC: %s header data for signing:\n", why);
1212 pdkim_quoteprint(hdata->s, hdata->ptr);
1213
1214 (void) exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod);
1215 exim_sha_update(&hhash_ctx, hdata->s, hdata->ptr);
1216 exim_sha_finish(&hhash_ctx, &hhash);
1217 debug_printf("ARC: header hash: "); pdkim_hexprint(hhash.data, hhash.len);
1218 }
1219
1220 if (FALSE /*need hash for Ed25519 or GCrypt signing*/ )
1221 {
1222 hctx hhash_ctx;
1223 (void) exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod);
1224 exim_sha_update(&hhash_ctx, hdata->s, hdata->ptr);
1225 exim_sha_finish(&hhash_ctx, &hhash);
1226 }
1227 else
1228 {
1229 hhash.data = hdata->s;
1230 hhash.len = hdata->ptr;
1231 }
1232
1233 if ( (errstr = exim_dkim_signing_init(privkey, &sctx))
1234 || (errstr = exim_dkim_sign(&sctx, hm, &hhash, sig)))
1235 {
1236 log_write(0, LOG_MAIN|LOG_PANIC, "ARC: %s signing: %s\n", why, errstr);
1237 return FALSE;
1238 }
1239 return TRUE;
1240 }
1241
1242
1243
1244 static gstring *
1245 arc_sign_append_sig(gstring * g, blob * sig)
1246 {
1247 /*debug_printf("%s: raw sig ", __FUNCTION__); pdkim_hexprint(sig->data, sig->len);*/
1248 sig->data = pdkim_encode_base64(sig);
1249 sig->len = Ustrlen(sig->data);
1250 for (;;)
1251 {
1252 int len = MIN(sig->len, 74);
1253 g = string_catn(g, sig->data, len);
1254 if ((sig->len -= len) == 0) break;
1255 sig->data += len;
1256 g = string_catn(g, US"\r\n\t ", 5);
1257 }
1258 g = string_catn(g, US";\r\n", 3);
1259 gstring_reset_unused(g);
1260 string_from_gstring(g);
1261 return g;
1262 }
1263
1264
1265 /* Append a constructed AMS including CRLF. Add it to the arc_ctx too. */
1266
1267 static gstring *
1268 arc_sign_append_ams(gstring * g, arc_ctx * ctx, int instance,
1269 const uschar * identity, const uschar * selector, blob * bodyhash,
1270 hdr_rlist * rheaders, const uschar * privkey)
1271 {
1272 uschar * s;
1273 gstring * hdata = NULL;
1274 int col;
1275 int hashtype = pdkim_hashname_to_hashtype(US"sha256", 6); /*XXX hardwired */
1276 blob sig;
1277 int ams_off;
1278 arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line));
1279 header_line * h = (header_line *)(al+1);
1280
1281 /* debug_printf("%s\n", __FUNCTION__); */
1282
1283 /* Construct the to-be-signed AMS pseudo-header: everything but the sig. */
1284
1285 ams_off = g->ptr;
1286 g = string_append(g, 10,
1287 ARC_HDR_AMS,
1288 US" i=", string_sprintf("%d", instance),
1289 US"; a=rsa-sha256; c=relaxed; d=", identity, /*XXX hardwired */
1290 US"; s=", selector,
1291 US";\r\n\tbh=", pdkim_encode_base64(bodyhash),
1292 US";\r\n\th=");
1293
1294 for(col = 3; rheaders; rheaders = rheaders->prev)
1295 {
1296 const uschar * hnames = US"DKIM-Signature:" PDKIM_DEFAULT_SIGN_HEADERS;
1297 uschar * name, * htext = rheaders->h->text;
1298 int sep = ':';
1299
1300 /* Spot headers of interest */
1301
1302 while ((name = string_nextinlist(&hnames, &sep, NULL, 0)))
1303 {
1304 int len = Ustrlen(name);
1305 if (strncasecmp(CCS htext, CCS name, len) == 0)
1306 {
1307 /* If too long, fold line in h= field */
1308
1309 if (col + len > 78) g = string_catn(g, US"\r\n\t ", 5), col = 3;
1310
1311 /* Add name to h= list */
1312
1313 g = string_catn(g, name, len);
1314 g = string_catn(g, US":", 1);
1315 col += len + 1;
1316
1317 /* Accumulate header for hashing/signing */
1318
1319 hdata = string_cat(hdata,
1320 pdkim_relax_header_n(htext, rheaders->h->slen, TRUE)); /*XXX hardwired */
1321 break;
1322 }
1323 }
1324 }
1325
1326 /* Lose the last colon from the h= list */
1327
1328 if (g->s[g->ptr - 1] == ':') g->ptr--;
1329
1330 g = string_catn(g, US";\r\n\tb=;", 7);
1331
1332 /* Include the pseudo-header in the accumulation */
1333
1334 s = pdkim_relax_header_n(g->s + ams_off, g->ptr - ams_off, FALSE);
1335 hdata = string_cat(hdata, s);
1336
1337 /* Calculate the signature from the accumulation */
1338 /*XXX does that need further relaxation? there are spaces embedded in the b= strings! */
1339
1340 if (!arc_sig_from_pseudoheader(hdata, hashtype, privkey, &sig, US"AMS"))
1341 return NULL;
1342
1343 /* Lose the trailing semicolon from the psuedo-header, and append the signature
1344 (folded over lines) and termination to complete it. */
1345
1346 g->ptr--;
1347 g = arc_sign_append_sig(g, &sig);
1348
1349 h->slen = g->ptr - ams_off;
1350 h->text = g->s + ams_off;
1351 al->complete = h;
1352 ctx->arcset_chain_last->hdr_ams = al;
1353
1354 DEBUG(D_transport) debug_printf("ARC: AMS '%.*s'\n", h->slen - 2, h->text);
1355 return g;
1356 }
1357
1358
1359
1360 /* Look for an arc= result in an A-R header blob. We know that its data
1361 happens to be a NUL-term string. */
1362
1363 static uschar *
1364 arc_ar_cv_status(blob * ar)
1365 {
1366 const uschar * resinfo = ar->data;
1367 int sep = ';';
1368 uschar * methodspec, * s;
1369
1370 while ((methodspec = string_nextinlist(&resinfo, &sep, NULL, 0)))
1371 if (Ustrncmp(methodspec, US"arc=", 4) == 0)
1372 {
1373 uschar c;
1374 for (s = methodspec += 4;
1375 (c = *s) && c != ';' && c != ' ' && c != '\r' && c != '\n'; ) s++;
1376 return string_copyn(methodspec, s - methodspec);
1377 }
1378 return NULL;
1379 }
1380
1381
1382
1383 /* Build the AS header and prepend it */
1384
1385 static gstring *
1386 arc_sign_prepend_as(gstring * arcset_interim, arc_ctx * ctx,
1387 int instance, const uschar * identity, const uschar * selector, blob * ar,
1388 const uschar * privkey)
1389 {
1390 gstring * arcset;
1391 arc_set * as;
1392 uschar * status = arc_ar_cv_status(ar);
1393 arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line));
1394 header_line * h = (header_line *)(al+1);
1395
1396 gstring * hdata = NULL;
1397 int hashtype = pdkim_hashname_to_hashtype(US"sha256", 6); /*XXX hardwired */
1398 blob sig;
1399
1400 /*
1401 - Generate AS
1402 - no body coverage
1403 - no h= tag; implicit coverage
1404 - arc status from A-R
1405 - if fail:
1406 - coverage is just the new ARC set
1407 including self (but with an empty b= in self)
1408 - if non-fail:
1409 - all ARC set headers, set-number order, aar then ams then as,
1410 including self (but with an empty b= in self)
1411 */
1412
1413 /* Construct the AS except for the signature */
1414
1415 arcset = string_append(NULL, 10,
1416 ARC_HDR_AS,
1417 US" i=", string_sprintf("%d", instance),
1418 US"; cv=", status,
1419 US"; a=rsa-sha256; d=", identity, /*XXX hardwired */
1420 US"; s=", selector, /*XXX same as AMS */
1421 US";\r\n\t b=;");
1422
1423 h->slen = arcset->ptr;
1424 h->text = arcset->s;
1425 al->complete = h;
1426 ctx->arcset_chain_last->hdr_as = al;
1427
1428 /* For any but "fail" chain-verify status, walk the entire chain in order by
1429 instance. For fail, only the new arc-set. Accumulate the elements walked. */
1430
1431 for (as = Ustrcmp(status, US"fail") == 0
1432 ? ctx->arcset_chain_last : ctx->arcset_chain;
1433 as; as = as->next)
1434 {
1435 /* Accumulate AAR then AMS then AS. Relaxed canonicalisation
1436 is required per standard. */
1437
1438 h = as->hdr_aar->complete;
1439 hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
1440 h = as->hdr_ams->complete;
1441 hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
1442 h = as->hdr_as->complete;
1443 hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, !!as->next));
1444 }
1445
1446 /* Calculate the signature from the accumulation */
1447
1448 if (!arc_sig_from_pseudoheader(hdata, hashtype, privkey, &sig, US"AS"))
1449 return NULL;
1450
1451 /* Lose the trailing semicolon */
1452 arcset->ptr--;
1453 arcset = arc_sign_append_sig(arcset, &sig);
1454 DEBUG(D_transport) debug_printf("ARC: AS '%.*s'\n", arcset->ptr - 2, arcset->s);
1455
1456 /* Finally, append the AMS and AAR to the new AS */
1457
1458 return string_catn(arcset, arcset_interim->s, arcset_interim->ptr);
1459 }
1460
1461
1462 /**************************************/
1463
1464 /* Return pointer to pdkim_bodyhash for given hash method, creating new
1465 method if needed.
1466 */
1467
1468 void *
1469 arc_ams_setup_sign_bodyhash(void)
1470 {
1471 int canon_head, canon_body;
1472
1473 DEBUG(D_transport) debug_printf("ARC: requesting bodyhash\n");
1474 pdkim_cstring_to_canons(US"relaxed", 7, &canon_head, &canon_body); /*XXX hardwired */
1475 return pdkim_set_bodyhash(&dkim_sign_ctx,
1476 pdkim_hashname_to_hashtype(US"sha256", 6), /*XXX hardwired */
1477 canon_body,
1478 -1);
1479 }
1480
1481
1482
1483 /* A "normal" header line, identified by DKIM processing. These arrive before
1484 the call to arc_sign(), which carries any newly-created DKIM headers - and
1485 those go textually before the normal ones in the message.
1486
1487 We have to take the feed from DKIM as, in the transport-filter case, the
1488 headers are not in memory at the time of the call to arc_sign().
1489
1490 Take a copy of the header and construct a reverse-order list.
1491 Also parse ARC-chain headers and build the chain struct, retaining pointers
1492 into the copies.
1493 */
1494
1495 static const uschar *
1496 arc_header_sign_feed(gstring * g)
1497 {
1498 uschar * s = string_copyn(g->s, g->ptr);
1499 headers_rlist = arc_rlist_entry(headers_rlist, s, g->ptr);
1500 return arc_try_header(&arc_sign_ctx, headers_rlist->h, TRUE);
1501 }
1502
1503
1504
1505 /* ARC signing. Called from the smtp transport, if the arc_sign option is set.
1506 The dkim_exim_sign() function has already been called, so will have hashed the
1507 message body for us so long as we requested a hash previously.
1508
1509 Arguments:
1510 signspec Three-element colon-sep list: identity, selector, privkey
1511 Already expanded
1512 sigheaders Any signature headers already generated, eg. by DKIM, or NULL
1513 errstr Error string
1514
1515 Return value
1516 Set of headers to prepend to the message, including the supplied sigheaders
1517 but not the plainheaders.
1518 */
1519
1520 gstring *
1521 arc_sign(const uschar * signspec, gstring * sigheaders, uschar ** errstr)
1522 {
1523 const uschar * identity, * selector, * privkey;
1524 int sep = 0;
1525 header_line * headers;
1526 hdr_rlist * rheaders;
1527 blob ar;
1528 int instance;
1529 gstring * g = NULL;
1530 pdkim_bodyhash * b;
1531
1532 /* Parse the signing specification */
1533
1534 identity = string_nextinlist(&signspec, &sep, NULL, 0);
1535 selector = string_nextinlist(&signspec, &sep, NULL, 0);
1536 if ( !*identity | !*selector
1537 || !(privkey = string_nextinlist(&signspec, &sep, NULL, 0)) || !*privkey)
1538 {
1539 log_write(0, LOG_MAIN|LOG_PANIC, "ARC: bad signing-specification");
1540 return NULL;
1541 }
1542 if (*privkey == '/' && !(privkey = expand_file_big_buffer(privkey)))
1543 return NULL;
1544
1545 DEBUG(D_transport) debug_printf("ARC: sign for %s\n", identity);
1546
1547 /*
1548 - scan headers for existing ARC chain & A-R (with matching system-identfier)
1549 - paniclog & skip on problems (no A-R)
1550 */
1551
1552 /* Make an rlist of any new DKIM headers, then add the "normals" rlist to it */
1553
1554 string_from_gstring(sigheaders);
1555 if ((rheaders = arc_sign_scan_headers(&arc_sign_ctx, sigheaders)))
1556 {
1557 hdr_rlist ** rp;
1558 for (rp = &rheaders; *rp; ) rp = &(*rp)->prev;
1559 *rp = headers_rlist;
1560 headers_rlist = rheaders;
1561 }
1562 else
1563 rheaders = headers_rlist;
1564 /* Finally, build a normal-order headers list */
1565 /*XXX only needed for hunt-the-AR? */
1566 {
1567 header_line * hnext = NULL;
1568 for (; rheaders; hnext = rheaders->h, rheaders = rheaders->prev)
1569 rheaders->h->next = hnext;
1570 headers = hnext;
1571 }
1572
1573 instance = arc_sign_ctx.arcset_chain_last ? arc_sign_ctx.arcset_chain_last->instance + 1 : 1;
1574
1575 if (!(arc_sign_find_ar(headers, identity, &ar)))
1576 {
1577 log_write(0, LOG_MAIN|LOG_PANIC, "ARC: no Authentication-Results header for signing");
1578 return sigheaders ? sigheaders : string_get(0);
1579 }
1580
1581 /*
1582 - Generate AAR
1583 - copy the A-R; prepend i= & identity
1584 */
1585
1586 g = arc_sign_append_aar(g, &arc_sign_ctx, identity, instance, &ar);
1587
1588 /*
1589 - Generate AMS
1590 - Looks fairly like a DKIM sig
1591 - Cover all DKIM sig headers as well as the usuals
1592 - ? oversigning?
1593 - Covers the data
1594 - we must have requested a suitable bodyhash previously
1595 */
1596
1597 b = arc_ams_setup_sign_bodyhash();
1598 g = arc_sign_append_ams(g, &arc_sign_ctx, instance, identity, selector,
1599 &b->bh, headers_rlist, privkey);
1600
1601 /*
1602 - Generate AS
1603 - no body coverage
1604 - no h= tag; implicit coverage
1605 - arc status from A-R
1606 - if fail:
1607 - coverage is just the new ARC set
1608 including self (but with an empty b= in self)
1609 - if non-fail:
1610 - all ARC set headers, set-number order, aar then ams then as,
1611 including self (but with an empty b= in self)
1612 */
1613
1614 g = arc_sign_prepend_as(g, &arc_sign_ctx, instance, identity, selector, &ar, privkey);
1615
1616 /* Finally, append the dkim headers and return the lot. */
1617
1618 g = string_catn(g, sigheaders->s, sigheaders->ptr);
1619 (void) string_from_gstring(g);
1620 gstring_reset_unused(g);
1621 return g;
1622 }
1623
1624
1625 /******************************************************************************/
1626
1627 /* Check to see if the line is an AMS and if so, set up to validate it.
1628 Called from the DKIM input processing. This must be done now as the message
1629 body data is hashed during input.
1630
1631 We call the DKIM code to request a body-hash; it has the facility already
1632 and the hash parameters might be common with other requests.
1633 */
1634
1635 static const uschar *
1636 arc_header_vfy_feed(gstring * g)
1637 {
1638 header_line h;
1639 arc_line al;
1640 pdkim_bodyhash * b;
1641 uschar * errstr;
1642
1643 if (!dkim_verify_ctx) return US"no dkim context";
1644
1645 if (strncmpic(ARC_HDR_AMS, g->s, ARC_HDRLEN_AMS) != 0) return US"not AMS";
1646
1647 DEBUG(D_receive) debug_printf("ARC: spotted AMS header\n");
1648 /* Parse the AMS header */
1649
1650 h.next = NULL;
1651 h.slen = g->size;
1652 h.text = g->s;
1653 memset(&al, 0, sizeof(arc_line));
1654 if ((errstr = arc_parse_line(&al, &h, ARC_HDRLEN_AMS, FALSE)))
1655 {
1656 DEBUG(D_acl) if (errstr) debug_printf("ARC: %s\n", errstr);
1657 return US"line parsing error";
1658 }
1659
1660 /* defaults */
1661 if (!al.c.data)
1662 {
1663 al.c_body.data = US"simple"; al.c_body.len = 6;
1664 al.c_head = al.c_body;
1665 }
1666
1667 /* Ask the dkim code to calc a bodyhash with those specs */
1668
1669 if (!(b = arc_ams_setup_vfy_bodyhash(&al)))
1670 return US"dkim hash setup fail";
1671
1672 /* Discard the reference; search again at verify time, knowing that one
1673 should have been created here. */
1674
1675 return NULL;
1676 }
1677
1678
1679
1680 /* A header line has been identified by DKIM processing.
1681
1682 Arguments:
1683 g Header line
1684 is_vfy TRUE for verify mode or FALSE for signing mode
1685
1686 Return:
1687 NULL for success, or an error string (probably unused)
1688 */
1689
1690 const uschar *
1691 arc_header_feed(gstring * g, BOOL is_vfy)
1692 {
1693 return is_vfy ? arc_header_vfy_feed(g) : arc_header_sign_feed(g);
1694 }
1695
1696
1697
1698 /******************************************************************************/
1699
1700 /* Construct an Authenticate-Results header portion, for the ARC module */
1701
1702 gstring *
1703 authres_arc(gstring * g)
1704 {
1705 if (arc_state)
1706 {
1707 arc_line * highest_ams;
1708 int start = 0; /* Compiler quietening */
1709 DEBUG(D_acl) start = g->ptr;
1710
1711 g = string_append(g, 2, US";\n\tarc=", arc_state);
1712 if (arc_received_instance > 0)
1713 {
1714 g = string_append(g, 3, US" (i=",
1715 string_sprintf("%d", arc_received_instance), US")");
1716 if (arc_state_reason)
1717 g = string_append(g, 3, US"(", arc_state_reason, US")");
1718 g = string_catn(g, US" header.s=", 10);
1719 highest_ams = arc_received->hdr_ams;
1720 g = string_catn(g, highest_ams->s.data, highest_ams->s.len);
1721
1722 g = string_append(g, 2,
1723 US" arc.oldest-pass=", string_sprintf("%d", arc_oldest_pass));
1724
1725 if (sender_host_address)
1726 g = string_append(g, 2, US" smtp.client-ip=", sender_host_address);
1727 }
1728 DEBUG(D_acl) debug_printf("ARC: authres '%.*s'\n",
1729 g->ptr - start - 3, g->s + start + 3);
1730 }
1731 else
1732 DEBUG(D_acl) debug_printf("ARC: no authres\n");
1733 return g;
1734 }
1735
1736
1737 # endif /* SUPPORT_SPF */
1738 #endif /* EXPERIMENTAL_ARC */
1739 /* vi: aw ai sw=2
1740 */