1323a451a530079a8ce656997f06c66f0728ac6f
[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 BOOL 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 uschar * s = al->i.data;
100 if (!s || !al->i.len) return 0;
101 return (unsigned) atoi(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;
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, * 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 return e;
499 }
500 headers_rlist = r;
501
502 if (!ctx->arcset_chain) return US"none";
503 return NULL;
504 }
505
506
507 static BOOL
508 arc_cv_match(arc_line * al, const uschar * s)
509 {
510 return Ustrncmp(s, al->cv.data, al->cv.len) == 0;
511 }
512
513 /******************************************************************************/
514
515 /* Return the hash of headers from the message that the AMS claims it
516 signed.
517 */
518
519 static void
520 arc_get_verify_hhash(arc_ctx * ctx, arc_line * ams, blob * hhash)
521 {
522 const uschar * headernames = string_copyn(ams->h.data, ams->h.len);
523 const uschar * hn;
524 int sep = ':';
525 hdr_rlist * r;
526 BOOL relaxed = Ustrncmp(US"relaxed", ams->c_head.data, ams->c_head.len) == 0;
527 int hashtype = pdkim_hashname_to_hashtype(
528 ams->a_hash.data, ams->a_hash.len);
529 hctx hhash_ctx;
530 const uschar * s;
531 int len;
532
533 if (!exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
534 {
535 DEBUG(D_acl)
536 debug_printf("ARC: hash setup error, possibly nonhandled hashtype\n");
537 return;
538 }
539
540 /* For each headername in the list from the AMS (walking in order)
541 walk the message headers in reverse order, adding to the hash any
542 found for the first time. For that last point, maintain used-marks
543 on the list of message headers. */
544
545 DEBUG(D_acl) debug_printf("ARC: AMS header data for verification:\n");
546
547 for (r = headers_rlist; r; r = r->prev)
548 r->used = FALSE;
549 while ((hn = string_nextinlist(&headernames, &sep, NULL, 0)))
550 for (r = headers_rlist; r; r = r->prev)
551 if ( !r->used
552 && strncasecmp(CCS (s = r->h->text), CCS hn, Ustrlen(hn)) == 0
553 )
554 {
555 if (relaxed) s = pdkim_relax_header_n(s, r->h->slen, TRUE);
556
557 len = Ustrlen(s);
558 DEBUG(D_acl) pdkim_quoteprint(s, len);
559 exim_sha_update(&hhash_ctx, s, Ustrlen(s));
560 r->used = TRUE;
561 break;
562 }
563
564 /* Finally add in the signature header (with the b= tag stripped) */
565
566 s = ams->rawsig_no_b_val.data, len = ams->rawsig_no_b_val.len;
567 if (relaxed)
568 len = Ustrlen(s = pdkim_relax_header_n(s, len, TRUE));
569 DEBUG(D_acl) pdkim_quoteprint(s, len);
570 exim_sha_update(&hhash_ctx, s, len);
571
572 exim_sha_finish(&hhash_ctx, hhash);
573 DEBUG(D_acl)
574 { debug_printf("ARC: header hash: "); pdkim_hexprint(hhash->data, hhash->len); }
575 return;
576 }
577
578
579
580
581 static pdkim_pubkey *
582 arc_line_to_pubkey(arc_line * al)
583 {
584 uschar * dns_txt;
585 pdkim_pubkey * p;
586
587 if (!(dns_txt = dkim_exim_query_dns_txt(string_sprintf("%.*s._domainkey.%.*s",
588 al->s.len, al->s.data, al->d.len, al->d.data))))
589 {
590 DEBUG(D_acl) debug_printf("pubkey dns lookup fail\n");
591 return NULL;
592 }
593
594 if ( !(p = pdkim_parse_pubkey_record(dns_txt))
595 || (Ustrcmp(p->srvtype, "*") != 0 && Ustrcmp(p->srvtype, "email") != 0)
596 )
597 {
598 DEBUG(D_acl) debug_printf("pubkey dns lookup format error\n");
599 return NULL;
600 }
601
602 /* If the pubkey limits use to specified hashes, reject unusable
603 signatures. XXX should we have looked for multiple dns records? */
604
605 if (p->hashes)
606 {
607 const uschar * list = p->hashes, * ele;
608 int sep = ':';
609
610 while ((ele = string_nextinlist(&list, &sep, NULL, 0)))
611 if (Ustrncmp(ele, al->a_hash.data, al->a_hash.len) == 0) break;
612 if (!ele)
613 {
614 DEBUG(D_acl) debug_printf("pubkey h=%s vs sig a=%.*s\n",
615 p->hashes, al->a.len, al->a.data);
616 return NULL;
617 }
618 }
619 return p;
620 }
621
622
623
624
625 static pdkim_bodyhash *
626 arc_ams_setup_vfy_bodyhash(arc_line * ams)
627 {
628 int canon_head, canon_body;
629 long bodylen;
630
631 pdkim_cstring_to_canons(ams->c.data, ams->c.len, &canon_head, &canon_body);
632 bodylen = ams->l.data
633 ? strtol(CS string_copyn(ams->l.data, ams->l.len), NULL, 10) : -1;
634
635 return pdkim_set_bodyhash(dkim_verify_ctx,
636 pdkim_hashname_to_hashtype(ams->a_hash.data, ams->a_hash.len),
637 canon_body,
638 bodylen);
639 }
640
641
642
643 /* Verify an AMS. This is a DKIM-sig header, but with an ARC i= tag
644 and without a DKIM v= tag.
645 */
646
647 static uschar *
648 arc_ams_verify(arc_ctx * ctx, arc_set * as)
649 {
650 arc_line * ams = as->hdr_ams;
651 pdkim_bodyhash * b;
652 pdkim_pubkey * p;
653 blob sighash;
654 blob hhash;
655 ev_ctx vctx;
656 int hashtype;
657 const uschar * errstr;
658
659 as->ams_verify_done = TRUE;
660
661 /* Check the AMS has all the required tags:
662 "a=" algorithm
663 "b=" signature
664 "bh=" body hash
665 "d=" domain (for key lookup)
666 "h=" headers (included in signature)
667 "s=" key-selector (for key lookup)
668 */
669 if ( !ams->a.data || !ams->b.data || !ams->bh.data || !ams->d.data
670 || !ams->h.data || !ams->s.data)
671 return US"fail";
672
673
674 /* The bodyhash should have been created earlier, and the dkim code should
675 have managed calculating it during message input. Find the reference to it. */
676
677 if (!(b = arc_ams_setup_vfy_bodyhash(ams)))
678 return US"fail";
679
680 DEBUG(D_acl)
681 {
682 debug_printf("ARC i=%d AMS Body bytes hashed: %lu\n"
683 " Body %.*s computed: ",
684 as->instance, b->signed_body_bytes,
685 ams->a_hash.len, ams->a_hash.data);
686 pdkim_hexprint(CUS b->bh.data, b->bh.len);
687 }
688
689 /* We know the bh-tag blob is of a nul-term string, so safe as a string */
690
691 if ( !ams->bh.data
692 || (pdkim_decode_base64(ams->bh.data, &sighash), sighash.len != b->bh.len)
693 || memcmp(sighash.data, b->bh.data, b->bh.len) != 0
694 )
695 {
696 DEBUG(D_acl)
697 {
698 debug_printf("ARC i=%d AMS Body hash from headers: ", as->instance);
699 pdkim_hexprint(sighash.data, sighash.len);
700 debug_printf("ARC i=%d AMS Body hash did NOT match\n", as->instance);
701 }
702 return US"body hash compare mismatch";
703 }
704
705 DEBUG(D_acl) debug_printf("ARC i=%d AMS Body hash compared OK\n", as->instance);
706
707 /* Get the public key from DNS */
708
709 if (!(p = arc_line_to_pubkey(ams)))
710 return US"pubkey problem";
711
712 /* We know the b-tag blob is of a nul-term string, so safe as a string */
713 pdkim_decode_base64(ams->b.data, &sighash);
714
715 arc_get_verify_hhash(ctx, ams, &hhash);
716
717 /* Setup the interface to the signing library */
718
719 if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx)))
720 {
721 DEBUG(D_acl) debug_printf("ARC verify init: %s\n", errstr);
722 return US"fail";
723 }
724
725 hashtype = pdkim_hashname_to_hashtype(ams->a_hash.data, ams->a_hash.len);
726
727 if ((errstr = exim_dkim_verify(&vctx,
728 pdkim_hashes[hashtype].exim_hashmethod, &hhash, &sighash)))
729 {
730 DEBUG(D_acl) debug_printf("ARC i=%d AMS verify %s\n", as->instance, errstr);
731 return US"ams sig verify fail";
732 }
733
734 DEBUG(D_acl) debug_printf("ARC i=%d AMS verify pass\n", as->instance);
735 as->ams_verify_passed = TRUE;
736 return NULL;
737 }
738
739
740
741 /* Check the sets are instance-continuous and that all
742 members are present. Check that no arc_seals are "fail".
743 Set the highest instance number global.
744 Verify the latest AMS.
745 */
746 static uschar *
747 arc_headers_check(arc_ctx * ctx)
748 {
749 arc_set * as;
750 int inst;
751 BOOL ams_fail_found = FALSE;
752 uschar * ret = NULL;
753
754 if (!(as = ctx->arcset_chain))
755 return US"none";
756
757 for(inst = 0; as; as = as->next)
758 {
759 if ( as->instance != ++inst
760 || !as->hdr_aar || !as->hdr_ams || !as->hdr_as
761 || arc_cv_match(as->hdr_as, US"fail")
762 )
763 {
764 DEBUG(D_acl) debug_printf("ARC i=%d fail"
765 " (cv, sequence or missing header)\n", as->instance);
766 ret = US"fail";
767 }
768
769 /* Evaluate the oldest-pass AMS validation while we're here.
770 It does not affect the AS chain validation but is reported as
771 auxilary info. */
772
773 if (!ams_fail_found)
774 if (arc_ams_verify(ctx, as))
775 ams_fail_found = TRUE;
776 else
777 arc_oldest_pass = inst;
778 }
779
780 arc_received = ctx->arcset_chain_last;
781 arc_received_instance = inst;
782 if (ret)
783 return ret;
784
785 /* We can skip the latest-AMS validation, if we already did it. */
786
787 as = ctx->arcset_chain_last;
788 if (as->ams_verify_done ? !as->ams_verify_passed : !!arc_ams_verify(ctx, as))
789 return US"fail";
790
791 return NULL;
792 }
793
794
795 /******************************************************************************/
796 static const uschar *
797 arc_seal_verify(arc_ctx * ctx, arc_set * as)
798 {
799 arc_line * hdr_as = as->hdr_as;
800 arc_set * as2;
801 int hashtype;
802 hctx hhash_ctx;
803 blob hhash_computed;
804 blob sighash;
805 ev_ctx vctx;
806 pdkim_pubkey * p;
807 const uschar * errstr;
808
809 DEBUG(D_acl) debug_printf("ARC: AS vfy i=%d\n", as->instance);
810 /*
811 1. If the value of the "cv" tag on that seal is "fail", the
812 chain state is "fail" and the algorithm stops here. (This
813 step SHOULD be skipped if the earlier step (2.1) was
814 performed) [it was]
815
816 2. In Boolean nomenclature: if ((i == 1 && cv != "none") or (cv
817 == "none" && i != 1)) then the chain state is "fail" and the
818 algorithm stops here (note that the ordering of the logic is
819 structured for short-circuit evaluation).
820 */
821
822 if ( as->instance == 1 && !arc_cv_match(hdr_as, US"none")
823 || arc_cv_match(hdr_as, US"none") && as->instance != 1
824 )
825 return US"fail";
826
827 /*
828 3. Initialize a hash function corresponding to the "a" tag of
829 the ARC-Seal.
830 */
831
832 hashtype = pdkim_hashname_to_hashtype(hdr_as->a_hash.data, hdr_as->a_hash.len);
833
834 if (!exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
835 {
836 DEBUG(D_acl)
837 debug_printf("ARC: hash setup error, possibly nonhandled hashtype\n");
838 return US"fail";
839 }
840
841 /*
842 4. Compute the canonicalized form of the ARC header fields, in
843 the order described in Section 5.4.2, using the "relaxed"
844 header canonicalization defined in Section 3.4.2 of
845 [RFC6376]. Pass the canonicalized result to the hash
846 function.
847 */
848
849 DEBUG(D_acl) debug_printf("ARC: AS header data for verification:\n");
850 for (as2 = ctx->arcset_chain;
851 as2 && as2->instance <= as->instance;
852 as2 = as2->next)
853 {
854 arc_line * al;
855 uschar * s;
856 int len;
857
858 al = as2->hdr_aar;
859 if (!(s = al->relaxed))
860 al->relaxed = s = pdkim_relax_header_n(al->complete->text,
861 al->complete->slen, TRUE);
862 len = Ustrlen(s);
863 DEBUG(D_acl) pdkim_quoteprint(s, len);
864 exim_sha_update(&hhash_ctx, s, len);
865
866 al = as2->hdr_ams;
867 if (!(s = al->relaxed))
868 al->relaxed = s = pdkim_relax_header_n(al->complete->text,
869 al->complete->slen, TRUE);
870 len = Ustrlen(s);
871 DEBUG(D_acl) pdkim_quoteprint(s, len);
872 exim_sha_update(&hhash_ctx, s, len);
873
874 al = as2->hdr_as;
875 if (as2->instance == as->instance)
876 s = pdkim_relax_header_n(al->rawsig_no_b_val.data,
877 al->rawsig_no_b_val.len, TRUE);
878 else if (!(s = al->relaxed))
879 al->relaxed = s = pdkim_relax_header_n(al->complete->text,
880 al->complete->slen, TRUE);
881 len = Ustrlen(s);
882 DEBUG(D_acl) pdkim_quoteprint(s, len);
883 exim_sha_update(&hhash_ctx, s, len);
884 }
885
886 /*
887 5. Retrieve the final digest from the hash function.
888 */
889
890 exim_sha_finish(&hhash_ctx, &hhash_computed);
891 DEBUG(D_acl)
892 {
893 debug_printf("ARC i=%d AS Header %.*s computed: ",
894 as->instance, hdr_as->a_hash.len, hdr_as->a_hash.data);
895 pdkim_hexprint(hhash_computed.data, hhash_computed.len);
896 }
897
898
899 /*
900 6. Retrieve the public key identified by the "s" and "d" tags in
901 the ARC-Seal, as described in Section 4.1.6.
902 */
903
904 if (!(p = arc_line_to_pubkey(hdr_as)))
905 return US"pubkey problem";
906
907 /*
908 7. Determine whether the signature portion ("b" tag) of the ARC-
909 Seal and the digest computed above are valid according to the
910 public key. (See also Section Section 8.4 for failure case
911 handling)
912
913 8. If the signature is not valid, the chain state is "fail" and
914 the algorithm stops here.
915 */
916
917 /* We know the b-tag blob is of a nul-term string, so safe as a string */
918 pdkim_decode_base64(hdr_as->b.data, &sighash);
919
920 if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx)))
921 {
922 DEBUG(D_acl) debug_printf("ARC verify init: %s\n", errstr);
923 return US"fail";
924 }
925
926 hashtype = pdkim_hashname_to_hashtype(hdr_as->a_hash.data, hdr_as->a_hash.len);
927
928 if ((errstr = exim_dkim_verify(&vctx,
929 pdkim_hashes[hashtype].exim_hashmethod,
930 &hhash_computed, &sighash)))
931 {
932 DEBUG(D_acl)
933 debug_printf("ARC i=%d AS headers verify: %s\n", as->instance, errstr);
934 return US"fail";
935 }
936
937 DEBUG(D_acl) debug_printf("ARC: AS vfy i=%d pass\n", as->instance);
938 return NULL;
939 }
940
941
942 static const uschar *
943 arc_verify_seals(arc_ctx * ctx)
944 {
945 arc_set * as = ctx->arcset_chain;
946
947 if (!as)
948 return US"none";
949
950 while (as)
951 {
952 if (arc_seal_verify(ctx, as)) return US"fail";
953 as = as->next;
954 }
955 DEBUG(D_acl) debug_printf("ARC: AS vfy overall pass\n");
956 return NULL;
957 }
958 /******************************************************************************/
959
960 /* Do ARC verification. Called from DATA ACL, on a verify = arc
961 condition. No arguments; we are checking globals.
962
963 Return: The ARC state, or NULL on error.
964 */
965
966 const uschar *
967 acl_verify_arc(void)
968 {
969 arc_ctx ctx = { NULL };
970 const uschar * res;
971
972 /* AS evaluation, per
973 https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-10#section-6
974 */
975 /* 1. Collect all ARC sets currently on the message. If there were
976 none, the ARC state is "none" and the algorithm stops here.
977 */
978
979 if ((res = arc_vfy_collect_hdrs(&ctx)))
980 goto out;
981
982 /* 2. If the form of any ARC set is invalid (e.g., does not contain
983 exactly one of each of the three ARC-specific header fields),
984 then the chain state is "fail" and the algorithm stops here.
985
986 1. To avoid the overhead of unnecessary computation and delay
987 from crypto and DNS operations, the cv value for all ARC-
988 Seal(s) MAY be checked at this point. If any of the values
989 are "fail", then the overall state of the chain is "fail" and
990 the algorithm stops here.
991
992 3. Conduct verification of the ARC-Message-Signature header field
993 bearing the highest instance number. If this verification fails,
994 then the chain state is "fail" and the algorithm stops here.
995 */
996
997 if ((res = arc_headers_check(&ctx)))
998 goto out;
999
1000 /* 4. For each ARC-Seal from the "N"th instance to the first, apply the
1001 following logic:
1002
1003 1. If the value of the "cv" tag on that seal is "fail", the
1004 chain state is "fail" and the algorithm stops here. (This
1005 step SHOULD be skipped if the earlier step (2.1) was
1006 performed)
1007
1008 2. In Boolean nomenclature: if ((i == 1 && cv != "none") or (cv
1009 == "none" && i != 1)) then the chain state is "fail" and the
1010 algorithm stops here (note that the ordering of the logic is
1011 structured for short-circuit evaluation).
1012
1013 3. Initialize a hash function corresponding to the "a" tag of
1014 the ARC-Seal.
1015
1016 4. Compute the canonicalized form of the ARC header fields, in
1017 the order described in Section 5.4.2, using the "relaxed"
1018 header canonicalization defined in Section 3.4.2 of
1019 [RFC6376]. Pass the canonicalized result to the hash
1020 function.
1021
1022 5. Retrieve the final digest from the hash function.
1023
1024 6. Retrieve the public key identified by the "s" and "d" tags in
1025 the ARC-Seal, as described in Section 4.1.6.
1026
1027 7. Determine whether the signature portion ("b" tag) of the ARC-
1028 Seal and the digest computed above are valid according to the
1029 public key. (See also Section Section 8.4 for failure case
1030 handling)
1031
1032 8. If the signature is not valid, the chain state is "fail" and
1033 the algorithm stops here.
1034
1035 5. If all seals pass validation, then the chain state is "pass", and
1036 the algorithm is complete.
1037 */
1038
1039 if ((res = arc_verify_seals(&ctx)))
1040 goto out;
1041
1042 res = US"pass";
1043
1044 out:
1045 return res;
1046 }
1047
1048 /******************************************************************************/
1049
1050 /* Prepend the header to the rlist */
1051
1052 static hdr_rlist *
1053 arc_rlist_entry(hdr_rlist * list, const uschar * s, int len)
1054 {
1055 hdr_rlist * r = store_get(sizeof(hdr_rlist) + sizeof(header_line));
1056 header_line * h = r->h = (header_line *)(r+1);
1057
1058 r->prev = list;
1059 r->used = FALSE;
1060 h->next = NULL;
1061 h->type = 0;
1062 h->slen = len;
1063 h->text = US s;
1064
1065 /* This works for either NL or CRLF lines; also nul-termination */
1066 while (*++s)
1067 if (*s == '\n' && s[1] != '\t' && s[1] != ' ') break;
1068 s++; /* move past end of line */
1069
1070 return r;
1071 }
1072
1073
1074 /* Walk the given headers strings identifying each header, and construct
1075 a reverse-order list. Also parse ARC-chain headers and build the chain
1076 struct, retaining pointers into the string.
1077 */
1078
1079 static hdr_rlist *
1080 arc_sign_scan_headers(arc_ctx * ctx, gstring * sigheaders)
1081 {
1082 const uschar * s;
1083 hdr_rlist * rheaders = NULL;
1084
1085 s = sigheaders ? sigheaders->s : NULL;
1086 if (s) while (*s)
1087 {
1088 uschar * s2;
1089
1090 /* This works for either NL or CRLF lines; also nul-termination */
1091 while (*++s2)
1092 if (*s2 == '\n' && s2[1] != '\t' && s2[1] != ' ') break;
1093 s2++; /* move past end of line */
1094
1095 rheaders = arc_rlist_entry(rheaders, s, s2 - s);
1096 s = s2;
1097 }
1098 return rheaders;
1099 }
1100
1101
1102
1103 /* Return the A-R content, without identity, with line-ending and
1104 NUL termination. */
1105
1106 static BOOL
1107 arc_sign_find_ar(header_line * headers, const uschar * identity, blob * ret)
1108 {
1109 header_line * h;
1110 int ilen = Ustrlen(identity);
1111
1112 ret->data = NULL;
1113 for(h = headers; h; h = h->next)
1114 {
1115 uschar * s = h->text, c;
1116 int len = h->slen;
1117
1118 if (Ustrncmp(s, HDR_AR, HDRLEN_AR) != 0) continue;
1119 s += HDRLEN_AR, len -= HDRLEN_AR; /* header name */
1120 while ( len > 0
1121 && (c = *s) && (c == ' ' || c == '\t' || c == '\r' || c == '\n'))
1122 s++, len--; /* FWS */
1123 if (Ustrncmp(s, identity, ilen) != 0) continue;
1124 s += ilen; len -= ilen; /* identity */
1125 if (len <= 0) continue;
1126 if ((c = *s) && c == ';') s++, len--; /* identity terminator */
1127 while ( len > 0
1128 && (c = *s) && (c == ' ' || c == '\t' || c == '\r' || c == '\n'))
1129 s++, len--; /* FWS */
1130 if (len <= 0) continue;
1131 ret->data = s;
1132 ret->len = len;
1133 return TRUE;
1134 }
1135 return FALSE;
1136 }
1137
1138
1139
1140 /* Append a constructed AAR including CRLF. Add it to the arc_ctx too. */
1141
1142 static gstring *
1143 arc_sign_append_aar(gstring * g, arc_ctx * ctx,
1144 const uschar * identity, int instance, blob * ar)
1145 {
1146 int aar_off = g ? g->ptr : 0;
1147 arc_set * as = store_get(sizeof(arc_set) + sizeof(arc_line) + sizeof(header_line));
1148 arc_line * al = (arc_line *)(as+1);
1149 header_line * h = (header_line *)(al+1);
1150
1151 g = string_catn(g, ARC_HDR_AAR, ARC_HDRLEN_AAR);
1152 g = string_cat(g, string_sprintf(" i=%d; %s;\r\n\t", instance, identity));
1153 g = string_catn(g, US ar->data, ar->len);
1154
1155 h->slen = g->ptr - aar_off;
1156 h->text = g->s + aar_off;
1157 al->complete = h;
1158 as->next = NULL;
1159 as->prev = ctx->arcset_chain_last;
1160 as->instance = instance;
1161 as->hdr_aar = al;
1162 if (instance == 1)
1163 ctx->arcset_chain = as;
1164 else
1165 ctx->arcset_chain_last->next = as;
1166 ctx->arcset_chain_last = as;
1167
1168 DEBUG(D_transport) debug_printf("ARC: AAR '%.*s'\n", h->slen - 2, h->text);
1169 return g;
1170 }
1171
1172
1173
1174 static BOOL
1175 arc_sig_from_pseudoheader(gstring * hdata, int hashtype, const uschar * privkey,
1176 blob * sig, const uschar * why)
1177 {
1178 hashmethod hm = /*sig->keytype == KEYTYPE_ED25519*/ FALSE
1179 ? HASH_SHA2_512 : pdkim_hashes[hashtype].exim_hashmethod;
1180 blob hhash;
1181 es_ctx sctx;
1182 const uschar * errstr;
1183
1184 DEBUG(D_transport)
1185 {
1186 hctx hhash_ctx;
1187 debug_printf("ARC: %s header data for signing:\n", why);
1188 pdkim_quoteprint(hdata->s, hdata->ptr);
1189
1190 (void) exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod);
1191 exim_sha_update(&hhash_ctx, hdata->s, hdata->ptr);
1192 exim_sha_finish(&hhash_ctx, &hhash);
1193 debug_printf("ARC: header hash: "); pdkim_hexprint(hhash.data, hhash.len);
1194 }
1195
1196 if (FALSE /*need hash for Ed25519 or GCrypt signing*/ )
1197 {
1198 hctx hhash_ctx;
1199 (void) exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod);
1200 exim_sha_update(&hhash_ctx, hdata->s, hdata->ptr);
1201 exim_sha_finish(&hhash_ctx, &hhash);
1202 }
1203 else
1204 {
1205 hhash.data = hdata->s;
1206 hhash.len = hdata->ptr;
1207 }
1208
1209 if ( (errstr = exim_dkim_signing_init(privkey, &sctx))
1210 || (errstr = exim_dkim_sign(&sctx, hm, &hhash, sig)))
1211 {
1212 log_write(0, LOG_MAIN|LOG_PANIC, "ARC: %s signing: %s\n", why, errstr);
1213 return FALSE;
1214 }
1215 return TRUE;
1216 }
1217
1218
1219
1220 static gstring *
1221 arc_sign_append_sig(gstring * g, blob * sig)
1222 {
1223 /*debug_printf("%s: raw sig ", __FUNCTION__); pdkim_hexprint(sig->data, sig->len);*/
1224 sig->data = pdkim_encode_base64(sig);
1225 sig->len = Ustrlen(sig->data);
1226 for (;;)
1227 {
1228 int len = MIN(sig->len, 74);
1229 g = string_catn(g, sig->data, len);
1230 if ((sig->len -= len) == 0) break;
1231 sig->data += len;
1232 g = string_catn(g, US"\r\n\t ", 5);
1233 }
1234 g = string_catn(g, US";\r\n", 3);
1235 gstring_reset_unused(g);
1236 string_from_gstring(g);
1237 return g;
1238 }
1239
1240
1241 /* Append a constructed AMS including CRLF. Add it to the arc_ctx too. */
1242
1243 static gstring *
1244 arc_sign_append_ams(gstring * g, arc_ctx * ctx, int instance,
1245 const uschar * identity, const uschar * selector, blob * bodyhash,
1246 hdr_rlist * rheaders, const uschar * privkey)
1247 {
1248 uschar * s;
1249 gstring * hdata = NULL;
1250 int col;
1251 int hashtype = pdkim_hashname_to_hashtype(US"sha256", 6); /*XXX hardwired */
1252 blob sig;
1253 int ams_off;
1254 arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line));
1255 header_line * h = (header_line *)(al+1);
1256
1257 /* debug_printf("%s\n", __FUNCTION__); */
1258
1259 /* Construct the to-be-signed AMS pseudo-header: everything but the sig. */
1260
1261 ams_off = g->ptr;
1262 g = string_append(g, 10,
1263 ARC_HDR_AMS,
1264 US" i=", string_sprintf("%d", instance),
1265 US"; a=rsa-sha256; c=relaxed; d=", identity, /*XXX hardwired */
1266 US"; s=", selector,
1267 US";\r\n\tbh=", pdkim_encode_base64(bodyhash),
1268 US";\r\n\th=");
1269
1270 for(col = 3; rheaders; rheaders = rheaders->prev)
1271 {
1272 const uschar * hnames = US"DKIM-Signature:" PDKIM_DEFAULT_SIGN_HEADERS;
1273 uschar * name, * htext = rheaders->h->text;
1274 int sep = ':';
1275
1276 /* Spot headers of interest */
1277
1278 while ((name = string_nextinlist(&hnames, &sep, NULL, 0)))
1279 {
1280 int len = Ustrlen(name);
1281 if (strncasecmp(CCS htext, CCS name, len) == 0)
1282 {
1283 /* If too long, fold line in h= field */
1284
1285 if (col + len > 78) g = string_catn(g, US"\r\n\t ", 5), col = 3;
1286
1287 /* Add name to h= list */
1288
1289 g = string_catn(g, name, len);
1290 g = string_catn(g, US":", 1);
1291 col += len + 1;
1292
1293 /* Accumulate header for hashing/signing */
1294
1295 hdata = string_cat(hdata,
1296 pdkim_relax_header_n(htext, rheaders->h->slen, TRUE)); /*XXX hardwired */
1297 break;
1298 }
1299 }
1300 }
1301
1302 /* Lose the last colon from the h= list */
1303
1304 if (g->s[g->ptr - 1] == ':') g->ptr--;
1305
1306 g = string_catn(g, US";\r\n\tb=;", 7);
1307
1308 /* Include the pseudo-header in the accumulation */
1309 /*XXX should that be prepended rather than appended? */
1310 /*XXX also need to include at the verify stage */
1311
1312 s = pdkim_relax_header_n(g->s + ams_off, g->ptr - ams_off, TRUE);
1313 hdata = string_cat(hdata, s);
1314
1315 /* Calculate the signature from the accumulation */
1316 /*XXX does that need further relaxation? there are spaces embedded in the b= strings! */
1317
1318 if (!arc_sig_from_pseudoheader(hdata, hashtype, privkey, &sig, US"AMS"))
1319 return NULL;
1320
1321 /* Lose the trailing semicolon from the psuedo-header, and append the signature
1322 (folded over lines) and termination to complete it. */
1323
1324 g->ptr--;
1325 g = arc_sign_append_sig(g, &sig);
1326
1327 h->slen = g->ptr - ams_off;
1328 h->text = g->s + ams_off;
1329 al->complete = h;
1330 ctx->arcset_chain_last->hdr_ams = al;
1331
1332 DEBUG(D_transport) debug_printf("ARC: AMS '%.*s'\n", h->slen - 2, h->text);
1333 return g;
1334 }
1335
1336
1337
1338 /* Look for an arc= result in an A-R header blob. We know that its data
1339 happens to be a NUL-term string. */
1340
1341 static uschar *
1342 arc_ar_cv_status(blob * ar)
1343 {
1344 const uschar * resinfo = ar->data;
1345 int sep = ';';
1346 uschar * methodspec, * s;
1347
1348 while ((methodspec = string_nextinlist(&resinfo, &sep, NULL, 0)))
1349 if (Ustrncmp(methodspec, US"arc=", 4) == 0)
1350 {
1351 uschar c;
1352 for (s = methodspec += 4;
1353 (c = *s) && c != ';' && c != ' ' && c != '\r' && c != '\n'; ) s++;
1354 return string_copyn(methodspec, s - methodspec);
1355 }
1356 return NULL;
1357 }
1358
1359
1360
1361 /* Build the AS header and prepend it */
1362
1363 static gstring *
1364 arc_sign_prepend_as(gstring * arcset_interim, arc_ctx * ctx,
1365 int instance, const uschar * identity, const uschar * selector, blob * ar,
1366 const uschar * privkey)
1367 {
1368 gstring * arcset;
1369 arc_set * as;
1370 uschar * status = arc_ar_cv_status(ar);
1371 arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line));
1372 header_line * h = (header_line *)(al+1);
1373 uschar * s;
1374
1375 gstring * hdata = NULL;
1376 int hashtype = pdkim_hashname_to_hashtype(US"sha256", 6); /*XXX hardwired */
1377 blob sig;
1378
1379 /*
1380 - Generate AS
1381 - no body coverage
1382 - no h= tag; implicit coverage
1383 - arc status from A-R
1384 - if fail:
1385 - coverage is just the new ARC set
1386 including self (but with an empty b= in self)
1387 - if non-fail:
1388 - all ARC set headers, set-number order, aar then ams then as,
1389 including self (but with an empty b= in self)
1390 */
1391
1392 /* Construct the AS except for the signature */
1393
1394 arcset = string_append(NULL, 10,
1395 ARC_HDR_AS,
1396 US" i=", string_sprintf("%d", instance),
1397 US"; cv=", status,
1398 US"; a=rsa-sha256; c=relaxed; d=", identity, /*XXX hardwired */
1399 US"; s=", selector, /*XXX same as AMS */
1400 US";\r\n\t b=;");
1401
1402 h->slen = arcset->ptr;
1403 h->text = arcset->s;
1404 al->complete = h;
1405 ctx->arcset_chain_last->hdr_as = al;
1406
1407 /* For any but "fail" chain-verify status, walk the entire chain in order by
1408 instance. For fail, only the new arc-set. Accumulate the elements walked. */
1409
1410 for (as = Ustrcmp(status, US"fail") == 0
1411 ? ctx->arcset_chain_last : ctx->arcset_chain;
1412 as; as = as->next)
1413 {
1414 /* Accumulate AAR then AMS then AS. Relaxed canonicalisation
1415 is required per standard. */
1416
1417 h = as->hdr_aar->complete;
1418 hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
1419 h = as->hdr_ams->complete;
1420 hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
1421 h = as->hdr_as->complete;
1422 hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
1423 }
1424
1425 /* Calculate the signature from the accumulation */
1426
1427 if (!arc_sig_from_pseudoheader(hdata, hashtype, privkey, &sig, US"AS"))
1428 return NULL;
1429
1430 /* Lose the trailing semicolon */
1431 arcset->ptr--;
1432 arcset = arc_sign_append_sig(arcset, &sig);
1433 DEBUG(D_transport) debug_printf("ARC: AS '%.*s'\n", arcset->ptr - 2, arcset->s);
1434
1435 /* Finally, append the AMS and AAR to the new AS */
1436
1437 return string_catn(arcset, arcset_interim->s, arcset_interim->ptr);
1438 }
1439
1440
1441 /**************************************/
1442
1443 /* Return pointer to pdkim_bodyhash for given hash method, creating new
1444 method if needed.
1445 */
1446
1447 void *
1448 arc_ams_setup_sign_bodyhash(void)
1449 {
1450 int canon_head, canon_body;
1451
1452 DEBUG(D_transport) debug_printf("ARC: requesting bodyhash\n");
1453 pdkim_cstring_to_canons(US"relaxed", 7, &canon_head, &canon_body); /*XXX hardwired */
1454 return pdkim_set_bodyhash(&dkim_sign_ctx,
1455 pdkim_hashname_to_hashtype(US"sha256", 6), /*XXX hardwired */
1456 canon_body,
1457 -1);
1458 }
1459
1460
1461
1462 /* A "normal" header line, identified by DKIM processing. These arrive before
1463 the call to arc_sign(), which carries any newly-created DKIM headers - and
1464 those go textually before the normal ones in the message.
1465
1466 We have to take the feed from DKIM as, in the transport-filter case, the
1467 headers are not in memory at the time of the call to arc_sign().
1468
1469 Take a copy of the header and construct a reverse-order list.
1470 Also parse ARC-chain headers and build the chain struct, retaining pointers
1471 into the copies.
1472 */
1473
1474 static const uschar *
1475 arc_header_sign_feed(gstring * g)
1476 {
1477 uschar * s = string_copyn(g->s, g->ptr);
1478 headers_rlist = arc_rlist_entry(headers_rlist, s, g->ptr);
1479 return arc_try_header(&arc_sign_ctx, headers_rlist->h, TRUE);
1480 }
1481
1482
1483
1484 /* ARC signing. Called from the smtp transport, if the arc_sign option is set.
1485 The dkim_exim_sign() function has already been called, so will have hashed the
1486 message body for us so long as we requested a hash previously.
1487
1488 Arguments:
1489 signspec Three-element colon-sep list: identity, selector, privkey
1490 Already expanded
1491 sigheaders Any signature headers already generated, eg. by DKIM, or NULL
1492 errstr Error string
1493
1494 Return value
1495 Set of headers to prepend to the message, including the supplied sigheaders
1496 but not the plainheaders.
1497 */
1498
1499 gstring *
1500 arc_sign(const uschar * signspec, gstring * sigheaders, uschar ** errstr)
1501 {
1502 const uschar * identity, * selector, * privkey;
1503 int sep = 0;
1504 header_line * headers;
1505 hdr_rlist * rheaders;
1506 blob ar;
1507 int instance;
1508 gstring * g = NULL;
1509 pdkim_bodyhash * b;
1510
1511 /* Parse the signing specification */
1512
1513 identity = string_nextinlist(&signspec, &sep, NULL, 0);
1514 selector = string_nextinlist(&signspec, &sep, NULL, 0);
1515 if ( !*identity | !*selector
1516 || !(privkey = string_nextinlist(&signspec, &sep, NULL, 0)) || !*privkey)
1517 {
1518 log_write(0, LOG_MAIN|LOG_PANIC, "ARC: bad signing-specification");
1519 return NULL;
1520 }
1521 if (*privkey == '/' && !(privkey = expand_file_big_buffer(privkey)))
1522 return NULL;
1523
1524 DEBUG(D_transport) debug_printf("ARC: sign for %s\n", identity);
1525
1526 /*
1527 - scan headers for existing ARC chain & A-R (with matching system-identfier)
1528 - paniclog & skip on problems (no A-R)
1529 */
1530
1531 /* Make an rlist of any new DKIM headers, then add the "normals" rlist to it */
1532
1533 string_from_gstring(sigheaders);
1534 if ((rheaders = arc_sign_scan_headers(&arc_sign_ctx, sigheaders)))
1535 {
1536 hdr_rlist ** rp;
1537 for (rp = &rheaders; *rp; ) rp = &(*rp)->prev;
1538 *rp = headers_rlist;
1539 headers_rlist = rheaders;
1540 }
1541 else
1542 rheaders = headers_rlist;
1543 /* Finally, build a normal-order headers list */
1544 /*XXX only needed for hunt-the-AR? */
1545 {
1546 header_line * hnext = NULL;
1547 for (; rheaders; hnext = rheaders->h, rheaders = rheaders->prev)
1548 rheaders->h->next = hnext;
1549 headers = hnext;
1550 }
1551
1552 instance = arc_sign_ctx.arcset_chain_last ? arc_sign_ctx.arcset_chain_last->instance + 1 : 1;
1553
1554 if (!(arc_sign_find_ar(headers, identity, &ar)))
1555 {
1556 log_write(0, LOG_MAIN|LOG_PANIC, "ARC: no Authentication-Results header for signing");
1557 return sigheaders ? sigheaders : string_get(0);
1558 }
1559
1560 /*
1561 - Generate AAR
1562 - copy the A-R; prepend i= & identity
1563 */
1564
1565 g = arc_sign_append_aar(g, &arc_sign_ctx, identity, instance, &ar);
1566
1567 /*
1568 - Generate AMS
1569 - Looks fairly like a DKIM sig
1570 - Cover all DKIM sig headers as well as the usuals
1571 - ? oversigning?
1572 - Covers the data
1573 - we must have requested a suitable bodyhash previously
1574 */
1575
1576 b = arc_ams_setup_sign_bodyhash();
1577 g = arc_sign_append_ams(g, &arc_sign_ctx, instance, identity, selector,
1578 &b->bh, headers_rlist, privkey);
1579
1580 /*
1581 - Generate AS
1582 - no body coverage
1583 - no h= tag; implicit coverage
1584 - arc status from A-R
1585 - if fail:
1586 - coverage is just the new ARC set
1587 including self (but with an empty b= in self)
1588 - if non-fail:
1589 - all ARC set headers, set-number order, aar then ams then as,
1590 including self (but with an empty b= in self)
1591 */
1592
1593 g = arc_sign_prepend_as(g, &arc_sign_ctx, instance, identity, selector, &ar, privkey);
1594
1595 /* Finally, append the dkim headers and return the lot. */
1596
1597 g = string_catn(g, sigheaders->s, sigheaders->ptr);
1598 (void) string_from_gstring(g);
1599 gstring_reset_unused(g);
1600 return g;
1601 }
1602
1603
1604 /******************************************************************************/
1605
1606 /* Check to see if the line is an AMS and if so, set up to validate it.
1607 Called from the DKIM input processing. This must be done now as the message
1608 body data is hashed during input.
1609
1610 We call the DKIM code to request a body-hash; it has the facility already
1611 and the hash parameters might be common with other requests.
1612 */
1613
1614 static const uschar *
1615 arc_header_vfy_feed(gstring * g)
1616 {
1617 header_line h;
1618 arc_line al;
1619 pdkim_bodyhash * b;
1620 uschar * errstr;
1621
1622 if (!dkim_verify_ctx) return US"no dkim context";
1623
1624 if (strncmpic(ARC_HDR_AMS, g->s, ARC_HDRLEN_AMS) != 0) return US"not AMS";
1625
1626 DEBUG(D_receive) debug_printf("ARC: spotted AMS header\n");
1627 /* Parse the AMS header */
1628
1629 h.next = NULL;
1630 h.slen = g->size;
1631 h.text = g->s;
1632 memset(&al, 0, sizeof(arc_line));
1633 if ((errstr = arc_parse_line(&al, &h, ARC_HDRLEN_AMS, FALSE)))
1634 {
1635 DEBUG(D_acl) if (errstr) debug_printf("ARC: %s\n", errstr);
1636 return US"line parsing error";
1637 }
1638
1639 /* defaults */
1640 if (!al.c.data)
1641 {
1642 al.c_body.data = US"simple"; al.c_body.len = 6;
1643 al.c_head = al.c_body;
1644 }
1645
1646 /* Ask the dkim code to calc a bodyhash with those specs */
1647
1648 if (!(b = arc_ams_setup_vfy_bodyhash(&al)))
1649 return US"dkim hash setup fail";
1650
1651 /* Discard the reference; search again at verify time, knowing that one
1652 should have been created here. */
1653
1654 return NULL;
1655 }
1656
1657
1658
1659 /* A header line has been identified by DKIM processing.
1660
1661 Arguments:
1662 g Header line
1663 is_vfy TRUE for verify mode or FALSE for signing mode
1664
1665 Return:
1666 NULL for success, or an error string (probably unused)
1667 */
1668
1669 const uschar *
1670 arc_header_feed(gstring * g, BOOL is_vfy)
1671 {
1672 return is_vfy ? arc_header_vfy_feed(g) : arc_header_sign_feed(g);
1673 }
1674
1675
1676
1677 /******************************************************************************/
1678
1679 /* Construct an Authenticate-Results header portion, for the ARC module */
1680
1681 gstring *
1682 authres_arc(gstring * g)
1683 {
1684 if (arc_state)
1685 {
1686 arc_line * highest_ams;
1687 int start;
1688 DEBUG(D_acl) start = g->ptr;
1689
1690 g = string_append(g, 2, US";\n\tarc=", arc_state);
1691 if (arc_received_instance > 0)
1692 {
1693 g = string_append(g, 3, US" (i=",
1694 string_sprintf("%d", arc_received_instance), US") header.s=");
1695 highest_ams = arc_received->hdr_ams;
1696 g = string_catn(g, highest_ams->s.data, highest_ams->s.len);
1697
1698 g = string_append(g, 2,
1699 US" arc.oldest-pass=", string_sprintf("%d", arc_oldest_pass));
1700
1701 if (sender_host_address)
1702 g = string_append(g, 2, US" smtp.client-ip=", sender_host_address);
1703 }
1704 DEBUG(D_acl) debug_printf("ARC: authres '%.*s'\n",
1705 g->ptr - start - 3, g->s + start + 3);
1706 }
1707 else
1708 DEBUG(D_acl) debug_printf("ARC: no authres\n");
1709 return g;
1710 }
1711
1712
1713 # endif /* SUPPORT_SPF */
1714 #endif /* EXPERIMENTAL_ARC */
1715 /* vi: aw ai sw=2
1716 */