+/*************************************************
+* Exim - an Internet mail transport agent *
+*************************************************/
+/* Experimental ARC support for Exim
+ Copyright (c) Jeremy Harris 2018
+ License: GPL
+*/
+
+#include "exim.h"
+#ifdef EXPERIMENTAL_ARC
+# if !defined SUPPORT_SPF
+# error SPF must also be enabled for ARC
+# elif defined DISABLE_DKIM
+# error DKIM must also be enabled for ARC
+# else
+
+# include "functions.h"
+# include "pdkim/pdkim.h"
+# include "pdkim/signing.h"
+
+extern pdkim_ctx * dkim_verify_ctx;
+extern pdkim_ctx dkim_sign_ctx;
+
+/******************************************************************************/
+
+typedef struct hdr_rlist {
+ struct hdr_rlist * prev;
+ BOOL used;
+ header_line * h;
+} hdr_rlist;
+
+typedef struct arc_line {
+ header_line * complete; /* including the header name; nul-term */
+ uschar * relaxed;
+
+ /* identified tag contents */
+ /*XXX t= for AS? */
+ blob i;
+ blob cv;
+ blob a;
+ blob b;
+ blob bh;
+ blob d;
+ blob h;
+ blob s;
+ blob c;
+ blob l;
+
+ /* tag content sub-portions */
+ blob a_algo;
+ blob a_hash;
+
+ blob c_head;
+ blob c_body;
+
+ /* modified copy of b= field in line */
+ blob rawsig_no_b_val;
+} arc_line;
+
+typedef struct arc_set {
+ struct arc_set * next;
+ struct arc_set * prev;
+
+ unsigned instance;
+ arc_line * hdr_aar;
+ arc_line * hdr_ams;
+ arc_line * hdr_as;
+
+ BOOL ams_verify_done;
+ BOOL ams_verify_passed;
+} arc_set;
+
+typedef struct arc_ctx {
+ arc_set * arcset_chain;
+ arc_set * arcset_chain_last;
+} arc_ctx;
+
+#define ARC_HDR_AAR US"ARC-Authentication-Results:"
+#define ARC_HDRLEN_AAR 27
+#define ARC_HDR_AMS US"ARC-Message-Signature:"
+#define ARC_HDRLEN_AMS 22
+#define ARC_HDR_AS US"ARC-Seal:"
+#define ARC_HDRLEN_AS 9
+#define HDR_AR US"Authentication-Results:"
+#define HDRLEN_AR 23
+
+static hdr_rlist * headers_rlist;
+static arc_ctx arc_sign_ctx = { NULL };
+
+
+/******************************************************************************/
+
+
+/* Get the instance number from the header.
+Return 0 on error */
+static unsigned
+arc_instance_from_hdr(const arc_line * al)
+{
+uschar * s = al->i.data;
+if (!s || !al->i.len) return 0;
+return (unsigned) atoi(s);
+}
+
+
+static uschar *
+skip_fws(uschar * s)
+{
+uschar c = *s;
+while (c && (c == ' ' || c == '\t' || c == '\n' || c == '\r')) c = *++s;
+return s;
+}
+
+
+/* Locate instance struct on chain, inserting a new one if
+needed. The chain is in increasing-instance-number order
+by the "next" link, and we have a "prev" link also.
+*/
+
+static arc_set *
+arc_find_set(arc_ctx * ctx, unsigned i)
+{
+arc_set ** pas, * as, * next, * prev;
+
+for (pas = &ctx->arcset_chain, prev = NULL, next = ctx->arcset_chain;
+ as = *pas; pas = &as->next)
+ {
+ if (as->instance > i) break;
+ if (as->instance == i)
+ {
+ DEBUG(D_acl) debug_printf("ARC: existing instance %u\n", i);
+ return as;
+ }
+ next = as->next;
+ prev = as;
+ }
+
+DEBUG(D_acl) debug_printf("ARC: new instance %u\n", i);
+*pas = as = store_get(sizeof(arc_set));
+memset(as, 0, sizeof(arc_set));
+as->next = next;
+as->prev = prev;
+as->instance = i;
+if (next)
+ next->prev = as;
+else
+ ctx->arcset_chain_last = as;
+return as;
+}
+
+
+
+/* Insert a tag content into the line structure.
+Note this is a reference to existing data, not a copy.
+Check for already-seen tag.
+The string-pointer is on the '=' for entry. Update it past the
+content (to the ;) on return;
+*/
+
+static uschar *
+arc_insert_tagvalue(arc_line * al, unsigned loff, uschar ** ss)
+{
+uschar * s = *ss;
+uschar c = *++s;
+blob * b = (blob *)(US al + loff);
+size_t len = 0;
+
+/* [FWS] tag-value [FWS] */
+
+if (b->data) return US"fail";
+s = skip_fws(s); /* FWS */
+
+b->data = s;
+while ((c = *s) && c != ';') { len++; s++; }
+*ss = s;
+while (len && ((c = s[-1]) == ' ' || c == '\t' || c == '\n' || c == '\r'))
+ { s--; len--; } /* FWS */
+b->len = len;
+return NULL;
+}
+
+
+/* Inspect a header line, noting known tag fields.
+Check for duplicates. */
+
+static uschar *
+arc_parse_line(arc_line * al, header_line * h, unsigned off, BOOL instance_only)
+{
+uschar * s = h->text + off;
+uschar * r;
+uschar c;
+
+al->complete = h;
+
+if (!instance_only)
+ {
+ al->rawsig_no_b_val.data = store_get(h->slen + 1);
+ memcpy(al->rawsig_no_b_val.data, h->text, off); /* copy the header name blind */
+ r = al->rawsig_no_b_val.data + off;
+ al->rawsig_no_b_val.len = off;
+ }
+
+/* tag-list = tag-spec *( ";" tag-spec ) [ ";" ] */
+
+while ((c = *s))
+ {
+ char tagchar;
+ uschar * t;
+ unsigned i = 0;
+ uschar * fieldstart = s;
+ uschar * bstart = NULL, * bend;
+
+ /* tag-spec = [FWS] tag-name [FWS] "=" [FWS] tag-value [FWS] */
+
+ s = skip_fws(s); /* FWS */
+ if (!*s) break;
+/* debug_printf("%s: consider '%s'\n", __FUNCTION__, s); */
+ tagchar = *s++;
+ s = skip_fws(s); /* FWS */
+ if (!*s) break;
+
+ if (!instance_only || tagchar == 'i') switch (tagchar)
+ {
+ case 'a': /* a= AMS algorithm */
+ {
+ if (*s != '=') return US"no 'a' value";
+ if (arc_insert_tagvalue(al, offsetof(arc_line, a), &s)) return US"a tag dup";
+
+ /* substructure: algo-hash (eg. rsa-sha256) */
+
+ t = al->a_algo.data = al->a.data;
+ while (*t != '-')
+ if (!*t++ || ++i > al->a.len) return US"no '-' in 'a' value";
+ al->a_algo.len = i;
+ if (*t++ != '-') return US"no '-' in 'a' value";
+ al->a_hash.data = t;
+ al->a_hash.len = al->a.len - i - 1;
+ }
+ break;
+ case 'b':
+ {
+ gstring * g = NULL;
+
+ switch (*s)
+ {
+ case '=': /* b= AMS signature */
+ if (al->b.data) return US"already b data";
+ bstart = s+1;
+
+ /* The signature can have FWS inserted in the content;
+ make a stripped copy */
+
+ while ((c = *++s) && c != ';')
+ if (c != ' ' && c != '\t' && c != '\n' && c != '\r')
+ g = string_catn(g, s, 1);
+ al->b.data = string_from_gstring(g);
+ al->b.len = g->ptr;
+ gstring_reset_unused(g);
+ bend = s;
+ break;
+ case 'h': /* bh= AMS body hash */
+ s = skip_fws(++s); /* FWS */
+ if (*s != '=') return US"no bh value";
+ if (al->bh.data) return US"already bh data";
+
+ /* The bodyhash can have FWS inserted in the content;
+ make a stripped copy */
+
+ while ((c = *++s) && c != ';')
+ if (c != ' ' && c != '\t' && c != '\n' && c != '\r')
+ g = string_catn(g, s, 1);
+ al->bh.data = string_from_gstring(g);
+ al->bh.len = g->ptr;
+ gstring_reset_unused(g);
+ break;
+ default:
+ return US"b? tag";
+ }
+ }
+ break;
+ case 'c':
+ switch (*s)
+ {
+ case '=': /* c= AMS canonicalisation */
+ if (arc_insert_tagvalue(al, offsetof(arc_line, c), &s)) return US"c tag dup";
+
+ /* substructure: head/body (eg. relaxed/simple)) */
+
+ t = al->c_head.data = al->c.data;
+ while (isalpha(*t))
+ if (!*t++ || ++i > al->a.len) break;
+ al->c_head.len = i;
+ if (*t++ == '/') /* /body is optional */
+ {
+ al->c_body.data = t;
+ al->c_body.len = al->c.len - i - 1;
+ }
+ else
+ {
+ al->c_body.data = US"simple";
+ al->c_body.len = 6;
+ }
+ break;
+ case 'v': /* cv= AS validity */
+ if (*++s != '=') return US"cv tag val";
+ if (arc_insert_tagvalue(al, offsetof(arc_line, cv), &s)) return US"cv tag dup";
+ break;
+ default:
+ return US"c? tag";
+ }
+ break;
+ case 'd': /* d= AMS domain */
+ if (*s != '=') return US"d tag val";
+ if (arc_insert_tagvalue(al, offsetof(arc_line, d), &s)) return US"d tag dup";
+ break;
+ case 'h': /* h= AMS headers */
+ if (*s != '=') return US"h tag val";
+ if (arc_insert_tagvalue(al, offsetof(arc_line, h), &s)) return US"h tag dup";
+ break;
+ case 'i': /* i= ARC set instance */
+ if (*s != '=') return US"i tag val";
+ if (arc_insert_tagvalue(al, offsetof(arc_line, i), &s)) return US"i tag dup";
+ if (instance_only) goto done;
+ break;
+ case 'l': /* l= bodylength */
+ if (*s != '=') return US"l tag val";
+ if (arc_insert_tagvalue(al, offsetof(arc_line, l), &s)) return US"l tag dup";
+ break;
+ case 's': /* s= AMS selector */
+ if (*s != '=') return US"s tag val";
+ if (arc_insert_tagvalue(al, offsetof(arc_line, s), &s)) return US"s tag dup";
+ break;
+ }
+
+ while ((c = *s) && c != ';') s++;
+ if (c) s++; /* ; after tag-spec */
+
+ /* for all but the b= tag, copy the field including FWS. For the b=,
+ drop the tag content. */
+
+ if (!instance_only)
+ if (bstart)
+ {
+ size_t n = bstart - fieldstart;
+ memcpy(r, fieldstart, n); /* FWS "b=" */
+ r += n;
+ al->rawsig_no_b_val.len += n;
+ n = s - bend;
+ memcpy(r, bend, n); /* FWS ";" */
+ r += n;
+ al->rawsig_no_b_val.len += n;
+ }
+ else
+ {
+ size_t n = s - fieldstart;
+ memcpy(r, fieldstart, n);
+ r += n;
+ al->rawsig_no_b_val.len += n;
+ }
+ }
+
+if (!instance_only)
+ *r = '\0';
+
+done:
+/* debug_printf("%s: finshed\n", __FUNCTION__); */
+return NULL;
+}
+
+
+/* Insert one header line in the correct set of the chain,
+adding instances as needed and checking for duplicate lines.
+*/
+
+static uschar *
+arc_insert_hdr(arc_ctx * ctx, header_line * h, unsigned off, unsigned hoff,
+ BOOL instance_only)
+{
+int i;
+arc_set * as;
+arc_line * al = store_get(sizeof(arc_line)), ** alp;
+uschar * e;
+
+memset(al, 0, sizeof(arc_line));
+
+if ((e = arc_parse_line(al, h, off, instance_only)))
+ {
+ DEBUG(D_acl) if (e) debug_printf("ARC: %s\n", e);
+ return US"line parse";
+ }
+if (!(i = arc_instance_from_hdr(al))) return US"instance find";
+if (!(as = arc_find_set(ctx, i))) return US"set find";
+if (*(alp = (arc_line **)(US as + hoff))) return US"dup hdr";
+
+*alp = al;
+return NULL;
+}
+
+
+
+
+static const uschar *
+arc_try_header(arc_ctx * ctx, header_line * h, BOOL instance_only)
+{
+const uschar * e;
+
+/*debug_printf("consider hdr '%s'\n", h->text);*/
+if (strncmpic(ARC_HDR_AAR, h->text, ARC_HDRLEN_AAR) == 0)
+ {
+ DEBUG(D_acl)
+ {
+ int len = h->slen;
+ uschar * s;
+ for (s = h->text + h->slen; s[-1] == '\r' || s[-1] == '\n'; )
+ s--, len--;
+ debug_printf("ARC: found AAR: %.*s\n", len, h->text);
+ }
+ if ((e = arc_insert_hdr(ctx, h, ARC_HDRLEN_AAR, offsetof(arc_set, hdr_aar),
+ TRUE)))
+ {
+ DEBUG(D_acl) debug_printf("inserting AAR: %s\n", e);
+ return US"inserting AAR";
+ }
+ }
+else if (strncmpic(ARC_HDR_AMS, h->text, ARC_HDRLEN_AMS) == 0)
+ {
+ arc_line * ams;
+
+ DEBUG(D_acl)
+ {
+ int len = h->slen;
+ uschar * s;
+ for (s = h->text + h->slen; s[-1] == '\r' || s[-1] == '\n'; )
+ s--, len--;
+ debug_printf("ARC: found AMS: %.*s\n", len, h->text);
+ }
+ if ((e = arc_insert_hdr(ctx, h, ARC_HDRLEN_AMS, offsetof(arc_set, hdr_ams),
+ instance_only)))
+ {
+ DEBUG(D_acl) debug_printf("inserting AMS: %s\n", e);
+ return US"inserting AMS";
+ }
+
+ /* defaults */
+ /*XXX dubious selection of ams here */
+ ams = ctx->arcset_chain->hdr_ams;
+ if (!ams->c.data)
+ {
+ ams->c_head.data = US"simple"; ams->c_head.len = 6;
+ ams->c_body = ams->c_head;
+ }
+ }
+else if (strncmpic(ARC_HDR_AS, h->text, ARC_HDRLEN_AS) == 0)
+ {
+ DEBUG(D_acl)
+ {
+ int len = h->slen;
+ uschar * s;
+ for (s = h->text + h->slen; s[-1] == '\r' || s[-1] == '\n'; )
+ s--, len--;
+ debug_printf("ARC: found AS: %.*s\n", len, h->text);
+ }
+ if ((e = arc_insert_hdr(ctx, h, ARC_HDRLEN_AS, offsetof(arc_set, hdr_as),
+ instance_only)))
+ {
+ DEBUG(D_acl) debug_printf("inserting AS: %s\n", e);
+ return US"inserting AS";
+ }
+ }
+return NULL;
+}
+
+
+
+/* Gather the chain of arc sets from the headers.
+Check for duplicates while that is done. Also build the
+reverse-order headers list;
+
+Return: ARC state if determined, eg. by lack of any ARC chain.
+*/
+
+static const uschar *
+arc_vfy_collect_hdrs(arc_ctx * ctx)
+{
+header_line * h;
+hdr_rlist * r, * rprev = NULL;
+const uschar * e;
+
+DEBUG(D_acl) debug_printf("ARC: collecting arc sets\n");
+for (h = header_list; h; h = h->next)
+ {
+ r = store_get(sizeof(hdr_rlist));
+ r->prev = rprev;
+ r->used = FALSE;
+ r->h = h;
+ rprev = r;
+
+ if ((e = arc_try_header(ctx, h, FALSE)))
+ return e;
+ }
+headers_rlist = r;
+
+if (!ctx->arcset_chain) return US"none";
+return NULL;
+}
+
+
+static BOOL
+arc_cv_match(arc_line * al, const uschar * s)
+{
+return Ustrncmp(s, al->cv.data, al->cv.len) == 0;
+}
+
+/******************************************************************************/
+
+/* Return the hash of headers from the message that the AMS claims it
+signed.
+*/
+
+static void
+arc_get_verify_hhash(arc_ctx * ctx, arc_line * ams, blob * hhash)
+{
+const uschar * headernames = string_copyn(ams->h.data, ams->h.len);
+const uschar * hn;
+int sep = ':';
+hdr_rlist * r;
+BOOL relaxed = Ustrncmp(US"relaxed", ams->c_head.data, ams->c_head.len) == 0;
+int hashtype = pdkim_hashname_to_hashtype(
+ ams->a_hash.data, ams->a_hash.len);
+hctx hhash_ctx;
+const uschar * s;
+int len;
+
+if (!exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
+ {
+ DEBUG(D_acl)
+ debug_printf("ARC: hash setup error, possibly nonhandled hashtype\n");
+ return;
+ }
+
+/* For each headername in the list from the AMS (walking in order)
+walk the message headers in reverse order, adding to the hash any
+found for the first time. For that last point, maintain used-marks
+on the list of message headers. */
+
+DEBUG(D_acl) debug_printf("ARC: AMS header data for verification:\n");
+
+for (r = headers_rlist; r; r = r->prev)
+ r->used = FALSE;
+while ((hn = string_nextinlist(&headernames, &sep, NULL, 0)))
+ for (r = headers_rlist; r; r = r->prev)
+ if ( !r->used
+ && strncasecmp(CCS (s = r->h->text), CCS hn, Ustrlen(hn)) == 0
+ )
+ {
+ if (relaxed) s = pdkim_relax_header_n(s, r->h->slen, TRUE);
+
+ len = Ustrlen(s);
+ DEBUG(D_acl) pdkim_quoteprint(s, len);
+ exim_sha_update(&hhash_ctx, s, Ustrlen(s));
+ r->used = TRUE;
+ break;
+ }
+
+/* Finally add in the signature header (with the b= tag stripped) */
+
+s = ams->rawsig_no_b_val.data, len = ams->rawsig_no_b_val.len;
+if (relaxed)
+ len = Ustrlen(s = pdkim_relax_header_n(s, len, TRUE));
+DEBUG(D_acl) pdkim_quoteprint(s, len);
+exim_sha_update(&hhash_ctx, s, len);
+
+exim_sha_finish(&hhash_ctx, hhash);
+DEBUG(D_acl)
+ { debug_printf("ARC: header hash: "); pdkim_hexprint(hhash->data, hhash->len); }
+return;
+}
+
+
+
+
+static pdkim_pubkey *
+arc_line_to_pubkey(arc_line * al)
+{
+uschar * dns_txt;
+pdkim_pubkey * p;
+
+if (!(dns_txt = dkim_exim_query_dns_txt(string_sprintf("%.*s._domainkey.%.*s",
+ al->s.len, al->s.data, al->d.len, al->d.data))))
+ {
+ DEBUG(D_acl) debug_printf("pubkey dns lookup fail\n");
+ return NULL;
+ }
+
+if ( !(p = pdkim_parse_pubkey_record(dns_txt))
+ || (Ustrcmp(p->srvtype, "*") != 0 && Ustrcmp(p->srvtype, "email") != 0)
+ )
+ {
+ DEBUG(D_acl) debug_printf("pubkey dns lookup format error\n");
+ return NULL;
+ }
+
+/* If the pubkey limits use to specified hashes, reject unusable
+signatures. XXX should we have looked for multiple dns records? */
+
+if (p->hashes)
+ {
+ const uschar * list = p->hashes, * ele;
+ int sep = ':';
+
+ while ((ele = string_nextinlist(&list, &sep, NULL, 0)))
+ if (Ustrncmp(ele, al->a_hash.data, al->a_hash.len) == 0) break;
+ if (!ele)
+ {
+ DEBUG(D_acl) debug_printf("pubkey h=%s vs sig a=%.*s\n",
+ p->hashes, al->a.len, al->a.data);
+ return NULL;
+ }
+ }
+return p;
+}
+
+
+
+
+static pdkim_bodyhash *
+arc_ams_setup_vfy_bodyhash(arc_line * ams)
+{
+int canon_head, canon_body;
+long bodylen;
+
+pdkim_cstring_to_canons(ams->c.data, ams->c.len, &canon_head, &canon_body);
+bodylen = ams->l.data
+ ? strtol(CS string_copyn(ams->l.data, ams->l.len), NULL, 10) : -1;
+
+return pdkim_set_bodyhash(dkim_verify_ctx,
+ pdkim_hashname_to_hashtype(ams->a_hash.data, ams->a_hash.len),
+ canon_body,
+ bodylen);
+}
+
+
+
+/* Verify an AMS. This is a DKIM-sig header, but with an ARC i= tag
+and without a DKIM v= tag.
+*/
+
+static uschar *
+arc_ams_verify(arc_ctx * ctx, arc_set * as)
+{
+arc_line * ams = as->hdr_ams;
+pdkim_bodyhash * b;
+pdkim_pubkey * p;
+blob sighash;
+blob hhash;
+ev_ctx vctx;
+int hashtype;
+const uschar * errstr;
+
+as->ams_verify_done = TRUE;
+
+/* Check the AMS has all the required tags:
+ "a=" algorithm
+ "b=" signature
+ "bh=" body hash
+ "d=" domain (for key lookup)
+ "h=" headers (included in signature)
+ "s=" key-selector (for key lookup)
+*/
+if ( !ams->a.data || !ams->b.data || !ams->bh.data || !ams->d.data
+ || !ams->h.data || !ams->s.data)
+ return US"fail";
+
+
+/* The bodyhash should have been created earlier, and the dkim code should
+have managed calculating it during message input. Find the reference to it. */
+
+if (!(b = arc_ams_setup_vfy_bodyhash(ams)))
+ return US"fail";
+
+DEBUG(D_acl)
+ {
+ debug_printf("ARC i=%d AMS Body bytes hashed: %lu\n"
+ " Body %.*s computed: ",
+ as->instance, b->signed_body_bytes,
+ ams->a_hash.len, ams->a_hash.data);
+ pdkim_hexprint(CUS b->bh.data, b->bh.len);
+ }
+
+/* We know the bh-tag blob is of a nul-term string, so safe as a string */
+
+if ( !ams->bh.data
+ || (pdkim_decode_base64(ams->bh.data, &sighash), sighash.len != b->bh.len)
+ || memcmp(sighash.data, b->bh.data, b->bh.len) != 0
+ )
+ {
+ DEBUG(D_acl)
+ {
+ debug_printf("ARC i=%d AMS Body hash from headers: ", as->instance);
+ pdkim_hexprint(sighash.data, sighash.len);
+ debug_printf("ARC i=%d AMS Body hash did NOT match\n", as->instance);
+ }
+ return US"body hash compare mismatch";
+ }
+
+DEBUG(D_acl) debug_printf("ARC i=%d AMS Body hash compared OK\n", as->instance);
+
+/* Get the public key from DNS */
+
+if (!(p = arc_line_to_pubkey(ams)))
+ return US"pubkey problem";
+
+/* We know the b-tag blob is of a nul-term string, so safe as a string */
+pdkim_decode_base64(ams->b.data, &sighash);
+
+arc_get_verify_hhash(ctx, ams, &hhash);
+
+/* Setup the interface to the signing library */
+
+if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx)))
+ {
+ DEBUG(D_acl) debug_printf("ARC verify init: %s\n", errstr);
+ return US"fail";
+ }
+
+hashtype = pdkim_hashname_to_hashtype(ams->a_hash.data, ams->a_hash.len);
+
+if ((errstr = exim_dkim_verify(&vctx,
+ pdkim_hashes[hashtype].exim_hashmethod, &hhash, &sighash)))
+ {
+ DEBUG(D_acl) debug_printf("ARC i=%d AMS verify %s\n", as->instance, errstr);
+ return US"ams sig verify fail";
+ }
+
+DEBUG(D_acl) debug_printf("ARC i=%d AMS verify pass\n", as->instance);
+as->ams_verify_passed = TRUE;
+return NULL;
+}
+
+
+
+/* Check the sets are instance-continuous and that all
+members are present. Check that no arc_seals are "fail".
+Set the highest instance number global.
+Verify the latest AMS.
+*/
+static uschar *
+arc_headers_check(arc_ctx * ctx)
+{
+arc_set * as;
+int inst;
+BOOL ams_fail_found = FALSE;
+uschar * ret = NULL;
+
+if (!(as = ctx->arcset_chain))
+ return US"none";
+
+for(inst = 0; as; as = as->next)
+ {
+ if ( as->instance != ++inst
+ || !as->hdr_aar || !as->hdr_ams || !as->hdr_as
+ || arc_cv_match(as->hdr_as, US"fail")
+ )
+ {
+ DEBUG(D_acl) debug_printf("ARC i=%d fail"
+ " (cv, sequence or missing header)\n", as->instance);
+ ret = US"fail";
+ }
+
+ /* Evaluate the oldest-pass AMS validation while we're here.
+ It does not affect the AS chain validation but is reported as
+ auxilary info. */
+
+ if (!ams_fail_found)
+ if (arc_ams_verify(ctx, as))
+ ams_fail_found = TRUE;
+ else
+ arc_oldest_pass = inst;
+ }
+
+arc_received = ctx->arcset_chain_last;
+arc_received_instance = inst;
+if (ret)
+ return ret;
+
+/* We can skip the latest-AMS validation, if we already did it. */
+
+as = ctx->arcset_chain_last;
+if (as->ams_verify_done ? !as->ams_verify_passed : !!arc_ams_verify(ctx, as))
+ return US"fail";
+
+return NULL;
+}
+
+
+/******************************************************************************/
+static const uschar *
+arc_seal_verify(arc_ctx * ctx, arc_set * as)
+{
+arc_line * hdr_as = as->hdr_as;
+arc_set * as2;
+int hashtype;
+hctx hhash_ctx;
+blob hhash_computed;
+blob sighash;
+ev_ctx vctx;
+pdkim_pubkey * p;
+const uschar * errstr;
+
+DEBUG(D_acl) debug_printf("ARC: AS vfy i=%d\n", as->instance);
+/*
+ 1. If the value of the "cv" tag on that seal is "fail", the
+ chain state is "fail" and the algorithm stops here. (This
+ step SHOULD be skipped if the earlier step (2.1) was
+ performed) [it was]
+
+ 2. In Boolean nomenclature: if ((i == 1 && cv != "none") or (cv
+ == "none" && i != 1)) then the chain state is "fail" and the
+ algorithm stops here (note that the ordering of the logic is
+ structured for short-circuit evaluation).
+*/
+
+if ( as->instance == 1 && !arc_cv_match(hdr_as, US"none")
+ || arc_cv_match(hdr_as, US"none") && as->instance != 1
+ )
+ return US"fail";
+
+/*
+ 3. Initialize a hash function corresponding to the "a" tag of
+ the ARC-Seal.
+*/
+
+hashtype = pdkim_hashname_to_hashtype(hdr_as->a_hash.data, hdr_as->a_hash.len);
+
+if (!exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
+ {
+ DEBUG(D_acl)
+ debug_printf("ARC: hash setup error, possibly nonhandled hashtype\n");
+ return US"fail";
+ }
+
+/*
+ 4. Compute the canonicalized form of the ARC header fields, in
+ the order described in Section 5.4.2, using the "relaxed"
+ header canonicalization defined in Section 3.4.2 of
+ [RFC6376]. Pass the canonicalized result to the hash
+ function.
+*/
+
+DEBUG(D_acl) debug_printf("ARC: AS header data for verification:\n");
+for (as2 = ctx->arcset_chain;
+ as2 && as2->instance <= as->instance;
+ as2 = as2->next)
+ {
+ arc_line * al;
+ uschar * s;
+ int len;
+
+ al = as2->hdr_aar;
+ if (!(s = al->relaxed))
+ al->relaxed = s = pdkim_relax_header_n(al->complete->text,
+ al->complete->slen, TRUE);
+ len = Ustrlen(s);
+ DEBUG(D_acl) pdkim_quoteprint(s, len);
+ exim_sha_update(&hhash_ctx, s, len);
+
+ al = as2->hdr_ams;
+ if (!(s = al->relaxed))
+ al->relaxed = s = pdkim_relax_header_n(al->complete->text,
+ al->complete->slen, TRUE);
+ len = Ustrlen(s);
+ DEBUG(D_acl) pdkim_quoteprint(s, len);
+ exim_sha_update(&hhash_ctx, s, len);
+
+ al = as2->hdr_as;
+ if (as2->instance == as->instance)
+ s = pdkim_relax_header_n(al->rawsig_no_b_val.data,
+ al->rawsig_no_b_val.len, TRUE);
+ else if (!(s = al->relaxed))
+ al->relaxed = s = pdkim_relax_header_n(al->complete->text,
+ al->complete->slen, TRUE);
+ len = Ustrlen(s);
+ DEBUG(D_acl) pdkim_quoteprint(s, len);
+ exim_sha_update(&hhash_ctx, s, len);
+ }
+
+/*
+ 5. Retrieve the final digest from the hash function.
+*/
+
+exim_sha_finish(&hhash_ctx, &hhash_computed);
+DEBUG(D_acl)
+ {
+ debug_printf("ARC i=%d AS Header %.*s computed: ",
+ as->instance, hdr_as->a_hash.len, hdr_as->a_hash.data);
+ pdkim_hexprint(hhash_computed.data, hhash_computed.len);
+ }
+
+
+/*
+ 6. Retrieve the public key identified by the "s" and "d" tags in
+ the ARC-Seal, as described in Section 4.1.6.
+*/
+
+if (!(p = arc_line_to_pubkey(hdr_as)))
+ return US"pubkey problem";
+
+/*
+ 7. Determine whether the signature portion ("b" tag) of the ARC-
+ Seal and the digest computed above are valid according to the
+ public key. (See also Section Section 8.4 for failure case
+ handling)
+
+ 8. If the signature is not valid, the chain state is "fail" and
+ the algorithm stops here.
+*/
+
+/* We know the b-tag blob is of a nul-term string, so safe as a string */
+pdkim_decode_base64(hdr_as->b.data, &sighash);
+
+if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx)))
+ {
+ DEBUG(D_acl) debug_printf("ARC verify init: %s\n", errstr);
+ return US"fail";
+ }
+
+hashtype = pdkim_hashname_to_hashtype(hdr_as->a_hash.data, hdr_as->a_hash.len);
+
+if ((errstr = exim_dkim_verify(&vctx,
+ pdkim_hashes[hashtype].exim_hashmethod,
+ &hhash_computed, &sighash)))
+ {
+ DEBUG(D_acl)
+ debug_printf("ARC i=%d AS headers verify: %s\n", as->instance, errstr);
+ return US"fail";
+ }
+
+DEBUG(D_acl) debug_printf("ARC: AS vfy i=%d pass\n", as->instance);
+return NULL;
+}
+
+
+static const uschar *
+arc_verify_seals(arc_ctx * ctx)
+{
+arc_set * as = ctx->arcset_chain;
+
+if (!as)
+ return US"none";
+
+while (as)
+ {
+ if (arc_seal_verify(ctx, as)) return US"fail";
+ as = as->next;
+ }
+DEBUG(D_acl) debug_printf("ARC: AS vfy overall pass\n");
+return NULL;
+}
+/******************************************************************************/
+
+/* Do ARC verification. Called from DATA ACL, on a verify = arc
+condition. No arguments; we are checking globals.
+
+Return: The ARC state, or NULL on error.
+*/
+
+const uschar *
+acl_verify_arc(void)
+{
+arc_ctx ctx = { NULL };
+const uschar * res;
+
+/* AS evaluation, per
+https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-10#section-6
+*/
+/* 1. Collect all ARC sets currently on the message. If there were
+ none, the ARC state is "none" and the algorithm stops here.
+*/
+
+if ((res = arc_vfy_collect_hdrs(&ctx)))
+ goto out;
+
+/* 2. If the form of any ARC set is invalid (e.g., does not contain
+ exactly one of each of the three ARC-specific header fields),
+ then the chain state is "fail" and the algorithm stops here.
+
+ 1. To avoid the overhead of unnecessary computation and delay
+ from crypto and DNS operations, the cv value for all ARC-
+ Seal(s) MAY be checked at this point. If any of the values
+ are "fail", then the overall state of the chain is "fail" and
+ the algorithm stops here.
+
+ 3. Conduct verification of the ARC-Message-Signature header field
+ bearing the highest instance number. If this verification fails,
+ then the chain state is "fail" and the algorithm stops here.
+*/
+
+if ((res = arc_headers_check(&ctx)))
+ goto out;
+
+/* 4. For each ARC-Seal from the "N"th instance to the first, apply the
+ following logic:
+
+ 1. If the value of the "cv" tag on that seal is "fail", the
+ chain state is "fail" and the algorithm stops here. (This
+ step SHOULD be skipped if the earlier step (2.1) was
+ performed)
+
+ 2. In Boolean nomenclature: if ((i == 1 && cv != "none") or (cv
+ == "none" && i != 1)) then the chain state is "fail" and the
+ algorithm stops here (note that the ordering of the logic is
+ structured for short-circuit evaluation).
+
+ 3. Initialize a hash function corresponding to the "a" tag of
+ the ARC-Seal.
+
+ 4. Compute the canonicalized form of the ARC header fields, in
+ the order described in Section 5.4.2, using the "relaxed"
+ header canonicalization defined in Section 3.4.2 of
+ [RFC6376]. Pass the canonicalized result to the hash
+ function.
+
+ 5. Retrieve the final digest from the hash function.
+
+ 6. Retrieve the public key identified by the "s" and "d" tags in
+ the ARC-Seal, as described in Section 4.1.6.
+
+ 7. Determine whether the signature portion ("b" tag) of the ARC-
+ Seal and the digest computed above are valid according to the
+ public key. (See also Section Section 8.4 for failure case
+ handling)
+
+ 8. If the signature is not valid, the chain state is "fail" and
+ the algorithm stops here.
+
+ 5. If all seals pass validation, then the chain state is "pass", and
+ the algorithm is complete.
+*/
+
+if ((res = arc_verify_seals(&ctx)))
+ goto out;
+
+res = US"pass";
+
+out:
+ return res;
+}
+
+/******************************************************************************/
+
+/* Prepend the header to the rlist */
+
+static hdr_rlist *
+arc_rlist_entry(hdr_rlist * list, const uschar * s, int len)
+{
+hdr_rlist * r = store_get(sizeof(hdr_rlist) + sizeof(header_line));
+header_line * h = r->h = (header_line *)(r+1);
+
+r->prev = list;
+r->used = FALSE;
+h->next = NULL;
+h->type = 0;
+h->slen = len;
+h->text = US s;
+
+/* This works for either NL or CRLF lines; also nul-termination */
+while (*++s)
+ if (*s == '\n' && s[1] != '\t' && s[1] != ' ') break;
+s++; /* move past end of line */
+
+return r;
+}
+
+
+/* Walk the given headers strings identifying each header, and construct
+a reverse-order list. Also parse ARC-chain headers and build the chain
+struct, retaining pointers into the string.
+*/
+
+static hdr_rlist *
+arc_sign_scan_headers(arc_ctx * ctx, gstring * sigheaders)
+{
+const uschar * s;
+hdr_rlist * rheaders = NULL;
+
+s = sigheaders ? sigheaders->s : NULL;
+if (s) while (*s)
+ {
+ uschar * s2;
+
+ /* This works for either NL or CRLF lines; also nul-termination */
+ while (*++s2)
+ if (*s2 == '\n' && s2[1] != '\t' && s2[1] != ' ') break;
+ s2++; /* move past end of line */
+
+ rheaders = arc_rlist_entry(rheaders, s, s2 - s);
+ s = s2;
+ }
+return rheaders;
+}
+
+
+
+/* Return the A-R content, without identity, with line-ending and
+NUL termination. */
+
+static BOOL
+arc_sign_find_ar(header_line * headers, const uschar * identity, blob * ret)
+{
+header_line * h;
+int ilen = Ustrlen(identity);
+
+ret->data = NULL;
+for(h = headers; h; h = h->next)
+ {
+ uschar * s = h->text, c;
+ int len = h->slen;
+
+ if (Ustrncmp(s, HDR_AR, HDRLEN_AR) != 0) continue;
+ s += HDRLEN_AR, len -= HDRLEN_AR; /* header name */
+ while ( len > 0
+ && (c = *s) && (c == ' ' || c == '\t' || c == '\r' || c == '\n'))
+ s++, len--; /* FWS */
+ if (Ustrncmp(s, identity, ilen) != 0) continue;
+ s += ilen; len -= ilen; /* identity */
+ if (len <= 0) continue;
+ if ((c = *s) && c == ';') s++, len--; /* identity terminator */
+ while ( len > 0
+ && (c = *s) && (c == ' ' || c == '\t' || c == '\r' || c == '\n'))
+ s++, len--; /* FWS */
+ if (len <= 0) continue;
+ ret->data = s;
+ ret->len = len;
+ return TRUE;
+ }
+return FALSE;
+}
+
+
+
+/* Append a constructed AAR including CRLF. Add it to the arc_ctx too. */
+
+static gstring *
+arc_sign_append_aar(gstring * g, arc_ctx * ctx,
+ const uschar * identity, int instance, blob * ar)
+{
+int aar_off = g ? g->ptr : 0;
+arc_set * as = store_get(sizeof(arc_set) + sizeof(arc_line) + sizeof(header_line));
+arc_line * al = (arc_line *)(as+1);
+header_line * h = (header_line *)(al+1);
+
+g = string_catn(g, ARC_HDR_AAR, ARC_HDRLEN_AAR);
+g = string_cat(g, string_sprintf(" i=%d; %s;\r\n\t", instance, identity));
+g = string_catn(g, US ar->data, ar->len);
+
+h->slen = g->ptr - aar_off;
+h->text = g->s + aar_off;
+al->complete = h;
+as->next = NULL;
+as->prev = ctx->arcset_chain_last;
+as->instance = instance;
+as->hdr_aar = al;
+if (instance == 1)
+ ctx->arcset_chain = as;
+else
+ ctx->arcset_chain_last->next = as;
+ctx->arcset_chain_last = as;
+
+DEBUG(D_transport) debug_printf("ARC: AAR '%.*s'\n", h->slen - 2, h->text);
+return g;
+}
+
+
+
+static BOOL
+arc_sig_from_pseudoheader(gstring * hdata, int hashtype, const uschar * privkey,
+ blob * sig, const uschar * why)
+{
+hashmethod hm = /*sig->keytype == KEYTYPE_ED25519*/ FALSE
+ ? HASH_SHA2_512 : pdkim_hashes[hashtype].exim_hashmethod;
+blob hhash;
+es_ctx sctx;
+const uschar * errstr;
+
+DEBUG(D_transport)
+ {
+ hctx hhash_ctx;
+ debug_printf("ARC: %s header data for signing:\n", why);
+ pdkim_quoteprint(hdata->s, hdata->ptr);
+
+ (void) exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod);
+ exim_sha_update(&hhash_ctx, hdata->s, hdata->ptr);
+ exim_sha_finish(&hhash_ctx, &hhash);
+ debug_printf("ARC: header hash: "); pdkim_hexprint(hhash.data, hhash.len);
+ }
+
+if (FALSE /*need hash for Ed25519 or GCrypt signing*/ )
+ {
+ hctx hhash_ctx;
+ (void) exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod);
+ exim_sha_update(&hhash_ctx, hdata->s, hdata->ptr);
+ exim_sha_finish(&hhash_ctx, &hhash);
+ }
+else
+ {
+ hhash.data = hdata->s;
+ hhash.len = hdata->ptr;
+ }
+
+if ( (errstr = exim_dkim_signing_init(privkey, &sctx))
+ || (errstr = exim_dkim_sign(&sctx, hm, &hhash, sig)))
+ {
+ log_write(0, LOG_MAIN|LOG_PANIC, "ARC: %s signing: %s\n", why, errstr);
+ return FALSE;
+ }
+return TRUE;
+}
+
+
+
+static gstring *
+arc_sign_append_sig(gstring * g, blob * sig)
+{
+/*debug_printf("%s: raw sig ", __FUNCTION__); pdkim_hexprint(sig->data, sig->len);*/
+sig->data = pdkim_encode_base64(sig);
+sig->len = Ustrlen(sig->data);
+for (;;)
+ {
+ int len = MIN(sig->len, 74);
+ g = string_catn(g, sig->data, len);
+ if ((sig->len -= len) == 0) break;
+ sig->data += len;
+ g = string_catn(g, US"\r\n\t ", 5);
+ }
+g = string_catn(g, US";\r\n", 3);
+gstring_reset_unused(g);
+string_from_gstring(g);
+return g;
+}
+
+
+/* Append a constructed AMS including CRLF. Add it to the arc_ctx too. */
+
+static gstring *
+arc_sign_append_ams(gstring * g, arc_ctx * ctx, int instance,
+ const uschar * identity, const uschar * selector, blob * bodyhash,
+ hdr_rlist * rheaders, const uschar * privkey)
+{
+uschar * s;
+gstring * hdata = NULL;
+int col;
+int hashtype = pdkim_hashname_to_hashtype(US"sha256", 6); /*XXX hardwired */
+blob sig;
+int ams_off;
+arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line));
+header_line * h = (header_line *)(al+1);
+
+/* debug_printf("%s\n", __FUNCTION__); */
+
+/* Construct the to-be-signed AMS pseudo-header: everything but the sig. */
+
+ams_off = g->ptr;
+g = string_append(g, 10,
+ ARC_HDR_AMS,
+ US" i=", string_sprintf("%d", instance),
+ US"; a=rsa-sha256; c=relaxed; d=", identity, /*XXX hardwired */
+ US"; s=", selector,
+ US";\r\n\tbh=", pdkim_encode_base64(bodyhash),
+ US";\r\n\th=");
+
+for(col = 3; rheaders; rheaders = rheaders->prev)
+ {
+ const uschar * hnames = US"DKIM-Signature:" PDKIM_DEFAULT_SIGN_HEADERS;
+ uschar * name, * htext = rheaders->h->text;
+ int sep = ':';
+
+ /* Spot headers of interest */
+
+ while ((name = string_nextinlist(&hnames, &sep, NULL, 0)))
+ {
+ int len = Ustrlen(name);
+ if (strncasecmp(CCS htext, CCS name, len) == 0)
+ {
+ /* If too long, fold line in h= field */
+
+ if (col + len > 78) g = string_catn(g, US"\r\n\t ", 5), col = 3;
+
+ /* Add name to h= list */
+
+ g = string_catn(g, name, len);
+ g = string_catn(g, US":", 1);
+ col += len + 1;
+
+ /* Accumulate header for hashing/signing */
+
+ hdata = string_cat(hdata,
+ pdkim_relax_header_n(htext, rheaders->h->slen, TRUE)); /*XXX hardwired */
+ break;
+ }
+ }
+ }
+
+/* Lose the last colon from the h= list */
+
+if (g->s[g->ptr - 1] == ':') g->ptr--;
+
+g = string_catn(g, US";\r\n\tb=;", 7);
+
+/* Include the pseudo-header in the accumulation */
+/*XXX should that be prepended rather than appended? */
+/*XXX also need to include at the verify stage */
+
+s = pdkim_relax_header_n(g->s + ams_off, g->ptr - ams_off, TRUE);
+hdata = string_cat(hdata, s);
+
+/* Calculate the signature from the accumulation */
+/*XXX does that need further relaxation? there are spaces embedded in the b= strings! */
+
+if (!arc_sig_from_pseudoheader(hdata, hashtype, privkey, &sig, US"AMS"))
+ return NULL;
+
+/* Lose the trailing semicolon from the psuedo-header, and append the signature
+(folded over lines) and termination to complete it. */
+
+g->ptr--;
+g = arc_sign_append_sig(g, &sig);
+
+h->slen = g->ptr - ams_off;
+h->text = g->s + ams_off;
+al->complete = h;
+ctx->arcset_chain_last->hdr_ams = al;
+
+DEBUG(D_transport) debug_printf("ARC: AMS '%.*s'\n", h->slen - 2, h->text);
+return g;
+}
+
+
+
+/* Look for an arc= result in an A-R header blob. We know that its data
+happens to be a NUL-term string. */
+
+static uschar *
+arc_ar_cv_status(blob * ar)
+{
+const uschar * resinfo = ar->data;
+int sep = ';';
+uschar * methodspec, * s;
+
+while ((methodspec = string_nextinlist(&resinfo, &sep, NULL, 0)))
+ if (Ustrncmp(methodspec, US"arc=", 4) == 0)
+ {
+ uschar c;
+ for (s = methodspec += 4;
+ (c = *s) && c != ';' && c != ' ' && c != '\r' && c != '\n'; ) s++;
+ return string_copyn(methodspec, s - methodspec);
+ }
+return NULL;
+}
+
+
+
+/* Build the AS header and prepend it */
+
+static gstring *
+arc_sign_prepend_as(gstring * arcset_interim, arc_ctx * ctx,
+ int instance, const uschar * identity, const uschar * selector, blob * ar,
+ const uschar * privkey)
+{
+gstring * arcset;
+arc_set * as;
+uschar * status = arc_ar_cv_status(ar);
+arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line));
+header_line * h = (header_line *)(al+1);
+uschar * s;
+
+gstring * hdata = NULL;
+int hashtype = pdkim_hashname_to_hashtype(US"sha256", 6); /*XXX hardwired */
+blob sig;
+
+/*
+- Generate AS
+ - no body coverage
+ - no h= tag; implicit coverage
+ - arc status from A-R
+ - if fail:
+ - coverage is just the new ARC set
+ including self (but with an empty b= in self)
+ - if non-fail:
+ - all ARC set headers, set-number order, aar then ams then as,
+ including self (but with an empty b= in self)
+*/
+
+/* Construct the AS except for the signature */
+
+arcset = string_append(NULL, 10,
+ ARC_HDR_AS,
+ US" i=", string_sprintf("%d", instance),
+ US"; cv=", status,
+ US"; a=rsa-sha256; c=relaxed; d=", identity, /*XXX hardwired */
+ US"; s=", selector, /*XXX same as AMS */
+ US";\r\n\t b=;");
+
+h->slen = arcset->ptr;
+h->text = arcset->s;
+al->complete = h;
+ctx->arcset_chain_last->hdr_as = al;
+
+/* For any but "fail" chain-verify status, walk the entire chain in order by
+instance. For fail, only the new arc-set. Accumulate the elements walked. */
+
+for (as = Ustrcmp(status, US"fail") == 0
+ ? ctx->arcset_chain_last : ctx->arcset_chain;
+ as; as = as->next)
+ {
+ /* Accumulate AAR then AMS then AS. Relaxed canonicalisation
+ is required per standard. */
+
+ h = as->hdr_aar->complete;
+ hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
+ h = as->hdr_ams->complete;
+ hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
+ h = as->hdr_as->complete;
+ hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
+ }
+
+/* Calculate the signature from the accumulation */
+
+if (!arc_sig_from_pseudoheader(hdata, hashtype, privkey, &sig, US"AS"))
+ return NULL;
+
+/* Lose the trailing semicolon */
+arcset->ptr--;
+arcset = arc_sign_append_sig(arcset, &sig);
+DEBUG(D_transport) debug_printf("ARC: AS '%.*s'\n", arcset->ptr - 2, arcset->s);
+
+/* Finally, append the AMS and AAR to the new AS */
+
+return string_catn(arcset, arcset_interim->s, arcset_interim->ptr);
+}
+
+
+/**************************************/
+
+/* Return pointer to pdkim_bodyhash for given hash method, creating new
+method if needed.
+*/
+
+void *
+arc_ams_setup_sign_bodyhash(void)
+{
+int canon_head, canon_body;
+
+DEBUG(D_transport) debug_printf("ARC: requesting bodyhash\n");
+pdkim_cstring_to_canons(US"relaxed", 7, &canon_head, &canon_body); /*XXX hardwired */
+return pdkim_set_bodyhash(&dkim_sign_ctx,
+ pdkim_hashname_to_hashtype(US"sha256", 6), /*XXX hardwired */
+ canon_body,
+ -1);
+}
+
+
+
+/* A "normal" header line, identified by DKIM processing. These arrive before
+the call to arc_sign(), which carries any newly-created DKIM headers - and
+those go textually before the normal ones in the message.
+
+We have to take the feed from DKIM as, in the transport-filter case, the
+headers are not in memory at the time of the call to arc_sign().
+
+Take a copy of the header and construct a reverse-order list.
+Also parse ARC-chain headers and build the chain struct, retaining pointers
+into the copies.
+*/
+
+static const uschar *
+arc_header_sign_feed(gstring * g)
+{
+uschar * s = string_copyn(g->s, g->ptr);
+headers_rlist = arc_rlist_entry(headers_rlist, s, g->ptr);
+return arc_try_header(&arc_sign_ctx, headers_rlist->h, TRUE);
+}
+
+
+
+/* ARC signing. Called from the smtp transport, if the arc_sign option is set.
+The dkim_exim_sign() function has already been called, so will have hashed the
+message body for us so long as we requested a hash previously.
+
+Arguments:
+ signspec Three-element colon-sep list: identity, selector, privkey
+ Already expanded
+ sigheaders Any signature headers already generated, eg. by DKIM, or NULL
+ errstr Error string
+
+Return value
+ Set of headers to prepend to the message, including the supplied sigheaders
+ but not the plainheaders.
+*/
+
+gstring *
+arc_sign(const uschar * signspec, gstring * sigheaders, uschar ** errstr)
+{
+const uschar * identity, * selector, * privkey;
+int sep = 0;
+header_line * headers;
+hdr_rlist * rheaders;
+blob ar;
+int instance;
+gstring * g = NULL;
+pdkim_bodyhash * b;
+
+/* Parse the signing specification */
+
+identity = string_nextinlist(&signspec, &sep, NULL, 0);
+selector = string_nextinlist(&signspec, &sep, NULL, 0);
+if ( !*identity | !*selector
+ || !(privkey = string_nextinlist(&signspec, &sep, NULL, 0)) || !*privkey)
+ {
+ log_write(0, LOG_MAIN|LOG_PANIC, "ARC: bad signing-specification");
+ return NULL;
+ }
+if (*privkey == '/' && !(privkey = expand_file_big_buffer(privkey)))
+ return NULL;
+
+DEBUG(D_transport) debug_printf("ARC: sign for %s\n", identity);
+
+/*
+- scan headers for existing ARC chain & A-R (with matching system-identfier)
+ - paniclog & skip on problems (no A-R)
+*/
+
+/* Make an rlist of any new DKIM headers, then add the "normals" rlist to it */
+
+string_from_gstring(sigheaders);
+if ((rheaders = arc_sign_scan_headers(&arc_sign_ctx, sigheaders)))
+ {
+ hdr_rlist ** rp;
+ for (rp = &rheaders; *rp; ) rp = &(*rp)->prev;
+ *rp = headers_rlist;
+ headers_rlist = rheaders;
+ }
+else
+ rheaders = headers_rlist;
+/* Finally, build a normal-order headers list */
+/*XXX only needed for hunt-the-AR? */
+{
+header_line * hnext = NULL;
+for (; rheaders; hnext = rheaders->h, rheaders = rheaders->prev)
+ rheaders->h->next = hnext;
+headers = hnext;
+}
+
+instance = arc_sign_ctx.arcset_chain_last ? arc_sign_ctx.arcset_chain_last->instance + 1 : 1;
+
+if (!(arc_sign_find_ar(headers, identity, &ar)))
+ {
+ log_write(0, LOG_MAIN|LOG_PANIC, "ARC: no Authentication-Results header for signing");
+ return sigheaders ? sigheaders : string_get(0);
+ }
+
+/*
+- Generate AAR
+ - copy the A-R; prepend i= & identity
+*/
+
+g = arc_sign_append_aar(g, &arc_sign_ctx, identity, instance, &ar);
+
+/*
+- Generate AMS
+ - Looks fairly like a DKIM sig
+ - Cover all DKIM sig headers as well as the usuals
+ - ? oversigning?
+ - Covers the data
+ - we must have requested a suitable bodyhash previously
+*/
+
+b = arc_ams_setup_sign_bodyhash();
+g = arc_sign_append_ams(g, &arc_sign_ctx, instance, identity, selector,
+ &b->bh, headers_rlist, privkey);
+
+/*
+- Generate AS
+ - no body coverage
+ - no h= tag; implicit coverage
+ - arc status from A-R
+ - if fail:
+ - coverage is just the new ARC set
+ including self (but with an empty b= in self)
+ - if non-fail:
+ - all ARC set headers, set-number order, aar then ams then as,
+ including self (but with an empty b= in self)
+*/
+
+g = arc_sign_prepend_as(g, &arc_sign_ctx, instance, identity, selector, &ar, privkey);
+
+/* Finally, append the dkim headers and return the lot. */
+
+g = string_catn(g, sigheaders->s, sigheaders->ptr);
+(void) string_from_gstring(g);
+gstring_reset_unused(g);
+return g;
+}
+
+
+/******************************************************************************/
+
+/* Check to see if the line is an AMS and if so, set up to validate it.
+Called from the DKIM input processing. This must be done now as the message
+body data is hashed during input.
+
+We call the DKIM code to request a body-hash; it has the facility already
+and the hash parameters might be common with other requests.
+*/
+
+static const uschar *
+arc_header_vfy_feed(gstring * g)
+{
+header_line h;
+arc_line al;
+pdkim_bodyhash * b;
+uschar * errstr;
+
+if (!dkim_verify_ctx) return US"no dkim context";
+
+if (strncmpic(ARC_HDR_AMS, g->s, ARC_HDRLEN_AMS) != 0) return US"not AMS";
+
+DEBUG(D_receive) debug_printf("ARC: spotted AMS header\n");
+/* Parse the AMS header */
+
+h.next = NULL;
+h.slen = g->size;
+h.text = g->s;
+memset(&al, 0, sizeof(arc_line));
+if ((errstr = arc_parse_line(&al, &h, ARC_HDRLEN_AMS, FALSE)))
+ {
+ DEBUG(D_acl) if (errstr) debug_printf("ARC: %s\n", errstr);
+ return US"line parsing error";
+ }
+
+/* defaults */
+if (!al.c.data)
+ {
+ al.c_body.data = US"simple"; al.c_body.len = 6;
+ al.c_head = al.c_body;
+ }
+
+/* Ask the dkim code to calc a bodyhash with those specs */
+
+if (!(b = arc_ams_setup_vfy_bodyhash(&al)))
+ return US"dkim hash setup fail";
+
+/* Discard the reference; search again at verify time, knowing that one
+should have been created here. */
+
+return NULL;
+}
+
+
+
+/* A header line has been identified by DKIM processing.
+
+Arguments:
+ g Header line
+ is_vfy TRUE for verify mode or FALSE for signing mode
+
+Return:
+ NULL for success, or an error string (probably unused)
+*/
+
+const uschar *
+arc_header_feed(gstring * g, BOOL is_vfy)
+{
+return is_vfy ? arc_header_vfy_feed(g) : arc_header_sign_feed(g);
+}
+
+
+
+/******************************************************************************/
+
+/* Construct an Authenticate-Results header portion, for the ARC module */
+
+gstring *
+authres_arc(gstring * g)
+{
+if (arc_state)
+ {
+ arc_line * highest_ams;
+ int start;
+ DEBUG(D_acl) start = g->ptr;
+
+ g = string_append(g, 2, US";\n\tarc=", arc_state);
+ if (arc_received_instance > 0)
+ {
+ g = string_append(g, 3, US" (i=",
+ string_sprintf("%d", arc_received_instance), US") header.s=");
+ highest_ams = arc_received->hdr_ams;
+ g = string_catn(g, highest_ams->s.data, highest_ams->s.len);
+
+ g = string_append(g, 2,
+ US" arc.oldest-pass=", string_sprintf("%d", arc_oldest_pass));
+
+ if (sender_host_address)
+ g = string_append(g, 2, US" smtp.client-ip=", sender_host_address);
+ }
+ DEBUG(D_acl) debug_printf("ARC: authres '%.*s'\n",
+ g->ptr - start - 3, g->s + start + 3);
+ }
+else
+ DEBUG(D_acl) debug_printf("ARC: no authres\n");
+return g;
+}
+
+
+# endif /* SUPPORT_SPF */
+#endif /* EXPERIMENTAL_ARC */
+/* vi: aw ai sw=2
+ */
git://git.exim.org / users / jgh / exim.git / commitdiff