X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/0ed25f66ccc56d56b3b5b7d64f4537bafbb42697..1d28cc061677bd07d9bed48dd84bd5c590247043:/src/src/arc.c

diff --git a/src/src/arc.c b/src/src/arc.c
index 06ca93736..30a66320e 100644
--- a/src/src/arc.c
+++ b/src/src/arc.c
@@ -2,15 +2,15 @@
 *     Exim - an Internet mail transport agent    *
 *************************************************/
 /* Experimental ARC support for Exim
-   Copyright (c) Jeremy Harris 2018
+   Copyright (c) Jeremy Harris 2018 - 2020
+   Copyright (c) The Exim Maintainers 2021 - 2022
    License: GPL
+   SPDX-License-Identifier: GPL-2.0-or-later
 */
 
 #include "exim.h"
-#ifdef EXPERIMENTAL_ARC
-# if !defined SUPPORT_SPF
-#  error SPF must also be enabled for ARC
-# elif defined DISABLE_DKIM
+#if defined EXPERIMENTAL_ARC
+# if defined DISABLE_DKIM
 #  error DKIM must also be enabled for ARC
 # else
 
@@ -21,6 +21,11 @@
 extern pdkim_ctx * dkim_verify_ctx;
 extern pdkim_ctx dkim_sign_ctx;
 
+#define ARC_SIGN_OPT_TSTAMP	BIT(0)
+#define ARC_SIGN_OPT_EXPIRE	BIT(1)
+
+#define ARC_SIGN_DEFAULT_EXPIRE_DELTA (60 * 60 * 24 * 30)	/* one month */
+
 /******************************************************************************/
 
 typedef struct hdr_rlist {
@@ -84,8 +89,11 @@ typedef struct arc_ctx {
 #define HDR_AR		US"Authentication-Results:"
 #define HDRLEN_AR	23
 
+static time_t now;
+static time_t expire;
 static hdr_rlist * headers_rlist;
 static arc_ctx arc_sign_ctx = { NULL };
+static arc_ctx arc_verify_ctx = { NULL };
 
 
 /******************************************************************************/
@@ -135,7 +143,7 @@ for (pas = &ctx->arcset_chain, prev = NULL, next = ctx->arcset_chain;
   }
 
 DEBUG(D_acl) debug_printf("ARC: new instance %u\n", i);
-*pas = as = store_get(sizeof(arc_set));
+*pas = as = store_get(sizeof(arc_set), GET_UNTAINTED);
 memset(as, 0, sizeof(arc_set));
 as->next = next;
 as->prev = prev;
@@ -193,7 +201,7 @@ al->complete = h;
 
 if (!instance_only)
   {
-  al->rawsig_no_b_val.data = store_get(h->slen + 1);
+  al->rawsig_no_b_val.data = store_get(h->slen + 1, GET_TAINTED);
   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;
@@ -252,9 +260,10 @@ while ((c = *s))
 	  while ((c = *++s) && c != ';')
 	    if (c != ' ' && c != '\t' && c != '\n' && c != '\r')
 	      g = string_catn(g, s, 1);
+	  if (!g) return US"no b= value";
 	  al->b.data = string_from_gstring(g);
 	  al->b.len = g->ptr;
-	  gstring_reset_unused(g);
+	  gstring_release_unused(g);
 	  bend = s;
 	  break;
 	case 'h':			/* bh= AMS body hash */
@@ -268,9 +277,10 @@ while ((c = *s))
 	  while ((c = *++s) && c != ';')
 	    if (c != ' ' && c != '\t' && c != '\n' && c != '\r')
 	      g = string_catn(g, s, 1);
+	  if (!g) return US"no bh= value";
 	  al->bh.data = string_from_gstring(g);
 	  al->bh.len = g->ptr;
-	  gstring_reset_unused(g);
+	  gstring_release_unused(g);
 	  break;
 	default:
 	  return US"b? tag";
@@ -373,11 +383,11 @@ 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)
+  BOOL instance_only, arc_line ** alp_ret)
 {
-int i;
+unsigned i;
 arc_set * as;
-arc_line * al = store_get(sizeof(arc_line)), ** alp;
+arc_line * al = store_get(sizeof(arc_line), GET_UNTAINTED), ** alp;
 uschar * e;
 
 memset(al, 0, sizeof(arc_line));
@@ -388,10 +398,12 @@ if ((e = arc_parse_line(al, h, off, instance_only)))
   return US"line parse";
   }
 if (!(i = arc_instance_from_hdr(al)))	return US"instance find";
+if (i > 50)				return US"overlarge instance number";
 if (!(as = arc_find_set(ctx, i)))	return US"set find";
 if (*(alp = (arc_line **)(US as + hoff))) return US"dup hdr";
 
 *alp = al;
+if (alp_ret) *alp_ret = al;
 return NULL;
 }
 
@@ -415,7 +427,7 @@ if (strncmpic(ARC_HDR_AAR, h->text, ARC_HDRLEN_AAR) == 0)
     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)))
+			  TRUE, NULL)))
     {
     DEBUG(D_acl) debug_printf("inserting AAR: %s\n", e);
     return US"inserting AAR";
@@ -434,15 +446,13 @@ else if (strncmpic(ARC_HDR_AMS, h->text, ARC_HDRLEN_AMS) == 0)
     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)))
+			  instance_only, &ams)))
     {
     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;
@@ -460,7 +470,7 @@ else if (strncmpic(ARC_HDR_AS, h->text, ARC_HDRLEN_AS) == 0)
     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)))
+			  instance_only, NULL)))
     {
     DEBUG(D_acl) debug_printf("inserting AS: %s\n", e);
     return US"inserting AS";
@@ -488,7 +498,7 @@ 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 = store_get(sizeof(hdr_rlist), GET_UNTAINTED);
   r->prev = rprev;
   r->used = FALSE;
   r->h = h;
@@ -533,7 +543,8 @@ hctx hhash_ctx;
 const uschar * s;
 int len;
 
-if (!exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
+if (  hashtype == -1
+   || !exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
   {
   DEBUG(D_acl)
       debug_printf("ARC: hash setup error, possibly nonhandled hashtype\n");
@@ -559,7 +570,7 @@ while ((hn = string_nextinlist(&headernames, &sep, NULL, 0)))
 
       len = Ustrlen(s);
       DEBUG(D_acl) pdkim_quoteprint(s, len);
-      exim_sha_update(&hhash_ctx, s, Ustrlen(s));
+      exim_sha_update_string(&hhash_ctx, s);
       r->used = TRUE;
       break;
       }
@@ -588,7 +599,7 @@ 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))))
+	  (int)al->s.len, al->s.data, (int)al->d.len, al->d.data))))
   {
   DEBUG(D_acl) debug_printf("pubkey dns lookup fail\n");
   return NULL;
@@ -628,9 +639,10 @@ return p;
 static pdkim_bodyhash *
 arc_ams_setup_vfy_bodyhash(arc_line * ams)
 {
-int canon_head, canon_body;
+int canon_head = -1, canon_body = -1;
 long bodylen;
 
+if (!ams->c.data) ams->c.data = US"simple";	/* RFC 6376 (DKIM) default */
 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;
@@ -725,7 +737,7 @@ 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)))
+if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx, NULL)))
   {
   DEBUG(D_acl) debug_printf("ARC verify init: %s\n", errstr);
   as->ams_verify_done = arc_state_reason = US"internal sigverify init error";
@@ -733,6 +745,11 @@ if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx)))
   }
 
 hashtype = pdkim_hashname_to_hashtype(ams->a_hash.data, ams->a_hash.len);
+if (hashtype == -1)
+  {
+  DEBUG(D_acl) debug_printf("ARC i=%d AMS verify bad a_hash\n", as->instance);
+  return as->ams_verify_done = arc_state_reason = US"AMS sig nonverify";
+  }
 
 if ((errstr = exim_dkim_verify(&vctx,
 	  pdkim_hashes[hashtype].exim_hashmethod, &hhash, &sighash)))
@@ -759,24 +776,26 @@ arc_headers_check(arc_ctx * ctx)
 arc_set * as;
 int inst;
 BOOL ams_fail_found = FALSE;
-uschar * ret = NULL;
 
-if (!(as = ctx->arcset_chain))
+if (!(as = ctx->arcset_chain_last))
   return US"none";
 
-for(inst = 0; as; as = as->next)
+for(inst = as->instance; as; as = as->prev, inst--)
   {
-  if (  as->instance != ++inst
-     || !as->hdr_aar || !as->hdr_ams || !as->hdr_as
-     || arc_cv_match(as->hdr_as, US"fail")
-     )
-    {
-    arc_state_reason = string_sprintf("i=%d fail"
-      " (cv, sequence or missing header)", as->instance);
-    DEBUG(D_acl) debug_printf("ARC %s\n", arc_state_reason);
-    ret = US"fail";
-    }
+  if (as->instance != inst)
+    arc_state_reason = string_sprintf("i=%d (sequence; expected %d)",
+      as->instance, inst);
+  else if (!as->hdr_aar || !as->hdr_ams || !as->hdr_as)
+    arc_state_reason = string_sprintf("i=%d (missing header)", as->instance);
+  else if (arc_cv_match(as->hdr_as, US"fail"))
+    arc_state_reason = string_sprintf("i=%d (cv)", as->instance);
+  else
+    goto good;
+
+  DEBUG(D_acl) debug_printf("ARC chain fail at %s\n", arc_state_reason);
+  return US"fail";
 
+  good:
   /* Evaluate the oldest-pass AMS validation while we're here.
   It does not affect the AS chain validation but is reported as
   auxilary info. */
@@ -788,23 +807,29 @@ for(inst = 0; as; as = as->next)
       arc_oldest_pass = inst;
   arc_state_reason = NULL;
   }
+if (inst != 0)
+  {
+  arc_state_reason = string_sprintf("(sequence; expected i=%d)", inst);
+  DEBUG(D_acl) debug_printf("ARC chain fail %s\n", arc_state_reason);
+  return US"fail";
+  }
 
 arc_received = ctx->arcset_chain_last;
-arc_received_instance = inst;
-if (ret)
-  return ret;
+arc_received_instance = arc_received->instance;
 
 /* 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)
+if (!as->ams_verify_passed)
   {
-  arc_state_reason = as->ams_verify_done;
-  return US"fail";
+  if (as->ams_verify_done)
+    {
+    arc_state_reason = as->ams_verify_done;
+    return US"fail";
+    }
+  if (!!arc_ams_verify(ctx, as))
+    return US"fail";
   }
-if (!!arc_ams_verify(ctx, as))
-  return US"fail";
-
 return NULL;
 }
 
@@ -851,7 +876,8 @@ if (  as->instance == 1 && !arc_cv_match(hdr_as, US"none")
 
 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))
+if (  hashtype == -1
+   || !exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
   {
   DEBUG(D_acl)
       debug_printf("ARC: hash setup error, possibly nonhandled hashtype\n");
@@ -940,14 +966,12 @@ if (!(p = arc_line_to_pubkey(hdr_as)))
 /* 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)))
+if ((errstr = exim_dkim_verify_init(&p->key, KEYFMT_DER, &vctx, NULL)))
   {
   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)))
@@ -966,16 +990,13 @@ return NULL;
 static const uschar *
 arc_verify_seals(arc_ctx * ctx)
 {
-arc_set * as = ctx->arcset_chain;
+arc_set * as = ctx->arcset_chain_last;
 
 if (!as)
   return US"none";
 
-while (as)
-  {
-  if (arc_seal_verify(ctx, as)) return US"fail";
-  as = as->next;
-  }
+for ( ; as; as = as->prev) if (arc_seal_verify(ctx, as)) return US"fail";
+
 DEBUG(D_acl) debug_printf("ARC: AS vfy overall pass\n");
 return NULL;
 }
@@ -990,9 +1011,10 @@ Return:  The ARC state, or NULL on error.
 const uschar *
 acl_verify_arc(void)
 {
-arc_ctx ctx = { NULL };
 const uschar * res;
 
+memset(&arc_verify_ctx, 0, sizeof(arc_verify_ctx));
+
 if (!dkim_verify_ctx)
   {
   DEBUG(D_acl) debug_printf("ARC: no DKIM verify context\n");
@@ -1006,7 +1028,7 @@ https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-10#section-6
        none, the ARC state is "none" and the algorithm stops here.
 */
 
-if ((res = arc_vfy_collect_hdrs(&ctx)))
+if ((res = arc_vfy_collect_hdrs(&arc_verify_ctx)))
   goto out;
 
 /* 2.  If the form of any ARC set is invalid (e.g., does not contain
@@ -1024,7 +1046,7 @@ if ((res = arc_vfy_collect_hdrs(&ctx)))
        then the chain state is "fail" and the algorithm stops here.
 */
 
-if ((res = arc_headers_check(&ctx)))
+if ((res = arc_headers_check(&arc_verify_ctx)))
   goto out;
 
 /* 4.  For each ARC-Seal from the "N"th instance to the first, apply the
@@ -1066,7 +1088,7 @@ if ((res = arc_headers_check(&ctx)))
        the algorithm is complete.
 */
 
-if ((res = arc_verify_seals(&ctx)))
+if ((res = arc_verify_seals(&arc_verify_ctx)))
   goto out;
 
 res = US"pass";
@@ -1082,7 +1104,7 @@ out:
 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));
+hdr_rlist * r = store_get(sizeof(hdr_rlist) + sizeof(header_line), GET_UNTAINTED);
 header_line * h = r->h = (header_line *)(r+1);
 
 r->prev = list;
@@ -1092,18 +1114,12 @@ 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.
+a reverse-order list.
 */
 
 static hdr_rlist *
@@ -1173,13 +1189,14 @@ 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));
+int aar_off = gstring_length(g);
+arc_set * as =
+  store_get(sizeof(arc_set) + sizeof(arc_line) + sizeof(header_line), GET_UNTAINTED);
 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_fmt_append(g, " i=%d; %s;\r\n\t", instance, identity);
 g = string_catn(g, US ar->data, ar->len);
 
 h->slen = g->ptr - aar_off;
@@ -1239,7 +1256,10 @@ else
 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);
+  log_write(0, LOG_MAIN, "ARC: %s signing: %s\n", why, errstr);
+  DEBUG(D_transport)
+    debug_printf("private key, or private-key file content, was: '%s'\n",
+      privkey);
   return FALSE;
   }
 return TRUE;
@@ -1262,7 +1282,7 @@ for (;;)
   g = string_catn(g, US"\r\n\t  ", 5);
   }
 g = string_catn(g, US";\r\n", 3);
-gstring_reset_unused(g);
+gstring_release_unused(g);
 string_from_gstring(g);
 return g;
 }
@@ -1273,7 +1293,7 @@ return g;
 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)
+  hdr_rlist * rheaders, const uschar * privkey, unsigned options)
 {
 uschar * s;
 gstring * hdata = NULL;
@@ -1281,7 +1301,7 @@ 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));
+arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line), GET_UNTAINTED);
 header_line * h = (header_line *)(al+1);
 
 /* debug_printf("%s\n", __FUNCTION__); */
@@ -1289,13 +1309,14 @@ header_line * h = (header_line *)(al+1);
 /* 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=");
+g = string_fmt_append(g, "%s i=%d; a=rsa-sha256; c=relaxed; d=%s; s=%s",
+      ARC_HDR_AMS, instance, identity, selector);	/*XXX hardwired a= */
+if (options & ARC_SIGN_OPT_TSTAMP)
+  g = string_fmt_append(g, "; t=%lu", (u_long)now);
+if (options & ARC_SIGN_OPT_EXPIRE)
+  g = string_fmt_append(g, "; x=%lu", (u_long)expire);
+g = string_fmt_append(g, ";\r\n\tbh=%s;\r\n\th=",
+      pdkim_encode_base64(bodyhash));
 
 for(col = 3; rheaders; rheaders = rheaders->prev)
   {
@@ -1391,13 +1412,13 @@ return US"none";
 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)
+  const uschar * privkey, unsigned options)
 {
 gstring * arcset;
-arc_set * as;
 uschar * status = arc_ar_cv_status(ar);
-arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line));
+arc_line * al = store_get(sizeof(header_line) + sizeof(arc_line), GET_UNTAINTED);
 header_line * h = (header_line *)(al+1);
+uschar * badline_str;
 
 gstring * hdata = NULL;
 int hashtype = pdkim_hashname_to_hashtype(US"sha256", 6);	/*XXX hardwired */
@@ -1415,15 +1436,20 @@ blob sig;
       - all ARC set headers, set-number order, aar then ams then as,
         including self (but with an empty b= in self)
 */
+DEBUG(D_transport) debug_printf("ARC: building AS for status '%s'\n", status);
 
 /* Construct the AS except for the signature */
 
-arcset = string_append(NULL, 10,
+arcset = string_append(NULL, 9,
 	  ARC_HDR_AS,
 	  US" i=", string_sprintf("%d", instance),
 	  US"; cv=", status,
 	  US"; a=rsa-sha256; d=", identity,			/*XXX hardwired */
-	  US"; s=", selector,					/*XXX same as AMS */
+	  US"; s=", selector);					/*XXX same as AMS */
+if (options & ARC_SIGN_OPT_TSTAMP)
+  arcset = string_append(arcset, 2,
+      US"; t=", string_sprintf("%lu", (u_long)now));
+arcset = string_cat(arcset,
 	  US";\r\n\t b=;");
 
 h->slen = arcset->ptr;
@@ -1434,18 +1460,25 @@ 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
+for (arc_set * as = Ustrcmp(status, US"fail") == 0
 	? ctx->arcset_chain_last : ctx->arcset_chain;
      as; as = as->next)
   {
+  arc_line * l;
   /* Accumulate AAR then AMS then AS.  Relaxed canonicalisation
   is required per standard. */
 
-  h = as->hdr_aar->complete;
+  badline_str = US"aar";
+  if (!(l = as->hdr_aar)) goto badline;
+  h = l->complete;
   hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
-  h = as->hdr_ams->complete;
+  badline_str = US"ams";
+  if (!(l = as->hdr_ams)) goto badline;
+  h = l->complete;
   hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
-  h = as->hdr_as->complete;
+  badline_str = US"as";
+  if (!(l = as->hdr_as)) goto badline;
+  h = l->complete;
   hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, !!as->next));
   }
 
@@ -1462,6 +1495,11 @@ 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);
+
+badline:
+  DEBUG(D_transport)
+    debug_printf("ARC: while building AS, missing %s in chain\n", badline_str);
+  return NULL;
 }
 
 
@@ -1486,6 +1524,15 @@ return pdkim_set_bodyhash(&dkim_sign_ctx,
 
 
 
+void
+arc_sign_init(void)
+{
+memset(&arc_sign_ctx, 0, sizeof(arc_sign_ctx));
+headers_rlist = NULL;
+}
+
+
+
 /* 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.
@@ -1508,12 +1555,30 @@ return arc_try_header(&arc_sign_ctx, headers_rlist->h, TRUE);
 
 
 
+/* Per RFCs 6376, 7489 the only allowed chars in either an ADMD id
+or a selector are ALPHA/DIGGIT/'-'/'.'
+
+Check, to help catch misconfigurations such as a missing selector
+element in the arc_sign list.
+*/
+
+static BOOL
+arc_valid_id(const uschar * s)
+{
+for (uschar c; c = *s++; )
+  if (!isalnum(c) && c != '-' && c != '.') return FALSE;
+return 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
+  signspec	Three-element colon-sep list: identity, selector, privkey.
+		Optional fourth element: comma-sep list of options.
 		Already expanded
   sigheaders	Any signature headers already generated, eg. by DKIM, or NULL
   errstr	Error string
@@ -1526,7 +1591,8 @@ Return value
 gstring *
 arc_sign(const uschar * signspec, gstring * sigheaders, uschar ** errstr)
 {
-const uschar * identity, * selector, * privkey;
+const uschar * identity, * selector, * privkey, * opts, * s;
+unsigned options = 0;
 int sep = 0;
 header_line * headers;
 hdr_rlist * rheaders;
@@ -1535,56 +1601,96 @@ int instance;
 gstring * g = NULL;
 pdkim_bodyhash * b;
 
+expire = now = 0;
+
 /* 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)
+if (!(identity = string_nextinlist(&signspec, &sep, NULL, 0)) || !*identity)
+  { s = US"identity"; goto bad_arg_ret; }
+if (!(selector = string_nextinlist(&signspec, &sep, NULL, 0)) || !*selector)
+  { s = US"selector"; goto bad_arg_ret; }
+if (!(privkey = string_nextinlist(&signspec, &sep, NULL, 0))  || !*privkey)
+  { s = US"privkey"; goto bad_arg_ret; }
+if (!arc_valid_id(identity))
+  { s = US"identity"; goto bad_arg_ret; }
+if (!arc_valid_id(selector))
+  { s = US"selector"; goto bad_arg_ret; }
+if (*privkey == '/' && !(privkey = expand_file_big_buffer(privkey)))
+  goto ret_sigheaders;
+
+if ((opts = string_nextinlist(&signspec, &sep, NULL, 0)))
   {
-  log_write(0, LOG_MAIN|LOG_PANIC, "ARC: bad signing-specification (%s)",
-    !*identity ? "identity" : !*selector ? "selector" : "private-key");
-  return NULL;
+  int osep = ',';
+  while ((s = string_nextinlist(&opts, &osep, NULL, 0)))
+    if (Ustrcmp(s, "timestamps") == 0)
+      {
+      options |= ARC_SIGN_OPT_TSTAMP;
+      if (!now) now = time(NULL);
+      }
+    else if (Ustrncmp(s, "expire", 6) == 0)
+      {
+      options |= ARC_SIGN_OPT_EXPIRE;
+      if (*(s += 6) == '=')
+	if (*++s == '+')
+	  {
+	  if (!(expire = (time_t)atoi(CS ++s)))
+	    expire = ARC_SIGN_DEFAULT_EXPIRE_DELTA;
+	  if (!now) now = time(NULL);
+	  expire += now;
+	  }
+	else
+	  expire = (time_t)atol(CS s);
+      else
+	{
+	if (!now) now = time(NULL);
+	expire = now + ARC_SIGN_DEFAULT_EXPIRE_DELTA;
+	}
+      }
   }
-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 */
+/* Make an rlist of any new DKIM headers, then add the "normals" rlist to it.
+Then scan the list for an A-R header. */
 
 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;
+  for (rp = &headers_rlist; *rp; ) rp = &(*rp)->prev;
+  *rp = 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;
+/*XXX also, we really should be accepting any number of ADMD-matching ARs */
+  {
+  header_line * hnext = NULL;
+  for (rheaders = headers_rlist; rheaders;
+       hnext = rheaders->h, rheaders = rheaders->prev)
+    rheaders->h->next = hnext;
+  headers = hnext;
+  }
 
 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);
+  log_write(0, LOG_MAIN, "ARC: no Authentication-Results header for signing");
+  goto ret_sigheaders;
   }
 
+/* We previously built the data-struct for the existing ARC chain, if any, using a headers
+feed from the DKIM module.  Use that to give the instance number for the ARC set we are
+about to build. */
+
+DEBUG(D_transport)
+  if (arc_sign_ctx.arcset_chain_last)
+    debug_printf("ARC: existing chain highest instance: %d\n",
+      arc_sign_ctx.arcset_chain_last->instance);
+  else
+    debug_printf("ARC: no existing chain\n");
+
+instance = arc_sign_ctx.arcset_chain_last ? arc_sign_ctx.arcset_chain_last->instance + 1 : 1;
+
 /*
 - Generate AAR
   - copy the A-R; prepend i= & identity
@@ -1603,7 +1709,7 @@ g = arc_sign_append_aar(g, &arc_sign_ctx, identity, instance, &ar);
 
 b = arc_ams_setup_sign_bodyhash();
 g = arc_sign_append_ams(g, &arc_sign_ctx, instance, identity, selector,
-      &b->bh, headers_rlist, privkey);
+      &b->bh, headers_rlist, privkey, options);
 
 /*
 - Generate AS
@@ -1618,14 +1724,26 @@ g = arc_sign_append_ams(g, &arc_sign_ctx, instance, identity, selector,
         including self (but with an empty b= in self)
 */
 
-g = arc_sign_prepend_as(g, &arc_sign_ctx, instance, identity, selector, &ar, privkey);
+if (g)
+  g = arc_sign_prepend_as(g, &arc_sign_ctx, instance, identity, selector, &ar,
+      privkey, options);
 
 /* 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;
+if (sigheaders) g = string_catn(g, sigheaders->s, sigheaders->ptr);
+
+out:
+  if (!g) return string_get(1);
+  (void) string_from_gstring(g);
+  gstring_release_unused(g);
+  return g;
+
+
+bad_arg_ret:
+  log_write(0, LOG_MAIN, "ARC: bad signing-specification (%s)", s);
+ret_sigheaders:
+  g = sigheaders;
+  goto out;
 }
 
 
@@ -1661,7 +1779,13 @@ 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";
+  goto badline;
+  }
+
+if (!al.a_hash.data)
+  {
+  DEBUG(D_acl) debug_printf("ARC: no a_hash from '%.*s'\n", h.slen, h.text);
+  goto badline;
   }
 
 /* defaults */
@@ -1680,6 +1804,9 @@ if (!(b = arc_ams_setup_vfy_bodyhash(&al)))
 should have been created here. */
 
 return NULL;
+
+badline:
+  return US"line parsing error";
 }
 
 
@@ -1704,7 +1831,37 @@ return is_vfy ? arc_header_vfy_feed(g) : arc_header_sign_feed(g);
 
 /******************************************************************************/
 
-/* Construct an Authenticate-Results header portion, for the ARC module */
+/* Construct the list of domains from the ARC chain after validation */
+
+uschar *
+fn_arc_domains(void)
+{
+arc_set * as;
+unsigned inst;
+gstring * g = NULL;
+
+for (as = arc_verify_ctx.arcset_chain, inst = 1; as; as = as->next, inst++)
+  {
+  arc_line * hdr_as = as->hdr_as;
+  if (hdr_as)
+    {
+    blob * d = &hdr_as->d;
+
+    for (; inst < as->instance; inst++)
+      g = string_catn(g, US":", 1);
+
+    g = d->data && d->len
+      ? string_append_listele_n(g, ':', d->data, d->len)
+      : string_catn(g, US":", 1);
+    }
+  else
+    g = string_catn(g, US":", 1);
+  }
+return g ? g->s : US"";
+}
+
+
+/* Construct an Authentication-Results header portion, for the ARC module */
 
 gstring *
 authres_arc(gstring * g)
@@ -1718,20 +1875,20 @@ if (arc_state)
   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")");
+    g = string_fmt_append(g, " (i=%d)", arc_received_instance);
     if (arc_state_reason)
       g = string_append(g, 3, US"(", arc_state_reason, US")");
     g = string_catn(g, US" header.s=", 10);
     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));
+    g = string_fmt_append(g, " arc.oldest-pass=%d", arc_oldest_pass);
 
     if (sender_host_address)
-      g = string_append(g, 2, US" smtp.client-ip=", sender_host_address);
+      g = string_append(g, 2, US" smtp.remote-ip=", sender_host_address);
     }
+  else if (arc_state_reason)
+    g = string_append(g, 3, US" (", arc_state_reason, US")");
   DEBUG(D_acl) debug_printf("ARC:  authres '%.*s'\n",
 		  g->ptr - start - 3, g->s + start + 3);
   }
@@ -1741,7 +1898,7 @@ return g;
 }
 
 
-# endif /* SUPPORT_SPF */
+# endif /* DISABLE_DKIM */
 #endif /* EXPERIMENTAL_ARC */
 /* vi: aw ai sw=2
  */