ARC: harden against malformed headers

[exim.git] / src / src / arc.c

diff --git a/src/src/arc.c b/src/src/arc.c
index a749c78efef68bafafb6d07850c5e9726d66b7df..e7ebb97196db5110f6114ff969df6d152ff58abc 100644 (file)
--- a/src/src/arc.c
+++ b/src/src/arc.c
@@ -21,6 +21,11 @@
 extern pdkim_ctx * dkim_verify_ctx;
 extern pdkim_ctx dkim_sign_ctx;
 
 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 {
 /******************************************************************************/
 
 typedef struct hdr_rlist {


@@ -84,8 +89,11 @@ typedef struct arc_ctx {
 #define HDR_AR         US"Authentication-Results:"
 #define HDRLEN_AR      23
 
 #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 hdr_rlist * headers_rlist;
 static arc_ctx arc_sign_ctx = { NULL };

+static arc_ctx arc_verify_ctx = { NULL };

 
 
 /******************************************************************************/
 
 
 /******************************************************************************/


@@ -252,6 +260,7 @@ while ((c = *s))
          while ((c = *++s) && c != ';')
            if (c != ' ' && c != '\t' && c != '\n' && c != '\r')
              g = string_catn(g, s, 1);
          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);
          al->b.data = string_from_gstring(g);
          al->b.len = g->ptr;
          gstring_reset_unused(g);


@@ -268,6 +277,7 @@ while ((c = *s))
          while ((c = *++s) && c != ';')
            if (c != ' ' && c != '\t' && c != '\n' && c != '\r')
              g = string_catn(g, s, 1);
          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);
          al->bh.data = string_from_gstring(g);
          al->bh.len = g->ptr;
          gstring_reset_unused(g);


@@ -375,7 +385,7 @@ static uschar *
 arc_insert_hdr(arc_ctx * ctx, header_line * h, unsigned off, unsigned hoff,
   BOOL instance_only)
 {
 arc_insert_hdr(arc_ctx * ctx, header_line * h, unsigned off, unsigned hoff,
   BOOL instance_only)
 {

-int i;
+unsigned i;

 arc_set * as;
 arc_line * al = store_get(sizeof(arc_line)), ** alp;
 uschar * e;
 arc_set * as;
 arc_line * al = store_get(sizeof(arc_line)), ** alp;
 uschar * e;


@@ -388,6 +398,7 @@ 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";
   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";
 
 if (!(as = arc_find_set(ctx, i)))      return US"set find";
 if (*(alp = (arc_line **)(US as + hoff))) return US"dup hdr";
 


@@ -564,11 +575,11 @@ while ((hn = string_nextinlist(&headernames, &sep, NULL, 0)))
       break;
       }
 
       break;
       }
 

-/* Finally add in the signature header (with the b= tag stripped) */
+/* Finally add in the signature header (with the b= tag stripped); no CRLF */

 
 s = ams->rawsig_no_b_val.data, len = ams->rawsig_no_b_val.len;
 if (relaxed)
 
 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));
+  len = Ustrlen(s = pdkim_relax_header_n(s, len, FALSE));

 DEBUG(D_acl) pdkim_quoteprint(s, len);
 exim_sha_update(&hhash_ctx, s, len);
 
 DEBUG(D_acl) pdkim_quoteprint(s, len);
 exim_sha_update(&hhash_ctx, s, len);
 


@@ -631,6 +642,7 @@ arc_ams_setup_vfy_bodyhash(arc_line * ams)
 int canon_head, canon_body;
 long bodylen;
 
 int canon_head, canon_body;
 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;
 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;


@@ -759,24 +771,26 @@ arc_headers_check(arc_ctx * ctx)
 arc_set * as;
 int inst;
 BOOL ams_fail_found = FALSE;
 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";
 
   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. */
   /* 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 +802,29 @@ for(inst = 0; as; as = as->next)
       arc_oldest_pass = inst;
   arc_state_reason = NULL;
   }
       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 = 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;
 
 /* 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;
 }
 
 return NULL;
 }
 


@@ -865,6 +885,8 @@ if (!exim_sha_init(&hhash_ctx, pdkim_hashes[hashtype].exim_hashmethod))
            header canonicalization defined in Section 3.4.2 of
            [RFC6376].  Pass the canonicalized result to the hash
            function.
            header canonicalization defined in Section 3.4.2 of
            [RFC6376].  Pass the canonicalized result to the hash
            function.

+
+Headers are CRLF-separated, but the last one is not crlf-terminated.

 */
 
 DEBUG(D_acl) debug_printf("ARC: AS header data for verification:\n");
 */
 
 DEBUG(D_acl) debug_printf("ARC: AS header data for verification:\n");


@@ -895,7 +917,7 @@ for (as2 = ctx->arcset_chain;
   al = as2->hdr_as;
   if (as2->instance == as->instance)
     s = pdkim_relax_header_n(al->rawsig_no_b_val.data,
   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);
+                                       al->rawsig_no_b_val.len, FALSE);

   else if (!(s = al->relaxed))
     al->relaxed = s = pdkim_relax_header_n(al->complete->text,
                                            al->complete->slen, TRUE);
   else if (!(s = al->relaxed))
     al->relaxed = s = pdkim_relax_header_n(al->complete->text,
                                            al->complete->slen, TRUE);


@@ -952,7 +974,7 @@ if ((errstr = exim_dkim_verify(&vctx,
   {
   DEBUG(D_acl)
     debug_printf("ARC i=%d AS headers verify: %s\n", as->instance, errstr);
   {
   DEBUG(D_acl)
     debug_printf("ARC i=%d AS headers verify: %s\n", as->instance, errstr);

-  arc_state_reason = US"seal sigverify init error";
+  arc_state_reason = US"seal sigverify error";

   return US"fail";
   }
 
   return US"fail";
   }
 


@@ -964,16 +986,13 @@ return NULL;
 static const uschar *
 arc_verify_seals(arc_ctx * ctx)
 {
 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";
 
 
 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;
 }
 DEBUG(D_acl) debug_printf("ARC: AS vfy overall pass\n");
 return NULL;
 }


@@ -988,9 +1007,16 @@ Return:  The ARC state, or NULL on error.
 const uschar *
 acl_verify_arc(void)
 {
 const uschar *
 acl_verify_arc(void)
 {

-arc_ctx ctx = { NULL };

 const uschar * res;
 
 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");
+  return NULL;
+  }
+

 /* AS evaluation, per
 https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-10#section-6
 */
 /* AS evaluation, per
 https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-10#section-6
 */


@@ -998,7 +1024,7 @@ https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-10#section-6
        none, the ARC state is "none" and the algorithm stops here.
 */
 
        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
   goto out;
 
 /* 2.  If the form of any ARC set is invalid (e.g., does not contain


@@ -1016,7 +1042,7 @@ if ((res = arc_vfy_collect_hdrs(&ctx)))
        then the chain state is "fail" and the algorithm stops here.
 */
 
        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
   goto out;
 
 /* 4.  For each ARC-Seal from the "N"th instance to the first, apply the


@@ -1058,7 +1084,7 @@ if ((res = arc_headers_check(&ctx)))
        the algorithm is complete.
 */
 
        the algorithm is complete.
 */
 

-if ((res = arc_verify_seals(&ctx)))
+if ((res = arc_verify_seals(&arc_verify_ctx)))

   goto out;
 
 res = US"pass";
   goto out;
 
 res = US"pass";


@@ -1094,8 +1120,7 @@ return r;
 
 
 /* Walk the given headers strings identifying each header, and construct
 
 
 /* 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 *
 */
 
 static hdr_rlist *


@@ -1171,7 +1196,7 @@ arc_line * al = (arc_line *)(as+1);
 header_line * h = (header_line *)(al+1);
 
 g = string_catn(g, ARC_HDR_AAR, ARC_HDRLEN_AAR);
 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;
 g = string_catn(g, US ar->data, ar->len);
 
 h->slen = g->ptr - aar_off;


@@ -1231,7 +1256,10 @@ else
 if (  (errstr = exim_dkim_signing_init(privkey, &sctx))
    || (errstr = exim_dkim_sign(&sctx, hm, &hhash, sig)))
   {
 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;
   return FALSE;
   }
 return TRUE;


@@ -1265,7 +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,
 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;
 {
 uschar * s;
 gstring * hdata = NULL;


@@ -1281,13 +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;
 /* 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)
   {
 
 for(col = 3; rheaders; rheaders = rheaders->prev)
   {


@@ -1328,10 +1357,8 @@ if (g->s[g->ptr - 1] == ':') g->ptr--;
 g = string_catn(g, US";\r\n\tb=;", 7);
 
 /* Include the pseudo-header in the accumulation */
 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);
+s = pdkim_relax_header_n(g->s + ams_off, g->ptr - ams_off, FALSE);

 hdata = string_cat(hdata, s);
 
 /* Calculate the signature from the accumulation */
 hdata = string_cat(hdata, s);
 
 /* Calculate the signature from the accumulation */


@@ -1375,7 +1402,7 @@ while ((methodspec = string_nextinlist(&resinfo, &sep, NULL, 0)))
          (c = *s) && c != ';' && c != ' ' && c != '\r' && c != '\n'; ) s++;
     return string_copyn(methodspec, s - methodspec);
     }
          (c = *s) && c != ';' && c != ' ' && c != '\r' && c != '\n'; ) s++;
     return string_copyn(methodspec, s - methodspec);
     }

-return NULL;
+return US"none";

 }
 
 
 }
 
 


@@ -1385,7 +1412,7 @@ return NULL;
 static gstring *
 arc_sign_prepend_as(gstring * arcset_interim, arc_ctx * ctx,
   int instance, const uschar * identity, const uschar * selector, blob * ar,
 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;
 {
 gstring * arcset;
 arc_set * as;


@@ -1412,12 +1439,16 @@ blob sig;
 
 /* Construct the AS except for the signature */
 
 
 /* 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,
          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"; a=rsa-sha256; d=", identity,                     /*XXX hardwired */
+         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;
          US";\r\n\t b=;");
 
 h->slen = arcset->ptr;


@@ -1440,7 +1471,7 @@ for (as = Ustrcmp(status, US"fail") == 0
   h = as->hdr_ams->complete;
   hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, TRUE));
   h = as->hdr_as->complete;
   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));
+  hdata = string_cat(hdata, pdkim_relax_header_n(h->text, h->slen, !!as->next));

   }
 
 /* Calculate the signature from the accumulation */
   }
 
 /* Calculate the signature from the accumulation */


@@ -1480,6 +1511,14 @@ return pdkim_set_bodyhash(&dkim_sign_ctx,
 
 
 
 
 
 

+void
+arc_sign_init(void)
+{
+memset(&arc_sign_ctx, 0, sizeof(arc_sign_ctx));
+}
+
+
+

 /* 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.
 /* 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.


@@ -1507,7 +1546,8 @@ 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:
 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
                Already expanded
   sigheaders   Any signature headers already generated, eg. by DKIM, or NULL
   errstr       Error string


@@ -1520,7 +1560,8 @@ Return value
 gstring *
 arc_sign(const uschar * signspec, gstring * sigheaders, uschar ** errstr)
 {
 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;
 int sep = 0;
 header_line * headers;
 hdr_rlist * rheaders;


@@ -1529,55 +1570,95 @@ int instance;
 gstring * g = NULL;
 pdkim_bodyhash * b;
 
 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);
 /* Parse the signing specification */
 
 identity = string_nextinlist(&signspec, &sep, NULL, 0);
 selector = string_nextinlist(&signspec, &sep, NULL, 0);

-if (  !*identity | !*selector
+if (  !*identity || !*selector

    || !(privkey = string_nextinlist(&signspec, &sep, NULL, 0)) || !*privkey)
   {
    || !(privkey = string_nextinlist(&signspec, &sep, NULL, 0)) || !*privkey)
   {

-  log_write(0, LOG_MAIN|LOG_PANIC, "ARC: bad signing-specification");
-  return NULL;
+  log_write(0, LOG_MAIN, "ARC: bad signing-specification (%s)",
+    !*identity ? "identity" : !*selector ? "selector" : "private-key");
+  return sigheaders ? sigheaders : string_get(0);

   }
 if (*privkey == '/' && !(privkey = expand_file_big_buffer(privkey)))
   }
 if (*privkey == '/' && !(privkey = expand_file_big_buffer(privkey)))

-  return NULL;
+  return sigheaders ? sigheaders : string_get(0);

 
 

-DEBUG(D_transport) debug_printf("ARC: sign for %s\n", identity);
+if ((opts = string_nextinlist(&signspec, &sep, NULL, 0)))
+  {
+  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;
+       }
+      }
+  }

 
 

-/*
-- scan headers for existing ARC chain & A-R (with matching system-identfier)
-  - paniclog & skip on problems (no A-R)
-*/
+DEBUG(D_transport) debug_printf("ARC: sign for %s\n", identity);

 
 

-/* 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;
 
 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? */
 /* 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)))
   {
 
 if (!(arc_sign_find_ar(headers, identity, &ar)))
   {

-  log_write(0, LOG_MAIN|LOG_PANIC, "ARC: no Authentication-Results header for signing");
+  log_write(0, LOG_MAIN, "ARC: no Authentication-Results header for signing");

   return sigheaders ? sigheaders : string_get(0);
   }
 
   return sigheaders ? sigheaders : string_get(0);
   }
 

+/* 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
 /*
 - Generate AAR
   - copy the A-R; prepend i= & identity


@@ -1596,7 +1677,7 @@ 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 = 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
 
 /*
 - Generate AS


@@ -1611,11 +1692,13 @@ g = arc_sign_append_ams(g, &arc_sign_ctx, instance, identity, selector,
         including self (but with an empty b= in self)
 */
 
         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. */
 
 
 /* Finally, append the dkim headers and return the lot. */
 

-g = string_catn(g, sigheaders->s, sigheaders->ptr);
+if (sigheaders) g = string_catn(g, sigheaders->s, sigheaders->ptr);

 (void) string_from_gstring(g);
 gstring_reset_unused(g);
 return g;
 (void) string_from_gstring(g);
 gstring_reset_unused(g);
 return g;


@@ -1697,7 +1780,37 @@ 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)
 
 gstring *
 authres_arc(gstring * g)


@@ -1711,20 +1824,20 @@ if (arc_state)
   g = string_append(g, 2, US";\n\tarc=", arc_state);
   if (arc_received_instance > 0)
     {
   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);
 
     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)
 
     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);
   }
   DEBUG(D_acl) debug_printf("ARC:  authres '%.*s'\n",
                  g->ptr - start - 3, g->s + start + 3);
   }