DKIM: Allow the DKIM ACL to override verification results. Bug 2186

This provides generic support, though is covers the need introduced
by https://datatracker.ietf.org/doc/draft-ietf-dcrup-dkim-usage/?include_text=1
(deprecating sha-1 and RSA keys shorter than 1024 bits).

7 files changed, 171 insertions, 92 deletions

diff --git a/src/src/acl.c b/src/src/acl.c
index 640989997..739cd91ae 100644
--- a/src/src/acl.c
+++ b/src/src/acl.c
@@ -852,6 +852,26 @@ while ((s = (*func)()) != NULL)
   compatibility. */
 
   if (c == ACLC_SET)
+#ifndef DISABLE_DKIM
+    if (  Ustrncmp(s, "dkim_verify_status", 18) == 0
+       || Ustrncmp(s, "dkim_verify_reason", 18) == 0)
+      {
+      uschar * endptr = s+18;
+
+      if (isalnum(*endptr))
+	{
+	*error = string_sprintf("invalid variable name after \"set\" in ACL "
+	  "modifier \"set %s\" "
+	  "(only \"dkim_verify_status\" or \"dkim_verify_reason\" permitted)",
+	  s);
+	return NULL;
+	}
+      cond->u.varname = string_copyn(s, 18);
+      s = endptr;
+      while (isspace(*s)) s++;
+      }
+    else
+#endif
     {
     uschar *endptr;
 
@@ -2899,8 +2919,19 @@ for (; cb != NULL; cb = cb->next)
 
     if (cb->type == ACLC_SET)
       {
-      debug_printf("acl_%s ", cb->u.varname);
-      lhswidth += 5 + Ustrlen(cb->u.varname);
+#ifndef DISABLE_DKIM
+      if (  Ustrcmp(cb->u.varname, "dkim_verify_status") == 0
+	 || Ustrcmp(cb->u.varname, "dkim_verify_reason") == 0)
+	{
+	debug_printf("%s ", cb->u.varname);
+	lhswidth += 19;
+	}
+      else
+#endif
+	{
+	debug_printf("acl_%s ", cb->u.varname);
+	lhswidth += 5 + Ustrlen(cb->u.varname);
+	}
       }
 
     debug_printf("= %s\n", cb->arg);
@@ -3402,7 +3433,7 @@ for (; cb != NULL; cb = cb->next)
 
     #ifndef DISABLE_DKIM
     case ACLC_DKIM_SIGNER:
-    if (dkim_cur_signer != NULL)
+    if (dkim_cur_signer)
       rc = match_isinlist(dkim_cur_signer,
                           &arg,0,NULL,NULL,MCL_STRING,TRUE,NULL);
     else
@@ -3410,7 +3441,7 @@ for (; cb != NULL; cb = cb->next)
     break;
 
     case ACLC_DKIM_STATUS:
-    rc = match_isinlist(dkim_exim_expand_query(DKIM_VERIFY_STATUS),
+    rc = match_isinlist(dkim_verify_status,
                         &arg,0,NULL,NULL,MCL_STRING,TRUE,NULL);
     break;
     #endif
@@ -3609,12 +3640,22 @@ for (; cb != NULL; cb = cb->next)
       {
       int old_pool = store_pool;
       if (  cb->u.varname[0] == 'c'
+#ifndef DISABLE_DKIM
+         || cb->u.varname[0] == 'd'
+#endif
 #ifndef DISABLE_EVENT
 	 || event_name		/* An event is being delivered */
 #endif
 	 )
         store_pool = POOL_PERM;
-      acl_var_create(cb->u.varname)->data.ptr = string_copy(arg);
+#ifndef DISABLE_DKIM	/* Overwriteable dkim result variables */
+      if (Ustrcmp(cb->u.varname, "dkim_verify_status") == 0)
+	dkim_verify_status = string_copy(arg);
+      else if (Ustrcmp(cb->u.varname, "dkim_verify_reason") == 0)
+	dkim_verify_reason = string_copy(arg);
+      else
+#endif
+	acl_var_create(cb->u.varname)->data.ptr = string_copy(arg);
       store_pool = old_pool;
       }
     break;
diff --git a/src/src/dkim.c b/src/src/dkim.c
index d31cae9c7..9a13e2a80 100644
--- a/src/src/dkim.c
+++ b/src/src/dkim.c
@@ -134,67 +134,35 @@ store_pool = dkim_verify_oldpool;
 }
 
 
-void
-dkim_exim_verify_finish(void)
+/* Log the result for the given signature */
+static void
+dkim_exim_verify_log_sig(pdkim_signature * sig)
 {
-pdkim_signature * sig = NULL;
-int rc;
-gstring * g = NULL;
-const uschar * errstr;
-
-store_pool = POOL_PERM;
-
-/* Delete eventual previous signature chain */
-
-dkim_signers = NULL;
-dkim_signatures = NULL;
-
-if (dkim_collect_error)
-  {
-  log_write(0, LOG_MAIN,
-      "DKIM: Error during validation, disabling signature verification: %.100s",
-      dkim_collect_error);
-  dkim_disable_verify = TRUE;
-  goto out;
-  }
-
-dkim_collect_input = FALSE;
-
-/* Finish DKIM operation and fetch link to signatures chain */
-
-rc = pdkim_feed_finish(dkim_verify_ctx, &dkim_signatures, &errstr);
-if (rc != PDKIM_OK)
-  {
-  log_write(0, LOG_MAIN, "DKIM: validation error: %.100s%s%s", pdkim_errstr(rc),
-	    errstr ? ": " : "", errstr ? errstr : US"");
-  goto out;
-  }
-
-for (sig = dkim_signatures; sig; sig = sig->next)
-  {
-  uschar * s;
-  gstring * logmsg;
-
-  /* Log a line for each signature */
-
-  if (!(s = sig->domain)) s = US"<UNSET>";
-  logmsg = string_append(NULL, 2, "d=", s);
-  if (!(s = sig->selector)) s = US"<UNSET>";
-  logmsg = string_append(logmsg, 2, " s=", s);
-  logmsg = string_append(logmsg, 7, 
-	" c=", sig->canon_headers == PDKIM_CANON_SIMPLE ? "simple" : "relaxed",
-	"/",   sig->canon_body    == PDKIM_CANON_SIMPLE ? "simple" : "relaxed",
-	" a=", dkim_sig_to_a_tag(sig),
-	string_sprintf(" b=" SIZE_T_FMT,
-			(int)sig->sighash.len > -1 ? sig->sighash.len * 8 : 0));
-  if ((s= sig->identity)) logmsg = string_append(logmsg, 2, " i=", s);
-  if (sig->created > 0) logmsg = string_cat(logmsg,
-				      string_sprintf(" t=%lu", sig->created));
-  if (sig->expires > 0) logmsg = string_cat(logmsg,
-				      string_sprintf(" x=%lu", sig->expires));
-  if (sig->bodylength > -1) logmsg = string_cat(logmsg,
-				      string_sprintf(" l=%lu", sig->bodylength));
-
+gstring * logmsg = string_catn(NULL, "DKIM: ", 6);
+uschar * s;
+
+if (!(s = sig->domain)) s = US"<UNSET>";
+logmsg = string_append(logmsg, 2, "d=", s);
+if (!(s = sig->selector)) s = US"<UNSET>";
+logmsg = string_append(logmsg, 2, " s=", s);
+logmsg = string_append(logmsg, 7, 
+" c=", sig->canon_headers == PDKIM_CANON_SIMPLE ? "simple" : "relaxed",
+"/",   sig->canon_body    == PDKIM_CANON_SIMPLE ? "simple" : "relaxed",
+" a=", dkim_sig_to_a_tag(sig),
+string_sprintf(" b=" SIZE_T_FMT,
+		(int)sig->sighash.len > -1 ? sig->sighash.len * 8 : 0));
+if ((s= sig->identity)) logmsg = string_append(logmsg, 2, " i=", s);
+if (sig->created > 0) logmsg = string_cat(logmsg,
+			      string_sprintf(" t=%lu", sig->created));
+if (sig->expires > 0) logmsg = string_cat(logmsg,
+			      string_sprintf(" x=%lu", sig->expires));
+if (sig->bodylength > -1) logmsg = string_cat(logmsg,
+			      string_sprintf(" l=%lu", sig->bodylength));
+
+if (  !dkim_verify_status
+   || (  dkim_verify_status == dkim_exim_expand_query(DKIM_VERIFY_STATUS)
+      && dkim_verify_reason == dkim_exim_expand_query(DKIM_VERIFY_REASON)
+   )  )
   switch (sig->verify_status)
     {
     case PDKIM_VERIFY_NONE:
@@ -207,7 +175,7 @@ for (sig = dkim_signatures; sig; sig = sig->next)
 	{
 	case PDKIM_VERIFY_INVALID_PUBKEY_UNAVAILABLE:
 	  logmsg = string_cat(logmsg,
-		        "public key record (currently?) unavailable]");
+			"public key record (currently?) unavailable]");
 	  break;
 
 	case PDKIM_VERIFY_INVALID_BUFFER_SIZE:
@@ -219,13 +187,13 @@ for (sig = dkim_signatures; sig; sig = sig->next)
 	  logmsg = string_cat(logmsg, "syntax error in public key record]");
 	  break;
 
-        case PDKIM_VERIFY_INVALID_SIGNATURE_ERROR:
-          logmsg = string_cat(logmsg, "signature tag missing or invalid]");
-          break;
+	case PDKIM_VERIFY_INVALID_SIGNATURE_ERROR:
+	  logmsg = string_cat(logmsg, "signature tag missing or invalid]");
+	  break;
 
-        case PDKIM_VERIFY_INVALID_DKIM_VERSION:
-          logmsg = string_cat(logmsg, "unsupported DKIM version]");
-          break;
+	case PDKIM_VERIFY_INVALID_DKIM_VERSION:
+	  logmsg = string_cat(logmsg, "unsupported DKIM version]");
+	  break;
 
 	default:
 	  logmsg = string_cat(logmsg, "unspecified problem]");
@@ -233,8 +201,7 @@ for (sig = dkim_signatures; sig; sig = sig->next)
       break;
 
     case PDKIM_VERIFY_FAIL:
-      logmsg =
-	string_cat(logmsg, " [verification failed - ");
+      logmsg = string_cat(logmsg, " [verification failed - ");
       switch (sig->verify_ext_status)
 	{
 	case PDKIM_VERIFY_FAIL_BODY:
@@ -256,18 +223,74 @@ for (sig = dkim_signatures; sig; sig = sig->next)
       logmsg = string_cat(logmsg, " [verification succeeded]");
       break;
     }
+else
+  logmsg = string_append(logmsg, 5,
+	    US" [", dkim_verify_status, US" - ", dkim_verify_reason, US"]");
+
+log_write(0, LOG_MAIN, string_from_gstring(logmsg));
+return;
+}
+
+
+/* Log a line for "the current" signature */
+void
+dkim_exim_verify_log_item(void)
+{
+dkim_exim_verify_log_sig(dkim_cur_sig);
+}
+
+
+/* Log a line for each signature */
+void
+dkim_exim_verify_log_all(void)
+{
+pdkim_signature * sig;
+for (sig = dkim_signatures; sig; sig = sig->next) dkim_exim_verify_log_sig(sig);
+}
 
-  log_write(0, LOG_MAIN, "DKIM: %s", string_from_gstring(logmsg));
 
-  /* Build a colon-separated list of signing domains (and identities, if present) in dkim_signers */
+void
+dkim_exim_verify_finish(void)
+{
+pdkim_signature * sig;
+int rc;
+gstring * g = NULL;
+const uschar * errstr;
 
-  if (sig->domain)
-    g = string_append_listele(g, ':', sig->domain);
+store_pool = POOL_PERM;
 
-  if (sig->identity)
-    g = string_append_listele(g, ':', sig->identity);
+/* Delete eventual previous signature chain */
 
-  /* Process next signature */
+dkim_signers = NULL;
+dkim_signatures = NULL;
+
+if (dkim_collect_error)
+  {
+  log_write(0, LOG_MAIN,
+      "DKIM: Error during validation, disabling signature verification: %.100s",
+      dkim_collect_error);
+  dkim_disable_verify = TRUE;
+  goto out;
+  }
+
+dkim_collect_input = FALSE;
+
+/* Finish DKIM operation and fetch link to signatures chain */
+
+rc = pdkim_feed_finish(dkim_verify_ctx, &dkim_signatures, &errstr);
+if (rc != PDKIM_OK)
+  {
+  log_write(0, LOG_MAIN, "DKIM: validation error: %.100s%s%s", pdkim_errstr(rc),
+	    errstr ? ": " : "", errstr ? errstr : US"");
+  goto out;
+  }
+
+/* Build a colon-separated list of signing domains (and identities, if present) in dkim_signers */
+
+for (sig = dkim_signatures; sig; sig = sig->next)
+  {
+  if (sig->domain)   g = string_append_listele(g, ':', sig->domain);
+  if (sig->identity) g = string_append_listele(g, ':', sig->identity);
   }
 
 if (g) dkim_signers = g->s;
@@ -309,6 +332,12 @@ for (sig = dkim_signatures; sig; sig = sig->next)
     dkim_signing_domain = US sig->domain;
     dkim_signing_selector = US sig->selector;
     dkim_key_length = sig->sighash.len * 8;
+
+    /* These two return static strings, so we can compare the addr
+    later to see if the ACL overwrote them.  Check that when logging */
+
+    dkim_verify_status = dkim_exim_expand_query(DKIM_VERIFY_STATUS);
+    dkim_verify_reason = dkim_exim_expand_query(DKIM_VERIFY_REASON);
     return;
     }
 }
@@ -365,12 +394,12 @@ switch (what)
       }
 
   case DKIM_CANON_HEADERS:
-  switch (dkim_cur_sig->canon_headers)
-    {
-    case PDKIM_CANON_RELAXED:	return US"relaxed";
-    case PDKIM_CANON_SIMPLE:
-    default:			return US"simple";
-    }
+    switch (dkim_cur_sig->canon_headers)
+      {
+      case PDKIM_CANON_RELAXED:	return US"relaxed";
+      case PDKIM_CANON_SIMPLE:
+      default:			return US"simple";
+      }
 
   case DKIM_COPIEDHEADERS:
     return dkim_cur_sig->copiedheaders
diff --git a/src/src/dkim.h b/src/src/dkim.h
index 735a1162a..f32aa6635 100644
--- a/src/src/dkim.h
+++ b/src/src/dkim.h
@@ -10,6 +10,8 @@ gstring * dkim_exim_sign(int, off_t, uschar *, struct ob_dkim *, const uschar **
 void    dkim_exim_verify_init(BOOL);
 void    dkim_exim_verify_feed(uschar *, int);
 void    dkim_exim_verify_finish(void);
+void    dkim_exim_verify_log_item(void);
+void    dkim_exim_verify_log_all(void);
 void    dkim_exim_acl_setup(uschar *);
 uschar *dkim_exim_expand_query(int);
 
diff --git a/src/src/expand.c b/src/src/expand.c
index 782467ff7..f44ddf8b8 100644
--- a/src/src/expand.c
+++ b/src/src/expand.c
@@ -508,8 +508,8 @@ static var_entry var_table[] = {
   { "dkim_key_testing",    vtype_dkim,        (void *)DKIM_KEY_TESTING },
   { "dkim_selector",       vtype_stringptr,   &dkim_signing_selector },
   { "dkim_signers",        vtype_stringptr,   &dkim_signers },
-  { "dkim_verify_reason",  vtype_dkim,        (void *)DKIM_VERIFY_REASON },
-  { "dkim_verify_status",  vtype_dkim,        (void *)DKIM_VERIFY_STATUS},
+  { "dkim_verify_reason",  vtype_stringptr,   &dkim_verify_reason },
+  { "dkim_verify_status",  vtype_stringptr,   &dkim_verify_status },
 #endif
 #ifdef EXPERIMENTAL_DMARC
   { "dmarc_ar_header",     vtype_stringptr,   &dmarc_ar_header },
diff --git a/src/src/globals.c b/src/src/globals.c
index 2a53835e9..5df84bd10 100644
--- a/src/src/globals.c
+++ b/src/src/globals.c
@@ -668,6 +668,8 @@ uschar *dkim_signers             = NULL;
 uschar *dkim_signing_domain      = NULL;
 uschar *dkim_signing_selector    = NULL;
 uschar *dkim_verify_signers      = US"$dkim_signers";
+uschar *dkim_verify_status	 = NULL;
+uschar *dkim_verify_reason	 = NULL;
 #endif
 #ifdef EXPERIMENTAL_DMARC
 BOOL    dmarc_has_been_checked  = FALSE;
diff --git a/src/src/globals.h b/src/src/globals.h
index 62336c275..37d4cada3 100644
--- a/src/src/globals.h
+++ b/src/src/globals.h
@@ -393,6 +393,8 @@ extern uschar *dkim_signers;           /* Expansion variable, holds colon-separa
 extern uschar *dkim_signing_domain;    /* Expansion variable, domain used for signing a message. */
 extern uschar *dkim_signing_selector;  /* Expansion variable, selector used for signing a message. */
 extern uschar *dkim_verify_signers;    /* Colon-separated list of domains for each of which we call the DKIM ACL */
+extern uschar *dkim_verify_status;     /* result for this signature */
+extern uschar *dkim_verify_reason;     /* result for this signature */
 #endif
 #ifdef EXPERIMENTAL_DMARC
 extern BOOL    dmarc_has_been_checked; /* Global variable to check if test has been called yet */
diff --git a/src/src/receive.c b/src/src/receive.c
index 31402925d..f181f1a51 100644
--- a/src/src/receive.c
+++ b/src/src/receive.c
@@ -3405,8 +3405,8 @@ else
         else
           {
           int sep = 0;
-          const uschar *ptr = dkim_verify_signers_expanded;
-          uschar *item = NULL;
+          const uschar * ptr = dkim_verify_signers_expanded;
+          uschar * item = NULL;
           gstring * seen_items = NULL;
 
           /* Default to OK when no items are present */
@@ -3452,6 +3452,7 @@ else
             dkim_exim_acl_setup(item);
             rc = acl_check(ACL_WHERE_DKIM, NULL, acl_smtp_dkim,
 		  &user_msg, &log_msg);
+	    dkim_exim_verify_log_item();
 
             if (rc != OK)
 	      {
@@ -3467,7 +3468,7 @@ else
             {
             recipients_count = 0;
             blackholed_by = US"DKIM ACL";
-            if (log_msg != NULL)
+            if (log_msg)
               blackhole_log_msg = string_sprintf(": %s", log_msg);
             }
           else if (rc != OK)
@@ -3481,6 +3482,8 @@ else
             }
           }
         }
+      else
+	dkim_exim_verify_log_all();
       }
 #endif /* DISABLE_DKIM */