Filter out zero-length MX records

[citadel.git] / citadel / domain.c

diff --git a/citadel/domain.c b/citadel/domain.c
index fda55e86e2f98d0dd0066d63412e96460b97cb7d..3c4f1455c375d03693a93b349db36b4bb32c9ec3 100644 (file)
--- a/citadel/domain.c
+++ b/citadel/domain.c
@@ -1,17 +1,20 @@
 /*
- * $Id$
- *
  * DNS lookup for SMTP sender
  *
+ * Copyright (c) 1987-2021 by the citadel.org team
+ *
+ * This program is open source software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
  */
 
 #include "sysdep.h"
-#include <stdlib.h>
-#include <unistd.h>
-#include <string.h>
-#include <netinet/in.h>
 #include <stdio.h>
-
+#include <syslog.h>
 #ifdef HAVE_RESOLV_H
 #include <arpa/nameser.h>
 #ifdef HAVE_ARPA_NAMESER_COMPAT_H
@@ -23,7 +26,6 @@
 #include "sysdep_decls.h"
 #include "citadel.h"
 #include "domain.h"
-#include "server.h"
 #include "internet_addressing.h"
 
 
@@ -113,21 +115,21 @@ int getmx(char *mxbuf, char *dest) {
 
        struct mx *mxrecs = NULL;
        int num_mxrecs = 0;
-       
+
        /* If we're configured to send all mail to a smart-host, then our
         * job here is really easy.
         */
        n = get_hosts(mxbuf, "smarthost");
-       if (n > 0) return(n);
+       if (n > 0) {
+               return(n);
+       }
 
        /*
         * No smart-host?  Look up the best MX for a site.
         * Make a call to the resolver library.
         */
 
-       ret = res_query(
-               dest,
-               C_IN, T_MX, (unsigned char *)answer.bytes, sizeof(answer)  );
+       ret = res_query(dest, C_IN, T_MX, (unsigned char *)answer.bytes, sizeof(answer));
 
        if (ret < 0) {
                mxrecs = malloc(sizeof(struct mx));
@@ -136,30 +138,25 @@ int getmx(char *mxbuf, char *dest) {
                num_mxrecs = 1;
        }
        else {
-
                /* If we had to truncate, shrink the number to avoid fireworks */
-               if (ret > sizeof(answer))
+               if (ret > sizeof(answer)) {
                        ret = sizeof(answer);
+               }
        
-               startptr = &answer.bytes[0];            /* start and end of buffer */
+               startptr = &answer.bytes[0];            // start and end of buffer
                endptr = &answer.bytes[ret];
-               ptr = startptr + HFIXEDSZ;      /* advance past header */
+               ptr = startptr + HFIXEDSZ;              // advance past header
        
                for (qdcount = ntohs(answer.header.qdcount); qdcount--; ptr += ret + QFIXEDSZ) {
                        if ((ret = dn_skipname(ptr, endptr)) < 0) {
-                               lprintf(CTDL_DEBUG, "dn_skipname error\n");
+                               syslog(LOG_DEBUG, "domain: dn_skipname error");
                                return(0);
                        }
                }
        
                while(1) {
                        memset(expanded_buf, 0, sizeof(expanded_buf));
-                       ret = dn_expand(startptr,
-                                       endptr,
-                                       ptr,
-                                       expanded_buf,
-                                       sizeof(expanded_buf)
-                                       );
+                       ret = dn_expand(startptr, endptr, ptr, expanded_buf, sizeof(expanded_buf));
                        if (ret < 0) break;
                        ptr += ret;
        
@@ -173,26 +170,23 @@ int getmx(char *mxbuf, char *dest) {
        
                        else {
                                GETSHORT(pref, ptr);
-                               ret = dn_expand(startptr,
-                                               endptr,
-                                               ptr,
-                                               expanded_buf,
-                                               sizeof(expanded_buf)
-                                               );
+                               ret = dn_expand(startptr, endptr, ptr, expanded_buf, sizeof(expanded_buf));
                                ptr += ret;
        
-                               ++num_mxrecs;
-                               if (mxrecs == NULL) {
-                                       mxrecs = malloc(sizeof(struct mx));
-                               }
-                               else {
-                                       mxrecs = realloc(mxrecs,
-                                           (sizeof(struct mx) * num_mxrecs) );
-                               }
+                               // If there are no MX records for the domain, resolv will give us a single one with zero length.
+                               // Make sure we only record actual MX records and not the blank.
+                               if (strlen(expanded_buf) > 0) {
+                                       ++num_mxrecs;
+                                       if (mxrecs == NULL) {
+                                               mxrecs = malloc(sizeof(struct mx));
+                                       }
+                                       else {
+                                               mxrecs = realloc(mxrecs, (sizeof(struct mx) * num_mxrecs) );
+                                       }
        
-                               mxrecs[num_mxrecs - 1].pref = pref;
-                               strcpy(mxrecs[num_mxrecs - 1].host,
-                                      expanded_buf);
+                                       mxrecs[num_mxrecs - 1].pref = pref;
+                                       strcpy(mxrecs[num_mxrecs - 1].host, expanded_buf);
+                               }
                        }
                }
        }
@@ -208,5 +202,10 @@ int getmx(char *mxbuf, char *dest) {
                strcat(mxbuf, "|");
        }
        free(mxrecs);
+
+       /*
+        * Append any fallback smart hosts we have configured.
+        */
+       num_mxrecs += get_hosts(&mxbuf[strlen(mxbuf)], "fallbackhost");
        return(num_mxrecs);
 }