Fix crash caused by looking up servers.bind when many servers defined.

CHANGELOG

@@ -75,7 +75,12 @@ version 2.73
 
 	    Add --tftp-no-fail option. Thanks to Stefan Tomanek for
 	    the patch.
-	
+
+	    Fix crash caused by looking up servers.bind, CHAOS text record,
+	    when more than about five --servers= lines are in the dnsmasq
+	    config. This causes memory corruption which causes a crash later.
+	    Thanks to Matt Coddington for sterling work chasing this down.
+
 	
 version 2.72
             Add ra-advrouter mode, for RFC-3775 mobile IPv6 support.

src/cache.c

@@ -1367,7 +1367,7 @@ int cache_make_stat(struct txt_record *t)
 		}
 	    port = prettyprint_addr(&serv->addr, daemon->addrbuff);
 	    lenp = p++; /* length */
-	    bytes_avail = (p - buff) + bufflen;
+	    bytes_avail = bufflen - (p - buff );
 	    bytes_needed = snprintf(p, bytes_avail, "%s#%d %u %u", daemon->addrbuff, port, queries, failed_queries);
 	    if (bytes_needed >= bytes_avail)
 	      {
@@ -1381,7 +1381,7 @@ int cache_make_stat(struct txt_record *t)
 		lenp = p - 1;
 		buff = new;
 		bufflen = newlen;
-		bytes_avail = (p - buff) + bufflen;
+		bytes_avail =  bufflen - (p - buff );
 		bytes_needed = snprintf(p, bytes_avail, "%s#%d %u %u", daemon->addrbuff, port, queries, failed_queries);
 	      }
 	    *lenp = bytes_needed;