Add --dns-loop-detect feature.

2025-12-20 02:38:32 +00:00 · 2014-07-29 16:34:14 +01:00
parent 6d8e8ac0fa
commit b5ea1cc255
12 changed files with 233 additions and 18 deletions
--- a/src/loop.c
+++ b/src/loop.c
@@ -0,0 +1,116 @@
+/* dnsmasq is Copyright (c) 2000-2014 Simon Kelley
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 dated June, 1991, or
+   (at your option) version 3 dated 29 June, 2007.
+ 
+   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.
+     
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "dnsmasq.h"
+
+#ifdef HAVE_LOOP
+static ssize_t loop_make_probe(u32 uid);
+
+void loop_send_probes()
+{
+   struct server *serv;
+   
+   if (!option_bool(OPT_LOOP_DETECT))
+     return;
+
+   /* Loop through all upstream servers not for particular domains, and send a query to that server which is
+      identifiable, via the uid. If we see that query back again, then the server is looping, and we should not use it. */
+   for (serv = daemon->servers; serv; serv = serv->next)
+     if (!(serv->flags & 
+	   (SERV_LITERAL_ADDRESS | SERV_NO_ADDR | SERV_USE_RESOLV | SERV_NO_REBIND | SERV_HAS_DOMAIN | SERV_FOR_NODOTS | SERV_LOOP)))
+       {
+	 ssize_t len = loop_make_probe(serv->uid);
+	 int fd;
+	 struct randfd *rfd = NULL;
+	 
+	 if (serv->sfd)
+	   fd = serv->sfd->fd;
+	 else 
+	   {
+	     if (!(rfd = allocate_rfd(serv->addr.sa.sa_family)))
+	       continue;
+	     fd = rfd->fd;
+	   }
+
+	 while (sendto(fd, daemon->packet, len, 0, &serv->addr.sa, sa_len(&serv->addr)) == -1 && retry_send());
+
+	 free_rfd(rfd);
+       }
+}
+  
+static ssize_t loop_make_probe(u32 uid)
+{
+  struct dns_header *header = (struct dns_header *)daemon->packet;
+  unsigned char *p = (unsigned char *)(header+1);
+
+  /* packet buffer overwritten */
+  daemon->srv_save = NULL;
+  
+  header->id = rand16();
+  header->ancount = header->nscount = header->arcount = htons(0);
+  header->qdcount = htons(1);
+  header->hb3 = HB3_RD;
+  header->hb4 = 0;
+  SET_OPCODE(header, QUERY);
+
+  *p++ = 8;
+  sprintf((char *)p, "%.8x", uid);
+  p += 8;
+  *p++ = strlen(LOOP_TEST_DOMAIN);
+  strcpy((char *)p, LOOP_TEST_DOMAIN); /* Add terminating zero */
+  p += strlen(LOOP_TEST_DOMAIN) + 1;
+
+  PUTSHORT(LOOP_TEST_TYPE, p);
+  PUTSHORT(C_IN, p);
+
+  return p - (unsigned char *)header;
+}
+  
+
+int detect_loop(char *query, int type)
+{
+  int i;
+  u32 uid;
+  struct server *serv;
+  
+  if (!option_bool(OPT_LOOP_DETECT))
+    return 0;
+
+  if (type != LOOP_TEST_TYPE ||
+      strlen(LOOP_TEST_DOMAIN) + 9 != strlen(query) ||
+      strstr(query, LOOP_TEST_DOMAIN) != query + 9)
+    return 0;
+
+  for (i = 0; i < 8; i++)
+    if (!isxdigit(query[i]))
+      return 0;
+
+  uid = strtol(query, NULL, 16);
+
+  for (serv = daemon->servers; serv; serv = serv->next)
+     if (!(serv->flags & 
+	   (SERV_LITERAL_ADDRESS | SERV_NO_ADDR | SERV_USE_RESOLV | SERV_NO_REBIND | SERV_HAS_DOMAIN | SERV_FOR_NODOTS | SERV_LOOP)) &&
+	 uid == serv->uid)
+       {
+	 serv->flags |= SERV_LOOP;
+	 check_servers(); /* log new state */
+	 return 1;
+       }
+
+  return 0;
+}
+
+#endif