src/loop.c

   1 /* dnsmasq is Copyright (c) 2000-2014 Simon Kelley
   2
   3    This program is free software; you can redistribute it and/or modify
   4    it under the terms of the GNU General Public License as published by
   5    the Free Software Foundation; version 2 dated June, 1991, or
   6    (at your option) version 3 dated 29 June, 2007.
   7
   8    This program is distributed in the hope that it will be useful,
   9    but WITHOUT ANY WARRANTY; without even the implied warranty of
  10    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11    GNU General Public License for more details.
  12
  13    You should have received a copy of the GNU General Public License
  14    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  15 */
  16
  17 #include "dnsmasq.h"
  18
  19 #ifdef HAVE_LOOP
  20 static ssize_t loop_make_probe(u32 uid);
  21
  22 void loop_send_probes()
  23 {
  24    struct server *serv;
  25
  26    if (!option_bool(OPT_LOOP_DETECT))
  27      return;
  28
  29    /* Loop through all upstream servers not for particular domains, and send a query to that server which is
  30       identifiable, via the uid. If we see that query back again, then the server is looping, and we should not use it. */
  31    for (serv = daemon->servers; serv; serv = serv->next)
  32      if (!(serv->flags &
  33            (SERV_LITERAL_ADDRESS | SERV_NO_ADDR | SERV_USE_RESOLV | SERV_NO_REBIND | SERV_HAS_DOMAIN | SERV_FOR_NODOTS | SERV_LOOP)))
  34        {
  35          ssize_t len = loop_make_probe(serv->uid);
  36          int fd;
  37          struct randfd *rfd = NULL;
  38
  39          if (serv->sfd)
  40            fd = serv->sfd->fd;
  41          else
  42            {
  43              if (!(rfd = allocate_rfd(serv->addr.sa.sa_family)))
  44                continue;
  45              fd = rfd->fd;
  46            }
  47
  48          while (sendto(fd, daemon->packet, len, 0, &serv->addr.sa, sa_len(&serv->addr)) == -1 && retry_send());
  49
  50          free_rfd(rfd);
  51        }
  52 }
  53
  54 static ssize_t loop_make_probe(u32 uid)
  55 {
  56   struct dns_header *header = (struct dns_header *)daemon->packet;
  57   unsigned char *p = (unsigned char *)(header+1);
  58
  59   /* packet buffer overwritten */
  60   daemon->srv_save = NULL;
  61
  62   header->id = rand16();
  63   header->ancount = header->nscount = header->arcount = htons(0);
  64   header->qdcount = htons(1);
  65   header->hb3 = HB3_RD;
  66   header->hb4 = 0;
  67   SET_OPCODE(header, QUERY);
  68
  69   *p++ = 8;
  70   sprintf((char *)p, "%.8x", uid);
  71   p += 8;
  72   *p++ = strlen(LOOP_TEST_DOMAIN);
  73   strcpy((char *)p, LOOP_TEST_DOMAIN); /* Add terminating zero */
  74   p += strlen(LOOP_TEST_DOMAIN) + 1;
  75
  76   PUTSHORT(LOOP_TEST_TYPE, p);
  77   PUTSHORT(C_IN, p);
  78
  79   return p - (unsigned char *)header;
  80 }
  81
  82
  83 int detect_loop(char *query, int type)
  84 {
  85   int i;
  86   u32 uid;
  87   struct server *serv;
  88
  89   if (!option_bool(OPT_LOOP_DETECT))
  90     return 0;
  91
  92   if (type != LOOP_TEST_TYPE ||
  93       strlen(LOOP_TEST_DOMAIN) + 9 != strlen(query) ||
  94       strstr(query, LOOP_TEST_DOMAIN) != query + 9)
  95     return 0;
  96
  97   for (i = 0; i < 8; i++)
  98     if (!isxdigit(query[i]))
  99       return 0;
 100
 101   uid = strtol(query, NULL, 16);
 102
 103   for (serv = daemon->servers; serv; serv = serv->next)
 104      if (!(serv->flags &
 105            (SERV_LITERAL_ADDRESS | SERV_NO_ADDR | SERV_USE_RESOLV | SERV_NO_REBIND | SERV_HAS_DOMAIN | SERV_FOR_NODOTS | SERV_LOOP)) &&
 106          uid == serv->uid)
 107        {
 108          serv->flags |= SERV_LOOP;
 109          check_servers(); /* log new state */
 110          return 1;
 111        }
 112
 113   return 0;
 114 }
 115
 116 #endif