release/src/router/dnsmasq/src/loop.c

   1 /* dnsmasq is Copyright (c) 2000-2016 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 (retry_send(sendto(fd, daemon->packet, len, 0,
  49                                   &serv->addr.sa, sa_len(&serv->addr))));
  50
  51          free_rfd(rfd);
  52        }
  53 }
  54
  55 static ssize_t loop_make_probe(u32 uid)
  56 {
  57   struct dns_header *header = (struct dns_header *)daemon->packet;
  58   unsigned char *p = (unsigned char *)(header+1);
  59
  60   /* packet buffer overwritten */
  61   daemon->srv_save = NULL;
  62
  63   header->id = rand16();
  64   header->ancount = header->nscount = header->arcount = htons(0);
  65   header->qdcount = htons(1);
  66   header->hb3 = HB3_RD;
  67   header->hb4 = 0;
  68   SET_OPCODE(header, QUERY);
  69
  70   *p++ = 8;
  71   sprintf((char *)p, "%.8x", uid);
  72   p += 8;
  73   *p++ = strlen(LOOP_TEST_DOMAIN);
  74   strcpy((char *)p, LOOP_TEST_DOMAIN); /* Add terminating zero */
  75   p += strlen(LOOP_TEST_DOMAIN) + 1;
  76
  77   PUTSHORT(LOOP_TEST_TYPE, p);
  78   PUTSHORT(C_IN, p);
  79
  80   return p - (unsigned char *)header;
  81 }
  82
  83
  84 int detect_loop(char *query, int type)
  85 {
  86   int i;
  87   u32 uid;
  88   struct server *serv;
  89
  90   if (!option_bool(OPT_LOOP_DETECT))
  91     return 0;
  92
  93   if (type != LOOP_TEST_TYPE ||
  94       strlen(LOOP_TEST_DOMAIN) + 9 != strlen(query) ||
  95       strstr(query, LOOP_TEST_DOMAIN) != query + 9)
  96     return 0;
  97
  98   for (i = 0; i < 8; i++)
  99     if (!isxdigit(query[i]))
 100       return 0;
 101
 102   uid = strtol(query, NULL, 16);
 103
 104   for (serv = daemon->servers; serv; serv = serv->next)
 105      if (!(serv->flags &
 106            (SERV_LITERAL_ADDRESS | SERV_NO_ADDR | SERV_USE_RESOLV | SERV_NO_REBIND | SERV_HAS_DOMAIN | SERV_FOR_NODOTS | SERV_LOOP)) &&
 107          uid == serv->uid)
 108        {
 109          serv->flags |= SERV_LOOP;
 110          check_servers(); /* log new state */
 111          return 1;
 112        }
 113
 114   return 0;
 115 }
 116
 117 #endif