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Version 8.2p1

    1: /* dnsmasq is Copyright (c) 2000-2022 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:    struct randfd_list *rfds = NULL;
   26:    
   27:    if (!option_bool(OPT_LOOP_DETECT))
   28:      return;
   29: 
   30:    /* Loop through all upstream servers not for particular domains, and send a query to that server which is
   31:       identifiable, via the uid. If we see that query back again, then the server is looping, and we should not use it. */
   32:    for (serv = daemon->servers; serv; serv = serv->next)
   33:      if (strlen(serv->domain) == 0 &&
   34: 	 !(serv->flags & (SERV_FOR_NODOTS)))
   35:        {
   36: 	 ssize_t len = loop_make_probe(serv->uid);
   37: 	 int fd;
   38: 	 
   39: 	 serv->flags &= ~SERV_LOOP;
   40: 
   41: 	 if ((fd = allocate_rfd(&rfds, serv)) == -1)
   42: 	   continue;
   43: 	 
   44: 	 while (retry_send(sendto(fd, daemon->packet, len, 0, 
   45: 				  &serv->addr.sa, sa_len(&serv->addr))));
   46:        }
   47: 
   48:    free_rfds(&rfds);
   49: }
   50:   
   51: static ssize_t loop_make_probe(u32 uid)
   52: {
   53:   struct dns_header *header = (struct dns_header *)daemon->packet;
   54:   unsigned char *p = (unsigned char *)(header+1);
   55:   
   56:   /* packet buffer overwritten */
   57:   daemon->srv_save = NULL;
   58:   
   59:   header->id = rand16();
   60:   header->ancount = header->nscount = header->arcount = htons(0);
   61:   header->qdcount = htons(1);
   62:   header->hb3 = HB3_RD;
   63:   header->hb4 = 0;
   64:   SET_OPCODE(header, QUERY);
   65: 
   66:   *p++ = 8;
   67:   sprintf((char *)p, "%.8x", uid);
   68:   p += 8;
   69:   *p++ = strlen(LOOP_TEST_DOMAIN);
   70:   strcpy((char *)p, LOOP_TEST_DOMAIN); /* Add terminating zero */
   71:   p += strlen(LOOP_TEST_DOMAIN) + 1;
   72: 
   73:   PUTSHORT(LOOP_TEST_TYPE, p);
   74:   PUTSHORT(C_IN, p);
   75: 
   76:   return p - (unsigned char *)header;
   77: }
   78:   
   79: 
   80: int detect_loop(char *query, int type)
   81: {
   82:   int i;
   83:   u32 uid;
   84:   struct server *serv;
   85:   
   86:   if (!option_bool(OPT_LOOP_DETECT))
   87:     return 0;
   88: 
   89:   if (type != LOOP_TEST_TYPE ||
   90:       strlen(LOOP_TEST_DOMAIN) + 9 != strlen(query) ||
   91:       strstr(query, LOOP_TEST_DOMAIN) != query + 9)
   92:     return 0;
   93: 
   94:   for (i = 0; i < 8; i++)
   95:     if (!isxdigit((unsigned char)query[i]))
   96:       return 0;
   97: 
   98:   uid = strtol(query, NULL, 16);
   99: 
  100:   for (serv = daemon->servers; serv; serv = serv->next)
  101:     if (strlen(serv->domain) == 0 &&
  102: 	!(serv->flags & SERV_LOOP) &&
  103: 	uid == serv->uid)
  104:       {
  105: 	serv->flags |= SERV_LOOP;
  106: 	check_servers(1); /* log new state - don't send more probes. */
  107: 	return 1;
  108:       }
  109:   
  110:   return 0;
  111: }
  112: 
  113: #endif