| /* 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 |