diff options
Diffstat (limited to 'src/loop.c')
| -rw-r--r-- | src/loop.c | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/src/loop.c b/src/loop.c new file mode 100644 index 0000000..bb377ad --- /dev/null +++ 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 |