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aff33962 | 1 | /* dnsmasq is Copyright (c) 2000-2015 Simon Kelley |
b5ea1cc2 SK |
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 |