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1 | /* |
2 | libloc - A library to determine the location of someone on the Internet | |
3 | ||
4 | Copyright (C) 2019 IPFire Development Team <info@ipfire.org> | |
5 | ||
6 | This library is free software; you can redistribute it and/or | |
7 | modify it under the terms of the GNU Lesser General Public | |
8 | License as published by the Free Software Foundation; either | |
9 | version 2.1 of the License, or (at your option) any later version. | |
10 | ||
11 | This library is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
14 | Lesser General Public License for more details. | |
15 | */ | |
16 | ||
f7b7019a MT |
17 | #include <arpa/nameser.h> |
18 | #include <arpa/nameser_compat.h> | |
f4fef543 MT |
19 | #include <resolv.h> |
20 | #include <string.h> | |
21 | #include <time.h> | |
22 | ||
23 | #include <loc/format.h> | |
24 | #include <loc/private.h> | |
25 | #include <loc/resolv.h> | |
26 | ||
27 | static int parse_timestamp(const unsigned char* txt, time_t* t) { | |
28 | struct tm ts; | |
29 | ||
30 | // Parse timestamp | |
31 | char* p = strptime((const char*)txt, "%a, %d %b %Y %H:%M:%S GMT", &ts); | |
32 | ||
33 | // If the whole string has been parsed, we convert the parse value to time_t | |
34 | if (p && !*p) { | |
35 | *t = mktime(&ts); | |
36 | ||
37 | // Otherwise we reset t | |
38 | } else { | |
39 | *t = 0; | |
40 | return -1; | |
41 | } | |
42 | ||
43 | return 0; | |
44 | } | |
45 | ||
46 | LOC_EXPORT int loc_discover_latest_version(struct loc_ctx* ctx, const char* domain, time_t* t) { | |
47 | // Initialise the resolver | |
48 | int r = res_init(); | |
49 | if (r) { | |
50 | ERROR(ctx, "res_init() failed\n"); | |
51 | return r; | |
52 | } | |
53 | ||
54 | // Fall back to default domain | |
55 | if (!domain) | |
56 | domain = LOC_DATABASE_DOMAIN_LATEST(LOC_DATABASE_VERSION); | |
57 | ||
58 | unsigned char answer[PACKETSZ]; | |
59 | int len; | |
60 | ||
61 | DEBUG(ctx, "Querying %s\n", domain); | |
62 | ||
63 | // Send a query | |
64 | if ((len = res_query(domain, C_IN, T_TXT, answer, sizeof(answer))) < 0 || len > PACKETSZ) { | |
65 | ERROR(ctx, "Could not query %s: \n", domain); | |
66 | ||
67 | return -1; | |
68 | } | |
69 | ||
70 | unsigned char* end = answer + len; | |
71 | unsigned char* payload = answer + sizeof(HEADER); | |
72 | ||
73 | // Expand domain name | |
74 | char host[128]; | |
75 | if ((len = dn_expand(answer, end, payload, host, sizeof(host))) < 0) { | |
76 | ERROR(ctx, "dn_expand() failed\n"); | |
77 | return -1; | |
78 | } | |
79 | ||
80 | // Payload starts after hostname | |
81 | payload += len; | |
82 | ||
83 | if (payload > end - 4) { | |
84 | ERROR(ctx, "DNS reply too short\n"); | |
85 | return -1; | |
86 | } | |
87 | ||
88 | int type; | |
89 | GETSHORT(type, payload); | |
90 | if (type != T_TXT) { | |
91 | ERROR(ctx, "DNS reply of unexpected type: %d\n", type); | |
92 | return -1; | |
93 | } | |
94 | ||
95 | // Skip class | |
96 | payload += INT16SZ; | |
97 | ||
98 | // Walk through CNAMEs | |
99 | unsigned int size = 0; | |
100 | int ttl; | |
101 | do { | |
102 | payload += size; | |
103 | ||
104 | if ((len = dn_expand(answer, end, payload, host, sizeof(host))) < 0) { | |
105 | ERROR(ctx, "dn_expand() failed\n"); | |
106 | return -1; | |
107 | } | |
108 | ||
109 | payload += len; | |
110 | ||
111 | if (payload > end - 10) { | |
112 | ERROR(ctx, "DNS reply too short\n"); | |
113 | return -1; | |
114 | } | |
115 | ||
116 | // Skip type, class, ttl | |
117 | GETSHORT(type, payload); | |
118 | payload += INT16SZ; | |
119 | GETLONG(ttl, payload); | |
120 | ||
121 | // Read size | |
122 | GETSHORT(size, payload); | |
123 | if (payload + size < answer || payload + size > end) { | |
124 | ERROR(ctx, "DNS RR overflow\n"); | |
125 | return -1; | |
126 | } | |
127 | } while (type == T_CNAME); | |
128 | ||
129 | if (type != T_TXT) { | |
130 | ERROR(ctx, "Not a TXT record\n"); | |
131 | return -1; | |
132 | } | |
133 | ||
134 | if (!size || (len = *payload) >= size || !len) { | |
135 | ERROR(ctx, "Broken TXT record (len = %d, size = %d)\n", len, size); | |
136 | return -1; | |
137 | } | |
138 | ||
139 | // Get start of the string | |
140 | unsigned char* txt = payload + 1; | |
141 | txt[len] = '\0'; | |
142 | ||
143 | DEBUG(ctx, "Resolved to: %s\n", txt); | |
144 | ||
145 | // Parse timestamp | |
146 | r = parse_timestamp(txt, t); | |
147 | ||
148 | return r; | |
149 | } |