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fa6ac2fc DC |
1 | /* |
2 | * icmpdnd - ICMP Domain Name responder daemon for Linux | |
3 | * Copyright (C) 2004 Fredrik Tolf <fredrik@dolda2000.com> | |
4 | * | |
5 | * This program is free software; you can redistribute it and/or modify | |
6 | * it under the terms of the GNU General Public License as published by | |
7 | * the Free Software Foundation; either version 2 of the License, or | |
8 | * (at your option) any later version. | |
9 | * | |
10 | * This program is distributed in the hope that it will be useful, | |
11 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | * GNU General Public License for more details. | |
14 | * | |
15 | * You should have received a copy of the GNU General Public License | |
16 | * along with this program; if not, write to the Free Software | |
17 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
18 | */ | |
19 | #include <stdlib.h> | |
20 | #include <unistd.h> | |
21 | #include <stdio.h> | |
22 | #include <string.h> | |
23 | #include <errno.h> | |
24 | #include <sys/socket.h> | |
25 | #include <netinet/in.h> | |
26 | #include <arpa/inet.h> | |
27 | #include <netinet/ip.h> | |
28 | #include <sys/types.h> | |
29 | ||
30 | struct icmphdr { | |
31 | u_int8_t type; | |
32 | u_int8_t code; | |
33 | u_int16_t checksum; | |
34 | }; | |
35 | ||
36 | struct reqhdr { | |
37 | u_int8_t type; | |
38 | u_int8_t code; | |
39 | u_int16_t checksum; | |
40 | u_int16_t id; | |
41 | u_int16_t seq; | |
42 | }; | |
43 | ||
44 | struct rephdr { | |
45 | u_int8_t type; | |
46 | u_int8_t code; | |
47 | u_int16_t checksum; | |
48 | u_int16_t id; | |
49 | u_int16_t seq; | |
50 | int32_t ttl; | |
51 | }; | |
52 | ||
53 | #define ICMP_NAMEREQ 37 | |
54 | #define ICMP_NAMEREP 38 | |
55 | ||
56 | #define TTL 3600 | |
57 | ||
58 | volatile int alive; | |
59 | ||
60 | size_t filldn(char *dst) | |
61 | { | |
62 | char *p, *p2, *dp; | |
63 | char namebuf[1024]; | |
64 | int hl; | |
65 | ||
66 | if(gethostname(namebuf, sizeof(namebuf)) < 0) { | |
67 | perror("gethostname"); | |
68 | exit(1); | |
69 | } | |
70 | hl = strlen(namebuf); | |
71 | namebuf[hl++] = '.'; | |
72 | if(getdomainname(namebuf + hl, sizeof(namebuf) - hl) < 0) { | |
73 | perror("getdomainname"); | |
74 | exit(1); | |
75 | } | |
76 | if(strlen(namebuf + hl) != 0) { | |
77 | hl = strlen(namebuf); | |
78 | namebuf[hl++] = '.'; | |
79 | } | |
80 | namebuf[hl] = 0; | |
81 | ||
82 | p = namebuf; | |
83 | dp = dst; | |
84 | while((p2 = strchr(p, '.')) != NULL) { | |
85 | *p2 = 0; | |
86 | *(dp++) = p2 - p; | |
87 | memcpy(dp, p, p2 - p); | |
88 | dp += p2 - p; | |
89 | p = p2 + 1; | |
90 | } | |
91 | *(dp++) = 0; | |
92 | ||
93 | return(dp - dst); | |
94 | } | |
95 | ||
96 | void cksum(void *hdr, size_t len) | |
97 | { | |
98 | struct icmphdr *ih; | |
99 | u_int8_t *cb; | |
100 | int i; | |
101 | int b1, b2; | |
102 | ||
103 | ih = (struct icmphdr *)hdr; | |
104 | cb = (u_int8_t *)hdr; | |
105 | ih->checksum = 0; | |
106 | b1 = b2 = 0; | |
107 | for(i = 0; i < (len & ~1); i += 2) { | |
108 | b1 += cb[i]; | |
109 | b2 += cb[i + 1]; | |
110 | } | |
111 | if(i & 1) | |
112 | b1 += cb[len - 1]; | |
113 | while(1) { | |
114 | if(b1 >= 256) { | |
115 | b2 += b1 >> 8; | |
116 | b1 &= 0xff; | |
117 | continue; | |
118 | } | |
119 | if(b2 >= 256) { | |
120 | b1 += b2 >> 8; | |
121 | b2 &= 0xff; | |
122 | continue; | |
123 | } | |
124 | break; | |
125 | } | |
126 | cb = (u_int8_t *)&ih->checksum; | |
127 | cb[0] = ~(u_int8_t)b1; | |
128 | cb[1] = ~(u_int8_t)b2; | |
129 | } | |
130 | ||
131 | int main(int argc, char **argv) | |
132 | { | |
133 | int ret; | |
134 | int s, namelen, datalen; | |
135 | unsigned char buf[65536]; | |
136 | struct sockaddr_in name; | |
137 | struct reqhdr req; | |
138 | struct rephdr rep; | |
139 | struct iphdr iphdr; | |
140 | ||
141 | if((s = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0) { | |
142 | perror("could not create raw socket"); | |
143 | exit(1); | |
144 | } | |
145 | ||
146 | alive = 1; | |
147 | while(alive) { | |
148 | namelen = sizeof(name); | |
149 | ret = recvfrom(s, buf, sizeof(buf), 0, (struct sockaddr *)&name, &namelen); | |
150 | if(ret < 0) { | |
151 | if(errno == EINTR) | |
152 | continue; | |
153 | perror("recvfrom"); | |
154 | exit(1); | |
155 | } | |
156 | if(ret < sizeof(iphdr)) | |
157 | continue; | |
158 | memcpy(&iphdr, buf, sizeof(iphdr)); | |
159 | if(iphdr.protocol != IPPROTO_ICMP) | |
160 | continue; | |
161 | if(ret < sizeof(iphdr) + sizeof(req)) | |
162 | continue; | |
163 | memcpy(&req, buf + sizeof(iphdr), sizeof(req)); | |
164 | if(req.type != ICMP_NAMEREQ) | |
165 | continue; | |
166 | rep.type = ICMP_NAMEREP; | |
167 | rep.code = 0; | |
168 | rep.id = req.id; | |
169 | rep.seq = req.seq; | |
170 | rep.ttl = htonl(TTL); | |
171 | memcpy(buf, &rep, sizeof(rep)); | |
172 | datalen = filldn(buf + sizeof(rep)); | |
173 | ||
174 | cksum(buf, datalen + sizeof(rep)); | |
175 | ||
176 | ret = sendto(s, buf, datalen + sizeof(rep), 0, (struct sockaddr *)&name, namelen); | |
177 | if(ret < 0) { | |
178 | perror("sendto"); | |
179 | exit(1); | |
180 | } | |
181 | } | |
182 | ||
183 | close(s); | |
184 | return(0); | |
185 | } |