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fa6ac2fc DC |
1 | /* |
2 | * icmpdnd - ICMP Domain Name responder daemon for Linux | |
b39da562 | 3 | * Copyright (C) 2005 Fredrik Tolf <fredrik@dolda2000.com> |
fa6ac2fc DC |
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> | |
b39da562 | 24 | #include <syslog.h> |
dcb0aee6 | 25 | #include <time.h> |
fa6ac2fc DC |
26 | #include <sys/socket.h> |
27 | #include <netinet/in.h> | |
28 | #include <arpa/inet.h> | |
29 | #include <netinet/ip.h> | |
30 | #include <sys/types.h> | |
31 | ||
32 | struct icmphdr { | |
33 | u_int8_t type; | |
34 | u_int8_t code; | |
35 | u_int16_t checksum; | |
36 | }; | |
37 | ||
38 | struct reqhdr { | |
39 | u_int8_t type; | |
40 | u_int8_t code; | |
41 | u_int16_t checksum; | |
42 | u_int16_t id; | |
43 | u_int16_t seq; | |
44 | }; | |
45 | ||
46 | struct rephdr { | |
47 | u_int8_t type; | |
48 | u_int8_t code; | |
49 | u_int16_t checksum; | |
50 | u_int16_t id; | |
51 | u_int16_t seq; | |
52 | int32_t ttl; | |
53 | }; | |
54 | ||
55 | #define ICMP_NAMEREQ 37 | |
56 | #define ICMP_NAMEREP 38 | |
57 | ||
fa6ac2fc DC |
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; | |
b39da562 DC |
134 | int c, s, namelen, datalen; |
135 | int daemonize, ttl; | |
fa6ac2fc DC |
136 | unsigned char buf[65536]; |
137 | struct sockaddr_in name; | |
138 | struct reqhdr req; | |
139 | struct rephdr rep; | |
140 | struct iphdr iphdr; | |
dcb0aee6 | 141 | time_t curtime, lasterr; |
b39da562 DC |
142 | |
143 | daemonize = 1; | |
144 | ttl = 3600; | |
145 | while((c = getopt(argc, argv, "nht:")) != -1) { | |
146 | switch(c) { | |
147 | case 't': | |
148 | ttl = atoi(optarg); | |
149 | break; | |
150 | case 'n': | |
151 | daemonize = 0; | |
152 | break; | |
153 | case 'h': | |
154 | case '?': | |
155 | case ':': | |
156 | default: | |
157 | fprintf(stderr, "usage: icmpdnd [-n]"); | |
158 | exit((c == 'h')?0:1); | |
159 | } | |
160 | } | |
161 | ||
fa6ac2fc DC |
162 | if((s = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0) { |
163 | perror("could not create raw socket"); | |
164 | exit(1); | |
165 | } | |
166 | ||
b39da562 DC |
167 | if(daemonize) |
168 | daemon(0, 0); | |
169 | ||
170 | openlog("icmpdnd", LOG_PID, LOG_DAEMON); | |
171 | ||
fa6ac2fc | 172 | alive = 1; |
dcb0aee6 | 173 | lasterr = 0; |
fa6ac2fc DC |
174 | while(alive) { |
175 | namelen = sizeof(name); | |
176 | ret = recvfrom(s, buf, sizeof(buf), 0, (struct sockaddr *)&name, &namelen); | |
dcb0aee6 DC |
177 | |
178 | curtime = time(NULL); | |
fa6ac2fc DC |
179 | if(ret < 0) { |
180 | if(errno == EINTR) | |
181 | continue; | |
b39da562 | 182 | syslog(LOG_ERR, "error in receiving datagram: %m"); |
dcb0aee6 DC |
183 | if(lasterr == curtime) { |
184 | syslog(LOG_CRIT, "exiting due to repeated errors"); | |
185 | exit(1); | |
186 | } | |
187 | lasterr = curtime; | |
fa6ac2fc | 188 | } |
dcb0aee6 | 189 | |
b39da562 | 190 | if(ret < sizeof(iphdr) + sizeof(req)) |
fa6ac2fc DC |
191 | continue; |
192 | memcpy(&iphdr, buf, sizeof(iphdr)); | |
b39da562 | 193 | memcpy(&req, buf + sizeof(iphdr), sizeof(req)); |
fa6ac2fc DC |
194 | if(iphdr.protocol != IPPROTO_ICMP) |
195 | continue; | |
fa6ac2fc DC |
196 | if(req.type != ICMP_NAMEREQ) |
197 | continue; | |
198 | rep.type = ICMP_NAMEREP; | |
199 | rep.code = 0; | |
200 | rep.id = req.id; | |
201 | rep.seq = req.seq; | |
b39da562 | 202 | rep.ttl = htonl(ttl); |
fa6ac2fc DC |
203 | memcpy(buf, &rep, sizeof(rep)); |
204 | datalen = filldn(buf + sizeof(rep)); | |
b39da562 | 205 | |
fa6ac2fc | 206 | cksum(buf, datalen + sizeof(rep)); |
b39da562 DC |
207 | |
208 | /* XXX: The correct source address needs to be filled in from | |
209 | * the request's destination address. */ | |
fa6ac2fc | 210 | ret = sendto(s, buf, datalen + sizeof(rep), 0, (struct sockaddr *)&name, namelen); |
1ac6ec0c | 211 | if(ret < 0) |
b39da562 | 212 | syslog(LOG_WARNING, "error in sending reply: %m"); |
fa6ac2fc DC |
213 | } |
214 | ||
215 | close(s); | |
216 | return(0); | |
217 | } |