| 1 | /* |
| 2 | * icmpdnd - ICMP Domain Name responder daemon for Linux |
| 3 | * Copyright (C) 2005 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 <syslog.h> |
| 25 | #include <time.h> |
| 26 | #include <sys/socket.h> |
| 27 | #include <sys/poll.h> |
| 28 | #include <netinet/in.h> |
| 29 | #include <arpa/inet.h> |
| 30 | #include <netinet/ip.h> |
| 31 | #include <sys/types.h> |
| 32 | #ifdef HAVE_CONFIG_H |
| 33 | #include "config.h" |
| 34 | #endif |
| 35 | |
| 36 | struct icmphdr { |
| 37 | u_int8_t type; |
| 38 | u_int8_t code; |
| 39 | u_int16_t checksum; |
| 40 | }; |
| 41 | |
| 42 | struct reqhdr { |
| 43 | u_int8_t type; |
| 44 | u_int8_t code; |
| 45 | u_int16_t checksum; |
| 46 | u_int16_t id; |
| 47 | u_int16_t seq; |
| 48 | }; |
| 49 | |
| 50 | struct rephdr { |
| 51 | u_int8_t type; |
| 52 | u_int8_t code; |
| 53 | u_int16_t checksum; |
| 54 | u_int16_t id; |
| 55 | u_int16_t seq; |
| 56 | int32_t ttl; |
| 57 | }; |
| 58 | |
| 59 | #define ICMP_NAMEREQ 37 |
| 60 | #define ICMP_NAMEREP 38 |
| 61 | |
| 62 | volatile int alive; |
| 63 | |
| 64 | size_t filldn(char *dst) |
| 65 | { |
| 66 | char *p, *p2, *dp; |
| 67 | char namebuf[1024]; |
| 68 | int hl; |
| 69 | |
| 70 | if(gethostname(namebuf, sizeof(namebuf)) < 0) { |
| 71 | perror("gethostname"); |
| 72 | exit(1); |
| 73 | } |
| 74 | hl = strlen(namebuf); |
| 75 | namebuf[hl++] = '.'; |
| 76 | if(getdomainname(namebuf + hl, sizeof(namebuf) - hl) < 0) { |
| 77 | perror("getdomainname"); |
| 78 | exit(1); |
| 79 | } |
| 80 | if(strlen(namebuf + hl) != 0) { |
| 81 | hl = strlen(namebuf); |
| 82 | namebuf[hl++] = '.'; |
| 83 | } |
| 84 | namebuf[hl] = 0; |
| 85 | |
| 86 | p = namebuf; |
| 87 | dp = dst; |
| 88 | while((p2 = strchr(p, '.')) != NULL) { |
| 89 | *p2 = 0; |
| 90 | *(dp++) = p2 - p; |
| 91 | memcpy(dp, p, p2 - p); |
| 92 | dp += p2 - p; |
| 93 | p = p2 + 1; |
| 94 | } |
| 95 | *(dp++) = 0; |
| 96 | |
| 97 | return(dp - dst); |
| 98 | } |
| 99 | |
| 100 | void cksum(void *hdr, size_t len) |
| 101 | { |
| 102 | struct icmphdr *ih; |
| 103 | u_int8_t *cb; |
| 104 | int i; |
| 105 | int b1, b2; |
| 106 | |
| 107 | ih = (struct icmphdr *)hdr; |
| 108 | cb = (u_int8_t *)hdr; |
| 109 | ih->checksum = 0; |
| 110 | b1 = b2 = 0; |
| 111 | for(i = 0; i < (len & ~1); i += 2) { |
| 112 | b1 += cb[i]; |
| 113 | b2 += cb[i + 1]; |
| 114 | } |
| 115 | if(i & 1) |
| 116 | b1 += cb[len - 1]; |
| 117 | while(1) { |
| 118 | if(b1 >= 256) { |
| 119 | b2 += b1 >> 8; |
| 120 | b1 &= 0xff; |
| 121 | continue; |
| 122 | } |
| 123 | if(b2 >= 256) { |
| 124 | b1 += b2 >> 8; |
| 125 | b2 &= 0xff; |
| 126 | continue; |
| 127 | } |
| 128 | break; |
| 129 | } |
| 130 | cb = (u_int8_t *)&ih->checksum; |
| 131 | cb[0] = ~(u_int8_t)b1; |
| 132 | cb[1] = ~(u_int8_t)b2; |
| 133 | } |
| 134 | |
| 135 | int main(int argc, char **argv) |
| 136 | { |
| 137 | int i, n, ret; |
| 138 | int c, cs, s4, s6, datalen; |
| 139 | int daemonize, ttl; |
| 140 | unsigned char buf[65536]; |
| 141 | struct sockaddr_storage name; |
| 142 | struct reqhdr req; |
| 143 | struct rephdr rep; |
| 144 | struct iphdr iphdr; |
| 145 | struct msghdr mhdr; |
| 146 | struct iovec iov; |
| 147 | char cmsgbuf[CMSG_SPACE(sizeof(struct in6_pktinfo))]; |
| 148 | size_t hdrlen; |
| 149 | struct pollfd pfd[2]; |
| 150 | time_t curtime, lasterr; |
| 151 | |
| 152 | daemonize = 1; |
| 153 | ttl = 3600; |
| 154 | while((c = getopt(argc, argv, "nht:")) != -1) { |
| 155 | switch(c) { |
| 156 | case 't': |
| 157 | ttl = atoi(optarg); |
| 158 | break; |
| 159 | case 'n': |
| 160 | daemonize = 0; |
| 161 | break; |
| 162 | case 'h': |
| 163 | case '?': |
| 164 | case ':': |
| 165 | default: |
| 166 | fprintf(stderr, "usage: icmpdnd [-n]"); |
| 167 | exit((c == 'h')?0:1); |
| 168 | } |
| 169 | } |
| 170 | |
| 171 | s4 = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP); |
| 172 | s6 = socket(PF_INET6, SOCK_RAW, IPPROTO_ICMP); |
| 173 | if((s4 < 0) && (s6 < 0)) { |
| 174 | perror("could not open raw socket"); |
| 175 | exit(1); |
| 176 | } |
| 177 | if(s6 >= 0) { |
| 178 | i = 1; |
| 179 | if(setsockopt(s6, IPPROTO_IPV6, IPV6_PKTINFO, &i, sizeof(i))) { |
| 180 | perror("could not set IPV6_PKTINFO sockopt"); |
| 181 | exit(1); |
| 182 | } |
| 183 | } |
| 184 | |
| 185 | if(daemonize) |
| 186 | daemon(0, 0); |
| 187 | |
| 188 | openlog("icmpdnd", LOG_PID | LOG_NDELAY, LOG_DAEMON); |
| 189 | |
| 190 | alive = 1; |
| 191 | lasterr = 0; |
| 192 | while(alive) { |
| 193 | n = 0; |
| 194 | if(s4 >= 0) { |
| 195 | pfd[n].fd = s4; |
| 196 | pfd[n].events = POLLIN; |
| 197 | n++; |
| 198 | } |
| 199 | if(s6 >= 0) { |
| 200 | pfd[n].fd = s6; |
| 201 | pfd[n].events = POLLIN; |
| 202 | n++; |
| 203 | } |
| 204 | ret = poll(pfd, n, -1); |
| 205 | |
| 206 | curtime = time(NULL); |
| 207 | if(ret < 0) { |
| 208 | if(errno == EINTR) |
| 209 | continue; |
| 210 | syslog(LOG_ERR, "error while polling sockets: %m"); |
| 211 | if(lasterr == curtime) { |
| 212 | syslog(LOG_CRIT, "exiting due to repeated errors"); |
| 213 | exit(1); |
| 214 | } |
| 215 | lasterr = curtime; |
| 216 | } |
| 217 | |
| 218 | for(i = 0; i < n; i++) { |
| 219 | if((pfd[i].revents & POLLIN) == 0) |
| 220 | continue; |
| 221 | cs = pfd[i].fd; |
| 222 | memset(&name, 0, sizeof(name)); |
| 223 | |
| 224 | iov.iov_len = sizeof(buf); |
| 225 | iov.iov_base = buf; |
| 226 | mhdr.msg_name = &name; |
| 227 | mhdr.msg_namelen = sizeof(name); |
| 228 | mhdr.msg_iov = &iov; |
| 229 | mhdr.msg_iovlen = 1; |
| 230 | mhdr.msg_control = cmsgbuf; |
| 231 | mhdr.msg_controllen = sizeof(cmsgbuf); |
| 232 | |
| 233 | ret = recvmsg(cs, &mhdr, 0); |
| 234 | if(ret < 0) { |
| 235 | syslog(LOG_WARNING, "error while receiving datagram: %m"); |
| 236 | continue; |
| 237 | } |
| 238 | |
| 239 | if(cs == s4) { |
| 240 | if(ret < sizeof(iphdr) + sizeof(req)) |
| 241 | continue; |
| 242 | hdrlen = sizeof(iphdr); |
| 243 | memcpy(&iphdr, buf, sizeof(iphdr)); |
| 244 | if(iphdr.protocol != IPPROTO_ICMP) |
| 245 | continue; |
| 246 | mhdr.msg_control = NULL; |
| 247 | mhdr.msg_controllen = 0; |
| 248 | } else if(cs == s6) { |
| 249 | if(ret < sizeof(req)) |
| 250 | continue; |
| 251 | ((struct sockaddr_in6 *)&name)->sin6_port = 0; |
| 252 | hdrlen = 0; |
| 253 | /* Just keep mhdr.msg_control. */ |
| 254 | } else { |
| 255 | syslog(LOG_CRIT, "strangeness!"); |
| 256 | abort(); |
| 257 | } |
| 258 | memcpy(&req, buf + hdrlen, sizeof(req)); |
| 259 | if(req.type != ICMP_NAMEREQ) |
| 260 | continue; |
| 261 | rep.type = ICMP_NAMEREP; |
| 262 | rep.code = 0; |
| 263 | rep.id = req.id; |
| 264 | rep.seq = req.seq; |
| 265 | rep.ttl = htonl(ttl); |
| 266 | memcpy(buf, &rep, sizeof(rep)); |
| 267 | datalen = filldn(buf + sizeof(rep)); |
| 268 | |
| 269 | cksum(buf, datalen + sizeof(rep)); |
| 270 | |
| 271 | iov.iov_len = sizeof(rep) + datalen; |
| 272 | iov.iov_base = buf; |
| 273 | mhdr.msg_iov = &iov; |
| 274 | mhdr.msg_iovlen = 1; |
| 275 | ret = sendmsg(cs, &mhdr, 0); |
| 276 | if(ret < 0) |
| 277 | syslog(LOG_WARNING, "error in sending reply: %m"); |
| 278 | } |
| 279 | } |
| 280 | |
| 281 | close(s4); |
| 282 | close(s6); |
| 283 | return(0); |
| 284 | } |
| 285 | |
| 286 | /* |
| 287 | * Local Variables: |
| 288 | * compile-command: "gcc -Wall -g -o icmpdnd icmpdnd.c" |
| 289 | * End: |
| 290 | */ |