| 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 | |
| 33 | struct icmphdr { |
| 34 | u_int8_t type; |
| 35 | u_int8_t code; |
| 36 | u_int16_t checksum; |
| 37 | }; |
| 38 | |
| 39 | struct reqhdr { |
| 40 | u_int8_t type; |
| 41 | u_int8_t code; |
| 42 | u_int16_t checksum; |
| 43 | u_int16_t id; |
| 44 | u_int16_t seq; |
| 45 | }; |
| 46 | |
| 47 | struct rephdr { |
| 48 | u_int8_t type; |
| 49 | u_int8_t code; |
| 50 | u_int16_t checksum; |
| 51 | u_int16_t id; |
| 52 | u_int16_t seq; |
| 53 | int32_t ttl; |
| 54 | }; |
| 55 | |
| 56 | #define ICMP_NAMEREQ 37 |
| 57 | #define ICMP_NAMEREP 38 |
| 58 | |
| 59 | volatile int alive; |
| 60 | |
| 61 | size_t filldn(char *dst) |
| 62 | { |
| 63 | char *p, *p2, *dp; |
| 64 | char namebuf[1024]; |
| 65 | int hl; |
| 66 | |
| 67 | if(gethostname(namebuf, sizeof(namebuf)) < 0) { |
| 68 | perror("gethostname"); |
| 69 | exit(1); |
| 70 | } |
| 71 | hl = strlen(namebuf); |
| 72 | namebuf[hl++] = '.'; |
| 73 | if(getdomainname(namebuf + hl, sizeof(namebuf) - hl) < 0) { |
| 74 | perror("getdomainname"); |
| 75 | exit(1); |
| 76 | } |
| 77 | if(strlen(namebuf + hl) != 0) { |
| 78 | hl = strlen(namebuf); |
| 79 | namebuf[hl++] = '.'; |
| 80 | } |
| 81 | namebuf[hl] = 0; |
| 82 | |
| 83 | p = namebuf; |
| 84 | dp = dst; |
| 85 | while((p2 = strchr(p, '.')) != NULL) { |
| 86 | *p2 = 0; |
| 87 | *(dp++) = p2 - p; |
| 88 | memcpy(dp, p, p2 - p); |
| 89 | dp += p2 - p; |
| 90 | p = p2 + 1; |
| 91 | } |
| 92 | *(dp++) = 0; |
| 93 | |
| 94 | return(dp - dst); |
| 95 | } |
| 96 | |
| 97 | void cksum(void *hdr, size_t len) |
| 98 | { |
| 99 | struct icmphdr *ih; |
| 100 | u_int8_t *cb; |
| 101 | int i; |
| 102 | int b1, b2; |
| 103 | |
| 104 | ih = (struct icmphdr *)hdr; |
| 105 | cb = (u_int8_t *)hdr; |
| 106 | ih->checksum = 0; |
| 107 | b1 = b2 = 0; |
| 108 | for(i = 0; i < (len & ~1); i += 2) { |
| 109 | b1 += cb[i]; |
| 110 | b2 += cb[i + 1]; |
| 111 | } |
| 112 | if(i & 1) |
| 113 | b1 += cb[len - 1]; |
| 114 | while(1) { |
| 115 | if(b1 >= 256) { |
| 116 | b2 += b1 >> 8; |
| 117 | b1 &= 0xff; |
| 118 | continue; |
| 119 | } |
| 120 | if(b2 >= 256) { |
| 121 | b1 += b2 >> 8; |
| 122 | b2 &= 0xff; |
| 123 | continue; |
| 124 | } |
| 125 | break; |
| 126 | } |
| 127 | cb = (u_int8_t *)&ih->checksum; |
| 128 | cb[0] = ~(u_int8_t)b1; |
| 129 | cb[1] = ~(u_int8_t)b2; |
| 130 | } |
| 131 | |
| 132 | int main(int argc, char **argv) |
| 133 | { |
| 134 | int i, n, ret; |
| 135 | int c, cs, s4, s6, namelen, datalen; |
| 136 | int daemonize, ttl; |
| 137 | unsigned char buf[65536]; |
| 138 | struct sockaddr_storage name; |
| 139 | struct reqhdr req; |
| 140 | struct rephdr rep; |
| 141 | struct iphdr iphdr; |
| 142 | size_t hdrlen; |
| 143 | struct pollfd pfd[2]; |
| 144 | time_t curtime, lasterr; |
| 145 | |
| 146 | daemonize = 1; |
| 147 | ttl = 3600; |
| 148 | while((c = getopt(argc, argv, "nht:")) != -1) { |
| 149 | switch(c) { |
| 150 | case 't': |
| 151 | ttl = atoi(optarg); |
| 152 | break; |
| 153 | case 'n': |
| 154 | daemonize = 0; |
| 155 | break; |
| 156 | case 'h': |
| 157 | case '?': |
| 158 | case ':': |
| 159 | default: |
| 160 | fprintf(stderr, "usage: icmpdnd [-n]"); |
| 161 | exit((c == 'h')?0:1); |
| 162 | } |
| 163 | } |
| 164 | |
| 165 | s4 = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP); |
| 166 | s6 = socket(PF_INET6, SOCK_RAW, IPPROTO_ICMP); |
| 167 | if((s4 < 0) && (s6 < 0)) { |
| 168 | perror("could not open raw socket"); |
| 169 | exit(1); |
| 170 | } |
| 171 | |
| 172 | if(daemonize) |
| 173 | daemon(0, 0); |
| 174 | |
| 175 | openlog("icmpdnd", LOG_PID | LOG_NDELAY, LOG_DAEMON); |
| 176 | |
| 177 | alive = 1; |
| 178 | lasterr = 0; |
| 179 | while(alive) { |
| 180 | n = 0; |
| 181 | if(s4 >= 0) { |
| 182 | pfd[n].fd = s4; |
| 183 | pfd[n].events = POLLIN; |
| 184 | n++; |
| 185 | } |
| 186 | if(s6 >= 0) { |
| 187 | pfd[n].fd = s6; |
| 188 | pfd[n].events = POLLIN; |
| 189 | n++; |
| 190 | } |
| 191 | ret = poll(pfd, n, -1); |
| 192 | |
| 193 | curtime = time(NULL); |
| 194 | if(ret < 0) { |
| 195 | if(errno == EINTR) |
| 196 | continue; |
| 197 | syslog(LOG_ERR, "error while polling sockets: %m"); |
| 198 | if(lasterr == curtime) { |
| 199 | syslog(LOG_CRIT, "exiting due to repeated errors"); |
| 200 | exit(1); |
| 201 | } |
| 202 | lasterr = curtime; |
| 203 | } |
| 204 | |
| 205 | for(i = 0; i < n; i++) { |
| 206 | if((pfd[i].revents & POLLIN) == 0) |
| 207 | continue; |
| 208 | cs = pfd[i].fd; |
| 209 | namelen = sizeof(name); |
| 210 | memset(&name, 0, sizeof(name)); |
| 211 | ret = recvfrom(cs, buf, sizeof(buf), 0, (struct sockaddr *)&name, &namelen); |
| 212 | if(ret < 0) { |
| 213 | syslog(LOG_WARNING, "error while receiving datagram: %m"); |
| 214 | continue; |
| 215 | } |
| 216 | |
| 217 | if(cs == s4) { |
| 218 | if(ret < sizeof(iphdr) + sizeof(req)) |
| 219 | continue; |
| 220 | hdrlen = sizeof(iphdr); |
| 221 | memcpy(&iphdr, buf, sizeof(iphdr)); |
| 222 | if(iphdr.protocol != IPPROTO_ICMP) |
| 223 | continue; |
| 224 | } else if(cs == s6) { |
| 225 | if(ret < sizeof(req)) |
| 226 | continue; |
| 227 | ((struct sockaddr_in6 *)&name)->sin6_port = 0; |
| 228 | hdrlen = 0; |
| 229 | } else { |
| 230 | syslog(LOG_CRIT, "strangeness!"); |
| 231 | abort(); |
| 232 | } |
| 233 | memcpy(&req, buf + hdrlen, sizeof(req)); |
| 234 | if(req.type != ICMP_NAMEREQ) |
| 235 | continue; |
| 236 | rep.type = ICMP_NAMEREP; |
| 237 | rep.code = 0; |
| 238 | rep.id = req.id; |
| 239 | rep.seq = req.seq; |
| 240 | rep.ttl = htonl(ttl); |
| 241 | memcpy(buf, &rep, sizeof(rep)); |
| 242 | datalen = filldn(buf + sizeof(rep)); |
| 243 | |
| 244 | cksum(buf, datalen + sizeof(rep)); |
| 245 | |
| 246 | /* XXX: The correct source address needs to be filled in from |
| 247 | * the request's destination address. */ |
| 248 | ret = sendto(cs, buf, datalen + sizeof(rep), 0, (struct sockaddr *)&name, namelen); |
| 249 | if(ret < 0) |
| 250 | syslog(LOG_WARNING, "error in sending reply: %m"); |
| 251 | } |
| 252 | } |
| 253 | |
| 254 | close(s4); |
| 255 | close(s6); |
| 256 | return(0); |
| 257 | } |