networking/zcip.c

   1 /*
   2  * RFC3927 ZeroConf IPv4 Link-Local addressing
   3  * (see <http://www.zeroconf.org/>)
   4  *
   5  * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
   6  * Copyright (C) 2004 by David Brownell
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16  * General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  21  * 02111-1307 USA
  22  */
  23
  24 /*
  25  * This can build as part of BusyBox or by itself:
  26  *
  27  *      $(CROSS_COMPILE)cc -Os -Wall -DNO_BUSYBOX -DDEBUG -o zcip zcip.c
  28  *
  29  * ZCIP just manages the 169.254.*.* addresses.  That network is not
  30  * routed at the IP level, though various proxies or bridges can
  31  * certainly be used.  Its naming is built over multicast DNS.
  32  */
  33
  34 /* TODO:
  35  - more real-world usage/testing, especially daemon mode
  36  - kernel packet filters to reduce scheduling noise
  37  - avoid silent script failures, especially under load...
  38  - link status monitoring (restart on link-up; stop on link-down)
  39 */
  40 #include <errno.h>
  41 #include <stdlib.h>
  42 #include <stdio.h>
  43 #include <string.h>
  44 #include <syslog.h>
  45 #include <poll.h>
  46 #include <time.h>
  47 #include <unistd.h>
  48
  49 #include <sys/ioctl.h>
  50 #include <sys/types.h>
  51 #include <sys/wait.h>
  52 #include <sys/time.h>
  53 #include <sys/socket.h>
  54
  55 #include <arpa/inet.h>
  56 #include <netinet/in.h>
  57 #include <netinet/ether.h>
  58 #include <net/ethernet.h>
  59 #include <net/if.h>
  60 #include <net/if_arp.h>
  61
  62 #include <linux/if_packet.h>
  63 #include <linux/sockios.h>
  64 #include "busybox.h"
  65 #include "libbb.h"
  66
  67 struct arp_packet {
  68         struct ether_header hdr;
  69         /* FIXME this part is netinet/if_ether.h "struct ether_arp" */
  70         struct arphdr arp;
  71         struct ether_addr source_addr;
  72         struct in_addr source_ip;
  73         struct ether_addr target_addr;
  74         struct in_addr target_ip;
  75 } __attribute__ ((__packed__));
  76
  77 /* 169.254.0.0 */
  78 static const uint32_t LINKLOCAL_ADDR = 0xa9fe0000;
  79
  80 /* protocol timeout parameters, specified in seconds */
  81 static const unsigned PROBE_WAIT = 1;
  82 static const unsigned PROBE_MIN = 1;
  83 static const unsigned PROBE_MAX = 2;
  84 static const unsigned PROBE_NUM = 3;
  85 static const unsigned MAX_CONFLICTS = 10;
  86 static const unsigned RATE_LIMIT_INTERVAL = 60;
  87 static const unsigned ANNOUNCE_WAIT = 2;
  88 static const unsigned ANNOUNCE_NUM = 2;
  89 static const unsigned ANNOUNCE_INTERVAL = 2;
  90 static const time_t DEFEND_INTERVAL = 10;
  91
  92 #define ZCIP_VERSION     "0.75 (18 April 2005)"
  93
  94 static const struct in_addr null_ip = { 0 };
  95 static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };
  96
  97
  98 /*
  99  * Pick a random link local IP address on 169.254/16, except that
 100  * the first and last 256 addresses are reserved.
 101  */
 102 static void
 103 pick(struct in_addr *ip)
 104 {
 105         unsigned        tmp;
 106
 107         /* use cheaper math than lrand48() mod N */
 108         do {
 109                 tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
 110         } while (tmp > (IN_CLASSB_HOST - 0x0200));
 111         ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
 112 }
 113
 114 /*
 115  * Broadcast an ARP packet.
 116  */
 117 static int
 118 arp(int fd, struct sockaddr *saddr, int op,
 119         const struct ether_addr *source_addr, struct in_addr source_ip,
 120         const struct ether_addr *target_addr, struct in_addr target_ip)
 121 {
 122         struct arp_packet p;
 123
 124         /* ether header */
 125         p.hdr.ether_type = htons(ETHERTYPE_ARP);
 126         memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
 127         memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
 128
 129         /* arp request */
 130         p.arp.ar_hrd = htons(ARPHRD_ETHER);
 131         p.arp.ar_pro = htons(ETHERTYPE_IP);
 132         p.arp.ar_hln = ETH_ALEN;
 133         p.arp.ar_pln = 4;
 134         p.arp.ar_op = htons(op);
 135         memcpy(&p.source_addr, source_addr, ETH_ALEN);
 136         memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
 137         memcpy(&p.target_addr, target_addr, ETH_ALEN);
 138         memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));
 139
 140         /* send it */
 141         if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
 142                 bb_perror_msg("sendto");
 143                 return -errno;
 144         }
 145         return 0;
 146 }
 147
 148 /*
 149  * Run a script.
 150  */
 151 static int
 152 run(char *script, char *arg, char *intf, struct in_addr *ip)
 153 {
 154         int pid, status;
 155         char *why;
 156
 157         if (script != NULL) {
 158                 if (ip != NULL) {
 159                         char *addr = inet_ntoa(*ip);
 160                         xsetenv("ip", addr);
 161                         syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
 162                 }
 163
 164                 pid = vfork();
 165                 if (pid < 0) {                  /* error */
 166                         why = "vfork";
 167                         goto bad;
 168                 } else if (pid == 0) {          /* child */
 169                         execl(script, script, arg, NULL);
 170                         bb_perror_msg_and_die("execl");
 171                 }
 172
 173                 if (waitpid(pid, &status, 0) <= 0) {
 174                         why = "waitpid";
 175                         goto bad;
 176                 }
 177                 if (WEXITSTATUS(status) != 0) {
 178                         bb_perror_msg("script %s failed, exit=%d", script, WEXITSTATUS(status));
 179                         return -errno;
 180                 }
 181         }
 182         return 0;
 183 bad:
 184         status = -errno;
 185         syslog(LOG_ERR, "%s %s, %s error: %s",
 186                 arg, intf, why, strerror(errno));
 187         return status;
 188 }
 189
 190 /*
 191  * Return milliseconds of random delay, up to "secs" seconds.
 192  */
 193 static inline unsigned
 194 ms_rdelay(unsigned secs)
 195 {
 196         return lrand48() % (secs * 1000);
 197 }
 198
 199 /*
 200  * main program
 201  */
 202
 203 #define FOREGROUND        1
 204 #define QUIT              2
 205 #define REQUEST           4
 206 #define VERBOSE           8
 207
 208 int zcip_main(int argc, char *argv[])
 209 {
 210         char *intf = NULL;
 211         char *script = NULL;
 212         char *why;
 213         struct sockaddr saddr;
 214         struct ether_addr addr;
 215         struct in_addr ip = { 0 };
 216         int fd;
 217         int ready = 0;
 218         suseconds_t timeout = 0;        /* milliseconds */
 219         time_t defend = 0;
 220         unsigned conflicts = 0;
 221         unsigned nprobes = 0;
 222         unsigned nclaims = 0;
 223         unsigned long t;
 224
 225         bb_opt_complementaly = "vf";
 226         /* parse commandline: prog [options] ifname script */
 227         t = bb_getopt_ulflags(argc, argv, "fqr:v", &why); /* reuse char* why */
 228
 229         argc -= optind;
 230         argv += optind;
 231
 232         if ((t & 0x80000000UL) || (argc < 1) || (argc > 2)) {
 233                 bb_show_usage();
 234         }
 235
 236         if (t & VERBOSE) {
 237                 bb_printf("%s: version %s\n", bb_applet_name, ZCIP_VERSION);
 238         }
 239         if ((t & REQUEST) && (inet_aton(why, &ip) == 0 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR)) {
 240                 bb_perror_msg_and_die("invalid link address");
 241         }
 242
 243         intf = argv[0];
 244         xsetenv("interface", intf);
 245         script = argv[1]; /* Could be NULL ? */
 246
 247         openlog(bb_applet_name, 0, LOG_DAEMON);
 248
 249         /* initialize the interface (modprobe, ifup, etc) */
 250         if (run(script, "init", intf, NULL) < 0)
 251                 return EXIT_FAILURE;
 252
 253         /* initialize saddr */
 254         memset(&saddr, 0, sizeof (saddr));
 255         strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
 256
 257         /* open an ARP socket */
 258         if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
 259                 why = "open";
 260 fail:
 261                 t |= FOREGROUND;
 262                 goto bad;
 263         }
 264         /* bind to the interface's ARP socket */
 265         if (bind(fd, &saddr, sizeof (saddr)) < 0) {
 266                 why = "bind";
 267                 goto fail;
 268         } else {
 269                 struct ifreq ifr;
 270                 short seed[3];
 271
 272                 /* get the interface's ethernet address */
 273                 memset(&ifr, 0, sizeof (ifr));
 274                 strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
 275                 if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
 276                         why = "get ethernet address";
 277                         goto fail;
 278                 }
 279                 memcpy(&addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 280
 281                 /* start with some stable ip address, either a function of
 282                    the hardware address or else the last address we used.
 283                    NOTE: the sequence of addresses we try changes only
 284                    depending on when we detect conflicts. */
 285                 memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 286                 seed48(seed);
 287                 if (ip.s_addr == 0)
 288                         pick(&ip);
 289         }
 290
 291         /* FIXME cases to handle:
 292             - zcip already running!
 293             - link already has local address... just defend/update */
 294
 295         /* daemonize now; don't delay system startup */
 296         if (!(t & FOREGROUND)) {
 297                 if (daemon(0, (t & VERBOSE)) < 0) {
 298                         why = "daemon";
 299                         goto bad;
 300                 }
 301                 syslog(LOG_INFO, "start, interface %s", intf);
 302         }
 303
 304         /* run the dynamic address negotiation protocol,
 305            restarting after address conflicts:
 306             - start with some address we want to try
 307             - short random delay
 308             - arp probes to see if another host else uses it
 309             - arp announcements that we're claiming it
 310             - use it
 311             - defend it, within limits */
 312         while (1) {
 313                 struct pollfd fds[1];
 314                 struct timeval tv1;
 315                 struct arp_packet p;
 316
 317                 fds[0].fd = fd;
 318                 fds[0].events = POLLIN;
 319                 fds[0].revents = 0;
 320
 321                 /* poll, being ready to adjust current timeout */
 322                 if (timeout > 0) {
 323                         gettimeofday(&tv1, NULL);
 324                         tv1.tv_usec += (timeout % 1000) * 1000;
 325                         while (tv1.tv_usec > 1000000) {
 326                                 tv1.tv_usec -= 1000000;
 327                                 tv1.tv_sec++;
 328                         }
 329                         tv1.tv_sec += timeout / 1000;
 330                 } else if (timeout == 0) {
 331                         timeout = ms_rdelay(PROBE_WAIT);
 332                         /* FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
 333                            make the kernel filter out all packets except
 334                            ones we'd care about. */
 335                 }
 336                 switch (poll(fds, 1, timeout)) {
 337
 338                 /* timeouts trigger protocol transitions */
 339                 case 0:
 340                         /* probes */
 341                         if (nprobes < PROBE_NUM) {
 342                                 nprobes++;
 343                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 344                                                 &addr, null_ip,
 345                                                 &null_addr, ip);
 346                                 if (nprobes < PROBE_NUM) {
 347                                         timeout = PROBE_MIN * 1000;
 348                                         timeout += ms_rdelay(PROBE_MAX
 349                                                         - PROBE_MIN);
 350                                 } else
 351                                         timeout = ANNOUNCE_WAIT * 1000;
 352                         }
 353                         /* then announcements */
 354                         else if (nclaims < ANNOUNCE_NUM) {
 355                                 nclaims++;
 356                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 357                                                 &addr, ip,
 358                                                 &addr, ip);
 359                                 if (nclaims < ANNOUNCE_NUM) {
 360                                         timeout = ANNOUNCE_INTERVAL * 1000;
 361                                 } else {
 362                                         /* link is ok to use earlier */
 363                                         run(script, "config", intf, &ip);
 364                                         ready = 1;
 365                                         conflicts = 0;
 366                                         timeout = -1;
 367
 368                                         /* NOTE:  all other exit paths
 369                                            should deconfig ... */
 370                                         if (t & QUIT)
 371                                                 return EXIT_SUCCESS;
 372                                         /* FIXME update filters */
 373                                 }
 374                         }
 375                         break;
 376
 377                 /* packets arriving */
 378                 case 1:
 379                         /* maybe adjust timeout */
 380                         if (timeout > 0) {
 381                                 struct timeval tv2;
 382
 383                                 gettimeofday(&tv2, NULL);
 384                                 if (timercmp(&tv1, &tv2, <)) {
 385                                         timeout = -1;
 386                                 } else {
 387                                         timersub(&tv1, &tv2, &tv1);
 388                                         timeout = 1000 * tv1.tv_sec
 389                                                         + tv1.tv_usec / 1000;
 390                                 }
 391                         }
 392                         if ((fds[0].revents & POLLIN) == 0) {
 393                                 if (fds[0].revents & POLLERR) {
 394                                         /* FIXME: links routinely go down;
 395                                            this shouldn't necessarily exit. */
 396                                         bb_perror_msg("%s: poll error", intf);
 397                                         if (ready) {
 398                                                 run(script, "deconfig", intf, &ip);
 399                                         }
 400                                         return EXIT_FAILURE;
 401                                 }
 402                                 continue;
 403                         }
 404                         /* read ARP packet */
 405                         if (recv(fd, &p, sizeof (p), 0) < 0) {
 406                                 why = "recv";
 407                                 goto bad;
 408                         }
 409                         if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
 410                                 continue;
 411
 412                         if (p.arp.ar_op != htons(ARPOP_REQUEST)
 413                                         && p.arp.ar_op != htons(ARPOP_REPLY))
 414                                 continue;
 415
 416                         /* some cases are always conflicts */
 417                         if ((p.source_ip.s_addr == ip.s_addr)
 418                                         && (memcmp(&addr, &p.source_addr,
 419                                                         ETH_ALEN) != 0)) {
 420 collision:
 421                                 if (ready) {
 422                                         time_t now = time(0);
 423
 424                                         if ((defend + DEFEND_INTERVAL)
 425                                                         < now) {
 426                                                 defend = now;
 427                                                 (void)arp(fd, &saddr,
 428                                                                 ARPOP_REQUEST,
 429                                                                 &addr, ip,
 430                                                                 &addr, ip);
 431                                                 timeout = -1;
 432                                                 continue;
 433                                         }
 434                                         defend = now;
 435                                         ready = 0;
 436                                         run(script, "deconfig", intf, &ip);
 437                                         /* FIXME rm filters: setsockopt(fd,
 438                                            SO_DETACH_FILTER, ...) */
 439                                 }
 440                                 conflicts++;
 441                                 if (conflicts >= MAX_CONFLICTS) {
 442                                         sleep(RATE_LIMIT_INTERVAL);
 443                                 }
 444                                 /* restart the whole protocol */
 445                                 pick(&ip);
 446                                 timeout = 0;
 447                                 nprobes = 0;
 448                                 nclaims = 0;
 449                         }
 450                         /* two hosts probing one address is a collision too */
 451                         else if (p.target_ip.s_addr == ip.s_addr
 452                                         && nclaims == 0
 453                                         && p.arp.ar_op == htons(ARPOP_REQUEST)
 454                                         && memcmp(&addr, &p.target_addr,
 455                                                         ETH_ALEN) != 0) {
 456                                 goto collision;
 457                         }
 458                         break;
 459
 460                 default:
 461                         why = "poll";
 462                         goto bad;
 463                 }
 464         }
 465 bad:
 466         if ( t & FOREGROUND) {
 467                 bb_perror_msg(why);
 468         } else {
 469                 syslog(LOG_ERR, "%s %s, %s error: %s",
 470                         bb_applet_name, intf, why, strerror(errno));
 471         }
 472         return EXIT_FAILURE;
 473 }