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  * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
   9  */
  10
  11 /*
  12  * This can build as part of BusyBox or by itself:
  13  *
  14  *      $(CROSS_COMPILE)cc -Os -Wall -DNO_BUSYBOX -DDEBUG -o zcip zcip.c
  15  *
  16  * ZCIP just manages the 169.254.*.* addresses.  That network is not
  17  * routed at the IP level, though various proxies or bridges can
  18  * certainly be used.  Its naming is built over multicast DNS.
  19  */
  20
  21 // #define      DEBUG
  22
  23 // TODO:
  24 // - more real-world usage/testing, especially daemon mode
  25 // - kernel packet filters to reduce scheduling noise
  26 // - avoid silent script failures, especially under load...
  27 // - link status monitoring (restart on link-up; stop on link-down)
  28
  29 #include <errno.h>
  30 #include <stdlib.h>
  31 #include <stdio.h>
  32 #include <string.h>
  33 #include <syslog.h>
  34 #include <poll.h>
  35 #include <time.h>
  36 #include <unistd.h>
  37
  38 #include <sys/ioctl.h>
  39 #include <sys/types.h>
  40 #include <sys/wait.h>
  41 #include <sys/time.h>
  42 #include <sys/socket.h>
  43
  44 #include <arpa/inet.h>
  45 #include <netinet/in.h>
  46 #include <netinet/ether.h>
  47 #include <net/ethernet.h>
  48 #include <net/if.h>
  49 #include <net/if_arp.h>
  50
  51 #include <linux/if_packet.h>
  52 #include <linux/sockios.h>
  53
  54
  55 struct arp_packet {
  56         struct ether_header hdr;
  57         // FIXME this part is netinet/if_ether.h "struct ether_arp"
  58         struct arphdr arp;
  59         struct ether_addr source_addr;
  60         struct in_addr source_ip;
  61         struct ether_addr target_addr;
  62         struct in_addr target_ip;
  63 } ATTRIBUTE_PACKED;
  64
  65 /* 169.254.0.0 */
  66 static const uint32_t LINKLOCAL_ADDR = 0xa9fe0000;
  67
  68 /* protocol timeout parameters, specified in seconds */
  69 static const unsigned PROBE_WAIT = 1;
  70 static const unsigned PROBE_MIN = 1;
  71 static const unsigned PROBE_MAX = 2;
  72 static const unsigned PROBE_NUM = 3;
  73 static const unsigned MAX_CONFLICTS = 10;
  74 static const unsigned RATE_LIMIT_INTERVAL = 60;
  75 static const unsigned ANNOUNCE_WAIT = 2;
  76 static const unsigned ANNOUNCE_NUM = 2;
  77 static const unsigned ANNOUNCE_INTERVAL = 2;
  78 static const time_t DEFEND_INTERVAL = 10;
  79
  80 static const unsigned char ZCIP_VERSION[] = "0.75 (18 April 2005)";
  81 static char *prog;
  82
  83 static const struct in_addr null_ip = { 0 };
  84 static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };
  85
  86 static int verbose = 0;
  87
  88 #ifdef DEBUG
  89
  90 #define DBG(fmt,args...) \
  91         fprintf(stderr, "%s: " fmt , prog , ## args)
  92 #define VDBG(fmt,args...) do { \
  93         if (verbose) fprintf(stderr, "%s: " fmt , prog ,## args); \
  94         } while (0)
  95 #else
  96
  97 #define DBG(fmt,args...) \
  98         do { } while (0)
  99 #define VDBG    DBG
 100 #endif                          /* DEBUG */
 101
 102 /**
 103  * Pick a random link local IP address on 169.254/16, except that
 104  * the first and last 256 addresses are reserved.
 105  */
 106 static void
 107 pick(struct in_addr *ip)
 108 {
 109         unsigned        tmp;
 110
 111         /* use cheaper math than lrand48() mod N */
 112         do {
 113                 tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
 114         } while (tmp > (IN_CLASSB_HOST - 0x0200));
 115         ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
 116 }
 117
 118 /**
 119  * Broadcast an ARP packet.
 120  */
 121 static int
 122 arp(int fd, struct sockaddr *saddr, int op,
 123         const struct ether_addr *source_addr, struct in_addr source_ip,
 124         const struct ether_addr *target_addr, struct in_addr target_ip)
 125 {
 126         struct arp_packet p;
 127
 128         // ether header
 129         p.hdr.ether_type = htons(ETHERTYPE_ARP);
 130         memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
 131         memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
 132
 133         // arp request
 134         p.arp.ar_hrd = htons(ARPHRD_ETHER);
 135         p.arp.ar_pro = htons(ETHERTYPE_IP);
 136         p.arp.ar_hln = ETH_ALEN;
 137         p.arp.ar_pln = 4;
 138         p.arp.ar_op = htons(op);
 139         memcpy(&p.source_addr, source_addr, ETH_ALEN);
 140         memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
 141         memcpy(&p.target_addr, target_addr, ETH_ALEN);
 142         memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));
 143
 144         // send it
 145         if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
 146                 perror("sendto");
 147                 return -errno;
 148         }
 149         return 0;
 150 }
 151
 152 /**
 153  * Run a script.
 154  */
 155 static int
 156 run(char *script, char *arg, char *intf, struct in_addr *ip)
 157 {
 158         int pid, status;
 159         char *why;
 160
 161         if (script != NULL) {
 162                 VDBG("%s run %s %s\n", intf, script, arg);
 163                 if (ip != NULL) {
 164                         char *addr = inet_ntoa(*ip);
 165                         setenv("ip", addr, 1);
 166                         syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
 167                 }
 168
 169                 pid = vfork();
 170                 if (pid < 0) {                  // error
 171                         why = "vfork";
 172                         goto bad;
 173                 } else if (pid == 0) {          // child
 174                         execl(script, script, arg, NULL);
 175                         perror("execl");
 176                         _exit(EXIT_FAILURE);
 177                 }
 178
 179                 if (waitpid(pid, &status, 0) <= 0) {
 180                         why = "waitpid";
 181                         goto bad;
 182                 }
 183                 if (WEXITSTATUS(status) != 0) {
 184                         fprintf(stderr, "%s: script %s failed, exit=%d\n",
 185                                         prog, script, WEXITSTATUS(status));
 186                         return -errno;
 187                 }
 188         }
 189         return 0;
 190 bad:
 191         status = -errno;
 192         syslog(LOG_ERR, "%s %s, %s error: %s",
 193                 arg, intf, why, strerror(errno));
 194         return status;
 195 }
 196
 197 #ifndef NO_BUSYBOX
 198 #include "busybox.h"
 199 #endif
 200
 201 /**
 202  * Print usage information.
 203  */
 204 static void ATTRIBUTE_NORETURN
 205 zcip_usage(const char *msg)
 206 {
 207         fprintf(stderr, "%s: %s\n", prog, msg);
 208 #ifdef  NO_BUSYBOX
 209         fprintf(stderr, "Usage: %s [OPTIONS] ifname script\n"
 210                         "\t-f              foreground mode (implied by -v)\n"
 211                         "\t-q              quit after address (no daemon)\n"
 212                         "\t-r 169.254.x.x  request this address first\n"
 213                         "\t-v              verbose; show version\n",
 214                         prog);
 215         exit(0);
 216 #else
 217         bb_show_usage();
 218 #endif
 219 }
 220
 221 /**
 222  * Return milliseconds of random delay, up to "secs" seconds.
 223  */
 224 static inline unsigned
 225 ms_rdelay(unsigned secs)
 226 {
 227         return lrand48() % (secs * 1000);
 228 }
 229
 230 /**
 231  * main program
 232  */
 233
 234 #ifdef  NO_BUSYBOX
 235 int
 236 main(int argc, char *argv[])
 237         __attribute__ ((weak, alias ("zcip_main")));
 238 #endif
 239
 240 int zcip_main(int argc, char *argv[])
 241 {
 242         char *intf = NULL;
 243         char *script = NULL;
 244         int quit = 0;
 245         int foreground = 0;
 246
 247         char *why;
 248         struct sockaddr saddr;
 249         struct ether_addr addr;
 250         struct in_addr ip = { 0 };
 251         int fd;
 252         int ready = 0;
 253         suseconds_t timeout = 0;        // milliseconds
 254         time_t defend = 0;
 255         unsigned conflicts = 0;
 256         unsigned nprobes = 0;
 257         unsigned nclaims = 0;
 258         int t;
 259
 260         // parse commandline: prog [options] ifname script
 261         prog = argv[0];
 262         while ((t = getopt(argc, argv, "fqr:v")) != EOF) {
 263                 switch (t) {
 264                 case 'f':
 265                         foreground = 1;
 266                         continue;
 267                 case 'q':
 268                         quit = 1;
 269                         continue;
 270                 case 'r':
 271                         if (inet_aton(optarg, &ip) == 0
 272                                         || (ntohl(ip.s_addr) & IN_CLASSB_NET)
 273                                                 != LINKLOCAL_ADDR) {
 274                                 zcip_usage("invalid link address");
 275                         }
 276                         continue;
 277                 case 'v':
 278                         if (!verbose)
 279                                 printf("%s: version %s\n", prog, ZCIP_VERSION);
 280                         verbose++;
 281                         foreground = 1;
 282                         continue;
 283                 default:
 284                         zcip_usage("bad option");
 285                 }
 286         }
 287         if (optind < argc - 1) {
 288                 intf = argv[optind++];
 289                 setenv("interface", intf, 1);
 290                 script = argv[optind++];
 291         }
 292         if (optind != argc || !intf)
 293                 zcip_usage("wrong number of arguments");
 294         openlog(prog, 0, LOG_DAEMON);
 295
 296         // initialize the interface (modprobe, ifup, etc)
 297         if (run(script, "init", intf, NULL) < 0)
 298                 return EXIT_FAILURE;
 299
 300         // initialize saddr
 301         memset(&saddr, 0, sizeof (saddr));
 302         strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
 303
 304         // open an ARP socket
 305         if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
 306                 why = "open";
 307 fail:
 308                 foreground = 1;
 309                 goto bad;
 310         }
 311         // bind to the interface's ARP socket
 312         if (bind(fd, &saddr, sizeof (saddr)) < 0) {
 313                 why = "bind";
 314                 goto fail;
 315         } else {
 316                 struct ifreq ifr;
 317                 short seed[3];
 318
 319                 // get the interface's ethernet address
 320                 memset(&ifr, 0, sizeof (ifr));
 321                 strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
 322                 if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
 323                         why = "get ethernet address";
 324                         goto fail;
 325                 }
 326                 memcpy(&addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 327
 328                 // start with some stable ip address, either a function of
 329                 // the hardware address or else the last address we used.
 330                 // NOTE: the sequence of addresses we try changes only
 331                 // depending on when we detect conflicts.
 332                 memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 333                 seed48(seed);
 334                 if (ip.s_addr == 0)
 335                         pick(&ip);
 336         }
 337
 338         // FIXME cases to handle:
 339         //  - zcip already running!
 340         //  - link already has local address... just defend/update
 341
 342         // daemonize now; don't delay system startup
 343         if (!foreground) {
 344                 if (daemon(0, verbose) < 0) {
 345                         why = "daemon";
 346                         goto bad;
 347                 }
 348                 syslog(LOG_INFO, "start, interface %s", intf);
 349         }
 350
 351         // run the dynamic address negotiation protocol,
 352         // restarting after address conflicts:
 353         //  - start with some address we want to try
 354         //  - short random delay
 355         //  - arp probes to see if another host else uses it
 356         //  - arp announcements that we're claiming it
 357         //  - use it
 358         //  - defend it, within limits
 359         while (1) {
 360                 struct pollfd fds[1];
 361                 struct timeval tv1;
 362                 struct arp_packet p;
 363
 364                 fds[0].fd = fd;
 365                 fds[0].events = POLLIN;
 366                 fds[0].revents = 0;
 367
 368                 // poll, being ready to adjust current timeout
 369                 if (timeout > 0) {
 370                         gettimeofday(&tv1, NULL);
 371                         tv1.tv_usec += (timeout % 1000) * 1000;
 372                         while (tv1.tv_usec > 1000000) {
 373                                 tv1.tv_usec -= 1000000;
 374                                 tv1.tv_sec++;
 375                         }
 376                         tv1.tv_sec += timeout / 1000;
 377                 } else if (timeout == 0) {
 378                         timeout = ms_rdelay(PROBE_WAIT);
 379                         // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
 380                         // make the kernel filter out all packets except
 381                         // ones we'd care about.
 382                 }
 383                 VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
 384                                 timeout, intf, nprobes, nclaims);
 385                 switch (poll(fds, 1, timeout)) {
 386
 387                 // timeouts trigger protocol transitions
 388                 case 0:
 389                         // probes
 390                         if (nprobes < PROBE_NUM) {
 391                                 nprobes++;
 392                                 VDBG("probe/%d %s@%s\n",
 393                                                 nprobes, intf, inet_ntoa(ip));
 394                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 395                                                 &addr, null_ip,
 396                                                 &null_addr, ip);
 397                                 if (nprobes < PROBE_NUM) {
 398                                         timeout = PROBE_MIN * 1000;
 399                                         timeout += ms_rdelay(PROBE_MAX
 400                                                         - PROBE_MIN);
 401                                 } else
 402                                         timeout = ANNOUNCE_WAIT * 1000;
 403                         }
 404                         // then announcements
 405                         else if (nclaims < ANNOUNCE_NUM) {
 406                                 nclaims++;
 407                                 VDBG("announce/%d %s@%s\n",
 408                                                 nclaims, intf, inet_ntoa(ip));
 409                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 410                                                 &addr, ip,
 411                                                 &addr, ip);
 412                                 if (nclaims < ANNOUNCE_NUM) {
 413                                         timeout = ANNOUNCE_INTERVAL * 1000;
 414                                 } else {
 415                                         // link is ok to use earlier
 416                                         run(script, "config", intf, &ip);
 417                                         ready = 1;
 418                                         conflicts = 0;
 419                                         timeout = -1;
 420
 421                                         // NOTE:  all other exit paths
 422                                         // should deconfig ...
 423                                         if (quit)
 424                                                 return EXIT_SUCCESS;
 425                                         // FIXME update filters
 426                                 }
 427                         }
 428                         break;
 429
 430                 // packets arriving
 431                 case 1:
 432                         // maybe adjust timeout
 433                         if (timeout > 0) {
 434                                 struct timeval tv2;
 435
 436                                 gettimeofday(&tv2, NULL);
 437                                 if (timercmp(&tv1, &tv2, <)) {
 438                                         timeout = -1;
 439                                 } else {
 440                                         timersub(&tv1, &tv2, &tv1);
 441                                         timeout = 1000 * tv1.tv_sec
 442                                                         + tv1.tv_usec / 1000;
 443                                 }
 444                         }
 445                         if ((fds[0].revents & POLLIN) == 0) {
 446                                 if (fds[0].revents & POLLERR) {
 447                                         // FIXME: links routinely go down;
 448                                         // this shouldn't necessarily exit.
 449                                         fprintf(stderr, "%s %s: poll error\n",
 450                                                         prog, intf);
 451                                         if (ready) {
 452                                                 run(script, "deconfig",
 453                                                                 intf, &ip);
 454                                         }
 455                                         return EXIT_FAILURE;
 456                                 }
 457                                 continue;
 458                         }
 459                         // read ARP packet
 460                         if (recv(fd, &p, sizeof (p), 0) < 0) {
 461                                 why = "recv";
 462                                 goto bad;
 463                         }
 464                         if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
 465                                 continue;
 466
 467                         VDBG("%s recv arp type=%d, op=%d,\n",
 468                                         intf, ntohs(p.hdr.ether_type),
 469                                         ntohs(p.arp.ar_op));
 470                         VDBG("\tsource=%s %s\n",
 471                                         ether_ntoa(&p.source_addr),
 472                                         inet_ntoa(p.source_ip));
 473                         VDBG("\ttarget=%s %s\n",
 474                                         ether_ntoa(&p.target_addr),
 475                                         inet_ntoa(p.target_ip));
 476                         if (p.arp.ar_op != htons(ARPOP_REQUEST)
 477                                         && p.arp.ar_op != htons(ARPOP_REPLY))
 478                                 continue;
 479
 480                         // some cases are always conflicts
 481                         if ((p.source_ip.s_addr == ip.s_addr)
 482                                         && (memcmp(&addr, &p.source_addr,
 483                                                         ETH_ALEN) != 0)) {
 484 collision:
 485                                 VDBG("%s ARP conflict from %s\n", intf,
 486                                                 ether_ntoa(&p.source_addr));
 487                                 if (ready) {
 488                                         time_t now = time(0);
 489
 490                                         if ((defend + DEFEND_INTERVAL)
 491                                                         < now) {
 492                                                 defend = now;
 493                                                 (void)arp(fd, &saddr,
 494                                                                 ARPOP_REQUEST,
 495                                                                 &addr, ip,
 496                                                                 &addr, ip);
 497                                                 VDBG("%s defend\n", intf);
 498                                                 timeout = -1;
 499                                                 continue;
 500                                         }
 501                                         defend = now;
 502                                         ready = 0;
 503                                         run(script, "deconfig", intf, &ip);
 504                                         // FIXME rm filters: setsockopt(fd,
 505                                         // SO_DETACH_FILTER, ...)
 506                                 }
 507                                 conflicts++;
 508                                 if (conflicts >= MAX_CONFLICTS) {
 509                                         VDBG("%s ratelimit\n", intf);
 510                                         sleep(RATE_LIMIT_INTERVAL);
 511                                 }
 512                                 // restart the whole protocol
 513                                 pick(&ip);
 514                                 timeout = 0;
 515                                 nprobes = 0;
 516                                 nclaims = 0;
 517                         }
 518                         // two hosts probing one address is a collision too
 519                         else if (p.target_ip.s_addr == ip.s_addr
 520                                         && nclaims == 0
 521                                         && p.arp.ar_op == htons(ARPOP_REQUEST)
 522                                         && memcmp(&addr, &p.target_addr,
 523                                                         ETH_ALEN) != 0) {
 524                                 goto collision;
 525                         }
 526                         break;
 527
 528                 default:
 529                         why = "poll";
 530                         goto bad;
 531                 }
 532         }
 533 bad:
 534         if (foreground)
 535                 perror(why);
 536         else
 537                 syslog(LOG_ERR, "%s %s, %s error: %s",
 538                         prog, intf, why, strerror(errno));
 539         return EXIT_FAILURE;
 540 }