networking/zcip.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * RFC3927 ZeroConf IPv4 Link-Local addressing
   4  * (see <http://www.zeroconf.org/>)
   5  *
   6  * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
   7  * Copyright (C) 2004 by David Brownell
   8  *
   9  * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
  10  */
  11
  12 /*
  13  * ZCIP just manages the 169.254.*.* addresses.  That network is not
  14  * routed at the IP level, though various proxies or bridges can
  15  * certainly be used.  Its naming is built over multicast DNS.
  16  */
  17
  18 //#define DEBUG
  19
  20 // TODO:
  21 // - more real-world usage/testing, especially daemon mode
  22 // - kernel packet filters to reduce scheduling noise
  23 // - avoid silent script failures, especially under load...
  24 // - link status monitoring (restart on link-up; stop on link-down)
  25
  26 #include "busybox.h"
  27 #include <errno.h>
  28 #include <string.h>
  29 #include <syslog.h>
  30 #include <poll.h>
  31 #include <time.h>
  32
  33 #include <sys/wait.h>
  34
  35 #include <netinet/ether.h>
  36 #include <net/ethernet.h>
  37 #include <net/if.h>
  38 #include <net/if_arp.h>
  39
  40 #include <linux/if_packet.h>
  41 #include <linux/sockios.h>
  42
  43
  44 struct arp_packet {
  45         struct ether_header hdr;
  46         struct ether_arp arp;
  47 } ATTRIBUTE_PACKED;
  48
  49 enum {
  50 /* 169.254.0.0 */
  51         LINKLOCAL_ADDR = 0xa9fe0000,
  52
  53 /* protocol timeout parameters, specified in seconds */
  54         PROBE_WAIT = 1,
  55         PROBE_MIN = 1,
  56         PROBE_MAX = 2,
  57         PROBE_NUM = 3,
  58         MAX_CONFLICTS = 10,
  59         RATE_LIMIT_INTERVAL = 60,
  60         ANNOUNCE_WAIT = 2,
  61         ANNOUNCE_NUM = 2,
  62         ANNOUNCE_INTERVAL = 2,
  63         DEFEND_INTERVAL = 10
  64 };
  65
  66 /* States during the configuration process. */
  67 enum {
  68         PROBE = 0,
  69         RATE_LIMIT_PROBE,
  70         ANNOUNCE,
  71         MONITOR,
  72         DEFEND
  73 };
  74
  75 #define DBG(fmt,args...) \
  76         do { } while (0)
  77 #define VDBG    DBG
  78
  79 /**
  80  * Pick a random link local IP address on 169.254/16, except that
  81  * the first and last 256 addresses are reserved.
  82  */
  83 static void pick(struct in_addr *ip)
  84 {
  85         unsigned        tmp;
  86
  87         /* use cheaper math than lrand48() mod N */
  88         do {
  89                 tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
  90         } while (tmp > (IN_CLASSB_HOST - 0x0200));
  91         ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
  92 }
  93
  94 /**
  95  * Broadcast an ARP packet.
  96  */
  97 static int arp(int fd, struct sockaddr *saddr, int op,
  98         const struct ether_addr *source_addr, struct in_addr source_ip,
  99         const struct ether_addr *target_addr, struct in_addr target_ip)
 100 {
 101         struct arp_packet p;
 102         memset(&p, 0, sizeof(p));
 103
 104         // ether header
 105         p.hdr.ether_type = htons(ETHERTYPE_ARP);
 106         memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
 107         memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
 108
 109         // arp request
 110         p.arp.arp_hrd = htons(ARPHRD_ETHER);
 111         p.arp.arp_pro = htons(ETHERTYPE_IP);
 112         p.arp.arp_hln = ETH_ALEN;
 113         p.arp.arp_pln = 4;
 114         p.arp.arp_op = htons(op);
 115         memcpy(&p.arp.arp_sha, source_addr, ETH_ALEN);
 116         memcpy(&p.arp.arp_spa, &source_ip, sizeof (p.arp.arp_spa));
 117         memcpy(&p.arp.arp_tha, target_addr, ETH_ALEN);
 118         memcpy(&p.arp.arp_tpa, &target_ip, sizeof (p.arp.arp_tpa));
 119
 120         // send it
 121         if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
 122                 perror("sendto");
 123                 return -errno;
 124         }
 125         return 0;
 126 }
 127
 128 /**
 129  * Run a script.
 130  * TODO: sort out stderr/syslog reporting.
 131  */
 132 static int run(char *script, char *arg, char *intf, struct in_addr *ip)
 133 {
 134         int pid, status;
 135         char *why;
 136
 137         if (script != NULL) {
 138                 VDBG("%s run %s %s\n", intf, script, arg);
 139                 if (ip != NULL) {
 140                         char *addr = inet_ntoa(*ip);
 141                         setenv("ip", addr, 1);
 142                         syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
 143                 }
 144
 145                 pid = vfork();
 146                 if (pid < 0) {                  // error
 147                         why = "vfork";
 148                         goto bad;
 149                 } else if (pid == 0) {          // child
 150                         execl(script, script, arg, NULL);
 151                         perror("execl");
 152                         _exit(EXIT_FAILURE);
 153                 }
 154
 155                 if (waitpid(pid, &status, 0) <= 0) {
 156                         why = "waitpid";
 157                         goto bad;
 158                 }
 159                 if (WEXITSTATUS(status) != 0) {
 160                         bb_error_msg("script %s failed, exit=%d\n",
 161                                         script, WEXITSTATUS(status));
 162                         return -errno;
 163                 }
 164         }
 165         return 0;
 166 bad:
 167         status = -errno;
 168         syslog(LOG_ERR, "%s %s, %s error: %s",
 169                 arg, intf, why, strerror(errno));
 170         return status;
 171 }
 172
 173
 174 /**
 175  * Return milliseconds of random delay, up to "secs" seconds.
 176  */
 177 static unsigned ATTRIBUTE_ALWAYS_INLINE ms_rdelay(unsigned secs)
 178 {
 179         return lrand48() % (secs * 1000);
 180 }
 181
 182 /**
 183  * main program
 184  */
 185
 186 /* Used to be auto variables on main() stack, but
 187  * most of them were zero-inited. Moving them to bss
 188  * is more space-efficient.
 189  */
 190 static  const struct in_addr null_ip; // = { 0 };
 191 static  const struct ether_addr null_addr; // = { {0, 0, 0, 0, 0, 0} };
 192
 193 static  struct sockaddr saddr; // memset(0);
 194 static  struct in_addr ip; // = { 0 };
 195 static  struct ifreq ifr; //memset(0);
 196
 197 static  char *intf; // = NULL;
 198 static  char *script; // = NULL;
 199 static  suseconds_t timeout; // = 0;    // milliseconds
 200 static  unsigned conflicts; // = 0;
 201 static  unsigned nprobes; // = 0;
 202 static  unsigned nclaims; // = 0;
 203 static  int ready; // = 0;
 204 static  int verbose; // = 0;
 205 static  int state = PROBE;
 206
 207 int zcip_main(int argc, char *argv[])
 208 {
 209         struct ether_addr eth_addr;
 210         char *why;
 211         int fd;
 212
 213         // parse commandline: prog [options] ifname script
 214 #define FOREGROUND (opts & 1)
 215 #define QUIT (opts & 2)
 216         char *r_opt;
 217         unsigned long opts;
 218
 219         bb_opt_complementally = "vv"; // -v options accumulate
 220         opts = bb_getopt_ulflags(argc, argv, "fqr:v", &r_opt, &verbose);
 221         if (opts & 4) {
 222                 if (inet_aton(r_opt, &ip) == 0
 223                 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR) {
 224                         bb_error_msg_and_die("invalid link address");
 225                 }
 226         }
 227         if (verbose) opts |= 1;
 228         argc -= optind;
 229         argv += optind;
 230         if (argc != 2)
 231                 bb_show_usage();
 232
 233         intf = argv[0];
 234         script = argv[1];
 235         setenv("interface", intf, 1);
 236         openlog(bb_applet_name, 0, LOG_DAEMON);
 237
 238         // initialize the interface (modprobe, ifup, etc)
 239         if (run(script, "init", intf, NULL) < 0)
 240                 return EXIT_FAILURE;
 241
 242         // initialize saddr
 243         //memset(&saddr, 0, sizeof (saddr));
 244         safe_strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
 245
 246         // open an ARP socket
 247         fd = xsocket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
 248         // bind to the interface's ARP socket
 249         xbind(fd, &saddr, sizeof (saddr));
 250
 251         // get the interface's ethernet address
 252         //memset(&ifr, 0, sizeof (ifr));
 253         strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
 254         if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
 255                 bb_perror_msg_and_die("get ethernet address");
 256         }
 257         memcpy(&eth_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 258
 259         // start with some stable ip address, either a function of
 260         // the hardware address or else the last address we used.
 261         // NOTE: the sequence of addresses we try changes only
 262         // depending on when we detect conflicts.
 263         // (SVID 3 bogon: who says that "short" is always 16 bits?)
 264         seed48( (unsigned short*)&ifr.ifr_hwaddr.sa_data );
 265         if (ip.s_addr == 0)
 266                 pick(&ip);
 267
 268         // FIXME cases to handle:
 269         //  - zcip already running!
 270         //  - link already has local address... just defend/update
 271
 272         // daemonize now; don't delay system startup
 273         if (!FOREGROUND) {
 274                 xdaemon(0, verbose);
 275                 syslog(LOG_INFO, "start, interface %s", intf);
 276         }
 277
 278         // run the dynamic address negotiation protocol,
 279         // restarting after address conflicts:
 280         //  - start with some address we want to try
 281         //  - short random delay
 282         //  - arp probes to see if another host else uses it
 283         //  - arp announcements that we're claiming it
 284         //  - use it
 285         //  - defend it, within limits
 286         while (1) {
 287                 struct pollfd fds[1];
 288                 struct timeval tv1;
 289                 struct arp_packet p;
 290
 291                 int source_ip_conflict = 0;
 292                 int target_ip_conflict = 0;
 293
 294                 fds[0].fd = fd;
 295                 fds[0].events = POLLIN;
 296                 fds[0].revents = 0;
 297
 298                 // poll, being ready to adjust current timeout
 299                 if (!timeout) {
 300                         timeout = ms_rdelay(PROBE_WAIT);
 301                         // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
 302                         // make the kernel filter out all packets except
 303                         // ones we'd care about.
 304                 }
 305                 // set tv1 to the point in time when we timeout
 306                 gettimeofday(&tv1, NULL);
 307                 tv1.tv_usec += (timeout % 1000) * 1000;
 308                 while (tv1.tv_usec > 1000000) {
 309                         tv1.tv_usec -= 1000000;
 310                         tv1.tv_sec++;
 311                 }
 312                 tv1.tv_sec += timeout / 1000;
 313
 314                 VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
 315                                 timeout, intf, nprobes, nclaims);
 316                 switch (poll(fds, 1, timeout)) {
 317
 318                 // timeout
 319                 case 0:
 320                         VDBG("state = %d\n", state);
 321                         switch (state) {
 322                         case PROBE:
 323                                 // timeouts in the PROBE state means no conflicting ARP packets
 324                                 // have been received, so we can progress through the states
 325                                 if (nprobes < PROBE_NUM) {
 326                                         nprobes++;
 327                                         VDBG("probe/%d %s@%s\n",
 328                                                         nprobes, intf, inet_ntoa(ip));
 329                                         (void)arp(fd, &saddr, ARPOP_REQUEST,
 330                                                         &eth_addr, null_ip,
 331                                                         &null_addr, ip);
 332                                         timeout = PROBE_MIN * 1000;
 333                                         timeout += ms_rdelay(PROBE_MAX
 334                                                         - PROBE_MIN);
 335                                 }
 336                                 else {
 337                                         // Switch to announce state.
 338                                         state = ANNOUNCE;
 339                                         nclaims = 0;
 340                                         VDBG("announce/%d %s@%s\n",
 341                                                         nclaims, intf, inet_ntoa(ip));
 342                                         (void)arp(fd, &saddr, ARPOP_REQUEST,
 343                                                         &eth_addr, ip,
 344                                                         &eth_addr, ip);
 345                                         timeout = ANNOUNCE_INTERVAL * 1000;
 346                                 }
 347                                 break;
 348                         case RATE_LIMIT_PROBE:
 349                                 // timeouts in the RATE_LIMIT_PROBE state means no conflicting ARP packets
 350                                 // have been received, so we can move immediately to the announce state
 351                                 state = ANNOUNCE;
 352                                 nclaims = 0;
 353                                 VDBG("announce/%d %s@%s\n",
 354                                                 nclaims, intf, inet_ntoa(ip));
 355                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 356                                                 &eth_addr, ip,
 357                                                 &eth_addr, ip);
 358                                 timeout = ANNOUNCE_INTERVAL * 1000;
 359                                 break;
 360                         case ANNOUNCE:
 361                                 // timeouts in the ANNOUNCE state means no conflicting ARP packets
 362                                 // have been received, so we can progress through the states
 363                                 if (nclaims < ANNOUNCE_NUM) {
 364                                         nclaims++;
 365                                         VDBG("announce/%d %s@%s\n",
 366                                                         nclaims, intf, inet_ntoa(ip));
 367                                         (void)arp(fd, &saddr, ARPOP_REQUEST,
 368                                                         &eth_addr, ip,
 369                                                         &eth_addr, ip);
 370                                         timeout = ANNOUNCE_INTERVAL * 1000;
 371                                 }
 372                                 else {
 373                                         // Switch to monitor state.
 374                                         state = MONITOR;
 375                                         // link is ok to use earlier
 376                                         // FIXME update filters
 377                                         run(script, "config", intf, &ip);
 378                                         ready = 1;
 379                                         conflicts = 0;
 380                                         timeout = -1; // Never timeout in the monitor state.
 381
 382                                         // NOTE:  all other exit paths
 383                                         // should deconfig ...
 384                                         if (QUIT)
 385                                                 return EXIT_SUCCESS;
 386                                 }
 387                                 break;
 388                         case DEFEND:
 389                                 // We won!  No ARP replies, so just go back to monitor.
 390                                 state = MONITOR;
 391                                 timeout = -1;
 392                                 conflicts = 0;
 393                                 break;
 394                         default:
 395                                 // Invalid, should never happen.  Restart the whole protocol.
 396                                 state = PROBE;
 397                                 pick(&ip);
 398                                 timeout = 0;
 399                                 nprobes = 0;
 400                                 nclaims = 0;
 401                                 break;
 402                         } // switch (state)
 403                         break; // case 0 (timeout)
 404                 // packets arriving
 405                 case 1:
 406                         // We need to adjust the timeout in case we didn't receive
 407                         // a conflicting packet.
 408                         if (timeout > 0) {
 409                                 struct timeval tv2;
 410
 411                                 gettimeofday(&tv2, NULL);
 412                                 if (timercmp(&tv1, &tv2, <)) {
 413                                         // Current time is greater than the expected timeout time.
 414                                         // Should never happen.
 415                                         VDBG("missed an expected timeout\n");
 416                                         timeout = 0;
 417                                 } else {
 418                                         VDBG("adjusting timeout\n");
 419                                         timersub(&tv1, &tv2, &tv1);
 420                                         timeout = 1000 * tv1.tv_sec
 421                                                         + tv1.tv_usec / 1000;
 422                                 }
 423                         }
 424
 425                         if ((fds[0].revents & POLLIN) == 0) {
 426                                 if (fds[0].revents & POLLERR) {
 427                                         // FIXME: links routinely go down;
 428                                         // this shouldn't necessarily exit.
 429                                         bb_error_msg("%s: poll error\n", intf);
 430                                         if (ready) {
 431                                                 run(script, "deconfig",
 432                                                                 intf, &ip);
 433                                         }
 434                                         return EXIT_FAILURE;
 435                                 }
 436                                 continue;
 437                         }
 438
 439                         // read ARP packet
 440                         if (recv(fd, &p, sizeof (p), 0) < 0) {
 441                                 why = "recv";
 442                                 goto bad;
 443                         }
 444                         if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
 445                                 continue;
 446
 447 #ifdef DEBUG
 448                         {
 449                                 struct ether_addr * sha = (struct ether_addr *) p.arp.arp_sha;
 450                                 struct ether_addr * tha = (struct ether_addr *) p.arp.arp_tha;
 451                                 struct in_addr * spa = (struct in_addr *) p.arp.arp_spa;
 452                                 struct in_addr * tpa = (struct in_addr *) p.arp.arp_tpa;
 453                                 VDBG("%s recv arp type=%d, op=%d,\n",
 454                                         intf, ntohs(p.hdr.ether_type),
 455                                         ntohs(p.arp.arp_op));
 456                                 VDBG("\tsource=%s %s\n",
 457                                         ether_ntoa(sha),
 458                                         inet_ntoa(*spa));
 459                                 VDBG("\ttarget=%s %s\n",
 460                                         ether_ntoa(tha),
 461                                         inet_ntoa(*tpa));
 462                         }
 463 #endif
 464                         if (p.arp.arp_op != htons(ARPOP_REQUEST)
 465                                         && p.arp.arp_op != htons(ARPOP_REPLY))
 466                                 continue;
 467
 468                         if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
 469                                 memcmp(&eth_addr, &p.arp.arp_sha, ETH_ALEN) != 0) {
 470                                 source_ip_conflict = 1;
 471                         }
 472                         if (memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
 473                                 p.arp.arp_op == htons(ARPOP_REQUEST) &&
 474                                 memcmp(&eth_addr, &p.arp.arp_tha, ETH_ALEN) != 0) {
 475                                 target_ip_conflict = 1;
 476                         }
 477
 478                         VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
 479                                 state, source_ip_conflict, target_ip_conflict);
 480                         switch (state) {
 481                         case PROBE:
 482                         case ANNOUNCE:
 483                                 // When probing or announcing, check for source IP conflicts
 484                                 // and other hosts doing ARP probes (target IP conflicts).
 485                                 if (source_ip_conflict || target_ip_conflict) {
 486                                         conflicts++;
 487                                         if (conflicts >= MAX_CONFLICTS) {
 488                                                 VDBG("%s ratelimit\n", intf);
 489                                                 timeout = RATE_LIMIT_INTERVAL * 1000;
 490                                                 state = RATE_LIMIT_PROBE;
 491                                         }
 492
 493                                         // restart the whole protocol
 494                                         pick(&ip);
 495                                         timeout = 0;
 496                                         nprobes = 0;
 497                                         nclaims = 0;
 498                                 }
 499                                 break;
 500                         case MONITOR:
 501                                 // If a conflict, we try to defend with a single ARP probe.
 502                                 if (source_ip_conflict) {
 503                                         VDBG("monitor conflict -- defending\n");
 504                                         state = DEFEND;
 505                                         timeout = DEFEND_INTERVAL * 1000;
 506                                         (void)arp(fd, &saddr,
 507                                                         ARPOP_REQUEST,
 508                                                         &eth_addr, ip,
 509                                                         &eth_addr, ip);
 510                                 }
 511                                 break;
 512                         case DEFEND:
 513                                 // Well, we tried.  Start over (on conflict).
 514                                 if (source_ip_conflict) {
 515                                         state = PROBE;
 516                                         VDBG("defend conflict -- starting over\n");
 517                                         ready = 0;
 518                                         run(script, "deconfig", intf, &ip);
 519
 520                                         // restart the whole protocol
 521                                         pick(&ip);
 522                                         timeout = 0;
 523                                         nprobes = 0;
 524                                         nclaims = 0;
 525                                 }
 526                                 break;
 527                         default:
 528                                 // Invalid, should never happen.  Restart the whole protocol.
 529                                 VDBG("invalid state -- starting over\n");
 530                                 state = PROBE;
 531                                 pick(&ip);
 532                                 timeout = 0;
 533                                 nprobes = 0;
 534                                 nclaims = 0;
 535                                 break;
 536                         } // switch state
 537
 538                         break; // case 1 (packets arriving)
 539                 default:
 540                         why = "poll";
 541                         goto bad;
 542                 } // switch poll
 543         }
 544 bad:
 545         if (FOREGROUND)
 546                 perror(why);
 547         else
 548                 syslog(LOG_ERR, "%s %s, %s error: %s",
 549                         bb_applet_name, intf, why, strerror(errno));
 550         return EXIT_FAILURE;
 551 }