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 enum {
  66 /* 169.254.0.0 */
  67         LINKLOCAL_ADDR = 0xa9fe0000,
  68
  69 /* protocol timeout parameters, specified in seconds */
  70         PROBE_WAIT = 1,
  71         PROBE_MIN = 1,
  72         PROBE_MAX = 2,
  73         PROBE_NUM = 3,
  74         MAX_CONFLICTS = 10,
  75         RATE_LIMIT_INTERVAL = 60,
  76         ANNOUNCE_WAIT = 2,
  77         ANNOUNCE_NUM = 2,
  78         ANNOUNCE_INTERVAL = 2,
  79         DEFEND_INTERVAL = 10
  80 };
  81
  82 static const unsigned char ZCIP_VERSION[] = "0.75 (18 April 2005)";
  83 static char *prog;
  84
  85 static const struct in_addr null_ip = { 0 };
  86 static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };
  87
  88 static int verbose = 0;
  89
  90 #ifdef DEBUG
  91
  92 #define DBG(fmt,args...) \
  93         fprintf(stderr, "%s: " fmt , prog , ## args)
  94 #define VDBG(fmt,args...) do { \
  95         if (verbose) fprintf(stderr, "%s: " fmt , prog ,## args); \
  96         } while (0)
  97 #else
  98
  99 #define DBG(fmt,args...) \
 100         do { } while (0)
 101 #define VDBG    DBG
 102 #endif                          /* DEBUG */
 103
 104 /**
 105  * Pick a random link local IP address on 169.254/16, except that
 106  * the first and last 256 addresses are reserved.
 107  */
 108 static void
 109 pick(struct in_addr *ip)
 110 {
 111         unsigned        tmp;
 112
 113         /* use cheaper math than lrand48() mod N */
 114         do {
 115                 tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
 116         } while (tmp > (IN_CLASSB_HOST - 0x0200));
 117         ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
 118 }
 119
 120 /**
 121  * Broadcast an ARP packet.
 122  */
 123 static int
 124 arp(int fd, struct sockaddr *saddr, int op,
 125         const struct ether_addr *source_addr, struct in_addr source_ip,
 126         const struct ether_addr *target_addr, struct in_addr target_ip)
 127 {
 128         struct arp_packet p;
 129
 130         // ether header
 131         p.hdr.ether_type = htons(ETHERTYPE_ARP);
 132         memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
 133         memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
 134
 135         // arp request
 136         p.arp.ar_hrd = htons(ARPHRD_ETHER);
 137         p.arp.ar_pro = htons(ETHERTYPE_IP);
 138         p.arp.ar_hln = ETH_ALEN;
 139         p.arp.ar_pln = 4;
 140         p.arp.ar_op = htons(op);
 141         memcpy(&p.source_addr, source_addr, ETH_ALEN);
 142         memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
 143         memcpy(&p.target_addr, target_addr, ETH_ALEN);
 144         memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));
 145
 146         // send it
 147         if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
 148                 perror("sendto");
 149                 return -errno;
 150         }
 151         return 0;
 152 }
 153
 154 /**
 155  * Run a script.
 156  */
 157 static int
 158 run(char *script, char *arg, char *intf, struct in_addr *ip)
 159 {
 160         int pid, status;
 161         char *why;
 162
 163         if (script != NULL) {
 164                 VDBG("%s run %s %s\n", intf, script, arg);
 165                 if (ip != NULL) {
 166                         char *addr = inet_ntoa(*ip);
 167                         setenv("ip", addr, 1);
 168                         syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
 169                 }
 170
 171                 pid = vfork();
 172                 if (pid < 0) {                  // error
 173                         why = "vfork";
 174                         goto bad;
 175                 } else if (pid == 0) {          // child
 176                         execl(script, script, arg, NULL);
 177                         perror("execl");
 178                         _exit(EXIT_FAILURE);
 179                 }
 180
 181                 if (waitpid(pid, &status, 0) <= 0) {
 182                         why = "waitpid";
 183                         goto bad;
 184                 }
 185                 if (WEXITSTATUS(status) != 0) {
 186                         fprintf(stderr, "%s: script %s failed, exit=%d\n",
 187                                         prog, script, WEXITSTATUS(status));
 188                         return -errno;
 189                 }
 190         }
 191         return 0;
 192 bad:
 193         status = -errno;
 194         syslog(LOG_ERR, "%s %s, %s error: %s",
 195                 arg, intf, why, strerror(errno));
 196         return status;
 197 }
 198
 199 #ifndef NO_BUSYBOX
 200 #include "busybox.h"
 201 #endif
 202
 203 /**
 204  * Print usage information.
 205  */
 206 static void ATTRIBUTE_NORETURN
 207 zcip_usage(const char *msg)
 208 {
 209         fprintf(stderr, "%s: %s\n", prog, msg);
 210 #ifdef  NO_BUSYBOX
 211         fprintf(stderr, "Usage: %s [OPTIONS] ifname script\n"
 212                         "\t-f              foreground mode (implied by -v)\n"
 213                         "\t-q              quit after address (no daemon)\n"
 214                         "\t-r 169.254.x.x  request this address first\n"
 215                         "\t-v              verbose; show version\n",
 216                         prog);
 217         exit(0);
 218 #else
 219         bb_show_usage();
 220 #endif
 221 }
 222
 223 /**
 224  * Return milliseconds of random delay, up to "secs" seconds.
 225  */
 226 static inline unsigned
 227 ms_rdelay(unsigned secs)
 228 {
 229         return lrand48() % (secs * 1000);
 230 }
 231
 232 /**
 233  * main program
 234  */
 235
 236 #ifdef  NO_BUSYBOX
 237 int
 238 main(int argc, char *argv[])
 239         __attribute__ ((weak, alias ("zcip_main")));
 240 #endif
 241
 242 int zcip_main(int argc, char *argv[])
 243 {
 244         char *intf = NULL;
 245         char *script = NULL;
 246         int quit = 0;
 247         int foreground = 0;
 248
 249         char *why;
 250         struct sockaddr saddr;
 251         struct ether_addr addr;
 252         struct in_addr ip = { 0 };
 253         int fd;
 254         int ready = 0;
 255         suseconds_t timeout = 0;        // milliseconds
 256         time_t defend = 0;
 257         unsigned conflicts = 0;
 258         unsigned nprobes = 0;
 259         unsigned nclaims = 0;
 260         int t;
 261
 262         // parse commandline: prog [options] ifname script
 263         prog = argv[0];
 264         while ((t = getopt(argc, argv, "fqr:v")) != EOF) {
 265                 switch (t) {
 266                 case 'f':
 267                         foreground = 1;
 268                         continue;
 269                 case 'q':
 270                         quit = 1;
 271                         continue;
 272                 case 'r':
 273                         if (inet_aton(optarg, &ip) == 0
 274                                         || (ntohl(ip.s_addr) & IN_CLASSB_NET)
 275                                                 != LINKLOCAL_ADDR) {
 276                                 zcip_usage("invalid link address");
 277                         }
 278                         continue;
 279                 case 'v':
 280                         if (!verbose)
 281                                 printf("%s: version %s\n", prog, ZCIP_VERSION);
 282                         verbose++;
 283                         foreground = 1;
 284                         continue;
 285                 default:
 286                         zcip_usage("bad option");
 287                 }
 288         }
 289         if (optind < argc - 1) {
 290                 intf = argv[optind++];
 291                 setenv("interface", intf, 1);
 292                 script = argv[optind++];
 293         }
 294         if (optind != argc || !intf)
 295                 zcip_usage("wrong number of arguments");
 296         openlog(prog, 0, LOG_DAEMON);
 297
 298         // initialize the interface (modprobe, ifup, etc)
 299         if (run(script, "init", intf, NULL) < 0)
 300                 return EXIT_FAILURE;
 301
 302         // initialize saddr
 303         memset(&saddr, 0, sizeof (saddr));
 304         strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
 305
 306         // open an ARP socket
 307         if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
 308                 why = "open";
 309 fail:
 310                 foreground = 1;
 311                 goto bad;
 312         }
 313         // bind to the interface's ARP socket
 314         if (bind(fd, &saddr, sizeof (saddr)) < 0) {
 315                 why = "bind";
 316                 goto fail;
 317         } else {
 318                 struct ifreq ifr;
 319                 unsigned short seed[3];
 320
 321                 // get the interface's ethernet address
 322                 memset(&ifr, 0, sizeof (ifr));
 323                 strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
 324                 if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
 325                         why = "get ethernet address";
 326                         goto fail;
 327                 }
 328                 memcpy(&addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 329
 330                 // start with some stable ip address, either a function of
 331                 // the hardware address or else the last address we used.
 332                 // NOTE: the sequence of addresses we try changes only
 333                 // depending on when we detect conflicts.
 334                 memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 335                 seed48(seed);
 336                 if (ip.s_addr == 0)
 337                         pick(&ip);
 338         }
 339
 340         // FIXME cases to handle:
 341         //  - zcip already running!
 342         //  - link already has local address... just defend/update
 343
 344         // daemonize now; don't delay system startup
 345         if (!foreground) {
 346                 if (daemon(0, verbose) < 0) {
 347                         why = "daemon";
 348                         goto bad;
 349                 }
 350                 syslog(LOG_INFO, "start, interface %s", intf);
 351         }
 352
 353         // run the dynamic address negotiation protocol,
 354         // restarting after address conflicts:
 355         //  - start with some address we want to try
 356         //  - short random delay
 357         //  - arp probes to see if another host else uses it
 358         //  - arp announcements that we're claiming it
 359         //  - use it
 360         //  - defend it, within limits
 361         while (1) {
 362                 struct pollfd fds[1];
 363                 struct timeval tv1;
 364                 struct arp_packet p;
 365
 366                 fds[0].fd = fd;
 367                 fds[0].events = POLLIN;
 368                 fds[0].revents = 0;
 369
 370                 // poll, being ready to adjust current timeout
 371                 if (timeout > 0) {
 372                         gettimeofday(&tv1, NULL);
 373                         tv1.tv_usec += (timeout % 1000) * 1000;
 374                         while (tv1.tv_usec > 1000000) {
 375                                 tv1.tv_usec -= 1000000;
 376                                 tv1.tv_sec++;
 377                         }
 378                         tv1.tv_sec += timeout / 1000;
 379                 } else if (timeout == 0) {
 380                         timeout = ms_rdelay(PROBE_WAIT);
 381                         // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
 382                         // make the kernel filter out all packets except
 383                         // ones we'd care about.
 384                 }
 385                 VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
 386                                 timeout, intf, nprobes, nclaims);
 387                 switch (poll(fds, 1, timeout)) {
 388
 389                 // timeouts trigger protocol transitions
 390                 case 0:
 391                         // probes
 392                         if (nprobes < PROBE_NUM) {
 393                                 nprobes++;
 394                                 VDBG("probe/%d %s@%s\n",
 395                                                 nprobes, intf, inet_ntoa(ip));
 396                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 397                                                 &addr, null_ip,
 398                                                 &null_addr, ip);
 399                                 if (nprobes < PROBE_NUM) {
 400                                         timeout = PROBE_MIN * 1000;
 401                                         timeout += ms_rdelay(PROBE_MAX
 402                                                         - PROBE_MIN);
 403                                 } else
 404                                         timeout = ANNOUNCE_WAIT * 1000;
 405                         }
 406                         // then announcements
 407                         else if (nclaims < ANNOUNCE_NUM) {
 408                                 nclaims++;
 409                                 VDBG("announce/%d %s@%s\n",
 410                                                 nclaims, intf, inet_ntoa(ip));
 411                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 412                                                 &addr, ip,
 413                                                 &addr, ip);
 414                                 if (nclaims < ANNOUNCE_NUM) {
 415                                         timeout = ANNOUNCE_INTERVAL * 1000;
 416                                 } else {
 417                                         // link is ok to use earlier
 418                                         run(script, "config", intf, &ip);
 419                                         ready = 1;
 420                                         conflicts = 0;
 421                                         timeout = -1;
 422
 423                                         // NOTE:  all other exit paths
 424                                         // should deconfig ...
 425                                         if (quit)
 426                                                 return EXIT_SUCCESS;
 427                                         // FIXME update filters
 428                                 }
 429                         }
 430                         break;
 431
 432                 // packets arriving
 433                 case 1:
 434                         // maybe adjust timeout
 435                         if (timeout > 0) {
 436                                 struct timeval tv2;
 437
 438                                 gettimeofday(&tv2, NULL);
 439                                 if (timercmp(&tv1, &tv2, <)) {
 440                                         timeout = -1;
 441                                 } else {
 442                                         timersub(&tv1, &tv2, &tv1);
 443                                         timeout = 1000 * tv1.tv_sec
 444                                                         + tv1.tv_usec / 1000;
 445                                 }
 446                         }
 447                         if ((fds[0].revents & POLLIN) == 0) {
 448                                 if (fds[0].revents & POLLERR) {
 449                                         // FIXME: links routinely go down;
 450                                         // this shouldn't necessarily exit.
 451                                         fprintf(stderr, "%s %s: poll error\n",
 452                                                         prog, intf);
 453                                         if (ready) {
 454                                                 run(script, "deconfig",
 455                                                                 intf, &ip);
 456                                         }
 457                                         return EXIT_FAILURE;
 458                                 }
 459                                 continue;
 460                         }
 461                         // read ARP packet
 462                         if (recv(fd, &p, sizeof (p), 0) < 0) {
 463                                 why = "recv";
 464                                 goto bad;
 465                         }
 466                         if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
 467                                 continue;
 468
 469                         VDBG("%s recv arp type=%d, op=%d,\n",
 470                                         intf, ntohs(p.hdr.ether_type),
 471                                         ntohs(p.arp.ar_op));
 472                         VDBG("\tsource=%s %s\n",
 473                                         ether_ntoa(&p.source_addr),
 474                                         inet_ntoa(p.source_ip));
 475                         VDBG("\ttarget=%s %s\n",
 476                                         ether_ntoa(&p.target_addr),
 477                                         inet_ntoa(p.target_ip));
 478                         if (p.arp.ar_op != htons(ARPOP_REQUEST)
 479                                         && p.arp.ar_op != htons(ARPOP_REPLY))
 480                                 continue;
 481
 482                         // some cases are always conflicts
 483                         if ((p.source_ip.s_addr == ip.s_addr)
 484                                         && (memcmp(&addr, &p.source_addr,
 485                                                         ETH_ALEN) != 0)) {
 486 collision:
 487                                 VDBG("%s ARP conflict from %s\n", intf,
 488                                                 ether_ntoa(&p.source_addr));
 489                                 if (ready) {
 490                                         time_t now = time(0);
 491
 492                                         if ((defend + DEFEND_INTERVAL)
 493                                                         < now) {
 494                                                 defend = now;
 495                                                 (void)arp(fd, &saddr,
 496                                                                 ARPOP_REQUEST,
 497                                                                 &addr, ip,
 498                                                                 &addr, ip);
 499                                                 VDBG("%s defend\n", intf);
 500                                                 timeout = -1;
 501                                                 continue;
 502                                         }
 503                                         defend = now;
 504                                         ready = 0;
 505                                         run(script, "deconfig", intf, &ip);
 506                                         // FIXME rm filters: setsockopt(fd,
 507                                         // SO_DETACH_FILTER, ...)
 508                                 }
 509                                 conflicts++;
 510                                 if (conflicts >= MAX_CONFLICTS) {
 511                                         VDBG("%s ratelimit\n", intf);
 512                                         sleep(RATE_LIMIT_INTERVAL);
 513                                 }
 514                                 // restart the whole protocol
 515                                 pick(&ip);
 516                                 timeout = 0;
 517                                 nprobes = 0;
 518                                 nclaims = 0;
 519                         }
 520                         // two hosts probing one address is a collision too
 521                         else if (p.target_ip.s_addr == ip.s_addr
 522                                         && nclaims == 0
 523                                         && p.arp.ar_op == htons(ARPOP_REQUEST)
 524                                         && memcmp(&addr, &p.target_addr,
 525                                                         ETH_ALEN) != 0) {
 526                                 goto collision;
 527                         }
 528                         break;
 529
 530                 default:
 531                         why = "poll";
 532                         goto bad;
 533                 }
 534         }
 535 bad:
 536         if (foreground)
 537                 perror(why);
 538         else
 539                 syslog(LOG_ERR, "%s %s, %s error: %s",
 540                         prog, intf, why, strerror(errno));
 541         return EXIT_FAILURE;
 542 }