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 // #define      DEBUG
  35
  36 // TODO:
  37 // - more real-world usage/testing, especially daemon mode
  38 // - kernel packet filters to reduce scheduling noise
  39 // - avoid silent script failures, especially under load...
  40 // - link status monitoring (restart on link-up; stop on link-down)
  41
  42 #include <errno.h>
  43 #include <stdlib.h>
  44 #include <stdio.h>
  45 #include <string.h>
  46 #include <syslog.h>
  47 #include <poll.h>
  48 #include <time.h>
  49 #include <unistd.h>
  50
  51 #include <sys/ioctl.h>
  52 #include <sys/types.h>
  53 #include <sys/wait.h>
  54 #include <sys/time.h>
  55 #include <sys/socket.h>
  56
  57 #include <arpa/inet.h>
  58 #include <netinet/in.h>
  59 #include <netinet/ether.h>
  60 #include <net/ethernet.h>
  61 #include <net/if.h>
  62 #include <net/if_arp.h>
  63
  64 #include <linux/if_packet.h>
  65 #include <linux/sockios.h>
  66
  67
  68 struct arp_packet {
  69         struct ether_header hdr;
  70         // FIXME this part is netinet/if_ether.h "struct ether_arp"
  71         struct arphdr arp;
  72         struct ether_addr source_addr;
  73         struct in_addr source_ip;
  74         struct ether_addr target_addr;
  75         struct in_addr target_ip;
  76 } __attribute__ ((__packed__));
  77
  78 /* 169.254.0.0 */
  79 static const uint32_t LINKLOCAL_ADDR = 0xa9fe0000;
  80
  81 /* protocol timeout parameters, specified in seconds */
  82 static const unsigned PROBE_WAIT = 1;
  83 static const unsigned PROBE_MIN = 1;
  84 static const unsigned PROBE_MAX = 2;
  85 static const unsigned PROBE_NUM = 3;
  86 static const unsigned MAX_CONFLICTS = 10;
  87 static const unsigned RATE_LIMIT_INTERVAL = 60;
  88 static const unsigned ANNOUNCE_WAIT = 2;
  89 static const unsigned ANNOUNCE_NUM = 2;
  90 static const unsigned ANNOUNCE_INTERVAL = 2;
  91 static const time_t DEFEND_INTERVAL = 10;
  92
  93 static const unsigned char ZCIP_VERSION[] = "0.75 (18 April 2005)";
  94 static char *prog;
  95
  96 static const struct in_addr null_ip = { 0 };
  97 static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };
  98
  99 static int verbose = 0;
 100
 101 #ifdef DEBUG
 102
 103 #define DBG(fmt,args...) \
 104         fprintf(stderr, "%s: " fmt , prog , ## args)
 105 #define VDBG(fmt,args...) do { \
 106         if (verbose) fprintf(stderr, "%s: " fmt , prog ,## args); \
 107         } while (0)
 108 #else
 109
 110 #define DBG(fmt,args...) \
 111         do { } while (0)
 112 #define VDBG    DBG
 113 #endif                          /* DEBUG */
 114
 115 /**
 116  * Pick a random link local IP address on 169.254/16, except that
 117  * the first and last 256 addresses are reserved.
 118  */
 119 static void
 120 pick(struct in_addr *ip)
 121 {
 122         unsigned        tmp;
 123
 124         /* use cheaper math than lrand48() mod N */
 125         do {
 126                 tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
 127         } while (tmp > (IN_CLASSB_HOST - 0x0200));
 128         ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
 129 }
 130
 131 /**
 132  * Broadcast an ARP packet.
 133  */
 134 static int
 135 arp(int fd, struct sockaddr *saddr, int op,
 136         const struct ether_addr *source_addr, struct in_addr source_ip,
 137         const struct ether_addr *target_addr, struct in_addr target_ip)
 138 {
 139         struct arp_packet p;
 140
 141         // ether header
 142         p.hdr.ether_type = htons(ETHERTYPE_ARP);
 143         memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
 144         memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
 145
 146         // arp request
 147         p.arp.ar_hrd = htons(ARPHRD_ETHER);
 148         p.arp.ar_pro = htons(ETHERTYPE_IP);
 149         p.arp.ar_hln = ETH_ALEN;
 150         p.arp.ar_pln = 4;
 151         p.arp.ar_op = htons(op);
 152         memcpy(&p.source_addr, source_addr, ETH_ALEN);
 153         memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
 154         memcpy(&p.target_addr, target_addr, ETH_ALEN);
 155         memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));
 156
 157         // send it
 158         if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
 159                 perror("sendto");
 160                 return -errno;
 161         }
 162         return 0;
 163 }
 164
 165 /**
 166  * Run a script.
 167  */
 168 static int
 169 run(char *script, char *arg, char *intf, struct in_addr *ip)
 170 {
 171         int pid, status;
 172         char *why;
 173
 174         if (script != NULL) {
 175                 VDBG("%s run %s %s\n", intf, script, arg);
 176                 if (ip != NULL) {
 177                         char *addr = inet_ntoa(*ip);
 178                         setenv("ip", addr, 1);
 179                         syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
 180                 }
 181
 182                 pid = vfork();
 183                 if (pid < 0) {                  // error
 184                         why = "vfork";
 185                         goto bad;
 186                 } else if (pid == 0) {          // child
 187                         execl(script, script, arg, NULL);
 188                         perror("execl");
 189                         _exit(EXIT_FAILURE);
 190                 }
 191
 192                 if (waitpid(pid, &status, 0) <= 0) {
 193                         why = "waitpid";
 194                         goto bad;
 195                 }
 196                 if (WEXITSTATUS(status) != 0) {
 197                         fprintf(stderr, "%s: script %s failed, exit=%d\n",
 198                                         prog, script, WEXITSTATUS(status));
 199                         return -errno;
 200                 }
 201         }
 202         return 0;
 203 bad:
 204         status = -errno;
 205         syslog(LOG_ERR, "%s %s, %s error: %s",
 206                 arg, intf, why, strerror(errno));
 207         return status;
 208 }
 209
 210 #ifndef NO_BUSYBOX
 211 #include "busybox.h"
 212 #endif
 213
 214 /**
 215  * Print usage information.
 216  */
 217 static void __attribute__ ((noreturn))
 218 usage(const char *msg)
 219 {
 220         fprintf(stderr, "%s: %s\n", prog, msg);
 221 #ifdef  NO_BUSYBOX
 222         fprintf(stderr, "Usage: %s [OPTIONS] ifname script\n"
 223                         "\t-f              foreground mode (implied by -v)\n"
 224                         "\t-q              quit after address (no daemon)\n"
 225                         "\t-r 169.254.x.x  request this address first\n"
 226                         "\t-v              verbose; show version\n",
 227                         prog);
 228         exit(0);
 229 #else
 230         bb_show_usage();
 231 #endif
 232 }
 233
 234 /**
 235  * Return milliseconds of random delay, up to "secs" seconds.
 236  */
 237 static inline unsigned
 238 ms_rdelay(unsigned secs)
 239 {
 240         return lrand48() % (secs * 1000);
 241 }
 242
 243 /**
 244  * main program
 245  */
 246
 247 #ifdef  NO_BUSYBOX
 248 int
 249 main(int argc, char *argv[])
 250         __attribute__ ((weak, alias ("zcip_main")));
 251 #endif
 252
 253 int zcip_main(int argc, char *argv[])
 254 {
 255         char *intf = NULL;
 256         char *script = NULL;
 257         int quit = 0;
 258         int foreground = 0;
 259
 260         char *why;
 261         struct sockaddr saddr;
 262         struct ether_addr addr;
 263         struct in_addr ip = { 0 };
 264         int fd;
 265         int ready = 0;
 266         suseconds_t timeout = 0;        // milliseconds
 267         time_t defend = 0;
 268         unsigned conflicts = 0;
 269         unsigned nprobes = 0;
 270         unsigned nclaims = 0;
 271         int t;
 272
 273         // parse commandline: prog [options] ifname script
 274         prog = argv[0];
 275         while ((t = getopt(argc, argv, "fqr:v")) != EOF) {
 276                 switch (t) {
 277                 case 'f':
 278                         foreground = 1;
 279                         continue;
 280                 case 'q':
 281                         quit = 1;
 282                         continue;
 283                 case 'r':
 284                         if (inet_aton(optarg, &ip) == 0
 285                                         || (ntohl(ip.s_addr) & IN_CLASSB_NET)
 286                                                 != LINKLOCAL_ADDR) {
 287                                 usage("invalid link address");
 288                         }
 289                         continue;
 290                 case 'v':
 291                         if (!verbose)
 292                                 printf("%s: version %s\n", prog, ZCIP_VERSION);
 293                         verbose++;
 294                         foreground = 1;
 295                         continue;
 296                 default:
 297                         usage("bad option");
 298                 }
 299         }
 300         if (optind < argc - 1) {
 301                 intf = argv[optind++];
 302                 setenv("interface", intf, 1);
 303                 script = argv[optind++];
 304         }
 305         if (optind != argc || !intf)
 306                 usage("wrong number of arguments");
 307         openlog(prog, 0, LOG_DAEMON);
 308
 309         // initialize the interface (modprobe, ifup, etc)
 310         if (run(script, "init", intf, NULL) < 0)
 311                 return EXIT_FAILURE;
 312
 313         // initialize saddr
 314         memset(&saddr, 0, sizeof (saddr));
 315         strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
 316
 317         // open an ARP socket
 318         if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
 319                 why = "open";
 320 fail:
 321                 foreground = 1;
 322                 goto bad;
 323         }
 324         // bind to the interface's ARP socket
 325         if (bind(fd, &saddr, sizeof (saddr)) < 0) {
 326                 why = "bind";
 327                 goto fail;
 328         } else {
 329                 struct ifreq ifr;
 330                 short seed[3];
 331
 332                 // get the interface's ethernet address
 333                 memset(&ifr, 0, sizeof (ifr));
 334                 strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
 335                 if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
 336                         why = "get ethernet address";
 337                         goto fail;
 338                 }
 339                 memcpy(&addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 340
 341                 // start with some stable ip address, either a function of
 342                 // the hardware address or else the last address we used.
 343                 // NOTE: the sequence of addresses we try changes only
 344                 // depending on when we detect conflicts.
 345                 memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 346                 seed48(seed);
 347                 if (ip.s_addr == 0)
 348                         pick(&ip);
 349         }
 350
 351         // FIXME cases to handle:
 352         //  - zcip already running!
 353         //  - link already has local address... just defend/update
 354
 355         // daemonize now; don't delay system startup
 356         if (!foreground) {
 357                 if (daemon(0, verbose) < 0) {
 358                         why = "daemon";
 359                         goto bad;
 360                 }
 361                 syslog(LOG_INFO, "start, interface %s", intf);
 362         }
 363
 364         // run the dynamic address negotiation protocol,
 365         // restarting after address conflicts:
 366         //  - start with some address we want to try
 367         //  - short random delay
 368         //  - arp probes to see if another host else uses it
 369         //  - arp announcements that we're claiming it
 370         //  - use it
 371         //  - defend it, within limits
 372         while (1) {
 373                 struct pollfd fds[1];
 374                 struct timeval tv1;
 375                 struct arp_packet p;
 376
 377                 fds[0].fd = fd;
 378                 fds[0].events = POLLIN;
 379                 fds[0].revents = 0;
 380
 381                 // poll, being ready to adjust current timeout
 382                 if (timeout > 0) {
 383                         gettimeofday(&tv1, NULL);
 384                         tv1.tv_usec += (timeout % 1000) * 1000;
 385                         while (tv1.tv_usec > 1000000) {
 386                                 tv1.tv_usec -= 1000000;
 387                                 tv1.tv_sec++;
 388                         }
 389                         tv1.tv_sec += timeout / 1000;
 390                 } else if (timeout == 0) {
 391                         timeout = ms_rdelay(PROBE_WAIT);
 392                         // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
 393                         // make the kernel filter out all packets except
 394                         // ones we'd care about.
 395                 }
 396                 VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
 397                                 timeout, intf, nprobes, nclaims);
 398                 switch (poll(fds, 1, timeout)) {
 399
 400                 // timeouts trigger protocol transitions
 401                 case 0:
 402                         // probes
 403                         if (nprobes < PROBE_NUM) {
 404                                 nprobes++;
 405                                 VDBG("probe/%d %s@%s\n",
 406                                                 nprobes, intf, inet_ntoa(ip));
 407                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 408                                                 &addr, null_ip,
 409                                                 &null_addr, ip);
 410                                 if (nprobes < PROBE_NUM) {
 411                                         timeout = PROBE_MIN * 1000;
 412                                         timeout += ms_rdelay(PROBE_MAX
 413                                                         - PROBE_MIN);
 414                                 } else
 415                                         timeout = ANNOUNCE_WAIT * 1000;
 416                         }
 417                         // then announcements
 418                         else if (nclaims < ANNOUNCE_NUM) {
 419                                 nclaims++;
 420                                 VDBG("announce/%d %s@%s\n",
 421                                                 nclaims, intf, inet_ntoa(ip));
 422                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 423                                                 &addr, ip,
 424                                                 &addr, ip);
 425                                 if (nclaims < ANNOUNCE_NUM) {
 426                                         timeout = ANNOUNCE_INTERVAL * 1000;
 427                                 } else {
 428                                         // link is ok to use earlier
 429                                         run(script, "config", intf, &ip);
 430                                         ready = 1;
 431                                         conflicts = 0;
 432                                         timeout = -1;
 433
 434                                         // NOTE:  all other exit paths
 435                                         // should deconfig ...
 436                                         if (quit)
 437                                                 return EXIT_SUCCESS;
 438                                         // FIXME update filters
 439                                 }
 440                         }
 441                         break;
 442
 443                 // packets arriving
 444                 case 1:
 445                         // maybe adjust timeout
 446                         if (timeout > 0) {
 447                                 struct timeval tv2;
 448
 449                                 gettimeofday(&tv2, NULL);
 450                                 if (timercmp(&tv1, &tv2, <)) {
 451                                         timeout = -1;
 452                                 } else {
 453                                         timersub(&tv1, &tv2, &tv1);
 454                                         timeout = 1000 * tv1.tv_sec
 455                                                         + tv1.tv_usec / 1000;
 456                                 }
 457                         }
 458                         if ((fds[0].revents & POLLIN) == 0) {
 459                                 if (fds[0].revents & POLLERR) {
 460                                         // FIXME: links routinely go down;
 461                                         // this shouldn't necessarily exit.
 462                                         fprintf(stderr, "%s %s: poll error\n",
 463                                                         prog, intf);
 464                                         if (ready) {
 465                                                 run(script, "deconfig",
 466                                                                 intf, &ip);
 467                                         }
 468                                         return EXIT_FAILURE;
 469                                 }
 470                                 continue;
 471                         }
 472                         // read ARP packet
 473                         if (recv(fd, &p, sizeof (p), 0) < 0) {
 474                                 why = "recv";
 475                                 goto bad;
 476                         }
 477                         if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
 478                                 continue;
 479
 480                         VDBG("%s recv arp type=%d, op=%d,\n",
 481                                         intf, ntohs(p.hdr.ether_type),
 482                                         ntohs(p.arp.ar_op));
 483                         VDBG("\tsource=%s %s\n",
 484                                         ether_ntoa(&p.source_addr),
 485                                         inet_ntoa(p.source_ip));
 486                         VDBG("\ttarget=%s %s\n",
 487                                         ether_ntoa(&p.target_addr),
 488                                         inet_ntoa(p.target_ip));
 489                         if (p.arp.ar_op != htons(ARPOP_REQUEST)
 490                                         && p.arp.ar_op != htons(ARPOP_REPLY))
 491                                 continue;
 492
 493                         // some cases are always conflicts
 494                         if ((p.source_ip.s_addr == ip.s_addr)
 495                                         && (memcmp(&addr, &p.source_addr,
 496                                                         ETH_ALEN) != 0)) {
 497 collision:
 498                                 VDBG("%s ARP conflict from %s\n", intf,
 499                                                 ether_ntoa(&p.source_addr));
 500                                 if (ready) {
 501                                         time_t now = time(0);
 502
 503                                         if ((defend + DEFEND_INTERVAL)
 504                                                         < now) {
 505                                                 defend = now;
 506                                                 (void)arp(fd, &saddr,
 507                                                                 ARPOP_REQUEST,
 508                                                                 &addr, ip,
 509                                                                 &addr, ip);
 510                                                 VDBG("%s defend\n", intf);
 511                                                 timeout = -1;
 512                                                 continue;
 513                                         }
 514                                         defend = now;
 515                                         ready = 0;
 516                                         run(script, "deconfig", intf, &ip);
 517                                         // FIXME rm filters: setsockopt(fd,
 518                                         // SO_DETACH_FILTER, ...)
 519                                 }
 520                                 conflicts++;
 521                                 if (conflicts >= MAX_CONFLICTS) {
 522                                         VDBG("%s ratelimit\n", intf);
 523                                         sleep(RATE_LIMIT_INTERVAL);
 524                                 }
 525                                 // restart the whole protocol
 526                                 pick(&ip);
 527                                 timeout = 0;
 528                                 nprobes = 0;
 529                                 nclaims = 0;
 530                         }
 531                         // two hosts probing one address is a collision too
 532                         else if (p.target_ip.s_addr == ip.s_addr
 533                                         && nclaims == 0
 534                                         && p.arp.ar_op == htons(ARPOP_REQUEST)
 535                                         && memcmp(&addr, &p.target_addr,
 536                                                         ETH_ALEN) != 0) {
 537                                 goto collision;
 538                         }
 539                         break;
 540
 541                 default:
 542                         why = "poll";
 543                         goto bad;
 544                 }
 545         }
 546 bad:
 547         if (foreground)
 548                 perror(why);
 549         else
 550                 syslog(LOG_ERR, "%s %s, %s error: %s",
 551                         prog, intf, why, strerror(errno));
 552         return EXIT_FAILURE;
 553 }