usr.sbin/arp/arp.c

   1 /*
   2  * Copyright (c) 1984, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Sun Microsystems, Inc.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  * @(#) Copyright (c) 1984, 1993 The Regents of the University of California.  All rights reserved.
  33  * @(#)from: arp.c      8.2 (Berkeley) 1/2/94
  34  * $FreeBSD: src/usr.sbin/arp/arp.c,v 1.22.2.12 2003/04/16 10:02:37 ru Exp $
  35  */
  36
  37 /*
  38  * arp - display, set, and delete arp table entries
  39  */
  40
  41
  42 #include <sys/param.h>
  43 #include <sys/file.h>
  44 #include <sys/socket.h>
  45 #include <sys/sockio.h>
  46 #include <sys/sysctl.h>
  47 #include <sys/ioctl.h>
  48 #include <sys/time.h>
  49
  50 #include <net/if.h>
  51 #include <net/if_dl.h>
  52 #include <net/if_types.h>
  53 #include <net/route.h>
  54
  55 #include <netinet/in.h>
  56 #include <netinet/if_ether.h>
  57
  58 #include <arpa/inet.h>
  59
  60 #include <ctype.h>
  61 #include <err.h>
  62 #include <errno.h>
  63 #include <netdb.h>
  64 #include <nlist.h>
  65 #include <paths.h>
  66 #include <stdio.h>
  67 #include <stdlib.h>
  68 #include <string.h>
  69 #include <unistd.h>
  70
  71 void search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
  72         struct sockaddr_inarp *sin, struct rt_msghdr *rtm));
  73 void print_entry(struct sockaddr_dl *sdl,
  74         struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
  75 void nuke_entry(struct sockaddr_dl *sdl,
  76         struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
  77 int delete(char *host, char *info);
  78 void usage(void);
  79 int set(int argc, char **argv);
  80 int get(char *host);
  81 int file(char *name);
  82 void getsocket(void);
  83 int my_ether_aton(char *a, struct ether_addr *n);
  84 int rtmsg(int cmd);
  85 int get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr);
  86
  87 static int pid;
  88 static int nflag;       /* no reverse dns lookups */
  89 static int aflag;       /* do it for all entries */
  90 static int cpuflag = -1;
  91 static int s = -1;
  92
  93 struct  sockaddr_in so_mask;
  94 struct  sockaddr_inarp blank_sin, sin_m;
  95 struct  sockaddr_dl blank_sdl, sdl_m;
  96 int     flags, doing_proxy, proxy_only, found_entry;
  97 time_t  expire_time;
  98 struct  {
  99         struct  rt_msghdr m_rtm;
 100         char    m_space[512];
 101 }       m_rtmsg;
 102
 103 /* which function we're supposed to do */
 104 #define F_GET           1
 105 #define F_SET           2
 106 #define F_FILESET       3
 107 #define F_REPLACE       4
 108 #define F_DELETE        5
 109
 110 #define SETFUNC(f)      { if (func) usage(); func = (f); }
 111
 112 int
 113 main(int argc, char **argv)
 114 {
 115         int ch, func = 0;
 116         int rtn = 0;
 117
 118         pid = getpid();
 119         while ((ch = getopt(argc, argv, "ac:ndfsS")) != -1)
 120                 switch((char)ch) {
 121                 case 'a':
 122                         aflag = 1;
 123                         break;
 124                 case 'c':
 125                         cpuflag = strtol(optarg, NULL, 0);
 126                         break;
 127                 case 'd':
 128                         SETFUNC(F_DELETE);
 129                         break;
 130                 case 'n':
 131                         nflag = 1;
 132                         break;
 133                 case 'S':
 134                         SETFUNC(F_REPLACE);
 135                         break;
 136                 case 's':
 137                         SETFUNC(F_SET);
 138                         break;
 139                 case 'f' :
 140                         SETFUNC(F_FILESET);
 141                         break;
 142                 case '?':
 143                 default:
 144                         usage();
 145                 }
 146         argc -= optind;
 147         argv += optind;
 148
 149         bzero(&so_mask, sizeof(so_mask));
 150         so_mask.sin_len = 8;
 151         so_mask.sin_addr.s_addr = 0xffffffff;
 152         bzero(&blank_sin, sizeof(blank_sin));
 153         blank_sin.sin_len = sizeof(blank_sin);
 154         blank_sin.sin_family = AF_INET;
 155         bzero(&blank_sdl, sizeof(blank_sdl));
 156         blank_sdl.sdl_len = sizeof(blank_sdl);
 157         blank_sdl.sdl_family = AF_LINK;
 158
 159         if (!func)
 160                 func = F_GET;
 161         switch (func) {
 162         case F_GET:
 163                 if (aflag) {
 164                         if (argc != 0)
 165                                 usage();
 166                         search(0, print_entry);
 167                 } else {
 168                         if (argc != 1)
 169                                 usage();
 170                         get(argv[0]);
 171                 }
 172                 break;
 173         case F_SET:
 174         case F_REPLACE:
 175                 if (argc < 2 || argc > 6)
 176                         usage();
 177                 if (func == F_REPLACE)
 178                         delete(argv[0], NULL);
 179                 rtn = set(argc, argv) ? 1 : 0;
 180                 break;
 181         case F_DELETE:
 182                 if (aflag) {
 183                         if (argc != 0)
 184                                 usage();
 185                         search(0, nuke_entry);
 186                 } else {
 187                         if (argc < 1 || argc > 2)
 188                                 usage();
 189                         rtn = delete(argv[0], argv[1]);
 190                 }
 191                 break;
 192         case F_FILESET:
 193                 if (argc != 1)
 194                         usage();
 195                 rtn = file(argv[0]);
 196                 break;
 197         }
 198
 199         return(rtn);
 200 }
 201
 202 /*
 203  * Process a file to set standard arp entries
 204  */
 205 int
 206 file(char *name)
 207 {
 208         FILE *fp;
 209         int i, retval;
 210         char line[100], arg[5][50], *args[5], *p;
 211
 212         if ((fp = fopen(name, "r")) == NULL)
 213                 errx(1, "cannot open %s", name);
 214         args[0] = &arg[0][0];
 215         args[1] = &arg[1][0];
 216         args[2] = &arg[2][0];
 217         args[3] = &arg[3][0];
 218         args[4] = &arg[4][0];
 219         retval = 0;
 220         while(fgets(line, 100, fp) != NULL) {
 221                 if ((p = strchr(line, '#')) != NULL)
 222                         *p = '\0';
 223                 for (p = line; isblank(*p); p++);
 224                 if (*p == '\n' || *p == '\0')
 225                         continue;
 226                 i = sscanf(p, "%49s %49s %49s %49s %49s", arg[0], arg[1],
 227                     arg[2], arg[3], arg[4]);
 228                 if (i < 2) {
 229                         warnx("bad line: %s", line);
 230                         retval = 1;
 231                         continue;
 232                 }
 233                 if (set(i, args))
 234                         retval = 1;
 235         }
 236         fclose(fp);
 237         return(retval);
 238 }
 239
 240 void
 241 getsocket(void)
 242 {
 243         if (s < 0) {
 244                 s = socket(PF_ROUTE, SOCK_RAW, 0);
 245                 if (s < 0)
 246                         err(1, "socket");
 247         }
 248 }
 249
 250 /*
 251  * Set an individual arp entry
 252  */
 253 int
 254 set(int argc, char **argv)
 255 {
 256         struct hostent *hp;
 257         struct sockaddr_inarp *addr = &sin_m;
 258         struct sockaddr_dl *sdl;
 259         struct rt_msghdr *rtm = &(m_rtmsg.m_rtm);
 260         struct ether_addr *ea;
 261         char *host = argv[0], *eaddr = argv[1];
 262
 263         getsocket();
 264         argc -= 2;
 265         argv += 2;
 266         sdl_m = blank_sdl;
 267         sin_m = blank_sin;
 268         addr->sin_addr.s_addr = inet_addr(host);
 269         if (addr->sin_addr.s_addr == INADDR_NONE) {
 270                 if (!(hp = gethostbyname(host))) {
 271                         warnx("%s: %s", host, hstrerror(h_errno));
 272                         return(1);
 273                 }
 274                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 275                     sizeof(addr->sin_addr));
 276         }
 277         doing_proxy = flags = proxy_only = expire_time = 0;
 278         while (argc-- > 0) {
 279                 if (strncmp(argv[0], "temp", 4) == 0) {
 280                         struct timespec sp;
 281
 282                         clock_gettime(CLOCK_MONOTONIC, &sp);
 283                         expire_time = sp.tv_sec + 20 * 60;
 284                 }
 285                 else if (strncmp(argv[0], "pub", 3) == 0) {
 286                         flags |= RTF_ANNOUNCE;
 287                         doing_proxy = 1;
 288                         if (argc && strncmp(argv[1], "only", 3) == 0) {
 289                                 proxy_only = 1;
 290                                 sin_m.sin_other = SIN_PROXY;
 291                                 argc--; argv++;
 292                         }
 293                 } else if (strncmp(argv[0], "trail", 5) == 0) {
 294                         printf("%s: Sending trailers is no longer supported\n",
 295                                 host);
 296                 }
 297                 argv++;
 298         }
 299         ea = (struct ether_addr *)LLADDR(&sdl_m);
 300         if (doing_proxy && !strcmp(eaddr, "auto")) {
 301                 if (!get_ether_addr(addr->sin_addr.s_addr, ea)) {
 302                         printf("no interface found for %s\n",
 303                                inet_ntoa(addr->sin_addr));
 304                         return(1);
 305                 }
 306                 sdl_m.sdl_alen = ETHER_ADDR_LEN;
 307         } else {
 308                 if (my_ether_aton(eaddr, ea) == 0)
 309                         sdl_m.sdl_alen = ETHER_ADDR_LEN;
 310         }
 311 tryagain:
 312         if (rtmsg(RTM_GET) < 0) {
 313                 warn("%s", host);
 314                 return(1);
 315         }
 316         addr = (struct sockaddr_inarp *)(rtm + 1);
 317         sdl = (struct sockaddr_dl *)(RT_ROUNDUP(addr->sin_len) + (char *)addr);
 318         if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
 319                 if (sdl->sdl_family == AF_LINK &&
 320                     (rtm->rtm_flags & RTF_LLINFO) &&
 321                     !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
 322                 case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
 323                 case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
 324                 case IFT_CARP:
 325                         goto overwrite;
 326                 }
 327                 if (doing_proxy == 0) {
 328                         printf("set: can only proxy for %s\n", host);
 329                         return(1);
 330                 }
 331                 if (sin_m.sin_other & SIN_PROXY) {
 332                         printf("set: proxy entry exists for non 802 device\n");
 333                         return(1);
 334                 }
 335                 sin_m.sin_other = SIN_PROXY;
 336                 proxy_only = 1;
 337                 goto tryagain;
 338         }
 339 overwrite:
 340         if (sdl->sdl_family != AF_LINK) {
 341                 printf("cannot intuit interface index and type for %s\n", host);
 342                 return(1);
 343         }
 344         sdl_m.sdl_type = sdl->sdl_type;
 345         sdl_m.sdl_index = sdl->sdl_index;
 346         return(rtmsg(RTM_ADD));
 347 }
 348
 349 /*
 350  * Display an individual arp entry
 351  */
 352 int
 353 get(char *host)
 354 {
 355         struct hostent *hp;
 356         struct sockaddr_inarp *addr = &sin_m;
 357
 358         sin_m = blank_sin;
 359         addr->sin_addr.s_addr = inet_addr(host);
 360         if (addr->sin_addr.s_addr == INADDR_NONE) {
 361                 if (!(hp = gethostbyname(host)))
 362                         errx(1, "%s: %s", host, hstrerror(h_errno));
 363                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 364                     sizeof(addr->sin_addr));
 365         }
 366         search(addr->sin_addr.s_addr, print_entry);
 367         if (found_entry == 0) {
 368                 printf("%s (%s) -- no entry\n",
 369                     host, inet_ntoa(addr->sin_addr));
 370                 return(1);
 371         }
 372         return(0);
 373 }
 374
 375 /*
 376  * Delete an arp entry
 377  */
 378 int
 379 delete(char *host, char *info)
 380 {
 381         struct hostent *hp;
 382         struct sockaddr_inarp *addr = &sin_m;
 383         struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
 384         struct sockaddr_dl *sdl;
 385
 386         getsocket();
 387         sin_m = blank_sin;
 388         if (info) {
 389                 if (strncmp(info, "pub", 3) == 0)
 390                         sin_m.sin_other = SIN_PROXY;
 391                 else
 392                         usage();
 393         }
 394         addr->sin_addr.s_addr = inet_addr(host);
 395         if (addr->sin_addr.s_addr == INADDR_NONE) {
 396                 if (!(hp = gethostbyname(host))) {
 397                         warnx("%s: %s", host, hstrerror(h_errno));
 398                         return(1);
 399                 }
 400                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 401                     sizeof(addr->sin_addr));
 402         }
 403 tryagain:
 404         if (rtmsg(RTM_GET) < 0) {
 405                 warn("%s", host);
 406                 return(1);
 407         }
 408         addr = (struct sockaddr_inarp *)(rtm + 1);
 409         sdl = (struct sockaddr_dl *)(RT_ROUNDUP(addr->sin_len) + (char *)addr);
 410         if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
 411                 if (sdl->sdl_family == AF_LINK &&
 412                     (rtm->rtm_flags & RTF_LLINFO) &&
 413                     !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
 414                 case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
 415                 case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
 416                 case IFT_CARP:
 417                         goto delete;
 418                 }
 419         }
 420         if (sin_m.sin_other & SIN_PROXY) {
 421                 fprintf(stderr, "delete: can't locate %s\n",host);
 422                 return(1);
 423         } else {
 424                 sin_m.sin_other = SIN_PROXY;
 425                 goto tryagain;
 426         }
 427 delete:
 428         if (sdl->sdl_family != AF_LINK) {
 429                 printf("cannot locate %s\n", host);
 430                 return(1);
 431         }
 432         if (aflag && (rtm->rtm_flags & RTF_STATIC)) {
 433                 sdl->sdl_alen = 0;
 434                 sdl->sdl_slen = 0;
 435                 if (rtmsg(RTM_CHANGE) == 0) {
 436                         printf("%s (%s) cleared\n",
 437                                 host, inet_ntoa(addr->sin_addr));
 438                         return(0);
 439                 }
 440         } else {
 441                 if (rtmsg(RTM_DELETE) == 0) {
 442                         printf("%s (%s) deleted\n",
 443                                 host, inet_ntoa(addr->sin_addr));
 444                         return(0);
 445                 }
 446         }
 447         return(1);
 448 }
 449
 450 /*
 451  * Search the arp table and do some action on matching entries
 452  */
 453 void
 454 search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
 455         struct sockaddr_inarp *sin, struct rt_msghdr *rtm))
 456 {
 457         int mib[7];
 458         int miblen;
 459         size_t needed;
 460         char *lim, *buf, *next;
 461         struct rt_msghdr *rtm;
 462         struct sockaddr_inarp *sin2;
 463         struct sockaddr_dl *sdl;
 464
 465         mib[0] = CTL_NET;
 466         mib[1] = PF_ROUTE;
 467         mib[2] = 0;
 468         mib[3] = AF_INET;
 469         mib[4] = NET_RT_FLAGS;
 470         mib[5] = RTF_LLINFO;
 471         if (cpuflag >= 0) {
 472             mib[6] = cpuflag;
 473             miblen = 7;
 474         } else {
 475             miblen = 6;
 476         }
 477         if (sysctl(mib, miblen, NULL, &needed, NULL, 0) < 0)
 478                 errx(1, "route-sysctl-estimate");
 479         if ((buf = malloc(needed)) == NULL)
 480                 errx(1, "malloc");
 481         if (sysctl(mib, miblen, buf, &needed, NULL, 0) < 0)
 482                 errx(1, "actual retrieval of routing table");
 483         lim = buf + needed;
 484         for (next = buf; next < lim; next += rtm->rtm_msglen) {
 485                 rtm = (struct rt_msghdr *)next;
 486                 sin2 = (struct sockaddr_inarp *)(rtm + 1);
 487                 sdl = (struct sockaddr_dl *)((char *)sin2 +
 488                             RT_ROUNDUP(sin2->sin_len));
 489                 if (addr) {
 490                         if (addr != sin2->sin_addr.s_addr)
 491                                 continue;
 492                         found_entry = 1;
 493                 }
 494                 (*action)(sdl, sin2, rtm);
 495         }
 496         free(buf);
 497 }
 498
 499 /*
 500  * Display an arp entry
 501  */
 502 void
 503 print_entry(struct sockaddr_dl *sdl,
 504         struct sockaddr_inarp *addr, struct rt_msghdr *rtm)
 505 {
 506         const char *host;
 507         struct hostent *hp;
 508         char ifname[IF_NAMESIZE];
 509
 510         if (nflag == 0)
 511                 hp = gethostbyaddr(&(addr->sin_addr), sizeof(addr->sin_addr),
 512                     AF_INET);
 513         else
 514                 hp = NULL;
 515         if (hp)
 516                 host = hp->h_name;
 517         else {
 518                 host = "?";
 519                 if (h_errno == TRY_AGAIN)
 520                         nflag = 1;
 521         }
 522         printf("%s (%s) at ", host, inet_ntoa(addr->sin_addr));
 523         if (sdl->sdl_alen)
 524                 printf("%s", ether_ntoa((struct ether_addr *)LLADDR(sdl)));
 525         else
 526                 printf("(incomplete)");
 527         if (if_indextoname(sdl->sdl_index, ifname) != NULL)
 528                 printf(" on %s", ifname);
 529         if (rtm->rtm_rmx.rmx_expire == 0)
 530                 printf(" permanent");
 531         if (addr->sin_other & SIN_PROXY)
 532                 printf(" published (proxy only)");
 533         if (rtm->rtm_addrs & RTA_NETMASK) {
 534                 addr = (struct sockaddr_inarp *)
 535                         (RT_ROUNDUP(sdl->sdl_len) + (char *)sdl);
 536                 if (addr->sin_addr.s_addr == 0xffffffff)
 537                         printf(" published");
 538                 if (addr->sin_len != 8)
 539                         printf("(weird)");
 540         }
 541         switch(sdl->sdl_type) {
 542             case IFT_ETHER:
 543                 printf(" [ethernet]");
 544                 break;
 545             case IFT_L2VLAN:
 546                 printf(" [vlan]");
 547                 break;
 548             case IFT_CARP:
 549                 printf(" [carp]");
 550             default:
 551                 break;
 552         }
 553
 554         printf("\n");
 555
 556 }
 557
 558 /*
 559  * Nuke an arp entry
 560  */
 561 void
 562 nuke_entry(struct sockaddr_dl *sdl __unused,
 563         struct sockaddr_inarp *addr, struct rt_msghdr *rtm __unused)
 564 {
 565         char ip[20];
 566
 567         snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr));
 568         delete(ip, NULL);
 569 }
 570
 571 int
 572 my_ether_aton(char *a, struct ether_addr *n)
 573 {
 574         struct ether_addr *ea;
 575
 576         if ((ea = ether_aton(a)) == NULL) {
 577                 warnx("invalid Ethernet address '%s'", a);
 578                 return(1);
 579         }
 580         *n = *ea;
 581         return(0);
 582 }
 583
 584 void
 585 usage(void)
 586 {
 587         fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
 588                 "usage: arp [-n] [-c cpu] hostname",
 589                 "       arp [-n] [-c cpu] -a",
 590                 "       arp -d hostname [pub]",
 591                 "       arp -d -a",
 592                 "       arp -s hostname ether_addr [temp] [pub [only]]",
 593                 "       arp -S hostname ether_addr [temp] [pub [only]]",
 594                 "       arp -f filename");
 595         exit(1);
 596 }
 597
 598 int
 599 rtmsg(int cmd)
 600 {
 601         static int seq;
 602         int rlen;
 603         struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
 604         char *cp = m_rtmsg.m_space;
 605         int l;
 606
 607         errno = 0;
 608         if (cmd == RTM_DELETE || cmd == RTM_CHANGE)
 609                 goto doit;
 610         bzero((char *)&m_rtmsg, sizeof(m_rtmsg));
 611         rtm->rtm_flags = flags;
 612         rtm->rtm_version = RTM_VERSION;
 613
 614         switch (cmd) {
 615         default:
 616                 errx(1, "internal wrong cmd");
 617         case RTM_ADD:
 618                 rtm->rtm_addrs |= RTA_GATEWAY;
 619                 rtm->rtm_rmx.rmx_expire = expire_time;
 620                 rtm->rtm_inits = RTV_EXPIRE;
 621                 rtm->rtm_flags |= (RTF_HOST | RTF_STATIC);
 622                 sin_m.sin_other = 0;
 623                 if (doing_proxy) {
 624                         if (proxy_only)
 625                                 sin_m.sin_other = SIN_PROXY;
 626                         else {
 627                                 rtm->rtm_addrs |= RTA_NETMASK;
 628                                 rtm->rtm_flags &= ~RTF_HOST;
 629                         }
 630                 }
 631                 /* FALLTHROUGH */
 632         case RTM_GET:
 633                 rtm->rtm_addrs |= RTA_DST;
 634         }
 635
 636 #define NEXTADDR(w, s)                                  \
 637         if (rtm->rtm_addrs & (w)) {                     \
 638                 bcopy((char *)&s, cp, sizeof(s));       \
 639                 cp += RT_ROUNDUP(sizeof(s));            \
 640         }
 641
 642         NEXTADDR(RTA_DST, sin_m);
 643         NEXTADDR(RTA_GATEWAY, sdl_m);
 644         NEXTADDR(RTA_NETMASK, so_mask);
 645
 646         rtm->rtm_msglen = cp - (char *)&m_rtmsg;
 647 doit:
 648         l = rtm->rtm_msglen;
 649         rtm->rtm_seq = ++seq;
 650         rtm->rtm_type = cmd;
 651         if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) {
 652                 if (errno != ESRCH || (cmd != RTM_DELETE && cmd != RTM_CHANGE)) {
 653                         warn("writing to routing socket");
 654                         return(-1);
 655                 }
 656         }
 657         do {
 658                 l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg));
 659         } while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid));
 660         if (l < 0)
 661                 warn("read from routing socket");
 662         return(0);
 663 }
 664
 665 /*
 666  * get_ether_addr - get the hardware address of an interface on the
 667  * the same subnet as ipaddr.
 668  */
 669 #define MAX_IFS         32
 670
 671 int
 672 get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr)
 673 {
 674         struct ifreq *ifr, *ifend, *ifp;
 675         u_int32_t ina, mask;
 676         struct sockaddr_dl *dla;
 677         struct ifreq ifreq;
 678         struct ifconf ifc;
 679         struct ifreq ifs[MAX_IFS];
 680         int sock;
 681
 682         sock = socket(AF_INET, SOCK_DGRAM, 0);
 683         if (sock < 0)
 684                 err(1, "socket");
 685
 686         ifc.ifc_len = sizeof(ifs);
 687         ifc.ifc_req = ifs;
 688         if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
 689                 warnx("ioctl(SIOCGIFCONF)");
 690                 close(sock);
 691                 return(0);
 692         }
 693
 694         /*
 695         * Scan through looking for an interface with an Internet
 696         * address on the same subnet as `ipaddr'.
 697         */
 698         ifend = (struct ifreq *) (ifc.ifc_buf + ifc.ifc_len);
 699         for (ifr = ifc.ifc_req; ifr < ifend; ) {
 700                 if (ifr->ifr_addr.sa_family == AF_INET) {
 701                         ina = ((struct sockaddr_in *)
 702                                 &ifr->ifr_addr)->sin_addr.s_addr;
 703                         strncpy(ifreq.ifr_name, ifr->ifr_name,
 704                                 sizeof(ifreq.ifr_name));
 705                         /*
 706                          * Check that the interface is up,
 707                          * and not point-to-point or loopback.
 708                          */
 709                         if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0)
 710                                 continue;
 711                         if ((ifreq.ifr_flags &
 712                              (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|
 713                                         IFF_LOOPBACK|IFF_NOARP))
 714                              != (IFF_UP|IFF_BROADCAST))
 715                                 goto nextif;
 716                         /*
 717                          * Get its netmask and check that it's on
 718                          * the right subnet.
 719                          */
 720                         if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0)
 721                                 continue;
 722                         mask = ((struct sockaddr_in *)
 723                                 &ifreq.ifr_addr)->sin_addr.s_addr;
 724                         if ((ipaddr & mask) != (ina & mask))
 725                                 goto nextif;
 726                         break;
 727                 }
 728 nextif:
 729                 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
 730                     + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
 731         }
 732
 733         if (ifr >= ifend) {
 734                 close(sock);
 735                 return(0);
 736         }
 737
 738         /*
 739         * Now scan through again looking for a link-level address
 740         * for this interface.
 741         */
 742         ifp = ifr;
 743         for (ifr = ifc.ifc_req; ifr < ifend; ) {
 744                 if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0
 745                     && ifr->ifr_addr.sa_family == AF_LINK) {
 746                         /*
 747                          * Found the link-level address - copy it out
 748                          */
 749                         dla = (struct sockaddr_dl *) &ifr->ifr_addr;
 750                         memcpy(hwaddr,  LLADDR(dla), dla->sdl_alen);
 751                         close (sock);
 752                         printf("using interface %s for proxy with address ",
 753                                 ifp->ifr_name);
 754                         printf("%s\n", ether_ntoa(hwaddr));
 755                         return(dla->sdl_alen);
 756                 }
 757                 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
 758                     + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
 759         }
 760         return(0);
 761 }