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. All advertising materials mentioning features or use of this software
  17  *    must display the following acknowledgement:
  18  *      This product includes software developed by the University of
  19  *      California, Berkeley and its contributors.
  20  * 4. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  *
  36  * @(#) Copyright (c) 1984, 1993 The Regents of the University of California.  All rights reserved.
  37  * @(#)from: arp.c      8.2 (Berkeley) 1/2/94
  38  * $FreeBSD: src/usr.sbin/arp/arp.c,v 1.22.2.12 2003/04/16 10:02:37 ru Exp $
  39  * $DragonFly: src/usr.sbin/arp/arp.c,v 1.10 2007/10/11 21:51:20 thomas Exp $
  40  */
  41
  42 /*
  43  * arp - display, set, and delete arp table entries
  44  */
  45
  46
  47 #include <sys/param.h>
  48 #include <sys/file.h>
  49 #include <sys/socket.h>
  50 #include <sys/sockio.h>
  51 #include <sys/sysctl.h>
  52 #include <sys/ioctl.h>
  53 #include <sys/time.h>
  54
  55 #include <net/if.h>
  56 #include <net/if_dl.h>
  57 #include <net/if_types.h>
  58 #include <net/route.h>
  59
  60 #include <netinet/in.h>
  61 #include <netinet/if_ether.h>
  62
  63 #include <arpa/inet.h>
  64
  65 #include <ctype.h>
  66 #include <err.h>
  67 #include <errno.h>
  68 #include <netdb.h>
  69 #include <nlist.h>
  70 #include <paths.h>
  71 #include <stdio.h>
  72 #include <stdlib.h>
  73 #include <strings.h>
  74 #include <unistd.h>
  75
  76 void search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
  77         struct sockaddr_inarp *sin, struct rt_msghdr *rtm));
  78 void print_entry(struct sockaddr_dl *sdl,
  79         struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
  80 void nuke_entry(struct sockaddr_dl *sdl,
  81         struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
  82 int delete(char *host, char *info);
  83 void usage(void);
  84 int set(int argc, char **argv);
  85 int get(char *host);
  86 int file(char *name);
  87 void getsocket(void);
  88 int my_ether_aton(char *a, struct ether_addr *n);
  89 int rtmsg(int cmd);
  90 int get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr);
  91
  92 static int pid;
  93 static int nflag;       /* no reverse dns lookups */
  94 static int aflag;       /* do it for all entries */
  95 static int cpuflag = -1;
  96 static int s = -1;
  97
  98 struct  sockaddr_in so_mask;
  99 struct  sockaddr_inarp blank_sin, sin_m;
 100 struct  sockaddr_dl blank_sdl, sdl_m;
 101 int     expire_time, flags, doing_proxy, proxy_only, found_entry;
 102 struct  {
 103         struct  rt_msghdr m_rtm;
 104         char    m_space[512];
 105 }       m_rtmsg;
 106
 107 /* which function we're supposed to do */
 108 #define F_GET           1
 109 #define F_SET           2
 110 #define F_FILESET       3
 111 #define F_REPLACE       4
 112 #define F_DELETE        5
 113
 114 #define ROUNDUP(a) \
 115         ((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
 116 #define SETFUNC(f)      { if (func) usage(); func = (f); }
 117
 118 int
 119 main(int argc, char **argv)
 120 {
 121         int ch, func = 0;
 122         int rtn = 0;
 123
 124         pid = getpid();
 125         while ((ch = getopt(argc, argv, "ac:ndfsS")) != -1)
 126                 switch((char)ch) {
 127                 case 'a':
 128                         aflag = 1;
 129                         break;
 130                 case 'c':
 131                         cpuflag = strtol(optarg, NULL, 0);
 132                         break;
 133                 case 'd':
 134                         SETFUNC(F_DELETE);
 135                         break;
 136                 case 'n':
 137                         nflag = 1;
 138                         break;
 139                 case 'S':
 140                         SETFUNC(F_REPLACE);
 141                         break;
 142                 case 's':
 143                         SETFUNC(F_SET);
 144                         break;
 145                 case 'f' :
 146                         SETFUNC(F_FILESET);
 147                         break;
 148                 case '?':
 149                 default:
 150                         usage();
 151                 }
 152         argc -= optind;
 153         argv += optind;
 154
 155         bzero(&so_mask, sizeof(so_mask));
 156         so_mask.sin_len = 8;
 157         so_mask.sin_addr.s_addr = 0xffffffff;
 158         bzero(&blank_sin, sizeof(blank_sin));
 159         blank_sin.sin_len = sizeof(blank_sin);
 160         blank_sin.sin_family = AF_INET;
 161         bzero(&blank_sdl, sizeof(blank_sdl));
 162         blank_sdl.sdl_len = sizeof(blank_sdl);
 163         blank_sdl.sdl_family = AF_LINK;
 164
 165         if (!func)
 166                 func = F_GET;
 167         switch (func) {
 168         case F_GET:
 169                 if (aflag) {
 170                         if (argc != 0)
 171                                 usage();
 172                         search(0, print_entry);
 173                 } else {
 174                         if (argc != 1)
 175                                 usage();
 176                         get(argv[0]);
 177                 }
 178                 break;
 179         case F_SET:
 180         case F_REPLACE:
 181                 if (argc < 2 || argc > 6)
 182                         usage();
 183                 if (func == F_REPLACE)
 184                         delete(argv[0], NULL);
 185                 rtn = set(argc, argv) ? 1 : 0;
 186                 break;
 187         case F_DELETE:
 188                 if (aflag) {
 189                         if (argc != 0)
 190                                 usage();
 191                         search(0, nuke_entry);
 192                 } else {
 193                         if (argc < 1 || argc > 2)
 194                                 usage();
 195                         rtn = delete(argv[0], argv[1]);
 196                 }
 197                 break;
 198         case F_FILESET:
 199                 if (argc != 1)
 200                         usage();
 201                 rtn = file(argv[0]);
 202                 break;
 203         }
 204
 205         return(rtn);
 206 }
 207
 208 /*
 209  * Process a file to set standard arp entries
 210  */
 211 int
 212 file(char *name)
 213 {
 214         FILE *fp;
 215         int i, retval;
 216         char line[100], arg[5][50], *args[5], *p;
 217
 218         if ((fp = fopen(name, "r")) == NULL)
 219                 errx(1, "cannot open %s", name);
 220         args[0] = &arg[0][0];
 221         args[1] = &arg[1][0];
 222         args[2] = &arg[2][0];
 223         args[3] = &arg[3][0];
 224         args[4] = &arg[4][0];
 225         retval = 0;
 226         while(fgets(line, 100, fp) != NULL) {
 227                 if ((p = strchr(line, '#')) != NULL)
 228                         *p = '\0';
 229                 for (p = line; isblank(*p); p++);
 230                 if (*p == '\n' || *p == '\0')
 231                         continue;
 232                 i = sscanf(p, "%49s %49s %49s %49s %49s", arg[0], arg[1],
 233                     arg[2], arg[3], arg[4]);
 234                 if (i < 2) {
 235                         warnx("bad line: %s", line);
 236                         retval = 1;
 237                         continue;
 238                 }
 239                 if (set(i, args))
 240                         retval = 1;
 241         }
 242         fclose(fp);
 243         return(retval);
 244 }
 245
 246 void
 247 getsocket(void)
 248 {
 249         if (s < 0) {
 250                 s = socket(PF_ROUTE, SOCK_RAW, 0);
 251                 if (s < 0)
 252                         err(1, "socket");
 253         }
 254 }
 255
 256 /*
 257  * Set an individual arp entry
 258  */
 259 int
 260 set(int argc, char **argv)
 261 {
 262         struct hostent *hp;
 263         struct sockaddr_inarp *addr = &sin_m;
 264         struct sockaddr_dl *sdl;
 265         struct rt_msghdr *rtm = &(m_rtmsg.m_rtm);
 266         struct ether_addr *ea;
 267         char *host = argv[0], *eaddr = argv[1];
 268
 269         getsocket();
 270         argc -= 2;
 271         argv += 2;
 272         sdl_m = blank_sdl;
 273         sin_m = blank_sin;
 274         addr->sin_addr.s_addr = inet_addr(host);
 275         if (addr->sin_addr.s_addr == INADDR_NONE) {
 276                 if (!(hp = gethostbyname(host))) {
 277                         warnx("%s: %s", host, hstrerror(h_errno));
 278                         return(1);
 279                 }
 280                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 281                     sizeof(addr->sin_addr));
 282         }
 283         doing_proxy = flags = proxy_only = expire_time = 0;
 284         while (argc-- > 0) {
 285                 if (strncmp(argv[0], "temp", 4) == 0) {
 286                         struct timeval tv;
 287                         gettimeofday(&tv, 0);
 288                         expire_time = tv.tv_sec + 20 * 60;
 289                 }
 290                 else if (strncmp(argv[0], "pub", 3) == 0) {
 291                         flags |= RTF_ANNOUNCE;
 292                         doing_proxy = 1;
 293                         if (argc && strncmp(argv[1], "only", 3) == 0) {
 294                                 proxy_only = 1;
 295                                 sin_m.sin_other = SIN_PROXY;
 296                                 argc--; argv++;
 297                         }
 298                 } else if (strncmp(argv[0], "trail", 5) == 0) {
 299                         printf("%s: Sending trailers is no longer supported\n",
 300                                 host);
 301                 }
 302                 argv++;
 303         }
 304         ea = (struct ether_addr *)LLADDR(&sdl_m);
 305         if (doing_proxy && !strcmp(eaddr, "auto")) {
 306                 if (!get_ether_addr(addr->sin_addr.s_addr, ea)) {
 307                         printf("no interface found for %s\n",
 308                                inet_ntoa(addr->sin_addr));
 309                         return(1);
 310                 }
 311                 sdl_m.sdl_alen = ETHER_ADDR_LEN;
 312         } else {
 313                 if (my_ether_aton(eaddr, ea) == 0)
 314                         sdl_m.sdl_alen = ETHER_ADDR_LEN;
 315         }
 316 tryagain:
 317         if (rtmsg(RTM_GET) < 0) {
 318                 warn("%s", host);
 319                 return(1);
 320         }
 321         addr = (struct sockaddr_inarp *)(rtm + 1);
 322         sdl = (struct sockaddr_dl *)(ROUNDUP(addr->sin_len) + (char *)addr);
 323         if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
 324                 if (sdl->sdl_family == AF_LINK &&
 325                     (rtm->rtm_flags & RTF_LLINFO) &&
 326                     !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
 327                 case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
 328                 case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
 329                         goto overwrite;
 330                 }
 331                 if (doing_proxy == 0) {
 332                         printf("set: can only proxy for %s\n", host);
 333                         return(1);
 334                 }
 335                 if (sin_m.sin_other & SIN_PROXY) {
 336                         printf("set: proxy entry exists for non 802 device\n");
 337                         return(1);
 338                 }
 339                 sin_m.sin_other = SIN_PROXY;
 340                 proxy_only = 1;
 341                 goto tryagain;
 342         }
 343 overwrite:
 344         if (sdl->sdl_family != AF_LINK) {
 345                 printf("cannot intuit interface index and type for %s\n", host);
 346                 return(1);
 347         }
 348         sdl_m.sdl_type = sdl->sdl_type;
 349         sdl_m.sdl_index = sdl->sdl_index;
 350         return(rtmsg(RTM_ADD));
 351 }
 352
 353 /*
 354  * Display an individual arp entry
 355  */
 356 int
 357 get(char *host)
 358 {
 359         struct hostent *hp;
 360         struct sockaddr_inarp *addr = &sin_m;
 361
 362         sin_m = blank_sin;
 363         addr->sin_addr.s_addr = inet_addr(host);
 364         if (addr->sin_addr.s_addr == INADDR_NONE) {
 365                 if (!(hp = gethostbyname(host)))
 366                         errx(1, "%s: %s", host, hstrerror(h_errno));
 367                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 368                     sizeof(addr->sin_addr));
 369         }
 370         search(addr->sin_addr.s_addr, print_entry);
 371         if (found_entry == 0) {
 372                 printf("%s (%s) -- no entry\n",
 373                     host, inet_ntoa(addr->sin_addr));
 374                 return(1);
 375         }
 376         return(0);
 377 }
 378
 379 /*
 380  * Delete an arp entry
 381  */
 382 int
 383 delete(char *host, char *info)
 384 {
 385         struct hostent *hp;
 386         struct sockaddr_inarp *addr = &sin_m;
 387         struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
 388         struct sockaddr_dl *sdl;
 389
 390         getsocket();
 391         sin_m = blank_sin;
 392         if (info) {
 393                 if (strncmp(info, "pub", 3) == 0)
 394                         sin_m.sin_other = SIN_PROXY;
 395                 else
 396                         usage();
 397         }
 398         addr->sin_addr.s_addr = inet_addr(host);
 399         if (addr->sin_addr.s_addr == INADDR_NONE) {
 400                 if (!(hp = gethostbyname(host))) {
 401                         warnx("%s: %s", host, hstrerror(h_errno));
 402                         return(1);
 403                 }
 404                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 405                     sizeof(addr->sin_addr));
 406         }
 407 tryagain:
 408         if (rtmsg(RTM_GET) < 0) {
 409                 warn("%s", host);
 410                 return(1);
 411         }
 412         addr = (struct sockaddr_inarp *)(rtm + 1);
 413         sdl = (struct sockaddr_dl *)(ROUNDUP(addr->sin_len) + (char *)addr);
 414         if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
 415                 if (sdl->sdl_family == AF_LINK &&
 416                     (rtm->rtm_flags & RTF_LLINFO) &&
 417                     !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
 418                 case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
 419                 case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
 420                         goto delete;
 421                 }
 422         }
 423         if (sin_m.sin_other & SIN_PROXY) {
 424                 fprintf(stderr, "delete: can't locate %s\n",host);
 425                 return(1);
 426         } else {
 427                 sin_m.sin_other = SIN_PROXY;
 428                 goto tryagain;
 429         }
 430 delete:
 431         if (sdl->sdl_family != AF_LINK) {
 432                 printf("cannot locate %s\n", host);
 433                 return(1);
 434         }
 435         if (aflag && (rtm->rtm_flags & RTF_STATIC)) {
 436                 sdl->sdl_alen = 0;
 437                 sdl->sdl_slen = 0;
 438                 if (rtmsg(RTM_CHANGE) == 0) {
 439                         printf("%s (%s) cleared\n",
 440                                 host, inet_ntoa(addr->sin_addr));
 441                         return(0);
 442                 }
 443         } else {
 444                 if (rtmsg(RTM_DELETE) == 0) {
 445                         printf("%s (%s) deleted\n",
 446                                 host, inet_ntoa(addr->sin_addr));
 447                         return(0);
 448                 }
 449         }
 450         return(1);
 451 }
 452
 453 /*
 454  * Search the arp table and do some action on matching entries
 455  */
 456 void
 457 search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
 458         struct sockaddr_inarp *sin, struct rt_msghdr *rtm))
 459 {
 460         int mib[7];
 461         int miblen;
 462         size_t needed;
 463         char *lim, *buf, *next;
 464         struct rt_msghdr *rtm;
 465         struct sockaddr_inarp *sin2;
 466         struct sockaddr_dl *sdl;
 467
 468         mib[0] = CTL_NET;
 469         mib[1] = PF_ROUTE;
 470         mib[2] = 0;
 471         mib[3] = AF_INET;
 472         mib[4] = NET_RT_FLAGS;
 473         mib[5] = RTF_LLINFO;
 474         if (cpuflag >= 0) {
 475             mib[6] = cpuflag;
 476             miblen = 7;
 477         } else {
 478             miblen = 6;
 479         }
 480         if (sysctl(mib, miblen, NULL, &needed, NULL, 0) < 0)
 481                 errx(1, "route-sysctl-estimate");
 482         if ((buf = malloc(needed)) == NULL)
 483                 errx(1, "malloc");
 484         if (sysctl(mib, miblen, buf, &needed, NULL, 0) < 0)
 485                 errx(1, "actual retrieval of routing table");
 486         lim = buf + needed;
 487         for (next = buf; next < lim; next += rtm->rtm_msglen) {
 488                 rtm = (struct rt_msghdr *)next;
 489                 sin2 = (struct sockaddr_inarp *)(rtm + 1);
 490                 sdl = (struct sockaddr_dl *)((char *)sin2 + ROUNDUP(sin2->sin_len));
 491                 if (addr) {
 492                         if (addr != sin2->sin_addr.s_addr)
 493                                 continue;
 494                         found_entry = 1;
 495                 }
 496                 (*action)(sdl, sin2, rtm);
 497         }
 498         free(buf);
 499 }
 500
 501 /*
 502  * Display an arp entry
 503  */
 504 void
 505 print_entry(struct sockaddr_dl *sdl,
 506         struct sockaddr_inarp *addr, struct rt_msghdr *rtm)
 507 {
 508         const char *host;
 509         struct hostent *hp;
 510         char ifname[IF_NAMESIZE];
 511         int seg;
 512
 513         if (nflag == 0)
 514                 hp = gethostbyaddr((caddr_t)&(addr->sin_addr),
 515                     sizeof(addr->sin_addr), AF_INET);
 516         else
 517                 hp = 0;
 518         if (hp)
 519                 host = hp->h_name;
 520         else {
 521                 host = "?";
 522                 if (h_errno == TRY_AGAIN)
 523                         nflag = 1;
 524         }
 525         printf("%s (%s) at ", host, inet_ntoa(addr->sin_addr));
 526         if (sdl->sdl_alen)
 527                 printf("%s", ether_ntoa((struct ether_addr *)LLADDR(sdl)));
 528         else
 529                 printf("(incomplete)");
 530         if (if_indextoname(sdl->sdl_index, ifname) != NULL)
 531                 printf(" on %s", ifname);
 532         if (rtm->rtm_rmx.rmx_expire == 0)
 533                 printf(" permanent");
 534         if (addr->sin_other & SIN_PROXY)
 535                 printf(" published (proxy only)");
 536         if (rtm->rtm_addrs & RTA_NETMASK) {
 537                 addr = (struct sockaddr_inarp *)
 538                         (ROUNDUP(sdl->sdl_len) + (char *)sdl);
 539                 if (addr->sin_addr.s_addr == 0xffffffff)
 540                         printf(" published");
 541                 if (addr->sin_len != 8)
 542                         printf("(weird)");
 543         }
 544         switch(sdl->sdl_type) {
 545             case IFT_ETHER:
 546                 printf(" [ethernet]");
 547                 break;
 548             case IFT_L2VLAN:
 549                 printf(" [vlan]");
 550                 break;
 551             default:
 552                 break;
 553         }
 554
 555         printf("\n");
 556
 557 }
 558
 559 /*
 560  * Nuke an arp entry
 561  */
 562 void
 563 nuke_entry(struct sockaddr_dl *sdl __unused,
 564         struct sockaddr_inarp *addr, struct rt_msghdr *rtm __unused)
 565 {
 566         char ip[20];
 567
 568         snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr));
 569         delete(ip, NULL);
 570 }
 571
 572 int
 573 my_ether_aton(char *a, struct ether_addr *n)
 574 {
 575         struct ether_addr *ea;
 576
 577         if ((ea = ether_aton(a)) == NULL) {
 578                 warnx("invalid Ethernet address '%s'", a);
 579                 return(1);
 580         }
 581         *n = *ea;
 582         return(0);
 583 }
 584
 585 void
 586 usage(void)
 587 {
 588         fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
 589                 "usage: arp [-n] [-c cpu] hostname",
 590                 "       arp [-n] [-c cpu] -a",
 591                 "       arp -d hostname [pub]",
 592                 "       arp -d -a",
 593                 "       arp -s hostname ether_addr [temp] [pub [only]]",
 594                 "       arp -S hostname ether_addr [temp] [pub [only]]",
 595                 "       arp -f filename");
 596         exit(1);
 597 }
 598
 599 int
 600 rtmsg(int cmd)
 601 {
 602         static int seq;
 603         int rlen;
 604         struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
 605         char *cp = m_rtmsg.m_space;
 606         int l;
 607
 608         errno = 0;
 609         if (cmd == RTM_DELETE || cmd == RTM_CHANGE)
 610                 goto doit;
 611         bzero((char *)&m_rtmsg, sizeof(m_rtmsg));
 612         rtm->rtm_flags = flags;
 613         rtm->rtm_version = RTM_VERSION;
 614
 615         switch (cmd) {
 616         default:
 617                 errx(1, "internal wrong cmd");
 618         case RTM_ADD:
 619                 rtm->rtm_addrs |= RTA_GATEWAY;
 620                 rtm->rtm_rmx.rmx_expire = expire_time;
 621                 rtm->rtm_inits = RTV_EXPIRE;
 622                 rtm->rtm_flags |= (RTF_HOST | RTF_STATIC);
 623                 sin_m.sin_other = 0;
 624                 if (doing_proxy) {
 625                         if (proxy_only)
 626                                 sin_m.sin_other = SIN_PROXY;
 627                         else {
 628                                 rtm->rtm_addrs |= RTA_NETMASK;
 629                                 rtm->rtm_flags &= ~RTF_HOST;
 630                         }
 631                 }
 632                 /* FALLTHROUGH */
 633         case RTM_GET:
 634                 rtm->rtm_addrs |= RTA_DST;
 635         }
 636 #define NEXTADDR(w, s) \
 637         if (rtm->rtm_addrs & (w)) { \
 638                 bcopy((char *)&s, cp, sizeof(s)); cp += ROUNDUP(sizeof(s));}
 639
 640         NEXTADDR(RTA_DST, sin_m);
 641         NEXTADDR(RTA_GATEWAY, sdl_m);
 642         NEXTADDR(RTA_NETMASK, so_mask);
 643
 644         rtm->rtm_msglen = cp - (char *)&m_rtmsg;
 645 doit:
 646         l = rtm->rtm_msglen;
 647         rtm->rtm_seq = ++seq;
 648         rtm->rtm_type = cmd;
 649         if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) {
 650                 if (errno != ESRCH || (cmd != RTM_DELETE && cmd != RTM_CHANGE)) {
 651                         warn("writing to routing socket");
 652                         return(-1);
 653                 }
 654         }
 655         do {
 656                 l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg));
 657         } while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid));
 658         if (l < 0)
 659                 warn("read from routing socket");
 660         return(0);
 661 }
 662
 663 /*
 664  * get_ether_addr - get the hardware address of an interface on the
 665  * the same subnet as ipaddr.
 666  */
 667 #define MAX_IFS         32
 668
 669 int
 670 get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr)
 671 {
 672         struct ifreq *ifr, *ifend, *ifp;
 673         u_int32_t ina, mask;
 674         struct sockaddr_dl *dla;
 675         struct ifreq ifreq;
 676         struct ifconf ifc;
 677         struct ifreq ifs[MAX_IFS];
 678         int sock;
 679
 680         sock = socket(AF_INET, SOCK_DGRAM, 0);
 681         if (sock < 0)
 682                 err(1, "socket");
 683
 684         ifc.ifc_len = sizeof(ifs);
 685         ifc.ifc_req = ifs;
 686         if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
 687                 warnx("ioctl(SIOCGIFCONF)");
 688                 close(sock);
 689                 return(0);
 690         }
 691
 692         /*
 693         * Scan through looking for an interface with an Internet
 694         * address on the same subnet as `ipaddr'.
 695         */
 696         ifend = (struct ifreq *) (ifc.ifc_buf + ifc.ifc_len);
 697         for (ifr = ifc.ifc_req; ifr < ifend; ) {
 698                 if (ifr->ifr_addr.sa_family == AF_INET) {
 699                         ina = ((struct sockaddr_in *)
 700                                 &ifr->ifr_addr)->sin_addr.s_addr;
 701                         strncpy(ifreq.ifr_name, ifr->ifr_name,
 702                                 sizeof(ifreq.ifr_name));
 703                         /*
 704                          * Check that the interface is up,
 705                          * and not point-to-point or loopback.
 706                          */
 707                         if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0)
 708                                 continue;
 709                         if ((ifreq.ifr_flags &
 710                              (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|
 711                                         IFF_LOOPBACK|IFF_NOARP))
 712                              != (IFF_UP|IFF_BROADCAST))
 713                                 goto nextif;
 714                         /*
 715                          * Get its netmask and check that it's on
 716                          * the right subnet.
 717                          */
 718                         if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0)
 719                                 continue;
 720                         mask = ((struct sockaddr_in *)
 721                                 &ifreq.ifr_addr)->sin_addr.s_addr;
 722                         if ((ipaddr & mask) != (ina & mask))
 723                                 goto nextif;
 724                         break;
 725                 }
 726 nextif:
 727                 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
 728                     + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
 729         }
 730
 731         if (ifr >= ifend) {
 732                 close(sock);
 733                 return(0);
 734         }
 735
 736         /*
 737         * Now scan through again looking for a link-level address
 738         * for this interface.
 739         */
 740         ifp = ifr;
 741         for (ifr = ifc.ifc_req; ifr < ifend; ) {
 742                 if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0
 743                     && ifr->ifr_addr.sa_family == AF_LINK) {
 744                         /*
 745                          * Found the link-level address - copy it out
 746                          */
 747                         dla = (struct sockaddr_dl *) &ifr->ifr_addr;
 748                         memcpy(hwaddr,  LLADDR(dla), dla->sdl_alen);
 749                         close (sock);
 750                         printf("using interface %s for proxy with address ",
 751                                 ifp->ifr_name);
 752                         printf("%s\n", ether_ntoa(hwaddr));
 753                         return(dla->sdl_alen);
 754                 }
 755                 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
 756                     + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
 757         }
 758         return(0);
 759 }