SAFE public projects git trees. - safe/jmp/linux-2.6/blob - net/ipv4/ip_options.c

   1 /*
   2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3  *              operating system.  INET is implemented using the  BSD Socket
   4  *              interface as the means of communication with the user level.
   5  *
   6  *              The options processing module for ip.c
   7  *
   8  * Authors:     A.N.Kuznetsov
   9  *
  10  */
  11
  12 #include <linux/capability.h>
  13 #include <linux/module.h>
  14 #include <linux/slab.h>
  15 #include <linux/types.h>
  16 #include <asm/uaccess.h>
  17 #include <linux/skbuff.h>
  18 #include <linux/ip.h>
  19 #include <linux/icmp.h>
  20 #include <linux/netdevice.h>
  21 #include <linux/rtnetlink.h>
  22 #include <net/sock.h>
  23 #include <net/ip.h>
  24 #include <net/icmp.h>
  25 #include <net/route.h>
  26 #include <net/cipso_ipv4.h>
  27
  28 /*
  29  * Write options to IP header, record destination address to
  30  * source route option, address of outgoing interface
  31  * (we should already know it, so that this  function is allowed be
  32  * called only after routing decision) and timestamp,
  33  * if we originate this datagram.
  34  *
  35  * daddr is real destination address, next hop is recorded in IP header.
  36  * saddr is address of outgoing interface.
  37  */
  38
  39 void ip_options_build(struct sk_buff * skb, struct ip_options * opt,
  40                             __be32 daddr, struct rtable *rt, int is_frag)
  41 {
  42         unsigned char *iph = skb_network_header(skb);
  43
  44         memcpy(&(IPCB(skb)->opt), opt, sizeof(struct ip_options));
  45         memcpy(iph+sizeof(struct iphdr), opt->__data, opt->optlen);
  46         opt = &(IPCB(skb)->opt);
  47
  48         if (opt->srr)
  49                 memcpy(iph+opt->srr+iph[opt->srr+1]-4, &daddr, 4);
  50
  51         if (!is_frag) {
  52                 if (opt->rr_needaddr)
  53                         ip_rt_get_source(iph+opt->rr+iph[opt->rr+2]-5, rt);
  54                 if (opt->ts_needaddr)
  55                         ip_rt_get_source(iph+opt->ts+iph[opt->ts+2]-9, rt);
  56                 if (opt->ts_needtime) {
  57                         struct timespec tv;
  58                         __be32 midtime;
  59                         getnstimeofday(&tv);
  60                         midtime = htonl((tv.tv_sec % 86400) * MSEC_PER_SEC + tv.tv_nsec / NSEC_PER_MSEC);
  61                         memcpy(iph+opt->ts+iph[opt->ts+2]-5, &midtime, 4);
  62                 }
  63                 return;
  64         }
  65         if (opt->rr) {
  66                 memset(iph+opt->rr, IPOPT_NOP, iph[opt->rr+1]);
  67                 opt->rr = 0;
  68                 opt->rr_needaddr = 0;
  69         }
  70         if (opt->ts) {
  71                 memset(iph+opt->ts, IPOPT_NOP, iph[opt->ts+1]);
  72                 opt->ts = 0;
  73                 opt->ts_needaddr = opt->ts_needtime = 0;
  74         }
  75 }
  76
  77 /*
  78  * Provided (sopt, skb) points to received options,
  79  * build in dopt compiled option set appropriate for answering.
  80  * i.e. invert SRR option, copy anothers,
  81  * and grab room in RR/TS options.
  82  *
  83  * NOTE: dopt cannot point to skb.
  84  */
  85
  86 int ip_options_echo(struct ip_options * dopt, struct sk_buff * skb)
  87 {
  88         struct ip_options *sopt;
  89         unsigned char *sptr, *dptr;
  90         int soffset, doffset;
  91         int     optlen;
  92         __be32  daddr;
  93
  94         memset(dopt, 0, sizeof(struct ip_options));
  95
  96         sopt = &(IPCB(skb)->opt);
  97
  98         if (sopt->optlen == 0) {
  99                 dopt->optlen = 0;
 100                 return 0;
 101         }
 102
 103         sptr = skb_network_header(skb);
 104         dptr = dopt->__data;
 105
 106         daddr = skb_rtable(skb)->rt_spec_dst;
 107
 108         if (sopt->rr) {
 109                 optlen  = sptr[sopt->rr+1];
 110                 soffset = sptr[sopt->rr+2];
 111                 dopt->rr = dopt->optlen + sizeof(struct iphdr);
 112                 memcpy(dptr, sptr+sopt->rr, optlen);
 113                 if (sopt->rr_needaddr && soffset <= optlen) {
 114                         if (soffset + 3 > optlen)
 115                                 return -EINVAL;
 116                         dptr[2] = soffset + 4;
 117                         dopt->rr_needaddr = 1;
 118                 }
 119                 dptr += optlen;
 120                 dopt->optlen += optlen;
 121         }
 122         if (sopt->ts) {
 123                 optlen = sptr[sopt->ts+1];
 124                 soffset = sptr[sopt->ts+2];
 125                 dopt->ts = dopt->optlen + sizeof(struct iphdr);
 126                 memcpy(dptr, sptr+sopt->ts, optlen);
 127                 if (soffset <= optlen) {
 128                         if (sopt->ts_needaddr) {
 129                                 if (soffset + 3 > optlen)
 130                                         return -EINVAL;
 131                                 dopt->ts_needaddr = 1;
 132                                 soffset += 4;
 133                         }
 134                         if (sopt->ts_needtime) {
 135                                 if (soffset + 3 > optlen)
 136                                         return -EINVAL;
 137                                 if ((dptr[3]&0xF) != IPOPT_TS_PRESPEC) {
 138                                         dopt->ts_needtime = 1;
 139                                         soffset += 4;
 140                                 } else {
 141                                         dopt->ts_needtime = 0;
 142
 143                                         if (soffset + 8 <= optlen) {
 144                                                 __be32 addr;
 145
 146                                                 memcpy(&addr, sptr+soffset-1, 4);
 147                                                 if (inet_addr_type(dev_net(skb_dst(skb)->dev), addr) != RTN_LOCAL) {
 148                                                         dopt->ts_needtime = 1;
 149                                                         soffset += 8;
 150                                                 }
 151                                         }
 152                                 }
 153                         }
 154                         dptr[2] = soffset;
 155                 }
 156                 dptr += optlen;
 157                 dopt->optlen += optlen;
 158         }
 159         if (sopt->srr) {
 160                 unsigned char * start = sptr+sopt->srr;
 161                 __be32 faddr;
 162
 163                 optlen  = start[1];
 164                 soffset = start[2];
 165                 doffset = 0;
 166                 if (soffset > optlen)
 167                         soffset = optlen + 1;
 168                 soffset -= 4;
 169                 if (soffset > 3) {
 170                         memcpy(&faddr, &start[soffset-1], 4);
 171                         for (soffset-=4, doffset=4; soffset > 3; soffset-=4, doffset+=4)
 172                                 memcpy(&dptr[doffset-1], &start[soffset-1], 4);
 173                         /*
 174                          * RFC1812 requires to fix illegal source routes.
 175                          */
 176                         if (memcmp(&ip_hdr(skb)->saddr,
 177                                    &start[soffset + 3], 4) == 0)
 178                                 doffset -= 4;
 179                 }
 180                 if (doffset > 3) {
 181                         memcpy(&start[doffset-1], &daddr, 4);
 182                         dopt->faddr = faddr;
 183                         dptr[0] = start[0];
 184                         dptr[1] = doffset+3;
 185                         dptr[2] = 4;
 186                         dptr += doffset+3;
 187                         dopt->srr = dopt->optlen + sizeof(struct iphdr);
 188                         dopt->optlen += doffset+3;
 189                         dopt->is_strictroute = sopt->is_strictroute;
 190                 }
 191         }
 192         if (sopt->cipso) {
 193                 optlen  = sptr[sopt->cipso+1];
 194                 dopt->cipso = dopt->optlen+sizeof(struct iphdr);
 195                 memcpy(dptr, sptr+sopt->cipso, optlen);
 196                 dptr += optlen;
 197                 dopt->optlen += optlen;
 198         }
 199         while (dopt->optlen & 3) {
 200                 *dptr++ = IPOPT_END;
 201                 dopt->optlen++;
 202         }
 203         return 0;
 204 }
 205
 206 /*
 207  *      Options "fragmenting", just fill options not
 208  *      allowed in fragments with NOOPs.
 209  *      Simple and stupid 8), but the most efficient way.
 210  */
 211
 212 void ip_options_fragment(struct sk_buff * skb)
 213 {
 214         unsigned char *optptr = skb_network_header(skb) + sizeof(struct iphdr);
 215         struct ip_options * opt = &(IPCB(skb)->opt);
 216         int  l = opt->optlen;
 217         int  optlen;
 218
 219         while (l > 0) {
 220                 switch (*optptr) {
 221                 case IPOPT_END:
 222                         return;
 223                 case IPOPT_NOOP:
 224                         l--;
 225                         optptr++;
 226                         continue;
 227                 }
 228                 optlen = optptr[1];
 229                 if (optlen<2 || optlen>l)
 230                   return;
 231                 if (!IPOPT_COPIED(*optptr))
 232                         memset(optptr, IPOPT_NOOP, optlen);
 233                 l -= optlen;
 234                 optptr += optlen;
 235         }
 236         opt->ts = 0;
 237         opt->rr = 0;
 238         opt->rr_needaddr = 0;
 239         opt->ts_needaddr = 0;
 240         opt->ts_needtime = 0;
 241         return;
 242 }
 243
 244 /*
 245  * Verify options and fill pointers in struct options.
 246  * Caller should clear *opt, and set opt->data.
 247  * If opt == NULL, then skb->data should point to IP header.
 248  */
 249
 250 int ip_options_compile(struct net *net,
 251                        struct ip_options * opt, struct sk_buff * skb)
 252 {
 253         int l;
 254         unsigned char * iph;
 255         unsigned char * optptr;
 256         int optlen;
 257         unsigned char * pp_ptr = NULL;
 258         struct rtable *rt = NULL;
 259
 260         if (skb != NULL) {
 261                 rt = skb_rtable(skb);
 262                 optptr = (unsigned char *)&(ip_hdr(skb)[1]);
 263         } else
 264                 optptr = opt->__data;
 265         iph = optptr - sizeof(struct iphdr);
 266
 267         for (l = opt->optlen; l > 0; ) {
 268                 switch (*optptr) {
 269                       case IPOPT_END:
 270                         for (optptr++, l--; l>0; optptr++, l--) {
 271                                 if (*optptr != IPOPT_END) {
 272                                         *optptr = IPOPT_END;
 273                                         opt->is_changed = 1;
 274                                 }
 275                         }
 276                         goto eol;
 277                       case IPOPT_NOOP:
 278                         l--;
 279                         optptr++;
 280                         continue;
 281                 }
 282                 optlen = optptr[1];
 283                 if (optlen<2 || optlen>l) {
 284                         pp_ptr = optptr;
 285                         goto error;
 286                 }
 287                 switch (*optptr) {
 288                       case IPOPT_SSRR:
 289                       case IPOPT_LSRR:
 290                         if (optlen < 3) {
 291                                 pp_ptr = optptr + 1;
 292                                 goto error;
 293                         }
 294                         if (optptr[2] < 4) {
 295                                 pp_ptr = optptr + 2;
 296                                 goto error;
 297                         }
 298                         /* NB: cf RFC-1812 5.2.4.1 */
 299                         if (opt->srr) {
 300                                 pp_ptr = optptr;
 301                                 goto error;
 302                         }
 303                         if (!skb) {
 304                                 if (optptr[2] != 4 || optlen < 7 || ((optlen-3) & 3)) {
 305                                         pp_ptr = optptr + 1;
 306                                         goto error;
 307                                 }
 308                                 memcpy(&opt->faddr, &optptr[3], 4);
 309                                 if (optlen > 7)
 310                                         memmove(&optptr[3], &optptr[7], optlen-7);
 311                         }
 312                         opt->is_strictroute = (optptr[0] == IPOPT_SSRR);
 313                         opt->srr = optptr - iph;
 314                         break;
 315                       case IPOPT_RR:
 316                         if (opt->rr) {
 317                                 pp_ptr = optptr;
 318                                 goto error;
 319                         }
 320                         if (optlen < 3) {
 321                                 pp_ptr = optptr + 1;
 322                                 goto error;
 323                         }
 324                         if (optptr[2] < 4) {
 325                                 pp_ptr = optptr + 2;
 326                                 goto error;
 327                         }
 328                         if (optptr[2] <= optlen) {
 329                                 if (optptr[2]+3 > optlen) {
 330                                         pp_ptr = optptr + 2;
 331                                         goto error;
 332                                 }
 333                                 if (skb) {
 334                                         memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);
 335                                         opt->is_changed = 1;
 336                                 }
 337                                 optptr[2] += 4;
 338                                 opt->rr_needaddr = 1;
 339                         }
 340                         opt->rr = optptr - iph;
 341                         break;
 342                       case IPOPT_TIMESTAMP:
 343                         if (opt->ts) {
 344                                 pp_ptr = optptr;
 345                                 goto error;
 346                         }
 347                         if (optlen < 4) {
 348                                 pp_ptr = optptr + 1;
 349                                 goto error;
 350                         }
 351                         if (optptr[2] < 5) {
 352                                 pp_ptr = optptr + 2;
 353                                 goto error;
 354                         }
 355                         if (optptr[2] <= optlen) {
 356                                 __be32 *timeptr = NULL;
 357                                 if (optptr[2]+3 > optptr[1]) {
 358                                         pp_ptr = optptr + 2;
 359                                         goto error;
 360                                 }
 361                                 switch (optptr[3]&0xF) {
 362                                       case IPOPT_TS_TSONLY:
 363                                         opt->ts = optptr - iph;
 364                                         if (skb)
 365                                                 timeptr = (__be32*)&optptr[optptr[2]-1];
 366                                         opt->ts_needtime = 1;
 367                                         optptr[2] += 4;
 368                                         break;
 369                                       case IPOPT_TS_TSANDADDR:
 370                                         if (optptr[2]+7 > optptr[1]) {
 371                                                 pp_ptr = optptr + 2;
 372                                                 goto error;
 373                                         }
 374                                         opt->ts = optptr - iph;
 375                                         if (skb) {
 376                                                 memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);
 377                                                 timeptr = (__be32*)&optptr[optptr[2]+3];
 378                                         }
 379                                         opt->ts_needaddr = 1;
 380                                         opt->ts_needtime = 1;
 381                                         optptr[2] += 8;
 382                                         break;
 383                                       case IPOPT_TS_PRESPEC:
 384                                         if (optptr[2]+7 > optptr[1]) {
 385                                                 pp_ptr = optptr + 2;
 386                                                 goto error;
 387                                         }
 388                                         opt->ts = optptr - iph;
 389                                         {
 390                                                 __be32 addr;
 391                                                 memcpy(&addr, &optptr[optptr[2]-1], 4);
 392                                                 if (inet_addr_type(net, addr) == RTN_UNICAST)
 393                                                         break;
 394                                                 if (skb)
 395                                                         timeptr = (__be32*)&optptr[optptr[2]+3];
 396                                         }
 397                                         opt->ts_needtime = 1;
 398                                         optptr[2] += 8;
 399                                         break;
 400                                       default:
 401                                         if (!skb && !capable(CAP_NET_RAW)) {
 402                                                 pp_ptr = optptr + 3;
 403                                                 goto error;
 404                                         }
 405                                         break;
 406                                 }
 407                                 if (timeptr) {
 408                                         struct timespec tv;
 409                                         __be32  midtime;
 410                                         getnstimeofday(&tv);
 411                                         midtime = htonl((tv.tv_sec % 86400) * MSEC_PER_SEC + tv.tv_nsec / NSEC_PER_MSEC);
 412                                         memcpy(timeptr, &midtime, sizeof(__be32));
 413                                         opt->is_changed = 1;
 414                                 }
 415                         } else {
 416                                 unsigned overflow = optptr[3]>>4;
 417                                 if (overflow == 15) {
 418                                         pp_ptr = optptr + 3;
 419                                         goto error;
 420                                 }
 421                                 opt->ts = optptr - iph;
 422                                 if (skb) {
 423                                         optptr[3] = (optptr[3]&0xF)|((overflow+1)<<4);
 424                                         opt->is_changed = 1;
 425                                 }
 426                         }
 427                         break;
 428                       case IPOPT_RA:
 429                         if (optlen < 4) {
 430                                 pp_ptr = optptr + 1;
 431                                 goto error;
 432                         }
 433                         if (optptr[2] == 0 && optptr[3] == 0)
 434                                 opt->router_alert = optptr - iph;
 435                         break;
 436                       case IPOPT_CIPSO:
 437                         if ((!skb && !capable(CAP_NET_RAW)) || opt->cipso) {
 438                                 pp_ptr = optptr;
 439                                 goto error;
 440                         }
 441                         opt->cipso = optptr - iph;
 442                         if (cipso_v4_validate(skb, &optptr)) {
 443                                 pp_ptr = optptr;
 444                                 goto error;
 445                         }
 446                         break;
 447                       case IPOPT_SEC:
 448                       case IPOPT_SID:
 449                       default:
 450                         if (!skb && !capable(CAP_NET_RAW)) {
 451                                 pp_ptr = optptr;
 452                                 goto error;
 453                         }
 454                         break;
 455                 }
 456                 l -= optlen;
 457                 optptr += optlen;
 458         }
 459
 460 eol:
 461         if (!pp_ptr)
 462                 return 0;
 463
 464 error:
 465         if (skb) {
 466                 icmp_send(skb, ICMP_PARAMETERPROB, 0, htonl((pp_ptr-iph)<<24));
 467         }
 468         return -EINVAL;
 469 }
 470
 471
 472 /*
 473  *      Undo all the changes done by ip_options_compile().
 474  */
 475
 476 void ip_options_undo(struct ip_options * opt)
 477 {
 478         if (opt->srr) {
 479                 unsigned  char * optptr = opt->__data+opt->srr-sizeof(struct  iphdr);
 480                 memmove(optptr+7, optptr+3, optptr[1]-7);
 481                 memcpy(optptr+3, &opt->faddr, 4);
 482         }
 483         if (opt->rr_needaddr) {
 484                 unsigned  char * optptr = opt->__data+opt->rr-sizeof(struct  iphdr);
 485                 optptr[2] -= 4;
 486                 memset(&optptr[optptr[2]-1], 0, 4);
 487         }
 488         if (opt->ts) {
 489                 unsigned  char * optptr = opt->__data+opt->ts-sizeof(struct  iphdr);
 490                 if (opt->ts_needtime) {
 491                         optptr[2] -= 4;
 492                         memset(&optptr[optptr[2]-1], 0, 4);
 493                         if ((optptr[3]&0xF) == IPOPT_TS_PRESPEC)
 494                                 optptr[2] -= 4;
 495                 }
 496                 if (opt->ts_needaddr) {
 497                         optptr[2] -= 4;
 498                         memset(&optptr[optptr[2]-1], 0, 4);
 499                 }
 500         }
 501 }
 502
 503 static struct ip_options *ip_options_get_alloc(const int optlen)
 504 {
 505         return kzalloc(sizeof(struct ip_options) + ((optlen + 3) & ~3),
 506                        GFP_KERNEL);
 507 }
 508
 509 static int ip_options_get_finish(struct net *net, struct ip_options **optp,
 510                                  struct ip_options *opt, int optlen)
 511 {
 512         while (optlen & 3)
 513                 opt->__data[optlen++] = IPOPT_END;
 514         opt->optlen = optlen;
 515         if (optlen && ip_options_compile(net, opt, NULL)) {
 516                 kfree(opt);
 517                 return -EINVAL;
 518         }
 519         kfree(*optp);
 520         *optp = opt;
 521         return 0;
 522 }
 523
 524 int ip_options_get_from_user(struct net *net, struct ip_options **optp,
 525                              unsigned char __user *data, int optlen)
 526 {
 527         struct ip_options *opt = ip_options_get_alloc(optlen);
 528
 529         if (!opt)
 530                 return -ENOMEM;
 531         if (optlen && copy_from_user(opt->__data, data, optlen)) {
 532                 kfree(opt);
 533                 return -EFAULT;
 534         }
 535         return ip_options_get_finish(net, optp, opt, optlen);
 536 }
 537
 538 int ip_options_get(struct net *net, struct ip_options **optp,
 539                    unsigned char *data, int optlen)
 540 {
 541         struct ip_options *opt = ip_options_get_alloc(optlen);
 542
 543         if (!opt)
 544                 return -ENOMEM;
 545         if (optlen)
 546                 memcpy(opt->__data, data, optlen);
 547         return ip_options_get_finish(net, optp, opt, optlen);
 548 }
 549
 550 void ip_forward_options(struct sk_buff *skb)
 551 {
 552         struct   ip_options * opt       = &(IPCB(skb)->opt);
 553         unsigned char * optptr;
 554         struct rtable *rt = skb_rtable(skb);
 555         unsigned char *raw = skb_network_header(skb);
 556
 557         if (opt->rr_needaddr) {
 558                 optptr = (unsigned char *)raw + opt->rr;
 559                 ip_rt_get_source(&optptr[optptr[2]-5], rt);
 560                 opt->is_changed = 1;
 561         }
 562         if (opt->srr_is_hit) {
 563                 int srrptr, srrspace;
 564
 565                 optptr = raw + opt->srr;
 566
 567                 for ( srrptr=optptr[2], srrspace = optptr[1];
 568                      srrptr <= srrspace;
 569                      srrptr += 4
 570                      ) {
 571                         if (srrptr + 3 > srrspace)
 572                                 break;
 573                         if (memcmp(&rt->rt_dst, &optptr[srrptr-1], 4) == 0)
 574                                 break;
 575                 }
 576                 if (srrptr + 3 <= srrspace) {
 577                         opt->is_changed = 1;
 578                         ip_rt_get_source(&optptr[srrptr-1], rt);
 579                         ip_hdr(skb)->daddr = rt->rt_dst;
 580                         optptr[2] = srrptr+4;
 581                 } else if (net_ratelimit())
 582                         printk(KERN_CRIT "ip_forward(): Argh! Destination lost!\n");
 583                 if (opt->ts_needaddr) {
 584                         optptr = raw + opt->ts;
 585                         ip_rt_get_source(&optptr[optptr[2]-9], rt);
 586                         opt->is_changed = 1;
 587                 }
 588         }
 589         if (opt->is_changed) {
 590                 opt->is_changed = 0;
 591                 ip_send_check(ip_hdr(skb));
 592         }
 593 }
 594
 595 int ip_options_rcv_srr(struct sk_buff *skb)
 596 {
 597         struct ip_options *opt = &(IPCB(skb)->opt);
 598         int srrspace, srrptr;
 599         __be32 nexthop;
 600         struct iphdr *iph = ip_hdr(skb);
 601         unsigned char *optptr = skb_network_header(skb) + opt->srr;
 602         struct rtable *rt = skb_rtable(skb);
 603         struct rtable *rt2;
 604         unsigned long orefdst;
 605         int err;
 606
 607         if (!opt->srr)
 608                 return 0;
 609
 610         if (skb->pkt_type != PACKET_HOST)
 611                 return -EINVAL;
 612         if (rt->rt_type == RTN_UNICAST) {
 613                 if (!opt->is_strictroute)
 614                         return 0;
 615                 icmp_send(skb, ICMP_PARAMETERPROB, 0, htonl(16<<24));
 616                 return -EINVAL;
 617         }
 618         if (rt->rt_type != RTN_LOCAL)
 619                 return -EINVAL;
 620
 621         for (srrptr=optptr[2], srrspace = optptr[1]; srrptr <= srrspace; srrptr += 4) {
 622                 if (srrptr + 3 > srrspace) {
 623                         icmp_send(skb, ICMP_PARAMETERPROB, 0, htonl((opt->srr+2)<<24));
 624                         return -EINVAL;
 625                 }
 626                 memcpy(&nexthop, &optptr[srrptr-1], 4);
 627
 628                 orefdst = skb->_skb_refdst;
 629                 skb_dst_set(skb, NULL);
 630                 err = ip_route_input(skb, nexthop, iph->saddr, iph->tos, skb->dev);
 631                 rt2 = skb_rtable(skb);
 632                 if (err || (rt2->rt_type != RTN_UNICAST && rt2->rt_type != RTN_LOCAL)) {
 633                         skb_dst_drop(skb);
 634                         skb->_skb_refdst = orefdst;
 635                         return -EINVAL;
 636                 }
 637                 refdst_drop(orefdst);
 638                 if (rt2->rt_type != RTN_LOCAL)
 639                         break;
 640                 /* Superfast 8) loopback forward */
 641                 memcpy(&iph->daddr, &optptr[srrptr-1], 4);
 642                 opt->is_changed = 1;
 643         }
 644         if (srrptr <= srrspace) {
 645                 opt->srr_is_hit = 1;
 646                 opt->is_changed = 1;
 647         }
 648         return 0;
 649 }