net/ipv4/fib_semantics.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  *              IPv4 Forwarding Information Base: semantics.
   7  *
   8  * Authors:     Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
   9  *
  10  *              This program is free software; you can redistribute it and/or
  11  *              modify it under the terms of the GNU General Public License
  12  *              as published by the Free Software Foundation; either version
  13  *              2 of the License, or (at your option) any later version.
  14  */
  15
  16 #include <asm/uaccess.h>
  17 #include <linux/bitops.h>
  18 #include <linux/types.h>
  19 #include <linux/kernel.h>
  20 #include <linux/jiffies.h>
  21 #include <linux/mm.h>
  22 #include <linux/string.h>
  23 #include <linux/socket.h>
  24 #include <linux/sockios.h>
  25 #include <linux/errno.h>
  26 #include <linux/in.h>
  27 #include <linux/inet.h>
  28 #include <linux/inetdevice.h>
  29 #include <linux/netdevice.h>
  30 #include <linux/if_arp.h>
  31 #include <linux/proc_fs.h>
  32 #include <linux/skbuff.h>
  33 #include <linux/init.h>
  34 #include <linux/slab.h>
  35
  36 #include <net/arp.h>
  37 #include <net/ip.h>
  38 #include <net/protocol.h>
  39 #include <net/route.h>
  40 #include <net/tcp.h>
  41 #include <net/sock.h>
  42 #include <net/ip_fib.h>
  43 #include <net/netlink.h>
  44 #include <net/nexthop.h>
  45
  46 #include "fib_lookup.h"
  47
  48 static DEFINE_SPINLOCK(fib_info_lock);
  49 static struct hlist_head *fib_info_hash;
  50 static struct hlist_head *fib_info_laddrhash;
  51 static unsigned int fib_info_hash_size;
  52 static unsigned int fib_info_cnt;
  53
  54 #define DEVINDEX_HASHBITS 8
  55 #define DEVINDEX_HASHSIZE (1U << DEVINDEX_HASHBITS)
  56 static struct hlist_head fib_info_devhash[DEVINDEX_HASHSIZE];
  57
  58 #ifdef CONFIG_IP_ROUTE_MULTIPATH
  59
  60 static DEFINE_SPINLOCK(fib_multipath_lock);
  61
  62 #define for_nexthops(fi) {                                              \
  63         int nhsel; const struct fib_nh *nh;                             \
  64         for (nhsel = 0, nh = (fi)->fib_nh;                              \
  65              nhsel < (fi)->fib_nhs;                                     \
  66              nh++, nhsel++)
  67
  68 #define change_nexthops(fi) {                                           \
  69         int nhsel; struct fib_nh *nexthop_nh;                           \
  70         for (nhsel = 0, nexthop_nh = (struct fib_nh *)((fi)->fib_nh);   \
  71              nhsel < (fi)->fib_nhs;                                     \
  72              nexthop_nh++, nhsel++)
  73
  74 #else /* CONFIG_IP_ROUTE_MULTIPATH */
  75
  76 /* Hope, that gcc will optimize it to get rid of dummy loop */
  77
  78 #define for_nexthops(fi) {                                              \
  79         int nhsel; const struct fib_nh *nh = (fi)->fib_nh;              \
  80         for (nhsel = 0; nhsel < 1; nhsel++)
  81
  82 #define change_nexthops(fi) {                                           \
  83         int nhsel;                                                      \
  84         struct fib_nh *nexthop_nh = (struct fib_nh *)((fi)->fib_nh);    \
  85         for (nhsel = 0; nhsel < 1; nhsel++)
  86
  87 #endif /* CONFIG_IP_ROUTE_MULTIPATH */
  88
  89 #define endfor_nexthops(fi) }
  90
  91
  92 const struct fib_prop fib_props[RTN_MAX + 1] = {
  93         [RTN_UNSPEC] = {
  94                 .error  = 0,
  95                 .scope  = RT_SCOPE_NOWHERE,
  96         },
  97         [RTN_UNICAST] = {
  98                 .error  = 0,
  99                 .scope  = RT_SCOPE_UNIVERSE,
 100         },
 101         [RTN_LOCAL] = {
 102                 .error  = 0,
 103                 .scope  = RT_SCOPE_HOST,
 104         },
 105         [RTN_BROADCAST] = {
 106                 .error  = 0,
 107                 .scope  = RT_SCOPE_LINK,
 108         },
 109         [RTN_ANYCAST] = {
 110                 .error  = 0,
 111                 .scope  = RT_SCOPE_LINK,
 112         },
 113         [RTN_MULTICAST] = {
 114                 .error  = 0,
 115                 .scope  = RT_SCOPE_UNIVERSE,
 116         },
 117         [RTN_BLACKHOLE] = {
 118                 .error  = -EINVAL,
 119                 .scope  = RT_SCOPE_UNIVERSE,
 120         },
 121         [RTN_UNREACHABLE] = {
 122                 .error  = -EHOSTUNREACH,
 123                 .scope  = RT_SCOPE_UNIVERSE,
 124         },
 125         [RTN_PROHIBIT] = {
 126                 .error  = -EACCES,
 127                 .scope  = RT_SCOPE_UNIVERSE,
 128         },
 129         [RTN_THROW] = {
 130                 .error  = -EAGAIN,
 131                 .scope  = RT_SCOPE_UNIVERSE,
 132         },
 133         [RTN_NAT] = {
 134                 .error  = -EINVAL,
 135                 .scope  = RT_SCOPE_NOWHERE,
 136         },
 137         [RTN_XRESOLVE] = {
 138                 .error  = -EINVAL,
 139                 .scope  = RT_SCOPE_NOWHERE,
 140         },
 141 };
 142
 143 static void free_nh_exceptions(struct fib_nh *nh)
 144 {
 145         struct fnhe_hash_bucket *hash = nh->nh_exceptions;
 146         int i;
 147
 148         for (i = 0; i < FNHE_HASH_SIZE; i++) {
 149                 struct fib_nh_exception *fnhe;
 150
 151                 fnhe = rcu_dereference_protected(hash[i].chain, 1);
 152                 while (fnhe) {
 153                         struct fib_nh_exception *next;
 154
 155                         next = rcu_dereference_protected(fnhe->fnhe_next, 1);
 156                         kfree(fnhe);
 157
 158                         fnhe = next;
 159                 }
 160         }
 161         kfree(hash);
 162 }
 163
 164 /* Release a nexthop info record */
 165 static void free_fib_info_rcu(struct rcu_head *head)
 166 {
 167         struct fib_info *fi = container_of(head, struct fib_info, rcu);
 168
 169         change_nexthops(fi) {
 170                 if (nexthop_nh->nh_dev)
 171                         dev_put(nexthop_nh->nh_dev);
 172                 if (nexthop_nh->nh_exceptions)
 173                         free_nh_exceptions(nexthop_nh);
 174                 if (nexthop_nh->nh_rth_output)
 175                         dst_release(&nexthop_nh->nh_rth_output->dst);
 176                 if (nexthop_nh->nh_rth_input)
 177                         dst_release(&nexthop_nh->nh_rth_input->dst);
 178         } endfor_nexthops(fi);
 179
 180         release_net(fi->fib_net);
 181         if (fi->fib_metrics != (u32 *) dst_default_metrics)
 182                 kfree(fi->fib_metrics);
 183         kfree(fi);
 184 }
 185
 186 void free_fib_info(struct fib_info *fi)
 187 {
 188         if (fi->fib_dead == 0) {
 189                 pr_warn("Freeing alive fib_info %p\n", fi);
 190                 return;
 191         }
 192         fib_info_cnt--;
 193 #ifdef CONFIG_IP_ROUTE_CLASSID
 194         change_nexthops(fi) {
 195                 if (nexthop_nh->nh_tclassid)
 196                         fi->fib_net->ipv4.fib_num_tclassid_users--;
 197         } endfor_nexthops(fi);
 198 #endif
 199         call_rcu(&fi->rcu, free_fib_info_rcu);
 200 }
 201
 202 void fib_release_info(struct fib_info *fi)
 203 {
 204         spin_lock_bh(&fib_info_lock);
 205         if (fi && --fi->fib_treeref == 0) {
 206                 hlist_del(&fi->fib_hash);
 207                 if (fi->fib_prefsrc)
 208                         hlist_del(&fi->fib_lhash);
 209                 change_nexthops(fi) {
 210                         if (!nexthop_nh->nh_dev)
 211                                 continue;
 212                         hlist_del(&nexthop_nh->nh_hash);
 213                 } endfor_nexthops(fi)
 214                 fi->fib_dead = 1;
 215                 fib_info_put(fi);
 216         }
 217         spin_unlock_bh(&fib_info_lock);
 218 }
 219
 220 static inline int nh_comp(const struct fib_info *fi, const struct fib_info *ofi)
 221 {
 222         const struct fib_nh *onh = ofi->fib_nh;
 223
 224         for_nexthops(fi) {
 225                 if (nh->nh_oif != onh->nh_oif ||
 226                     nh->nh_gw  != onh->nh_gw ||
 227                     nh->nh_scope != onh->nh_scope ||
 228 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 229                     nh->nh_weight != onh->nh_weight ||
 230 #endif
 231 #ifdef CONFIG_IP_ROUTE_CLASSID
 232                     nh->nh_tclassid != onh->nh_tclassid ||
 233 #endif
 234                     ((nh->nh_flags ^ onh->nh_flags) & ~RTNH_F_DEAD))
 235                         return -1;
 236                 onh++;
 237         } endfor_nexthops(fi);
 238         return 0;
 239 }
 240
 241 static inline unsigned int fib_devindex_hashfn(unsigned int val)
 242 {
 243         unsigned int mask = DEVINDEX_HASHSIZE - 1;
 244
 245         return (val ^
 246                 (val >> DEVINDEX_HASHBITS) ^
 247                 (val >> (DEVINDEX_HASHBITS * 2))) & mask;
 248 }
 249
 250 static inline unsigned int fib_info_hashfn(const struct fib_info *fi)
 251 {
 252         unsigned int mask = (fib_info_hash_size - 1);
 253         unsigned int val = fi->fib_nhs;
 254
 255         val ^= (fi->fib_protocol << 8) | fi->fib_scope;
 256         val ^= (__force u32)fi->fib_prefsrc;
 257         val ^= fi->fib_priority;
 258         for_nexthops(fi) {
 259                 val ^= fib_devindex_hashfn(nh->nh_oif);
 260         } endfor_nexthops(fi)
 261
 262         return (val ^ (val >> 7) ^ (val >> 12)) & mask;
 263 }
 264
 265 static struct fib_info *fib_find_info(const struct fib_info *nfi)
 266 {
 267         struct hlist_head *head;
 268         struct hlist_node *node;
 269         struct fib_info *fi;
 270         unsigned int hash;
 271
 272         hash = fib_info_hashfn(nfi);
 273         head = &fib_info_hash[hash];
 274
 275         hlist_for_each_entry(fi, node, head, fib_hash) {
 276                 if (!net_eq(fi->fib_net, nfi->fib_net))
 277                         continue;
 278                 if (fi->fib_nhs != nfi->fib_nhs)
 279                         continue;
 280                 if (nfi->fib_protocol == fi->fib_protocol &&
 281                     nfi->fib_scope == fi->fib_scope &&
 282                     nfi->fib_prefsrc == fi->fib_prefsrc &&
 283                     nfi->fib_priority == fi->fib_priority &&
 284                     memcmp(nfi->fib_metrics, fi->fib_metrics,
 285                            sizeof(u32) * RTAX_MAX) == 0 &&
 286                     ((nfi->fib_flags ^ fi->fib_flags) & ~RTNH_F_DEAD) == 0 &&
 287                     (nfi->fib_nhs == 0 || nh_comp(fi, nfi) == 0))
 288                         return fi;
 289         }
 290
 291         return NULL;
 292 }
 293
 294 /* Check, that the gateway is already configured.
 295  * Used only by redirect accept routine.
 296  */
 297 int ip_fib_check_default(__be32 gw, struct net_device *dev)
 298 {
 299         struct hlist_head *head;
 300         struct hlist_node *node;
 301         struct fib_nh *nh;
 302         unsigned int hash;
 303
 304         spin_lock(&fib_info_lock);
 305
 306         hash = fib_devindex_hashfn(dev->ifindex);
 307         head = &fib_info_devhash[hash];
 308         hlist_for_each_entry(nh, node, head, nh_hash) {
 309                 if (nh->nh_dev == dev &&
 310                     nh->nh_gw == gw &&
 311                     !(nh->nh_flags & RTNH_F_DEAD)) {
 312                         spin_unlock(&fib_info_lock);
 313                         return 0;
 314                 }
 315         }
 316
 317         spin_unlock(&fib_info_lock);
 318
 319         return -1;
 320 }
 321
 322 static inline size_t fib_nlmsg_size(struct fib_info *fi)
 323 {
 324         size_t payload = NLMSG_ALIGN(sizeof(struct rtmsg))
 325                          + nla_total_size(4) /* RTA_TABLE */
 326                          + nla_total_size(4) /* RTA_DST */
 327                          + nla_total_size(4) /* RTA_PRIORITY */
 328                          + nla_total_size(4); /* RTA_PREFSRC */
 329
 330         /* space for nested metrics */
 331         payload += nla_total_size((RTAX_MAX * nla_total_size(4)));
 332
 333         if (fi->fib_nhs) {
 334                 /* Also handles the special case fib_nhs == 1 */
 335
 336                 /* each nexthop is packed in an attribute */
 337                 size_t nhsize = nla_total_size(sizeof(struct rtnexthop));
 338
 339                 /* may contain flow and gateway attribute */
 340                 nhsize += 2 * nla_total_size(4);
 341
 342                 /* all nexthops are packed in a nested attribute */
 343                 payload += nla_total_size(fi->fib_nhs * nhsize);
 344         }
 345
 346         return payload;
 347 }
 348
 349 void rtmsg_fib(int event, __be32 key, struct fib_alias *fa,
 350                int dst_len, u32 tb_id, struct nl_info *info,
 351                unsigned int nlm_flags)
 352 {
 353         struct sk_buff *skb;
 354         u32 seq = info->nlh ? info->nlh->nlmsg_seq : 0;
 355         int err = -ENOBUFS;
 356
 357         skb = nlmsg_new(fib_nlmsg_size(fa->fa_info), GFP_KERNEL);
 358         if (skb == NULL)
 359                 goto errout;
 360
 361         err = fib_dump_info(skb, info->pid, seq, event, tb_id,
 362                             fa->fa_type, key, dst_len,
 363                             fa->fa_tos, fa->fa_info, nlm_flags);
 364         if (err < 0) {
 365                 /* -EMSGSIZE implies BUG in fib_nlmsg_size() */
 366                 WARN_ON(err == -EMSGSIZE);
 367                 kfree_skb(skb);
 368                 goto errout;
 369         }
 370         rtnl_notify(skb, info->nl_net, info->pid, RTNLGRP_IPV4_ROUTE,
 371                     info->nlh, GFP_KERNEL);
 372         return;
 373 errout:
 374         if (err < 0)
 375                 rtnl_set_sk_err(info->nl_net, RTNLGRP_IPV4_ROUTE, err);
 376 }
 377
 378 /* Return the first fib alias matching TOS with
 379  * priority less than or equal to PRIO.
 380  */
 381 struct fib_alias *fib_find_alias(struct list_head *fah, u8 tos, u32 prio)
 382 {
 383         if (fah) {
 384                 struct fib_alias *fa;
 385                 list_for_each_entry(fa, fah, fa_list) {
 386                         if (fa->fa_tos > tos)
 387                                 continue;
 388                         if (fa->fa_info->fib_priority >= prio ||
 389                             fa->fa_tos < tos)
 390                                 return fa;
 391                 }
 392         }
 393         return NULL;
 394 }
 395
 396 int fib_detect_death(struct fib_info *fi, int order,
 397                      struct fib_info **last_resort, int *last_idx, int dflt)
 398 {
 399         struct neighbour *n;
 400         int state = NUD_NONE;
 401
 402         n = neigh_lookup(&arp_tbl, &fi->fib_nh[0].nh_gw, fi->fib_dev);
 403         if (n) {
 404                 state = n->nud_state;
 405                 neigh_release(n);
 406         }
 407         if (state == NUD_REACHABLE)
 408                 return 0;
 409         if ((state & NUD_VALID) && order != dflt)
 410                 return 0;
 411         if ((state & NUD_VALID) ||
 412             (*last_idx < 0 && order > dflt)) {
 413                 *last_resort = fi;
 414                 *last_idx = order;
 415         }
 416         return 1;
 417 }
 418
 419 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 420
 421 static int fib_count_nexthops(struct rtnexthop *rtnh, int remaining)
 422 {
 423         int nhs = 0;
 424
 425         while (rtnh_ok(rtnh, remaining)) {
 426                 nhs++;
 427                 rtnh = rtnh_next(rtnh, &remaining);
 428         }
 429
 430         /* leftover implies invalid nexthop configuration, discard it */
 431         return remaining > 0 ? 0 : nhs;
 432 }
 433
 434 static int fib_get_nhs(struct fib_info *fi, struct rtnexthop *rtnh,
 435                        int remaining, struct fib_config *cfg)
 436 {
 437         change_nexthops(fi) {
 438                 int attrlen;
 439
 440                 if (!rtnh_ok(rtnh, remaining))
 441                         return -EINVAL;
 442
 443                 nexthop_nh->nh_flags =
 444                         (cfg->fc_flags & ~0xFF) | rtnh->rtnh_flags;
 445                 nexthop_nh->nh_oif = rtnh->rtnh_ifindex;
 446                 nexthop_nh->nh_weight = rtnh->rtnh_hops + 1;
 447
 448                 attrlen = rtnh_attrlen(rtnh);
 449                 if (attrlen > 0) {
 450                         struct nlattr *nla, *attrs = rtnh_attrs(rtnh);
 451
 452                         nla = nla_find(attrs, attrlen, RTA_GATEWAY);
 453                         nexthop_nh->nh_gw = nla ? nla_get_be32(nla) : 0;
 454 #ifdef CONFIG_IP_ROUTE_CLASSID
 455                         nla = nla_find(attrs, attrlen, RTA_FLOW);
 456                         nexthop_nh->nh_tclassid = nla ? nla_get_u32(nla) : 0;
 457                         if (nexthop_nh->nh_tclassid)
 458                                 fi->fib_net->ipv4.fib_num_tclassid_users++;
 459 #endif
 460                 }
 461
 462                 rtnh = rtnh_next(rtnh, &remaining);
 463         } endfor_nexthops(fi);
 464
 465         return 0;
 466 }
 467
 468 #endif
 469
 470 int fib_nh_match(struct fib_config *cfg, struct fib_info *fi)
 471 {
 472 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 473         struct rtnexthop *rtnh;
 474         int remaining;
 475 #endif
 476
 477         if (cfg->fc_priority && cfg->fc_priority != fi->fib_priority)
 478                 return 1;
 479
 480         if (cfg->fc_oif || cfg->fc_gw) {
 481                 if ((!cfg->fc_oif || cfg->fc_oif == fi->fib_nh->nh_oif) &&
 482                     (!cfg->fc_gw  || cfg->fc_gw == fi->fib_nh->nh_gw))
 483                         return 0;
 484                 return 1;
 485         }
 486
 487 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 488         if (cfg->fc_mp == NULL)
 489                 return 0;
 490
 491         rtnh = cfg->fc_mp;
 492         remaining = cfg->fc_mp_len;
 493
 494         for_nexthops(fi) {
 495                 int attrlen;
 496
 497                 if (!rtnh_ok(rtnh, remaining))
 498                         return -EINVAL;
 499
 500                 if (rtnh->rtnh_ifindex && rtnh->rtnh_ifindex != nh->nh_oif)
 501                         return 1;
 502
 503                 attrlen = rtnh_attrlen(rtnh);
 504                 if (attrlen < 0) {
 505                         struct nlattr *nla, *attrs = rtnh_attrs(rtnh);
 506
 507                         nla = nla_find(attrs, attrlen, RTA_GATEWAY);
 508                         if (nla && nla_get_be32(nla) != nh->nh_gw)
 509                                 return 1;
 510 #ifdef CONFIG_IP_ROUTE_CLASSID
 511                         nla = nla_find(attrs, attrlen, RTA_FLOW);
 512                         if (nla && nla_get_u32(nla) != nh->nh_tclassid)
 513                                 return 1;
 514 #endif
 515                 }
 516
 517                 rtnh = rtnh_next(rtnh, &remaining);
 518         } endfor_nexthops(fi);
 519 #endif
 520         return 0;
 521 }
 522
 523
 524 /*
 525  * Picture
 526  * -------
 527  *
 528  * Semantics of nexthop is very messy by historical reasons.
 529  * We have to take into account, that:
 530  * a) gateway can be actually local interface address,
 531  *    so that gatewayed route is direct.
 532  * b) gateway must be on-link address, possibly
 533  *    described not by an ifaddr, but also by a direct route.
 534  * c) If both gateway and interface are specified, they should not
 535  *    contradict.
 536  * d) If we use tunnel routes, gateway could be not on-link.
 537  *
 538  * Attempt to reconcile all of these (alas, self-contradictory) conditions
 539  * results in pretty ugly and hairy code with obscure logic.
 540  *
 541  * I chose to generalized it instead, so that the size
 542  * of code does not increase practically, but it becomes
 543  * much more general.
 544  * Every prefix is assigned a "scope" value: "host" is local address,
 545  * "link" is direct route,
 546  * [ ... "site" ... "interior" ... ]
 547  * and "universe" is true gateway route with global meaning.
 548  *
 549  * Every prefix refers to a set of "nexthop"s (gw, oif),
 550  * where gw must have narrower scope. This recursion stops
 551  * when gw has LOCAL scope or if "nexthop" is declared ONLINK,
 552  * which means that gw is forced to be on link.
 553  *
 554  * Code is still hairy, but now it is apparently logically
 555  * consistent and very flexible. F.e. as by-product it allows
 556  * to co-exists in peace independent exterior and interior
 557  * routing processes.
 558  *
 559  * Normally it looks as following.
 560  *
 561  * {universe prefix}  -> (gw, oif) [scope link]
 562  *                |
 563  *                |-> {link prefix} -> (gw, oif) [scope local]
 564  *                                      |
 565  *                                      |-> {local prefix} (terminal node)
 566  */
 567 static int fib_check_nh(struct fib_config *cfg, struct fib_info *fi,
 568                         struct fib_nh *nh)
 569 {
 570         int err;
 571         struct net *net;
 572         struct net_device *dev;
 573
 574         net = cfg->fc_nlinfo.nl_net;
 575         if (nh->nh_gw) {
 576                 struct fib_result res;
 577
 578                 if (nh->nh_flags & RTNH_F_ONLINK) {
 579
 580                         if (cfg->fc_scope >= RT_SCOPE_LINK)
 581                                 return -EINVAL;
 582                         if (inet_addr_type(net, nh->nh_gw) != RTN_UNICAST)
 583                                 return -EINVAL;
 584                         dev = __dev_get_by_index(net, nh->nh_oif);
 585                         if (!dev)
 586                                 return -ENODEV;
 587                         if (!(dev->flags & IFF_UP))
 588                                 return -ENETDOWN;
 589                         nh->nh_dev = dev;
 590                         dev_hold(dev);
 591                         nh->nh_scope = RT_SCOPE_LINK;
 592                         return 0;
 593                 }
 594                 rcu_read_lock();
 595                 {
 596                         struct flowi4 fl4 = {
 597                                 .daddr = nh->nh_gw,
 598                                 .flowi4_scope = cfg->fc_scope + 1,
 599                                 .flowi4_oif = nh->nh_oif,
 600                         };
 601
 602                         /* It is not necessary, but requires a bit of thinking */
 603                         if (fl4.flowi4_scope < RT_SCOPE_LINK)
 604                                 fl4.flowi4_scope = RT_SCOPE_LINK;
 605                         err = fib_lookup(net, &fl4, &res);
 606                         if (err) {
 607                                 rcu_read_unlock();
 608                                 return err;
 609                         }
 610                 }
 611                 err = -EINVAL;
 612                 if (res.type != RTN_UNICAST && res.type != RTN_LOCAL)
 613                         goto out;
 614                 nh->nh_scope = res.scope;
 615                 nh->nh_oif = FIB_RES_OIF(res);
 616                 nh->nh_dev = dev = FIB_RES_DEV(res);
 617                 if (!dev)
 618                         goto out;
 619                 dev_hold(dev);
 620                 err = (dev->flags & IFF_UP) ? 0 : -ENETDOWN;
 621         } else {
 622                 struct in_device *in_dev;
 623
 624                 if (nh->nh_flags & (RTNH_F_PERVASIVE | RTNH_F_ONLINK))
 625                         return -EINVAL;
 626
 627                 rcu_read_lock();
 628                 err = -ENODEV;
 629                 in_dev = inetdev_by_index(net, nh->nh_oif);
 630                 if (in_dev == NULL)
 631                         goto out;
 632                 err = -ENETDOWN;
 633                 if (!(in_dev->dev->flags & IFF_UP))
 634                         goto out;
 635                 nh->nh_dev = in_dev->dev;
 636                 dev_hold(nh->nh_dev);
 637                 nh->nh_scope = RT_SCOPE_HOST;
 638                 err = 0;
 639         }
 640 out:
 641         rcu_read_unlock();
 642         return err;
 643 }
 644
 645 static inline unsigned int fib_laddr_hashfn(__be32 val)
 646 {
 647         unsigned int mask = (fib_info_hash_size - 1);
 648
 649         return ((__force u32)val ^
 650                 ((__force u32)val >> 7) ^
 651                 ((__force u32)val >> 14)) & mask;
 652 }
 653
 654 static struct hlist_head *fib_info_hash_alloc(int bytes)
 655 {
 656         if (bytes <= PAGE_SIZE)
 657                 return kzalloc(bytes, GFP_KERNEL);
 658         else
 659                 return (struct hlist_head *)
 660                         __get_free_pages(GFP_KERNEL | __GFP_ZERO,
 661                                          get_order(bytes));
 662 }
 663
 664 static void fib_info_hash_free(struct hlist_head *hash, int bytes)
 665 {
 666         if (!hash)
 667                 return;
 668
 669         if (bytes <= PAGE_SIZE)
 670                 kfree(hash);
 671         else
 672                 free_pages((unsigned long) hash, get_order(bytes));
 673 }
 674
 675 static void fib_info_hash_move(struct hlist_head *new_info_hash,
 676                                struct hlist_head *new_laddrhash,
 677                                unsigned int new_size)
 678 {
 679         struct hlist_head *old_info_hash, *old_laddrhash;
 680         unsigned int old_size = fib_info_hash_size;
 681         unsigned int i, bytes;
 682
 683         spin_lock_bh(&fib_info_lock);
 684         old_info_hash = fib_info_hash;
 685         old_laddrhash = fib_info_laddrhash;
 686         fib_info_hash_size = new_size;
 687
 688         for (i = 0; i < old_size; i++) {
 689                 struct hlist_head *head = &fib_info_hash[i];
 690                 struct hlist_node *node, *n;
 691                 struct fib_info *fi;
 692
 693                 hlist_for_each_entry_safe(fi, node, n, head, fib_hash) {
 694                         struct hlist_head *dest;
 695                         unsigned int new_hash;
 696
 697                         hlist_del(&fi->fib_hash);
 698
 699                         new_hash = fib_info_hashfn(fi);
 700                         dest = &new_info_hash[new_hash];
 701                         hlist_add_head(&fi->fib_hash, dest);
 702                 }
 703         }
 704         fib_info_hash = new_info_hash;
 705
 706         for (i = 0; i < old_size; i++) {
 707                 struct hlist_head *lhead = &fib_info_laddrhash[i];
 708                 struct hlist_node *node, *n;
 709                 struct fib_info *fi;
 710
 711                 hlist_for_each_entry_safe(fi, node, n, lhead, fib_lhash) {
 712                         struct hlist_head *ldest;
 713                         unsigned int new_hash;
 714
 715                         hlist_del(&fi->fib_lhash);
 716
 717                         new_hash = fib_laddr_hashfn(fi->fib_prefsrc);
 718                         ldest = &new_laddrhash[new_hash];
 719                         hlist_add_head(&fi->fib_lhash, ldest);
 720                 }
 721         }
 722         fib_info_laddrhash = new_laddrhash;
 723
 724         spin_unlock_bh(&fib_info_lock);
 725
 726         bytes = old_size * sizeof(struct hlist_head *);
 727         fib_info_hash_free(old_info_hash, bytes);
 728         fib_info_hash_free(old_laddrhash, bytes);
 729 }
 730
 731 __be32 fib_info_update_nh_saddr(struct net *net, struct fib_nh *nh)
 732 {
 733         nh->nh_saddr = inet_select_addr(nh->nh_dev,
 734                                         nh->nh_gw,
 735                                         nh->nh_parent->fib_scope);
 736         nh->nh_saddr_genid = atomic_read(&net->ipv4.dev_addr_genid);
 737
 738         return nh->nh_saddr;
 739 }
 740
 741 struct fib_info *fib_create_info(struct fib_config *cfg)
 742 {
 743         int err;
 744         struct fib_info *fi = NULL;
 745         struct fib_info *ofi;
 746         int nhs = 1;
 747         struct net *net = cfg->fc_nlinfo.nl_net;
 748
 749         if (cfg->fc_type > RTN_MAX)
 750                 goto err_inval;
 751
 752         /* Fast check to catch the most weird cases */
 753         if (fib_props[cfg->fc_type].scope > cfg->fc_scope)
 754                 goto err_inval;
 755
 756 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 757         if (cfg->fc_mp) {
 758                 nhs = fib_count_nexthops(cfg->fc_mp, cfg->fc_mp_len);
 759                 if (nhs == 0)
 760                         goto err_inval;
 761         }
 762 #endif
 763
 764         err = -ENOBUFS;
 765         if (fib_info_cnt >= fib_info_hash_size) {
 766                 unsigned int new_size = fib_info_hash_size << 1;
 767                 struct hlist_head *new_info_hash;
 768                 struct hlist_head *new_laddrhash;
 769                 unsigned int bytes;
 770
 771                 if (!new_size)
 772                         new_size = 1;
 773                 bytes = new_size * sizeof(struct hlist_head *);
 774                 new_info_hash = fib_info_hash_alloc(bytes);
 775                 new_laddrhash = fib_info_hash_alloc(bytes);
 776                 if (!new_info_hash || !new_laddrhash) {
 777                         fib_info_hash_free(new_info_hash, bytes);
 778                         fib_info_hash_free(new_laddrhash, bytes);
 779                 } else
 780                         fib_info_hash_move(new_info_hash, new_laddrhash, new_size);
 781
 782                 if (!fib_info_hash_size)
 783                         goto failure;
 784         }
 785
 786         fi = kzalloc(sizeof(*fi)+nhs*sizeof(struct fib_nh), GFP_KERNEL);
 787         if (fi == NULL)
 788                 goto failure;
 789         if (cfg->fc_mx) {
 790                 fi->fib_metrics = kzalloc(sizeof(u32) * RTAX_MAX, GFP_KERNEL);
 791                 if (!fi->fib_metrics)
 792                         goto failure;
 793         } else
 794                 fi->fib_metrics = (u32 *) dst_default_metrics;
 795         fib_info_cnt++;
 796
 797         fi->fib_net = hold_net(net);
 798         fi->fib_protocol = cfg->fc_protocol;
 799         fi->fib_scope = cfg->fc_scope;
 800         fi->fib_flags = cfg->fc_flags;
 801         fi->fib_priority = cfg->fc_priority;
 802         fi->fib_prefsrc = cfg->fc_prefsrc;
 803
 804         fi->fib_nhs = nhs;
 805         change_nexthops(fi) {
 806                 nexthop_nh->nh_parent = fi;
 807         } endfor_nexthops(fi)
 808
 809         if (cfg->fc_mx) {
 810                 struct nlattr *nla;
 811                 int remaining;
 812
 813                 nla_for_each_attr(nla, cfg->fc_mx, cfg->fc_mx_len, remaining) {
 814                         int type = nla_type(nla);
 815
 816                         if (type) {
 817                                 u32 val;
 818
 819                                 if (type > RTAX_MAX)
 820                                         goto err_inval;
 821                                 val = nla_get_u32(nla);
 822                                 if (type == RTAX_ADVMSS && val > 65535 - 40)
 823                                         val = 65535 - 40;
 824                                 if (type == RTAX_MTU && val > 65535 - 15)
 825                                         val = 65535 - 15;
 826                                 fi->fib_metrics[type - 1] = val;
 827                         }
 828                 }
 829         }
 830
 831         if (cfg->fc_mp) {
 832 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 833                 err = fib_get_nhs(fi, cfg->fc_mp, cfg->fc_mp_len, cfg);
 834                 if (err != 0)
 835                         goto failure;
 836                 if (cfg->fc_oif && fi->fib_nh->nh_oif != cfg->fc_oif)
 837                         goto err_inval;
 838                 if (cfg->fc_gw && fi->fib_nh->nh_gw != cfg->fc_gw)
 839                         goto err_inval;
 840 #ifdef CONFIG_IP_ROUTE_CLASSID
 841                 if (cfg->fc_flow && fi->fib_nh->nh_tclassid != cfg->fc_flow)
 842                         goto err_inval;
 843 #endif
 844 #else
 845                 goto err_inval;
 846 #endif
 847         } else {
 848                 struct fib_nh *nh = fi->fib_nh;
 849
 850                 nh->nh_oif = cfg->fc_oif;
 851                 nh->nh_gw = cfg->fc_gw;
 852                 nh->nh_flags = cfg->fc_flags;
 853 #ifdef CONFIG_IP_ROUTE_CLASSID
 854                 nh->nh_tclassid = cfg->fc_flow;
 855                 if (nh->nh_tclassid)
 856                         fi->fib_net->ipv4.fib_num_tclassid_users++;
 857 #endif
 858 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 859                 nh->nh_weight = 1;
 860 #endif
 861         }
 862
 863         if (fib_props[cfg->fc_type].error) {
 864                 if (cfg->fc_gw || cfg->fc_oif || cfg->fc_mp)
 865                         goto err_inval;
 866                 goto link_it;
 867         } else {
 868                 switch (cfg->fc_type) {
 869                 case RTN_UNICAST:
 870                 case RTN_LOCAL:
 871                 case RTN_BROADCAST:
 872                 case RTN_ANYCAST:
 873                 case RTN_MULTICAST:
 874                         break;
 875                 default:
 876                         goto err_inval;
 877                 }
 878         }
 879
 880         if (cfg->fc_scope > RT_SCOPE_HOST)
 881                 goto err_inval;
 882
 883         if (cfg->fc_scope == RT_SCOPE_HOST) {
 884                 struct fib_nh *nh = fi->fib_nh;
 885
 886                 /* Local address is added. */
 887                 if (nhs != 1 || nh->nh_gw)
 888                         goto err_inval;
 889                 nh->nh_scope = RT_SCOPE_NOWHERE;
 890                 nh->nh_dev = dev_get_by_index(net, fi->fib_nh->nh_oif);
 891                 err = -ENODEV;
 892                 if (nh->nh_dev == NULL)
 893                         goto failure;
 894         } else {
 895                 change_nexthops(fi) {
 896                         err = fib_check_nh(cfg, fi, nexthop_nh);
 897                         if (err != 0)
 898                                 goto failure;
 899                 } endfor_nexthops(fi)
 900         }
 901
 902         if (fi->fib_prefsrc) {
 903                 if (cfg->fc_type != RTN_LOCAL || !cfg->fc_dst ||
 904                     fi->fib_prefsrc != cfg->fc_dst)
 905                         if (inet_addr_type(net, fi->fib_prefsrc) != RTN_LOCAL)
 906                                 goto err_inval;
 907         }
 908
 909         change_nexthops(fi) {
 910                 fib_info_update_nh_saddr(net, nexthop_nh);
 911         } endfor_nexthops(fi)
 912
 913 link_it:
 914         ofi = fib_find_info(fi);
 915         if (ofi) {
 916                 fi->fib_dead = 1;
 917                 free_fib_info(fi);
 918                 ofi->fib_treeref++;
 919                 return ofi;
 920         }
 921
 922         fi->fib_treeref++;
 923         atomic_inc(&fi->fib_clntref);
 924         spin_lock_bh(&fib_info_lock);
 925         hlist_add_head(&fi->fib_hash,
 926                        &fib_info_hash[fib_info_hashfn(fi)]);
 927         if (fi->fib_prefsrc) {
 928                 struct hlist_head *head;
 929
 930                 head = &fib_info_laddrhash[fib_laddr_hashfn(fi->fib_prefsrc)];
 931                 hlist_add_head(&fi->fib_lhash, head);
 932         }
 933         change_nexthops(fi) {
 934                 struct hlist_head *head;
 935                 unsigned int hash;
 936
 937                 if (!nexthop_nh->nh_dev)
 938                         continue;
 939                 hash = fib_devindex_hashfn(nexthop_nh->nh_dev->ifindex);
 940                 head = &fib_info_devhash[hash];
 941                 hlist_add_head(&nexthop_nh->nh_hash, head);
 942         } endfor_nexthops(fi)
 943         spin_unlock_bh(&fib_info_lock);
 944         return fi;
 945
 946 err_inval:
 947         err = -EINVAL;
 948
 949 failure:
 950         if (fi) {
 951                 fi->fib_dead = 1;
 952                 free_fib_info(fi);
 953         }
 954
 955         return ERR_PTR(err);
 956 }
 957
 958 int fib_dump_info(struct sk_buff *skb, u32 pid, u32 seq, int event,
 959                   u32 tb_id, u8 type, __be32 dst, int dst_len, u8 tos,
 960                   struct fib_info *fi, unsigned int flags)
 961 {
 962         struct nlmsghdr *nlh;
 963         struct rtmsg *rtm;
 964
 965         nlh = nlmsg_put(skb, pid, seq, event, sizeof(*rtm), flags);
 966         if (nlh == NULL)
 967                 return -EMSGSIZE;
 968
 969         rtm = nlmsg_data(nlh);
 970         rtm->rtm_family = AF_INET;
 971         rtm->rtm_dst_len = dst_len;
 972         rtm->rtm_src_len = 0;
 973         rtm->rtm_tos = tos;
 974         if (tb_id < 256)
 975                 rtm->rtm_table = tb_id;
 976         else
 977                 rtm->rtm_table = RT_TABLE_COMPAT;
 978         if (nla_put_u32(skb, RTA_TABLE, tb_id))
 979                 goto nla_put_failure;
 980         rtm->rtm_type = type;
 981         rtm->rtm_flags = fi->fib_flags;
 982         rtm->rtm_scope = fi->fib_scope;
 983         rtm->rtm_protocol = fi->fib_protocol;
 984
 985         if (rtm->rtm_dst_len &&
 986             nla_put_be32(skb, RTA_DST, dst))
 987                 goto nla_put_failure;
 988         if (fi->fib_priority &&
 989             nla_put_u32(skb, RTA_PRIORITY, fi->fib_priority))
 990                 goto nla_put_failure;
 991         if (rtnetlink_put_metrics(skb, fi->fib_metrics) < 0)
 992                 goto nla_put_failure;
 993
 994         if (fi->fib_prefsrc &&
 995             nla_put_be32(skb, RTA_PREFSRC, fi->fib_prefsrc))
 996                 goto nla_put_failure;
 997         if (fi->fib_nhs == 1) {
 998                 if (fi->fib_nh->nh_gw &&
 999                     nla_put_be32(skb, RTA_GATEWAY, fi->fib_nh->nh_gw))
1000                         goto nla_put_failure;
1001                 if (fi->fib_nh->nh_oif &&
1002                     nla_put_u32(skb, RTA_OIF, fi->fib_nh->nh_oif))
1003                         goto nla_put_failure;
1004 #ifdef CONFIG_IP_ROUTE_CLASSID
1005                 if (fi->fib_nh[0].nh_tclassid &&
1006                     nla_put_u32(skb, RTA_FLOW, fi->fib_nh[0].nh_tclassid))
1007                         goto nla_put_failure;
1008 #endif
1009         }
1010 #ifdef CONFIG_IP_ROUTE_MULTIPATH
1011         if (fi->fib_nhs > 1) {
1012                 struct rtnexthop *rtnh;
1013                 struct nlattr *mp;
1014
1015                 mp = nla_nest_start(skb, RTA_MULTIPATH);
1016                 if (mp == NULL)
1017                         goto nla_put_failure;
1018
1019                 for_nexthops(fi) {
1020                         rtnh = nla_reserve_nohdr(skb, sizeof(*rtnh));
1021                         if (rtnh == NULL)
1022                                 goto nla_put_failure;
1023
1024                         rtnh->rtnh_flags = nh->nh_flags & 0xFF;
1025                         rtnh->rtnh_hops = nh->nh_weight - 1;
1026                         rtnh->rtnh_ifindex = nh->nh_oif;
1027
1028                         if (nh->nh_gw &&
1029                             nla_put_be32(skb, RTA_GATEWAY, nh->nh_gw))
1030                                 goto nla_put_failure;
1031 #ifdef CONFIG_IP_ROUTE_CLASSID
1032                         if (nh->nh_tclassid &&
1033                             nla_put_u32(skb, RTA_FLOW, nh->nh_tclassid))
1034                                 goto nla_put_failure;
1035 #endif
1036                         /* length of rtnetlink header + attributes */
1037                         rtnh->rtnh_len = nlmsg_get_pos(skb) - (void *) rtnh;
1038                 } endfor_nexthops(fi);
1039
1040                 nla_nest_end(skb, mp);
1041         }
1042 #endif
1043         return nlmsg_end(skb, nlh);
1044
1045 nla_put_failure:
1046         nlmsg_cancel(skb, nlh);
1047         return -EMSGSIZE;
1048 }
1049
1050 /*
1051  * Update FIB if:
1052  * - local address disappeared -> we must delete all the entries
1053  *   referring to it.
1054  * - device went down -> we must shutdown all nexthops going via it.
1055  */
1056 int fib_sync_down_addr(struct net *net, __be32 local)
1057 {
1058         int ret = 0;
1059         unsigned int hash = fib_laddr_hashfn(local);
1060         struct hlist_head *head = &fib_info_laddrhash[hash];
1061         struct hlist_node *node;
1062         struct fib_info *fi;
1063
1064         if (fib_info_laddrhash == NULL || local == 0)
1065                 return 0;
1066
1067         hlist_for_each_entry(fi, node, head, fib_lhash) {
1068                 if (!net_eq(fi->fib_net, net))
1069                         continue;
1070                 if (fi->fib_prefsrc == local) {
1071                         fi->fib_flags |= RTNH_F_DEAD;
1072                         ret++;
1073                 }
1074         }
1075         return ret;
1076 }
1077
1078 int fib_sync_down_dev(struct net_device *dev, int force)
1079 {
1080         int ret = 0;
1081         int scope = RT_SCOPE_NOWHERE;
1082         struct fib_info *prev_fi = NULL;
1083         unsigned int hash = fib_devindex_hashfn(dev->ifindex);
1084         struct hlist_head *head = &fib_info_devhash[hash];
1085         struct hlist_node *node;
1086         struct fib_nh *nh;
1087
1088         if (force)
1089                 scope = -1;
1090
1091         hlist_for_each_entry(nh, node, head, nh_hash) {
1092                 struct fib_info *fi = nh->nh_parent;
1093                 int dead;
1094
1095                 BUG_ON(!fi->fib_nhs);
1096                 if (nh->nh_dev != dev || fi == prev_fi)
1097                         continue;
1098                 prev_fi = fi;
1099                 dead = 0;
1100                 change_nexthops(fi) {
1101                         if (nexthop_nh->nh_flags & RTNH_F_DEAD)
1102                                 dead++;
1103                         else if (nexthop_nh->nh_dev == dev &&
1104                                  nexthop_nh->nh_scope != scope) {
1105                                 nexthop_nh->nh_flags |= RTNH_F_DEAD;
1106 #ifdef CONFIG_IP_ROUTE_MULTIPATH
1107                                 spin_lock_bh(&fib_multipath_lock);
1108                                 fi->fib_power -= nexthop_nh->nh_power;
1109                                 nexthop_nh->nh_power = 0;
1110                                 spin_unlock_bh(&fib_multipath_lock);
1111 #endif
1112                                 dead++;
1113                         }
1114 #ifdef CONFIG_IP_ROUTE_MULTIPATH
1115                         if (force > 1 && nexthop_nh->nh_dev == dev) {
1116                                 dead = fi->fib_nhs;
1117                                 break;
1118                         }
1119 #endif
1120                 } endfor_nexthops(fi)
1121                 if (dead == fi->fib_nhs) {
1122                         fi->fib_flags |= RTNH_F_DEAD;
1123                         ret++;
1124                 }
1125         }
1126
1127         return ret;
1128 }
1129
1130 /* Must be invoked inside of an RCU protected region.  */
1131 void fib_select_default(struct fib_result *res)
1132 {
1133         struct fib_info *fi = NULL, *last_resort = NULL;
1134         struct list_head *fa_head = res->fa_head;
1135         struct fib_table *tb = res->table;
1136         int order = -1, last_idx = -1;
1137         struct fib_alias *fa;
1138
1139         list_for_each_entry_rcu(fa, fa_head, fa_list) {
1140                 struct fib_info *next_fi = fa->fa_info;
1141
1142                 if (next_fi->fib_scope != res->scope ||
1143                     fa->fa_type != RTN_UNICAST)
1144                         continue;
1145
1146                 if (next_fi->fib_priority > res->fi->fib_priority)
1147                         break;
1148                 if (!next_fi->fib_nh[0].nh_gw ||
1149                     next_fi->fib_nh[0].nh_scope != RT_SCOPE_LINK)
1150                         continue;
1151
1152                 fib_alias_accessed(fa);
1153
1154                 if (fi == NULL) {
1155                         if (next_fi != res->fi)
1156                                 break;
1157                 } else if (!fib_detect_death(fi, order, &last_resort,
1158                                              &last_idx, tb->tb_default)) {
1159                         fib_result_assign(res, fi);
1160                         tb->tb_default = order;
1161                         goto out;
1162                 }
1163                 fi = next_fi;
1164                 order++;
1165         }
1166
1167         if (order <= 0 || fi == NULL) {
1168                 tb->tb_default = -1;
1169                 goto out;
1170         }
1171
1172         if (!fib_detect_death(fi, order, &last_resort, &last_idx,
1173                                 tb->tb_default)) {
1174                 fib_result_assign(res, fi);
1175                 tb->tb_default = order;
1176                 goto out;
1177         }
1178
1179         if (last_idx >= 0)
1180                 fib_result_assign(res, last_resort);
1181         tb->tb_default = last_idx;
1182 out:
1183         return;
1184 }
1185
1186 #ifdef CONFIG_IP_ROUTE_MULTIPATH
1187
1188 /*
1189  * Dead device goes up. We wake up dead nexthops.
1190  * It takes sense only on multipath routes.
1191  */
1192 int fib_sync_up(struct net_device *dev)
1193 {
1194         struct fib_info *prev_fi;
1195         unsigned int hash;
1196         struct hlist_head *head;
1197         struct hlist_node *node;
1198         struct fib_nh *nh;
1199         int ret;
1200
1201         if (!(dev->flags & IFF_UP))
1202                 return 0;
1203
1204         prev_fi = NULL;
1205         hash = fib_devindex_hashfn(dev->ifindex);
1206         head = &fib_info_devhash[hash];
1207         ret = 0;
1208
1209         hlist_for_each_entry(nh, node, head, nh_hash) {
1210                 struct fib_info *fi = nh->nh_parent;
1211                 int alive;
1212
1213                 BUG_ON(!fi->fib_nhs);
1214                 if (nh->nh_dev != dev || fi == prev_fi)
1215                         continue;
1216
1217                 prev_fi = fi;
1218                 alive = 0;
1219                 change_nexthops(fi) {
1220                         if (!(nexthop_nh->nh_flags & RTNH_F_DEAD)) {
1221                                 alive++;
1222                                 continue;
1223                         }
1224                         if (nexthop_nh->nh_dev == NULL ||
1225                             !(nexthop_nh->nh_dev->flags & IFF_UP))
1226                                 continue;
1227                         if (nexthop_nh->nh_dev != dev ||
1228                             !__in_dev_get_rtnl(dev))
1229                                 continue;
1230                         alive++;
1231                         spin_lock_bh(&fib_multipath_lock);
1232                         nexthop_nh->nh_power = 0;
1233                         nexthop_nh->nh_flags &= ~RTNH_F_DEAD;
1234                         spin_unlock_bh(&fib_multipath_lock);
1235                 } endfor_nexthops(fi)
1236
1237                 if (alive > 0) {
1238                         fi->fib_flags &= ~RTNH_F_DEAD;
1239                         ret++;
1240                 }
1241         }
1242
1243         return ret;
1244 }
1245
1246 /*
1247  * The algorithm is suboptimal, but it provides really
1248  * fair weighted route distribution.
1249  */
1250 void fib_select_multipath(struct fib_result *res)
1251 {
1252         struct fib_info *fi = res->fi;
1253         int w;
1254
1255         spin_lock_bh(&fib_multipath_lock);
1256         if (fi->fib_power <= 0) {
1257                 int power = 0;
1258                 change_nexthops(fi) {
1259                         if (!(nexthop_nh->nh_flags & RTNH_F_DEAD)) {
1260                                 power += nexthop_nh->nh_weight;
1261                                 nexthop_nh->nh_power = nexthop_nh->nh_weight;
1262                         }
1263                 } endfor_nexthops(fi);
1264                 fi->fib_power = power;
1265                 if (power <= 0) {
1266                         spin_unlock_bh(&fib_multipath_lock);
1267                         /* Race condition: route has just become dead. */
1268                         res->nh_sel = 0;
1269                         return;
1270                 }
1271         }
1272
1273
1274         /* w should be random number [0..fi->fib_power-1],
1275          * it is pretty bad approximation.
1276          */
1277
1278         w = jiffies % fi->fib_power;
1279
1280         change_nexthops(fi) {
1281                 if (!(nexthop_nh->nh_flags & RTNH_F_DEAD) &&
1282                     nexthop_nh->nh_power) {
1283                         w -= nexthop_nh->nh_power;
1284                         if (w <= 0) {
1285                                 nexthop_nh->nh_power--;
1286                                 fi->fib_power--;
1287                                 res->nh_sel = nhsel;
1288                                 spin_unlock_bh(&fib_multipath_lock);
1289                                 return;
1290                         }
1291                 }
1292         } endfor_nexthops(fi);
1293
1294         /* Race condition: route has just become dead. */
1295         res->nh_sel = 0;
1296         spin_unlock_bh(&fib_multipath_lock);
1297 }
1298 #endif