net/core/netfilter.c

   1 /* netfilter.c: look after the filters for various protocols.
   2  * Heavily influenced by the old firewall.c by David Bonn and Alan Cox.
   3  *
   4  * Thanks to Rob `CmdrTaco' Malda for not influencing this code in any
   5  * way.
   6  *
   7  * Rusty Russell (C)2000 -- This code is GPL.
   8  *
   9  * February 2000: Modified by James Morris to have 1 queue per protocol.
  10  * 15-Mar-2000:   Added NF_REPEAT --RR.
  11  * 08-May-2003:   Internal logging interface added by Jozsef Kadlecsik.
  12  */
  13 #include <linux/config.h>
  14 #include <linux/kernel.h>
  15 #include <linux/netfilter.h>
  16 #include <net/protocol.h>
  17 #include <linux/init.h>
  18 #include <linux/skbuff.h>
  19 #include <linux/wait.h>
  20 #include <linux/module.h>
  21 #include <linux/interrupt.h>
  22 #include <linux/if.h>
  23 #include <linux/netdevice.h>
  24 #include <linux/inetdevice.h>
  25 #include <linux/tcp.h>
  26 #include <linux/udp.h>
  27 #include <linux/icmp.h>
  28 #include <net/sock.h>
  29 #include <net/route.h>
  30 #include <linux/ip.h>
  31
  32 /* In this code, we can be waiting indefinitely for userspace to
  33  * service a packet if a hook returns NF_QUEUE.  We could keep a count
  34  * of skbuffs queued for userspace, and not deregister a hook unless
  35  * this is zero, but that sucks.  Now, we simply check when the
  36  * packets come back: if the hook is gone, the packet is discarded. */
  37 #ifdef CONFIG_NETFILTER_DEBUG
  38 #define NFDEBUG(format, args...)  printk(format , ## args)
  39 #else
  40 #define NFDEBUG(format, args...)
  41 #endif
  42
  43 /* Sockopts only registered and called from user context, so
  44    net locking would be overkill.  Also, [gs]etsockopt calls may
  45    sleep. */
  46 static DECLARE_MUTEX(nf_sockopt_mutex);
  47
  48 struct list_head nf_hooks[NPROTO][NF_MAX_HOOKS];
  49 static LIST_HEAD(nf_sockopts);
  50 static DEFINE_SPINLOCK(nf_hook_lock);
  51
  52 /*
  53  * A queue handler may be registered for each protocol.  Each is protected by
  54  * long term mutex.  The handler must provide an an outfn() to accept packets
  55  * for queueing and must reinject all packets it receives, no matter what.
  56  */
  57 static struct nf_queue_handler_t {
  58         nf_queue_outfn_t outfn;
  59         void *data;
  60 } queue_handler[NPROTO];
  61 static DEFINE_RWLOCK(queue_handler_lock);
  62
  63 int nf_register_hook(struct nf_hook_ops *reg)
  64 {
  65         struct list_head *i;
  66
  67         spin_lock_bh(&nf_hook_lock);
  68         list_for_each(i, &nf_hooks[reg->pf][reg->hooknum]) {
  69                 if (reg->priority < ((struct nf_hook_ops *)i)->priority)
  70                         break;
  71         }
  72         list_add_rcu(&reg->list, i->prev);
  73         spin_unlock_bh(&nf_hook_lock);
  74
  75         synchronize_net();
  76         return 0;
  77 }
  78
  79 void nf_unregister_hook(struct nf_hook_ops *reg)
  80 {
  81         spin_lock_bh(&nf_hook_lock);
  82         list_del_rcu(&reg->list);
  83         spin_unlock_bh(&nf_hook_lock);
  84
  85         synchronize_net();
  86 }
  87
  88 /* Do exclusive ranges overlap? */
  89 static inline int overlap(int min1, int max1, int min2, int max2)
  90 {
  91         return max1 > min2 && min1 < max2;
  92 }
  93
  94 /* Functions to register sockopt ranges (exclusive). */
  95 int nf_register_sockopt(struct nf_sockopt_ops *reg)
  96 {
  97         struct list_head *i;
  98         int ret = 0;
  99
 100         if (down_interruptible(&nf_sockopt_mutex) != 0)
 101                 return -EINTR;
 102
 103         list_for_each(i, &nf_sockopts) {
 104                 struct nf_sockopt_ops *ops = (struct nf_sockopt_ops *)i;
 105                 if (ops->pf == reg->pf
 106                     && (overlap(ops->set_optmin, ops->set_optmax,
 107                                 reg->set_optmin, reg->set_optmax)
 108                         || overlap(ops->get_optmin, ops->get_optmax,
 109                                    reg->get_optmin, reg->get_optmax))) {
 110                         NFDEBUG("nf_sock overlap: %u-%u/%u-%u v %u-%u/%u-%u\n",
 111                                 ops->set_optmin, ops->set_optmax,
 112                                 ops->get_optmin, ops->get_optmax,
 113                                 reg->set_optmin, reg->set_optmax,
 114                                 reg->get_optmin, reg->get_optmax);
 115                         ret = -EBUSY;
 116                         goto out;
 117                 }
 118         }
 119
 120         list_add(&reg->list, &nf_sockopts);
 121 out:
 122         up(&nf_sockopt_mutex);
 123         return ret;
 124 }
 125
 126 void nf_unregister_sockopt(struct nf_sockopt_ops *reg)
 127 {
 128         /* No point being interruptible: we're probably in cleanup_module() */
 129  restart:
 130         down(&nf_sockopt_mutex);
 131         if (reg->use != 0) {
 132                 /* To be woken by nf_sockopt call... */
 133                 /* FIXME: Stuart Young's name appears gratuitously. */
 134                 set_current_state(TASK_UNINTERRUPTIBLE);
 135                 reg->cleanup_task = current;
 136                 up(&nf_sockopt_mutex);
 137                 schedule();
 138                 goto restart;
 139         }
 140         list_del(&reg->list);
 141         up(&nf_sockopt_mutex);
 142 }
 143
 144 /* Call get/setsockopt() */
 145 static int nf_sockopt(struct sock *sk, int pf, int val,
 146                       char __user *opt, int *len, int get)
 147 {
 148         struct list_head *i;
 149         struct nf_sockopt_ops *ops;
 150         int ret;
 151
 152         if (down_interruptible(&nf_sockopt_mutex) != 0)
 153                 return -EINTR;
 154
 155         list_for_each(i, &nf_sockopts) {
 156                 ops = (struct nf_sockopt_ops *)i;
 157                 if (ops->pf == pf) {
 158                         if (get) {
 159                                 if (val >= ops->get_optmin
 160                                     && val < ops->get_optmax) {
 161                                         ops->use++;
 162                                         up(&nf_sockopt_mutex);
 163                                         ret = ops->get(sk, val, opt, len);
 164                                         goto out;
 165                                 }
 166                         } else {
 167                                 if (val >= ops->set_optmin
 168                                     && val < ops->set_optmax) {
 169                                         ops->use++;
 170                                         up(&nf_sockopt_mutex);
 171                                         ret = ops->set(sk, val, opt, *len);
 172                                         goto out;
 173                                 }
 174                         }
 175                 }
 176         }
 177         up(&nf_sockopt_mutex);
 178         return -ENOPROTOOPT;
 179
 180  out:
 181         down(&nf_sockopt_mutex);
 182         ops->use--;
 183         if (ops->cleanup_task)
 184                 wake_up_process(ops->cleanup_task);
 185         up(&nf_sockopt_mutex);
 186         return ret;
 187 }
 188
 189 int nf_setsockopt(struct sock *sk, int pf, int val, char __user *opt,
 190                   int len)
 191 {
 192         return nf_sockopt(sk, pf, val, opt, &len, 0);
 193 }
 194
 195 int nf_getsockopt(struct sock *sk, int pf, int val, char __user *opt, int *len)
 196 {
 197         return nf_sockopt(sk, pf, val, opt, len, 1);
 198 }
 199
 200 static unsigned int nf_iterate(struct list_head *head,
 201                                struct sk_buff **skb,
 202                                int hook,
 203                                const struct net_device *indev,
 204                                const struct net_device *outdev,
 205                                struct list_head **i,
 206                                int (*okfn)(struct sk_buff *),
 207                                int hook_thresh)
 208 {
 209         unsigned int verdict;
 210
 211         /*
 212          * The caller must not block between calls to this
 213          * function because of risk of continuing from deleted element.
 214          */
 215         list_for_each_continue_rcu(*i, head) {
 216                 struct nf_hook_ops *elem = (struct nf_hook_ops *)*i;
 217
 218                 if (hook_thresh > elem->priority)
 219                         continue;
 220
 221                 /* Optimization: we don't need to hold module
 222                    reference here, since function can't sleep. --RR */
 223                 verdict = elem->hook(hook, skb, indev, outdev, okfn);
 224                 if (verdict != NF_ACCEPT) {
 225 #ifdef CONFIG_NETFILTER_DEBUG
 226                         if (unlikely(verdict > NF_MAX_VERDICT)) {
 227                                 NFDEBUG("Evil return from %p(%u).\n",
 228                                         elem->hook, hook);
 229                                 continue;
 230                         }
 231 #endif
 232                         if (verdict != NF_REPEAT)
 233                                 return verdict;
 234                         *i = (*i)->prev;
 235                 }
 236         }
 237         return NF_ACCEPT;
 238 }
 239
 240 int nf_register_queue_handler(int pf, nf_queue_outfn_t outfn, void *data)
 241 {
 242         int ret;
 243
 244         write_lock_bh(&queue_handler_lock);
 245         if (queue_handler[pf].outfn)
 246                 ret = -EBUSY;
 247         else {
 248                 queue_handler[pf].outfn = outfn;
 249                 queue_handler[pf].data = data;
 250                 ret = 0;
 251         }
 252         write_unlock_bh(&queue_handler_lock);
 253
 254         return ret;
 255 }
 256
 257 /* The caller must flush their queue before this */
 258 int nf_unregister_queue_handler(int pf)
 259 {
 260         write_lock_bh(&queue_handler_lock);
 261         queue_handler[pf].outfn = NULL;
 262         queue_handler[pf].data = NULL;
 263         write_unlock_bh(&queue_handler_lock);
 264
 265         return 0;
 266 }
 267
 268 /*
 269  * Any packet that leaves via this function must come back
 270  * through nf_reinject().
 271  */
 272 static int nf_queue(struct sk_buff *skb,
 273                     struct list_head *elem,
 274                     int pf, unsigned int hook,
 275                     struct net_device *indev,
 276                     struct net_device *outdev,
 277                     int (*okfn)(struct sk_buff *))
 278 {
 279         int status;
 280         struct nf_info *info;
 281 #ifdef CONFIG_BRIDGE_NETFILTER
 282         struct net_device *physindev = NULL;
 283         struct net_device *physoutdev = NULL;
 284 #endif
 285
 286         /* QUEUE == DROP if noone is waiting, to be safe. */
 287         read_lock(&queue_handler_lock);
 288         if (!queue_handler[pf].outfn) {
 289                 read_unlock(&queue_handler_lock);
 290                 kfree_skb(skb);
 291                 return 1;
 292         }
 293
 294         info = kmalloc(sizeof(*info), GFP_ATOMIC);
 295         if (!info) {
 296                 if (net_ratelimit())
 297                         printk(KERN_ERR "OOM queueing packet %p\n",
 298                                skb);
 299                 read_unlock(&queue_handler_lock);
 300                 kfree_skb(skb);
 301                 return 1;
 302         }
 303
 304         *info = (struct nf_info) {
 305                 (struct nf_hook_ops *)elem, pf, hook, indev, outdev, okfn };
 306
 307         /* If it's going away, ignore hook. */
 308         if (!try_module_get(info->elem->owner)) {
 309                 read_unlock(&queue_handler_lock);
 310                 kfree(info);
 311                 return 0;
 312         }
 313
 314         /* Bump dev refs so they don't vanish while packet is out */
 315         if (indev) dev_hold(indev);
 316         if (outdev) dev_hold(outdev);
 317
 318 #ifdef CONFIG_BRIDGE_NETFILTER
 319         if (skb->nf_bridge) {
 320                 physindev = skb->nf_bridge->physindev;
 321                 if (physindev) dev_hold(physindev);
 322                 physoutdev = skb->nf_bridge->physoutdev;
 323                 if (physoutdev) dev_hold(physoutdev);
 324         }
 325 #endif
 326
 327         status = queue_handler[pf].outfn(skb, info, queue_handler[pf].data);
 328         read_unlock(&queue_handler_lock);
 329
 330         if (status < 0) {
 331                 /* James M doesn't say fuck enough. */
 332                 if (indev) dev_put(indev);
 333                 if (outdev) dev_put(outdev);
 334 #ifdef CONFIG_BRIDGE_NETFILTER
 335                 if (physindev) dev_put(physindev);
 336                 if (physoutdev) dev_put(physoutdev);
 337 #endif
 338                 module_put(info->elem->owner);
 339                 kfree(info);
 340                 kfree_skb(skb);
 341                 return 1;
 342         }
 343         return 1;
 344 }
 345
 346 /* Returns 1 if okfn() needs to be executed by the caller,
 347  * -EPERM for NF_DROP, 0 otherwise. */
 348 int nf_hook_slow(int pf, unsigned int hook, struct sk_buff **pskb,
 349                  struct net_device *indev,
 350                  struct net_device *outdev,
 351                  int (*okfn)(struct sk_buff *),
 352                  int hook_thresh)
 353 {
 354         struct list_head *elem;
 355         unsigned int verdict;
 356         int ret = 0;
 357
 358         /* We may already have this, but read-locks nest anyway */
 359         rcu_read_lock();
 360
 361         elem = &nf_hooks[pf][hook];
 362 next_hook:
 363         verdict = nf_iterate(&nf_hooks[pf][hook], pskb, hook, indev,
 364                              outdev, &elem, okfn, hook_thresh);
 365         if (verdict == NF_ACCEPT || verdict == NF_STOP) {
 366                 ret = 1;
 367                 goto unlock;
 368         } else if (verdict == NF_DROP) {
 369                 kfree_skb(*pskb);
 370                 ret = -EPERM;
 371         } else if (verdict == NF_QUEUE) {
 372                 NFDEBUG("nf_hook: Verdict = QUEUE.\n");
 373                 if (!nf_queue(*pskb, elem, pf, hook, indev, outdev, okfn))
 374                         goto next_hook;
 375         }
 376 unlock:
 377         rcu_read_unlock();
 378         return ret;
 379 }
 380
 381 void nf_reinject(struct sk_buff *skb, struct nf_info *info,
 382                  unsigned int verdict)
 383 {
 384         struct list_head *elem = &info->elem->list;
 385         struct list_head *i;
 386
 387         rcu_read_lock();
 388
 389         /* Release those devices we held, or Alexey will kill me. */
 390         if (info->indev) dev_put(info->indev);
 391         if (info->outdev) dev_put(info->outdev);
 392 #ifdef CONFIG_BRIDGE_NETFILTER
 393         if (skb->nf_bridge) {
 394                 if (skb->nf_bridge->physindev)
 395                         dev_put(skb->nf_bridge->physindev);
 396                 if (skb->nf_bridge->physoutdev)
 397                         dev_put(skb->nf_bridge->physoutdev);
 398         }
 399 #endif
 400
 401         /* Drop reference to owner of hook which queued us. */
 402         module_put(info->elem->owner);
 403
 404         list_for_each_rcu(i, &nf_hooks[info->pf][info->hook]) {
 405                 if (i == elem)
 406                         break;
 407         }
 408
 409         if (elem == &nf_hooks[info->pf][info->hook]) {
 410                 /* The module which sent it to userspace is gone. */
 411                 NFDEBUG("%s: module disappeared, dropping packet.\n",
 412                         __FUNCTION__);
 413                 verdict = NF_DROP;
 414         }
 415
 416         /* Continue traversal iff userspace said ok... */
 417         if (verdict == NF_REPEAT) {
 418                 elem = elem->prev;
 419                 verdict = NF_ACCEPT;
 420         }
 421
 422         if (verdict == NF_ACCEPT) {
 423         next_hook:
 424                 verdict = nf_iterate(&nf_hooks[info->pf][info->hook],
 425                                      &skb, info->hook,
 426                                      info->indev, info->outdev, &elem,
 427                                      info->okfn, INT_MIN);
 428         }
 429
 430         switch (verdict) {
 431         case NF_ACCEPT:
 432                 info->okfn(skb);
 433                 break;
 434
 435         case NF_QUEUE:
 436                 if (!nf_queue(skb, elem, info->pf, info->hook,
 437                               info->indev, info->outdev, info->okfn))
 438                         goto next_hook;
 439                 break;
 440         }
 441         rcu_read_unlock();
 442
 443         if (verdict == NF_DROP)
 444                 kfree_skb(skb);
 445
 446         kfree(info);
 447         return;
 448 }
 449
 450 #ifdef CONFIG_INET
 451 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
 452 int ip_route_me_harder(struct sk_buff **pskb)
 453 {
 454         struct iphdr *iph = (*pskb)->nh.iph;
 455         struct rtable *rt;
 456         struct flowi fl = {};
 457         struct dst_entry *odst;
 458         unsigned int hh_len;
 459
 460         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
 461          * packets with foreign saddr to appear on the NF_IP_LOCAL_OUT hook.
 462          */
 463         if (inet_addr_type(iph->saddr) == RTN_LOCAL) {
 464                 fl.nl_u.ip4_u.daddr = iph->daddr;
 465                 fl.nl_u.ip4_u.saddr = iph->saddr;
 466                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
 467                 fl.oif = (*pskb)->sk ? (*pskb)->sk->sk_bound_dev_if : 0;
 468 #ifdef CONFIG_IP_ROUTE_FWMARK
 469                 fl.nl_u.ip4_u.fwmark = (*pskb)->nfmark;
 470 #endif
 471                 fl.proto = iph->protocol;
 472                 if (ip_route_output_key(&rt, &fl) != 0)
 473                         return -1;
 474
 475                 /* Drop old route. */
 476                 dst_release((*pskb)->dst);
 477                 (*pskb)->dst = &rt->u.dst;
 478         } else {
 479                 /* non-local src, find valid iif to satisfy
 480                  * rp-filter when calling ip_route_input. */
 481                 fl.nl_u.ip4_u.daddr = iph->saddr;
 482                 if (ip_route_output_key(&rt, &fl) != 0)
 483                         return -1;
 484
 485                 odst = (*pskb)->dst;
 486                 if (ip_route_input(*pskb, iph->daddr, iph->saddr,
 487                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
 488                         dst_release(&rt->u.dst);
 489                         return -1;
 490                 }
 491                 dst_release(&rt->u.dst);
 492                 dst_release(odst);
 493         }
 494
 495         if ((*pskb)->dst->error)
 496                 return -1;
 497
 498         /* Change in oif may mean change in hh_len. */
 499         hh_len = (*pskb)->dst->dev->hard_header_len;
 500         if (skb_headroom(*pskb) < hh_len) {
 501                 struct sk_buff *nskb;
 502
 503                 nskb = skb_realloc_headroom(*pskb, hh_len);
 504                 if (!nskb)
 505                         return -1;
 506                 if ((*pskb)->sk)
 507                         skb_set_owner_w(nskb, (*pskb)->sk);
 508                 kfree_skb(*pskb);
 509                 *pskb = nskb;
 510         }
 511
 512         return 0;
 513 }
 514 EXPORT_SYMBOL(ip_route_me_harder);
 515
 516 int skb_ip_make_writable(struct sk_buff **pskb, unsigned int writable_len)
 517 {
 518         struct sk_buff *nskb;
 519
 520         if (writable_len > (*pskb)->len)
 521                 return 0;
 522
 523         /* Not exclusive use of packet?  Must copy. */
 524         if (skb_shared(*pskb) || skb_cloned(*pskb))
 525                 goto copy_skb;
 526
 527         return pskb_may_pull(*pskb, writable_len);
 528
 529 copy_skb:
 530         nskb = skb_copy(*pskb, GFP_ATOMIC);
 531         if (!nskb)
 532                 return 0;
 533         BUG_ON(skb_is_nonlinear(nskb));
 534
 535         /* Rest of kernel will get very unhappy if we pass it a
 536            suddenly-orphaned skbuff */
 537         if ((*pskb)->sk)
 538                 skb_set_owner_w(nskb, (*pskb)->sk);
 539         kfree_skb(*pskb);
 540         *pskb = nskb;
 541         return 1;
 542 }
 543 EXPORT_SYMBOL(skb_ip_make_writable);
 544 #endif /*CONFIG_INET*/
 545
 546 /* Internal logging interface, which relies on the real
 547    LOG target modules */
 548
 549 #define NF_LOG_PREFIXLEN                128
 550
 551 static nf_logfn *nf_logging[NPROTO]; /* = NULL */
 552 static int reported = 0;
 553 static DEFINE_SPINLOCK(nf_log_lock);
 554
 555 int nf_log_register(int pf, nf_logfn *logfn)
 556 {
 557         int ret = -EBUSY;
 558
 559         /* Any setup of logging members must be done before
 560          * substituting pointer. */
 561         spin_lock(&nf_log_lock);
 562         if (!nf_logging[pf]) {
 563                 rcu_assign_pointer(nf_logging[pf], logfn);
 564                 ret = 0;
 565         }
 566         spin_unlock(&nf_log_lock);
 567         return ret;
 568 }
 569
 570 void nf_log_unregister(int pf, nf_logfn *logfn)
 571 {
 572         spin_lock(&nf_log_lock);
 573         if (nf_logging[pf] == logfn)
 574                 nf_logging[pf] = NULL;
 575         spin_unlock(&nf_log_lock);
 576
 577         /* Give time to concurrent readers. */
 578         synchronize_net();
 579 }
 580
 581 void nf_log_packet(int pf,
 582                    unsigned int hooknum,
 583                    const struct sk_buff *skb,
 584                    const struct net_device *in,
 585                    const struct net_device *out,
 586                    const char *fmt, ...)
 587 {
 588         va_list args;
 589         char prefix[NF_LOG_PREFIXLEN];
 590         nf_logfn *logfn;
 591
 592         rcu_read_lock();
 593         logfn = rcu_dereference(nf_logging[pf]);
 594         if (logfn) {
 595                 va_start(args, fmt);
 596                 vsnprintf(prefix, sizeof(prefix), fmt, args);
 597                 va_end(args);
 598                 /* We must read logging before nf_logfn[pf] */
 599                 logfn(hooknum, skb, in, out, prefix);
 600         } else if (!reported) {
 601                 printk(KERN_WARNING "nf_log_packet: can\'t log yet, "
 602                        "no backend logging module loaded in!\n");
 603                 reported++;
 604         }
 605         rcu_read_unlock();
 606 }
 607 EXPORT_SYMBOL(nf_log_register);
 608 EXPORT_SYMBOL(nf_log_unregister);
 609 EXPORT_SYMBOL(nf_log_packet);
 610
 611 /* This does not belong here, but locally generated errors need it if connection
 612    tracking in use: without this, connection may not be in hash table, and hence
 613    manufactured ICMP or RST packets will not be associated with it. */
 614 void (*ip_ct_attach)(struct sk_buff *, struct sk_buff *);
 615
 616 void nf_ct_attach(struct sk_buff *new, struct sk_buff *skb)
 617 {
 618         void (*attach)(struct sk_buff *, struct sk_buff *);
 619
 620         if (skb->nfct && (attach = ip_ct_attach) != NULL) {
 621                 mb(); /* Just to be sure: must be read before executing this */
 622                 attach(new, skb);
 623         }
 624 }
 625
 626 void __init netfilter_init(void)
 627 {
 628         int i, h;
 629
 630         for (i = 0; i < NPROTO; i++) {
 631                 for (h = 0; h < NF_MAX_HOOKS; h++)
 632                         INIT_LIST_HEAD(&nf_hooks[i][h]);
 633         }
 634 }
 635
 636 EXPORT_SYMBOL(ip_ct_attach);
 637 EXPORT_SYMBOL(nf_ct_attach);
 638 EXPORT_SYMBOL(nf_getsockopt);
 639 EXPORT_SYMBOL(nf_hook_slow);
 640 EXPORT_SYMBOL(nf_hooks);
 641 EXPORT_SYMBOL(nf_register_hook);
 642 EXPORT_SYMBOL(nf_register_queue_handler);
 643 EXPORT_SYMBOL(nf_register_sockopt);
 644 EXPORT_SYMBOL(nf_reinject);
 645 EXPORT_SYMBOL(nf_setsockopt);
 646 EXPORT_SYMBOL(nf_unregister_hook);
 647 EXPORT_SYMBOL(nf_unregister_queue_handler);
 648 EXPORT_SYMBOL(nf_unregister_sockopt);