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Linux/net/ipv4/ip_input.c

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  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 Internet Protocol (IP) module.
  7  *
  8  * Authors:     Ross Biro
  9  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 10  *              Donald Becker, <becker@super.org>
 11  *              Alan Cox, <alan@lxorguk.ukuu.org.uk>
 12  *              Richard Underwood
 13  *              Stefan Becker, <stefanb@yello.ping.de>
 14  *              Jorge Cwik, <jorge@laser.satlink.net>
 15  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 16  *
 17  *
 18  * Fixes:
 19  *              Alan Cox        :       Commented a couple of minor bits of surplus code
 20  *              Alan Cox        :       Undefining IP_FORWARD doesn't include the code
 21  *                                      (just stops a compiler warning).
 22  *              Alan Cox        :       Frames with >=MAX_ROUTE record routes, strict routes or loose routes
 23  *                                      are junked rather than corrupting things.
 24  *              Alan Cox        :       Frames to bad broadcast subnets are dumped
 25  *                                      We used to process them non broadcast and
 26  *                                      boy could that cause havoc.
 27  *              Alan Cox        :       ip_forward sets the free flag on the
 28  *                                      new frame it queues. Still crap because
 29  *                                      it copies the frame but at least it
 30  *                                      doesn't eat memory too.
 31  *              Alan Cox        :       Generic queue code and memory fixes.
 32  *              Fred Van Kempen :       IP fragment support (borrowed from NET2E)
 33  *              Gerhard Koerting:       Forward fragmented frames correctly.
 34  *              Gerhard Koerting:       Fixes to my fix of the above 8-).
 35  *              Gerhard Koerting:       IP interface addressing fix.
 36  *              Linus Torvalds  :       More robustness checks
 37  *              Alan Cox        :       Even more checks: Still not as robust as it ought to be
 38  *              Alan Cox        :       Save IP header pointer for later
 39  *              Alan Cox        :       ip option setting
 40  *              Alan Cox        :       Use ip_tos/ip_ttl settings
 41  *              Alan Cox        :       Fragmentation bogosity removed
 42  *                                      (Thanks to Mark.Bush@prg.ox.ac.uk)
 43  *              Dmitry Gorodchanin :    Send of a raw packet crash fix.
 44  *              Alan Cox        :       Silly ip bug when an overlength
 45  *                                      fragment turns up. Now frees the
 46  *                                      queue.
 47  *              Linus Torvalds/ :       Memory leakage on fragmentation
 48  *              Alan Cox        :       handling.
 49  *              Gerhard Koerting:       Forwarding uses IP priority hints
 50  *              Teemu Rantanen  :       Fragment problems.
 51  *              Alan Cox        :       General cleanup, comments and reformat
 52  *              Alan Cox        :       SNMP statistics
 53  *              Alan Cox        :       BSD address rule semantics. Also see
 54  *                                      UDP as there is a nasty checksum issue
 55  *                                      if you do things the wrong way.
 56  *              Alan Cox        :       Always defrag, moved IP_FORWARD to the config.in file
 57  *              Alan Cox        :       IP options adjust sk->priority.
 58  *              Pedro Roque     :       Fix mtu/length error in ip_forward.
 59  *              Alan Cox        :       Avoid ip_chk_addr when possible.
 60  *      Richard Underwood       :       IP multicasting.
 61  *              Alan Cox        :       Cleaned up multicast handlers.
 62  *              Alan Cox        :       RAW sockets demultiplex in the BSD style.
 63  *              Gunther Mayer   :       Fix the SNMP reporting typo
 64  *              Alan Cox        :       Always in group 224.0.0.1
 65  *      Pauline Middelink       :       Fast ip_checksum update when forwarding
 66  *                                      Masquerading support.
 67  *              Alan Cox        :       Multicast loopback error for 224.0.0.1
 68  *              Alan Cox        :       IP_MULTICAST_LOOP option.
 69  *              Alan Cox        :       Use notifiers.
 70  *              Bjorn Ekwall    :       Removed ip_csum (from slhc.c too)
 71  *              Bjorn Ekwall    :       Moved ip_fast_csum to ip.h (inline!)
 72  *              Stefan Becker   :       Send out ICMP HOST REDIRECT
 73  *      Arnt Gulbrandsen        :       ip_build_xmit
 74  *              Alan Cox        :       Per socket routing cache
 75  *              Alan Cox        :       Fixed routing cache, added header cache.
 76  *              Alan Cox        :       Loopback didn't work right in original ip_build_xmit - fixed it.
 77  *              Alan Cox        :       Only send ICMP_REDIRECT if src/dest are the same net.
 78  *              Alan Cox        :       Incoming IP option handling.
 79  *              Alan Cox        :       Set saddr on raw output frames as per BSD.
 80  *              Alan Cox        :       Stopped broadcast source route explosions.
 81  *              Alan Cox        :       Can disable source routing
 82  *              Takeshi Sone    :       Masquerading didn't work.
 83  *      Dave Bonn,Alan Cox      :       Faster IP forwarding whenever possible.
 84  *              Alan Cox        :       Memory leaks, tramples, misc debugging.
 85  *              Alan Cox        :       Fixed multicast (by popular demand 8))
 86  *              Alan Cox        :       Fixed forwarding (by even more popular demand 8))
 87  *              Alan Cox        :       Fixed SNMP statistics [I think]
 88  *      Gerhard Koerting        :       IP fragmentation forwarding fix
 89  *              Alan Cox        :       Device lock against page fault.
 90  *              Alan Cox        :       IP_HDRINCL facility.
 91  *      Werner Almesberger      :       Zero fragment bug
 92  *              Alan Cox        :       RAW IP frame length bug
 93  *              Alan Cox        :       Outgoing firewall on build_xmit
 94  *              A.N.Kuznetsov   :       IP_OPTIONS support throughout the kernel
 95  *              Alan Cox        :       Multicast routing hooks
 96  *              Jos Vos         :       Do accounting *before* call_in_firewall
 97  *      Willy Konynenberg       :       Transparent proxying support
 98  *
 99  *
100  *
101  * To Fix:
102  *              IP fragmentation wants rewriting cleanly. The RFC815 algorithm is much more efficient
103  *              and could be made very efficient with the addition of some virtual memory hacks to permit
104  *              the allocation of a buffer that can then be 'grown' by twiddling page tables.
105  *              Output fragmentation wants updating along with the buffer management to use a single
106  *              interleaved copy algorithm so that fragmenting has a one copy overhead. Actual packet
107  *              output should probably do its own fragmentation at the UDP/RAW layer. TCP shouldn't cause
108  *              fragmentation anyway.
109  *
110  *              This program is free software; you can redistribute it and/or
111  *              modify it under the terms of the GNU General Public License
112  *              as published by the Free Software Foundation; either version
113  *              2 of the License, or (at your option) any later version.
114  */
115 
116 #define pr_fmt(fmt) "IPv4: " fmt
117 
118 #include <linux/module.h>
119 #include <linux/types.h>
120 #include <linux/kernel.h>
121 #include <linux/string.h>
122 #include <linux/errno.h>
123 #include <linux/slab.h>
124 
125 #include <linux/net.h>
126 #include <linux/socket.h>
127 #include <linux/sockios.h>
128 #include <linux/in.h>
129 #include <linux/inet.h>
130 #include <linux/inetdevice.h>
131 #include <linux/netdevice.h>
132 #include <linux/etherdevice.h>
133 
134 #include <net/snmp.h>
135 #include <net/ip.h>
136 #include <net/protocol.h>
137 #include <net/route.h>
138 #include <linux/skbuff.h>
139 #include <net/sock.h>
140 #include <net/arp.h>
141 #include <net/icmp.h>
142 #include <net/raw.h>
143 #include <net/checksum.h>
144 #include <net/inet_ecn.h>
145 #include <linux/netfilter_ipv4.h>
146 #include <net/xfrm.h>
147 #include <linux/mroute.h>
148 #include <linux/netlink.h>
149 #include <net/dst_metadata.h>
150 
151 /*
152  *      Process Router Attention IP option (RFC 2113)
153  */
154 bool ip_call_ra_chain(struct sk_buff *skb)
155 {
156         struct ip_ra_chain *ra;
157         u8 protocol = ip_hdr(skb)->protocol;
158         struct sock *last = NULL;
159         struct net_device *dev = skb->dev;
160         struct net *net = dev_net(dev);
161 
162         for (ra = rcu_dereference(net->ipv4.ra_chain); ra; ra = rcu_dereference(ra->next)) {
163                 struct sock *sk = ra->sk;
164 
165                 /* If socket is bound to an interface, only report
166                  * the packet if it came  from that interface.
167                  */
168                 if (sk && inet_sk(sk)->inet_num == protocol &&
169                     (!sk->sk_bound_dev_if ||
170                      sk->sk_bound_dev_if == dev->ifindex)) {
171                         if (ip_is_fragment(ip_hdr(skb))) {
172                                 if (ip_defrag(net, skb, IP_DEFRAG_CALL_RA_CHAIN))
173                                         return true;
174                         }
175                         if (last) {
176                                 struct sk_buff *skb2 = skb_clone(skb, GFP_ATOMIC);
177                                 if (skb2)
178                                         raw_rcv(last, skb2);
179                         }
180                         last = sk;
181                 }
182         }
183 
184         if (last) {
185                 raw_rcv(last, skb);
186                 return true;
187         }
188         return false;
189 }
190 
191 void ip_protocol_deliver_rcu(struct net *net, struct sk_buff *skb, int protocol)
192 {
193         const struct net_protocol *ipprot;
194         int raw, ret;
195 
196 resubmit:
197         raw = raw_local_deliver(skb, protocol);
198 
199         ipprot = rcu_dereference(inet_protos[protocol]);
200         if (ipprot) {
201                 if (!ipprot->no_policy) {
202                         if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
203                                 kfree_skb(skb);
204                                 return;
205                         }
206                         nf_reset(skb);
207                 }
208                 ret = ipprot->handler(skb);
209                 if (ret < 0) {
210                         protocol = -ret;
211                         goto resubmit;
212                 }
213                 __IP_INC_STATS(net, IPSTATS_MIB_INDELIVERS);
214         } else {
215                 if (!raw) {
216                         if (xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
217                                 __IP_INC_STATS(net, IPSTATS_MIB_INUNKNOWNPROTOS);
218                                 icmp_send(skb, ICMP_DEST_UNREACH,
219                                           ICMP_PROT_UNREACH, 0);
220                         }
221                         kfree_skb(skb);
222                 } else {
223                         __IP_INC_STATS(net, IPSTATS_MIB_INDELIVERS);
224                         consume_skb(skb);
225                 }
226         }
227 }
228 
229 static int ip_local_deliver_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
230 {
231         __skb_pull(skb, skb_network_header_len(skb));
232 
233         rcu_read_lock();
234         ip_protocol_deliver_rcu(net, skb, ip_hdr(skb)->protocol);
235         rcu_read_unlock();
236 
237         return 0;
238 }
239 
240 /*
241  *      Deliver IP Packets to the higher protocol layers.
242  */
243 int ip_local_deliver(struct sk_buff *skb)
244 {
245         /*
246          *      Reassemble IP fragments.
247          */
248         struct net *net = dev_net(skb->dev);
249 
250         if (ip_is_fragment(ip_hdr(skb))) {
251                 if (ip_defrag(net, skb, IP_DEFRAG_LOCAL_DELIVER))
252                         return 0;
253         }
254 
255         return NF_HOOK(NFPROTO_IPV4, NF_INET_LOCAL_IN,
256                        net, NULL, skb, skb->dev, NULL,
257                        ip_local_deliver_finish);
258 }
259 
260 static inline bool ip_rcv_options(struct sk_buff *skb, struct net_device *dev)
261 {
262         struct ip_options *opt;
263         const struct iphdr *iph;
264 
265         /* It looks as overkill, because not all
266            IP options require packet mangling.
267            But it is the easiest for now, especially taking
268            into account that combination of IP options
269            and running sniffer is extremely rare condition.
270                                               --ANK (980813)
271         */
272         if (skb_cow(skb, skb_headroom(skb))) {
273                 __IP_INC_STATS(dev_net(dev), IPSTATS_MIB_INDISCARDS);
274                 goto drop;
275         }
276 
277         iph = ip_hdr(skb);
278         opt = &(IPCB(skb)->opt);
279         opt->optlen = iph->ihl*4 - sizeof(struct iphdr);
280 
281         if (ip_options_compile(dev_net(dev), opt, skb)) {
282                 __IP_INC_STATS(dev_net(dev), IPSTATS_MIB_INHDRERRORS);
283                 goto drop;
284         }
285 
286         if (unlikely(opt->srr)) {
287                 struct in_device *in_dev = __in_dev_get_rcu(dev);
288 
289                 if (in_dev) {
290                         if (!IN_DEV_SOURCE_ROUTE(in_dev)) {
291                                 if (IN_DEV_LOG_MARTIANS(in_dev))
292                                         net_info_ratelimited("source route option %pI4 -> %pI4\n",
293                                                              &iph->saddr,
294                                                              &iph->daddr);
295                                 goto drop;
296                         }
297                 }
298 
299                 if (ip_options_rcv_srr(skb, dev))
300                         goto drop;
301         }
302 
303         return false;
304 drop:
305         return true;
306 }
307 
308 static int ip_rcv_finish_core(struct net *net, struct sock *sk,
309                               struct sk_buff *skb, struct net_device *dev)
310 {
311         const struct iphdr *iph = ip_hdr(skb);
312         int (*edemux)(struct sk_buff *skb);
313         struct rtable *rt;
314         int err;
315 
316         if (net->ipv4.sysctl_ip_early_demux &&
317             !skb_dst(skb) &&
318             !skb->sk &&
319             !ip_is_fragment(iph)) {
320                 const struct net_protocol *ipprot;
321                 int protocol = iph->protocol;
322 
323                 ipprot = rcu_dereference(inet_protos[protocol]);
324                 if (ipprot && (edemux = READ_ONCE(ipprot->early_demux))) {
325                         err = edemux(skb);
326                         if (unlikely(err))
327                                 goto drop_error;
328                         /* must reload iph, skb->head might have changed */
329                         iph = ip_hdr(skb);
330                 }
331         }
332 
333         /*
334          *      Initialise the virtual path cache for the packet. It describes
335          *      how the packet travels inside Linux networking.
336          */
337         if (!skb_valid_dst(skb)) {
338                 err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
339                                            iph->tos, dev);
340                 if (unlikely(err))
341                         goto drop_error;
342         }
343 
344 #ifdef CONFIG_IP_ROUTE_CLASSID
345         if (unlikely(skb_dst(skb)->tclassid)) {
346                 struct ip_rt_acct *st = this_cpu_ptr(ip_rt_acct);
347                 u32 idx = skb_dst(skb)->tclassid;
348                 st[idx&0xFF].o_packets++;
349                 st[idx&0xFF].o_bytes += skb->len;
350                 st[(idx>>16)&0xFF].i_packets++;
351                 st[(idx>>16)&0xFF].i_bytes += skb->len;
352         }
353 #endif
354 
355         if (iph->ihl > 5 && ip_rcv_options(skb, dev))
356                 goto drop;
357 
358         rt = skb_rtable(skb);
359         if (rt->rt_type == RTN_MULTICAST) {
360                 __IP_UPD_PO_STATS(net, IPSTATS_MIB_INMCAST, skb->len);
361         } else if (rt->rt_type == RTN_BROADCAST) {
362                 __IP_UPD_PO_STATS(net, IPSTATS_MIB_INBCAST, skb->len);
363         } else if (skb->pkt_type == PACKET_BROADCAST ||
364                    skb->pkt_type == PACKET_MULTICAST) {
365                 struct in_device *in_dev = __in_dev_get_rcu(dev);
366 
367                 /* RFC 1122 3.3.6:
368                  *
369                  *   When a host sends a datagram to a link-layer broadcast
370                  *   address, the IP destination address MUST be a legal IP
371                  *   broadcast or IP multicast address.
372                  *
373                  *   A host SHOULD silently discard a datagram that is received
374                  *   via a link-layer broadcast (see Section 2.4) but does not
375                  *   specify an IP multicast or broadcast destination address.
376                  *
377                  * This doesn't explicitly say L2 *broadcast*, but broadcast is
378                  * in a way a form of multicast and the most common use case for
379                  * this is 802.11 protecting against cross-station spoofing (the
380                  * so-called "hole-196" attack) so do it for both.
381                  */
382                 if (in_dev &&
383                     IN_DEV_ORCONF(in_dev, DROP_UNICAST_IN_L2_MULTICAST))
384                         goto drop;
385         }
386 
387         return NET_RX_SUCCESS;
388 
389 drop:
390         kfree_skb(skb);
391         return NET_RX_DROP;
392 
393 drop_error:
394         if (err == -EXDEV)
395                 __NET_INC_STATS(net, LINUX_MIB_IPRPFILTER);
396         goto drop;
397 }
398 
399 static int ip_rcv_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
400 {
401         struct net_device *dev = skb->dev;
402         int ret;
403 
404         /* if ingress device is enslaved to an L3 master device pass the
405          * skb to its handler for processing
406          */
407         skb = l3mdev_ip_rcv(skb);
408         if (!skb)
409                 return NET_RX_SUCCESS;
410 
411         ret = ip_rcv_finish_core(net, sk, skb, dev);
412         if (ret != NET_RX_DROP)
413                 ret = dst_input(skb);
414         return ret;
415 }
416 
417 /*
418  *      Main IP Receive routine.
419  */
420 static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
421 {
422         const struct iphdr *iph;
423         u32 len;
424 
425         /* When the interface is in promisc. mode, drop all the crap
426          * that it receives, do not try to analyse it.
427          */
428         if (skb->pkt_type == PACKET_OTHERHOST)
429                 goto drop;
430 
431 
432         __IP_UPD_PO_STATS(net, IPSTATS_MIB_IN, skb->len);
433 
434         skb = skb_share_check(skb, GFP_ATOMIC);
435         if (!skb) {
436                 __IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
437                 goto out;
438         }
439 
440         if (!pskb_may_pull(skb, sizeof(struct iphdr)))
441                 goto inhdr_error;
442 
443         iph = ip_hdr(skb);
444 
445         /*
446          *      RFC1122: 3.2.1.2 MUST silently discard any IP frame that fails the checksum.
447          *
448          *      Is the datagram acceptable?
449          *
450          *      1.      Length at least the size of an ip header
451          *      2.      Version of 4
452          *      3.      Checksums correctly. [Speed optimisation for later, skip loopback checksums]
453          *      4.      Doesn't have a bogus length
454          */
455 
456         if (iph->ihl < 5 || iph->version != 4)
457                 goto inhdr_error;
458 
459         BUILD_BUG_ON(IPSTATS_MIB_ECT1PKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_ECT_1);
460         BUILD_BUG_ON(IPSTATS_MIB_ECT0PKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_ECT_0);
461         BUILD_BUG_ON(IPSTATS_MIB_CEPKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_CE);
462         __IP_ADD_STATS(net,
463                        IPSTATS_MIB_NOECTPKTS + (iph->tos & INET_ECN_MASK),
464                        max_t(unsigned short, 1, skb_shinfo(skb)->gso_segs));
465 
466         if (!pskb_may_pull(skb, iph->ihl*4))
467                 goto inhdr_error;
468 
469         iph = ip_hdr(skb);
470 
471         if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
472                 goto csum_error;
473 
474         len = ntohs(iph->tot_len);
475         if (skb->len < len) {
476                 __IP_INC_STATS(net, IPSTATS_MIB_INTRUNCATEDPKTS);
477                 goto drop;
478         } else if (len < (iph->ihl*4))
479                 goto inhdr_error;
480 
481         /* Our transport medium may have padded the buffer out. Now we know it
482          * is IP we can trim to the true length of the frame.
483          * Note this now means skb->len holds ntohs(iph->tot_len).
484          */
485         if (pskb_trim_rcsum(skb, len)) {
486                 __IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
487                 goto drop;
488         }
489 
490         iph = ip_hdr(skb);
491         skb->transport_header = skb->network_header + iph->ihl*4;
492 
493         /* Remove any debris in the socket control block */
494         memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
495         IPCB(skb)->iif = skb->skb_iif;
496 
497         /* Must drop socket now because of tproxy. */
498         skb_orphan(skb);
499 
500         return skb;
501 
502 csum_error:
503         __IP_INC_STATS(net, IPSTATS_MIB_CSUMERRORS);
504 inhdr_error:
505         __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
506 drop:
507         kfree_skb(skb);
508 out:
509         return NULL;
510 }
511 
512 /*
513  * IP receive entry point
514  */
515 int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt,
516            struct net_device *orig_dev)
517 {
518         struct net *net = dev_net(dev);
519 
520         skb = ip_rcv_core(skb, net);
521         if (skb == NULL)
522                 return NET_RX_DROP;
523         return NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING,
524                        net, NULL, skb, dev, NULL,
525                        ip_rcv_finish);
526 }
527 
528 static void ip_sublist_rcv_finish(struct list_head *head)
529 {
530         struct sk_buff *skb, *next;
531 
532         list_for_each_entry_safe(skb, next, head, list) {
533                 skb_list_del_init(skb);
534                 dst_input(skb);
535         }
536 }
537 
538 static void ip_list_rcv_finish(struct net *net, struct sock *sk,
539                                struct list_head *head)
540 {
541         struct dst_entry *curr_dst = NULL;
542         struct sk_buff *skb, *next;
543         struct list_head sublist;
544 
545         INIT_LIST_HEAD(&sublist);
546         list_for_each_entry_safe(skb, next, head, list) {
547                 struct net_device *dev = skb->dev;
548                 struct dst_entry *dst;
549 
550                 skb_list_del_init(skb);
551                 /* if ingress device is enslaved to an L3 master device pass the
552                  * skb to its handler for processing
553                  */
554                 skb = l3mdev_ip_rcv(skb);
555                 if (!skb)
556                         continue;
557                 if (ip_rcv_finish_core(net, sk, skb, dev) == NET_RX_DROP)
558                         continue;
559 
560                 dst = skb_dst(skb);
561                 if (curr_dst != dst) {
562                         /* dispatch old sublist */
563                         if (!list_empty(&sublist))
564                                 ip_sublist_rcv_finish(&sublist);
565                         /* start new sublist */
566                         INIT_LIST_HEAD(&sublist);
567                         curr_dst = dst;
568                 }
569                 list_add_tail(&skb->list, &sublist);
570         }
571         /* dispatch final sublist */
572         ip_sublist_rcv_finish(&sublist);
573 }
574 
575 static void ip_sublist_rcv(struct list_head *head, struct net_device *dev,
576                            struct net *net)
577 {
578         NF_HOOK_LIST(NFPROTO_IPV4, NF_INET_PRE_ROUTING, net, NULL,
579                      head, dev, NULL, ip_rcv_finish);
580         ip_list_rcv_finish(net, NULL, head);
581 }
582 
583 /* Receive a list of IP packets */
584 void ip_list_rcv(struct list_head *head, struct packet_type *pt,
585                  struct net_device *orig_dev)
586 {
587         struct net_device *curr_dev = NULL;
588         struct net *curr_net = NULL;
589         struct sk_buff *skb, *next;
590         struct list_head sublist;
591 
592         INIT_LIST_HEAD(&sublist);
593         list_for_each_entry_safe(skb, next, head, list) {
594                 struct net_device *dev = skb->dev;
595                 struct net *net = dev_net(dev);
596 
597                 skb_list_del_init(skb);
598                 skb = ip_rcv_core(skb, net);
599                 if (skb == NULL)
600                         continue;
601 
602                 if (curr_dev != dev || curr_net != net) {
603                         /* dispatch old sublist */
604                         if (!list_empty(&sublist))
605                                 ip_sublist_rcv(&sublist, curr_dev, curr_net);
606                         /* start new sublist */
607                         INIT_LIST_HEAD(&sublist);
608                         curr_dev = dev;
609                         curr_net = net;
610                 }
611                 list_add_tail(&skb->list, &sublist);
612         }
613         /* dispatch final sublist */
614         ip_sublist_rcv(&sublist, curr_dev, curr_net);
615 }
616 

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