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Linux/net/ipv4/ip_input.c

  1 /*
  2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
  3  *              operating system.  INET is implemented using the  BSD Socket
  4  *              interface as the means of communication with the user level.
  5  *
  6  *              The 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(ip_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                     net_eq(sock_net(sk), net)) {
172                         if (ip_is_fragment(ip_hdr(skb))) {
173                                 if (ip_defrag(net, skb, IP_DEFRAG_CALL_RA_CHAIN))
174                                         return true;
175                         }
176                         if (last) {
177                                 struct sk_buff *skb2 = skb_clone(skb, GFP_ATOMIC);
178                                 if (skb2)
179                                         raw_rcv(last, skb2);
180                         }
181                         last = sk;
182                 }
183         }
184 
185         if (last) {
186                 raw_rcv(last, skb);
187                 return true;
188         }
189         return false;
190 }
191 
192 static int ip_local_deliver_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
193 {
194         __skb_pull(skb, skb_network_header_len(skb));
195 
196         rcu_read_lock();
197         {
198                 int protocol = ip_hdr(skb)->protocol;
199                 const struct net_protocol *ipprot;
200                 int raw;
201 
202         resubmit:
203                 raw = raw_local_deliver(skb, protocol);
204 
205                 ipprot = rcu_dereference(inet_protos[protocol]);
206                 if (ipprot) {
207                         int ret;
208 
209                         if (!ipprot->no_policy) {
210                                 if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
211                                         kfree_skb(skb);
212                                         goto out;
213                                 }
214                                 nf_reset(skb);
215                         }
216                         ret = ipprot->handler(skb);
217                         if (ret < 0) {
218                                 protocol = -ret;
219                                 goto resubmit;
220                         }
221                         __IP_INC_STATS(net, IPSTATS_MIB_INDELIVERS);
222                 } else {
223                         if (!raw) {
224                                 if (xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
225                                         __IP_INC_STATS(net, IPSTATS_MIB_INUNKNOWNPROTOS);
226                                         icmp_send(skb, ICMP_DEST_UNREACH,
227                                                   ICMP_PROT_UNREACH, 0);
228                                 }
229                                 kfree_skb(skb);
230                         } else {
231                                 __IP_INC_STATS(net, IPSTATS_MIB_INDELIVERS);
232                                 consume_skb(skb);
233                         }
234                 }
235         }
236  out:
237         rcu_read_unlock();
238 
239         return 0;
240 }
241 
242 /*
243  *      Deliver IP Packets to the higher protocol layers.
244  */
245 int ip_local_deliver(struct sk_buff *skb)
246 {
247         /*
248          *      Reassemble IP fragments.
249          */
250         struct net *net = dev_net(skb->dev);
251 
252         if (ip_is_fragment(ip_hdr(skb))) {
253                 if (ip_defrag(net, skb, IP_DEFRAG_LOCAL_DELIVER))
254                         return 0;
255         }
256 
257         return NF_HOOK(NFPROTO_IPV4, NF_INET_LOCAL_IN,
258                        net, NULL, skb, skb->dev, NULL,
259                        ip_local_deliver_finish);
260 }
261 
262 static inline bool ip_rcv_options(struct sk_buff *skb)
263 {
264         struct ip_options *opt;
265         const struct iphdr *iph;
266         struct net_device *dev = skb->dev;
267 
268         /* It looks as overkill, because not all
269            IP options require packet mangling.
270            But it is the easiest for now, especially taking
271            into account that combination of IP options
272            and running sniffer is extremely rare condition.
273                                               --ANK (980813)
274         */
275         if (skb_cow(skb, skb_headroom(skb))) {
276                 __IP_INC_STATS(dev_net(dev), IPSTATS_MIB_INDISCARDS);
277                 goto drop;
278         }
279 
280         iph = ip_hdr(skb);
281         opt = &(IPCB(skb)->opt);
282         opt->optlen = iph->ihl*4 - sizeof(struct iphdr);
283 
284         if (ip_options_compile(dev_net(dev), opt, skb)) {
285                 __IP_INC_STATS(dev_net(dev), IPSTATS_MIB_INHDRERRORS);
286                 goto drop;
287         }
288 
289         if (unlikely(opt->srr)) {
290                 struct in_device *in_dev = __in_dev_get_rcu(dev);
291 
292                 if (in_dev) {
293                         if (!IN_DEV_SOURCE_ROUTE(in_dev)) {
294                                 if (IN_DEV_LOG_MARTIANS(in_dev))
295                                         net_info_ratelimited("source route option %pI4 -> %pI4\n",
296                                                              &iph->saddr,
297                                                              &iph->daddr);
298                                 goto drop;
299                         }
300                 }
301 
302                 if (ip_options_rcv_srr(skb))
303                         goto drop;
304         }
305 
306         return false;
307 drop:
308         return true;
309 }
310 
311 static int ip_rcv_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
312 {
313         const struct iphdr *iph = ip_hdr(skb);
314         struct rtable *rt;
315 
316         /* if ingress device is enslaved to an L3 master device pass the
317          * skb to its handler for processing
318          */
319         skb = l3mdev_ip_rcv(skb);
320         if (!skb)
321                 return NET_RX_SUCCESS;
322 
323         if (net->ipv4.sysctl_ip_early_demux &&
324             !skb_dst(skb) &&
325             !skb->sk &&
326             !ip_is_fragment(iph)) {
327                 const struct net_protocol *ipprot;
328                 int protocol = iph->protocol;
329 
330                 ipprot = rcu_dereference(inet_protos[protocol]);
331                 if (ipprot && ipprot->early_demux) {
332                         ipprot->early_demux(skb);
333                         /* must reload iph, skb->head might have changed */
334                         iph = ip_hdr(skb);
335                 }
336         }
337 
338         /*
339          *      Initialise the virtual path cache for the packet. It describes
340          *      how the packet travels inside Linux networking.
341          */
342         if (!skb_valid_dst(skb)) {
343                 int err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
344                                                iph->tos, skb->dev);
345                 if (unlikely(err)) {
346                         if (err == -EXDEV)
347                                 __NET_INC_STATS(net, LINUX_MIB_IPRPFILTER);
348                         goto drop;
349                 }
350         }
351 
352 #ifdef CONFIG_IP_ROUTE_CLASSID
353         if (unlikely(skb_dst(skb)->tclassid)) {
354                 struct ip_rt_acct *st = this_cpu_ptr(ip_rt_acct);
355                 u32 idx = skb_dst(skb)->tclassid;
356                 st[idx&0xFF].o_packets++;
357                 st[idx&0xFF].o_bytes += skb->len;
358                 st[(idx>>16)&0xFF].i_packets++;
359                 st[(idx>>16)&0xFF].i_bytes += skb->len;
360         }
361 #endif
362 
363         if (iph->ihl > 5 && ip_rcv_options(skb))
364                 goto drop;
365 
366         rt = skb_rtable(skb);
367         if (rt->rt_type == RTN_MULTICAST) {
368                 __IP_UPD_PO_STATS(net, IPSTATS_MIB_INMCAST, skb->len);
369         } else if (rt->rt_type == RTN_BROADCAST) {
370                 __IP_UPD_PO_STATS(net, IPSTATS_MIB_INBCAST, skb->len);
371         } else if (skb->pkt_type == PACKET_BROADCAST ||
372                    skb->pkt_type == PACKET_MULTICAST) {
373                 struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
374 
375                 /* RFC 1122 3.3.6:
376                  *
377                  *   When a host sends a datagram to a link-layer broadcast
378                  *   address, the IP destination address MUST be a legal IP
379                  *   broadcast or IP multicast address.
380                  *
381                  *   A host SHOULD silently discard a datagram that is received
382                  *   via a link-layer broadcast (see Section 2.4) but does not
383                  *   specify an IP multicast or broadcast destination address.
384                  *
385                  * This doesn't explicitly say L2 *broadcast*, but broadcast is
386                  * in a way a form of multicast and the most common use case for
387                  * this is 802.11 protecting against cross-station spoofing (the
388                  * so-called "hole-196" attack) so do it for both.
389                  */
390                 if (in_dev &&
391                     IN_DEV_ORCONF(in_dev, DROP_UNICAST_IN_L2_MULTICAST))
392                         goto drop;
393         }
394 
395         return dst_input(skb);
396 
397 drop:
398         kfree_skb(skb);
399         return NET_RX_DROP;
400 }
401 
402 /*
403  *      Main IP Receive routine.
404  */
405 int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev)
406 {
407         const struct iphdr *iph;
408         struct net *net;
409         u32 len;
410 
411         /* When the interface is in promisc. mode, drop all the crap
412          * that it receives, do not try to analyse it.
413          */
414         if (skb->pkt_type == PACKET_OTHERHOST)
415                 goto drop;
416 
417 
418         net = dev_net(dev);
419         __IP_UPD_PO_STATS(net, IPSTATS_MIB_IN, skb->len);
420 
421         skb = skb_share_check(skb, GFP_ATOMIC);
422         if (!skb) {
423                 __IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
424                 goto out;
425         }
426 
427         if (!pskb_may_pull(skb, sizeof(struct iphdr)))
428                 goto inhdr_error;
429 
430         iph = ip_hdr(skb);
431 
432         /*
433          *      RFC1122: 3.2.1.2 MUST silently discard any IP frame that fails the checksum.
434          *
435          *      Is the datagram acceptable?
436          *
437          *      1.      Length at least the size of an ip header
438          *      2.      Version of 4
439          *      3.      Checksums correctly. [Speed optimisation for later, skip loopback checksums]
440          *      4.      Doesn't have a bogus length
441          */
442 
443         if (iph->ihl < 5 || iph->version != 4)
444                 goto inhdr_error;
445 
446         BUILD_BUG_ON(IPSTATS_MIB_ECT1PKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_ECT_1);
447         BUILD_BUG_ON(IPSTATS_MIB_ECT0PKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_ECT_0);
448         BUILD_BUG_ON(IPSTATS_MIB_CEPKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_CE);
449         __IP_ADD_STATS(net,
450                        IPSTATS_MIB_NOECTPKTS + (iph->tos & INET_ECN_MASK),
451                        max_t(unsigned short, 1, skb_shinfo(skb)->gso_segs));
452 
453         if (!pskb_may_pull(skb, iph->ihl*4))
454                 goto inhdr_error;
455 
456         iph = ip_hdr(skb);
457 
458         if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
459                 goto csum_error;
460 
461         len = ntohs(iph->tot_len);
462         if (skb->len < len) {
463                 __IP_INC_STATS(net, IPSTATS_MIB_INTRUNCATEDPKTS);
464                 goto drop;
465         } else if (len < (iph->ihl*4))
466                 goto inhdr_error;
467 
468         /* Our transport medium may have padded the buffer out. Now we know it
469          * is IP we can trim to the true length of the frame.
470          * Note this now means skb->len holds ntohs(iph->tot_len).
471          */
472         if (pskb_trim_rcsum(skb, len)) {
473                 __IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
474                 goto drop;
475         }
476 
477         skb->transport_header = skb->network_header + iph->ihl*4;
478 
479         /* Remove any debris in the socket control block */
480         memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
481         IPCB(skb)->iif = skb->skb_iif;
482 
483         /* Must drop socket now because of tproxy. */
484         skb_orphan(skb);
485 
486         return NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING,
487                        net, NULL, skb, dev, NULL,
488                        ip_rcv_finish);
489 
490 csum_error:
491         __IP_INC_STATS(net, IPSTATS_MIB_CSUMERRORS);
492 inhdr_error:
493         __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
494 drop:
495         kfree_skb(skb);
496 out:
497         return NET_RX_DROP;
498 }
499 

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