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 <linux/netfilter_ipv4.h>
 145 #include <net/xfrm.h>
 146 #include <linux/mroute.h>
 147 #include <linux/netlink.h>
 148
 149 /*
 150  *      Process Router Attention IP option (RFC 2113)
 151  */
 152 bool ip_call_ra_chain(struct sk_buff *skb)
 153 {
 154         struct ip_ra_chain *ra;
 155         u8 protocol = ip_hdr(skb)->protocol;
 156         struct sock *last = NULL;
 157         struct net_device *dev = skb->dev;
 158
 159         for (ra = rcu_dereference(ip_ra_chain); ra; ra = rcu_dereference(ra->next)) {
 160                 struct sock *sk = ra->sk;
 161
 162                 /* If socket is bound to an interface, only report
 163                  * the packet if it came  from that interface.
 164                  */
 165                 if (sk && inet_sk(sk)->inet_num == protocol &&
 166                     (!sk->sk_bound_dev_if ||
 167                      sk->sk_bound_dev_if == dev->ifindex) &&
 168                     net_eq(sock_net(sk), dev_net(dev))) {
 169                         if (ip_is_fragment(ip_hdr(skb))) {
 170                                 if (ip_defrag(skb, IP_DEFRAG_CALL_RA_CHAIN))
 171                                         return true;
 172                         }
 173                         if (last) {
 174                                 struct sk_buff *skb2 = skb_clone(skb, GFP_ATOMIC);
 175                                 if (skb2)
 176                                         raw_rcv(last, skb2);
 177                         }
 178                         last = sk;
 179                 }
 180         }
 181
 182         if (last) {
 183                 raw_rcv(last, skb);
 184                 return true;
 185         }
 186         return false;
 187 }
 188
 189 static int ip_local_deliver_finish(struct sk_buff *skb)
 190 {
 191         struct net *net = dev_net(skb->dev);
 192
 193         __skb_pull(skb, ip_hdrlen(skb));
 194
 195         /* Point into the IP datagram, just past the header. */
 196         skb_reset_transport_header(skb);
 197
 198         rcu_read_lock();
 199         {
 200                 int protocol = ip_hdr(skb)->protocol;
 201                 const struct net_protocol *ipprot;
 202                 int raw;
 203
 204         resubmit:
 205                 raw = raw_local_deliver(skb, protocol);
 206
 207                 ipprot = rcu_dereference(inet_protos[protocol]);
 208                 if (ipprot != NULL) {
 209                         int ret;
 210
 211                         if (!ipprot->no_policy) {
 212                                 if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
 213                                         kfree_skb(skb);
 214                                         goto out;
 215                                 }
 216                                 nf_reset(skb);
 217                         }
 218                         ret = ipprot->handler(skb);
 219                         if (ret < 0) {
 220                                 protocol = -ret;
 221                                 goto resubmit;
 222                         }
 223                         IP_INC_STATS_BH(net, IPSTATS_MIB_INDELIVERS);
 224                 } else {
 225                         if (!raw) {
 226                                 if (xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
 227                                         IP_INC_STATS_BH(net, IPSTATS_MIB_INUNKNOWNPROTOS);
 228                                         icmp_send(skb, ICMP_DEST_UNREACH,
 229                                                   ICMP_PROT_UNREACH, 0);
 230                                 }
 231                                 kfree_skb(skb);
 232                         } else {
 233                                 IP_INC_STATS_BH(net, IPSTATS_MIB_INDELIVERS);
 234                                 consume_skb(skb);
 235                         }
 236                 }
 237         }
 238  out:
 239         rcu_read_unlock();
 240
 241         return 0;
 242 }
 243
 244 /*
 245  *      Deliver IP Packets to the higher protocol layers.
 246  */
 247 int ip_local_deliver(struct sk_buff *skb)
 248 {
 249         /*
 250          *      Reassemble IP fragments.
 251          */
 252
 253         if (ip_is_fragment(ip_hdr(skb))) {
 254                 if (ip_defrag(skb, IP_DEFRAG_LOCAL_DELIVER))
 255                         return 0;
 256         }
 257
 258         return NF_HOOK(NFPROTO_IPV4, NF_INET_LOCAL_IN, 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_BH(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_BH(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 int sysctl_ip_early_demux __read_mostly = 1;
 312 EXPORT_SYMBOL(sysctl_ip_early_demux);
 313
 314 static int ip_rcv_finish(struct sk_buff *skb)
 315 {
 316         const struct iphdr *iph = ip_hdr(skb);
 317         struct rtable *rt;
 318
 319         if (sysctl_ip_early_demux && !skb_dst(skb)) {
 320                 const struct net_protocol *ipprot;
 321                 int protocol = iph->protocol;
 322
 323                 ipprot = rcu_dereference(inet_protos[protocol]);
 324                 if (ipprot && ipprot->early_demux) {
 325                         ipprot->early_demux(skb);
 326                         /* must reload iph, skb->head might have changed */
 327                         iph = ip_hdr(skb);
 328                 }
 329         }
 330
 331         /*
 332          *      Initialise the virtual path cache for the packet. It describes
 333          *      how the packet travels inside Linux networking.
 334          */
 335         if (!skb_dst(skb)) {
 336                 int err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
 337                                                iph->tos, skb->dev);
 338                 if (unlikely(err)) {
 339                         if (err == -EXDEV)
 340                                 NET_INC_STATS_BH(dev_net(skb->dev),
 341                                                  LINUX_MIB_IPRPFILTER);
 342                         goto drop;
 343                 }
 344         }
 345
 346 #ifdef CONFIG_IP_ROUTE_CLASSID
 347         if (unlikely(skb_dst(skb)->tclassid)) {
 348                 struct ip_rt_acct *st = this_cpu_ptr(ip_rt_acct);
 349                 u32 idx = skb_dst(skb)->tclassid;
 350                 st[idx&0xFF].o_packets++;
 351                 st[idx&0xFF].o_bytes += skb->len;
 352                 st[(idx>>16)&0xFF].i_packets++;
 353                 st[(idx>>16)&0xFF].i_bytes += skb->len;
 354         }
 355 #endif
 356
 357         if (iph->ihl > 5 && ip_rcv_options(skb))
 358                 goto drop;
 359
 360         rt = skb_rtable(skb);
 361         if (rt->rt_type == RTN_MULTICAST) {
 362                 IP_UPD_PO_STATS_BH(dev_net(rt->dst.dev), IPSTATS_MIB_INMCAST,
 363                                 skb->len);
 364         } else if (rt->rt_type == RTN_BROADCAST)
 365                 IP_UPD_PO_STATS_BH(dev_net(rt->dst.dev), IPSTATS_MIB_INBCAST,
 366                                 skb->len);
 367
 368         return dst_input(skb);
 369
 370 drop:
 371         kfree_skb(skb);
 372         return NET_RX_DROP;
 373 }
 374
 375 /*
 376  *      Main IP Receive routine.
 377  */
 378 int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev)
 379 {
 380         const struct iphdr *iph;
 381         u32 len;
 382
 383         /* When the interface is in promisc. mode, drop all the crap
 384          * that it receives, do not try to analyse it.
 385          */
 386         if (skb->pkt_type == PACKET_OTHERHOST)
 387                 goto drop;
 388
 389
 390         IP_UPD_PO_STATS_BH(dev_net(dev), IPSTATS_MIB_IN, skb->len);
 391
 392         if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL) {
 393                 IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INDISCARDS);
 394                 goto out;
 395         }
 396
 397         if (!pskb_may_pull(skb, sizeof(struct iphdr)))
 398                 goto inhdr_error;
 399
 400         iph = ip_hdr(skb);
 401
 402         /*
 403          *      RFC1122: 3.2.1.2 MUST silently discard any IP frame that fails the checksum.
 404          *
 405          *      Is the datagram acceptable?
 406          *
 407          *      1.      Length at least the size of an ip header
 408          *      2.      Version of 4
 409          *      3.      Checksums correctly. [Speed optimisation for later, skip loopback checksums]
 410          *      4.      Doesn't have a bogus length
 411          */
 412
 413         if (iph->ihl < 5 || iph->version != 4)
 414                 goto inhdr_error;
 415
 416         if (!pskb_may_pull(skb, iph->ihl*4))
 417                 goto inhdr_error;
 418
 419         iph = ip_hdr(skb);
 420
 421         if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
 422                 goto csum_error;
 423
 424         len = ntohs(iph->tot_len);
 425         if (skb->len < len) {
 426                 IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INTRUNCATEDPKTS);
 427                 goto drop;
 428         } else if (len < (iph->ihl*4))
 429                 goto inhdr_error;
 430
 431         /* Our transport medium may have padded the buffer out. Now we know it
 432          * is IP we can trim to the true length of the frame.
 433          * Note this now means skb->len holds ntohs(iph->tot_len).
 434          */
 435         if (pskb_trim_rcsum(skb, len)) {
 436                 IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INDISCARDS);
 437                 goto drop;
 438         }
 439
 440         /* Remove any debris in the socket control block */
 441         memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
 442
 443         /* Must drop socket now because of tproxy. */
 444         skb_orphan(skb);
 445
 446         return NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING, skb, dev, NULL,
 447                        ip_rcv_finish);
 448
 449 csum_error:
 450         IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_CSUMERRORS);
 451 inhdr_error:
 452         IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INHDRERRORS);
 453 drop:
 454         kfree_skb(skb);
 455 out:
 456         return NET_RX_DROP;
 457 }