net/ipv4/netfilter/ip_conntrack_proto_tcp.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  * Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>:
   9  *      - Real stateful connection tracking
  10  *      - Modified state transitions table
  11  *      - Window scaling support added
  12  *      - SACK support added
  13  *
  14  * Willy Tarreau:
  15  *      - State table bugfixes
  16  *      - More robust state changes
  17  *      - Tuning timer parameters
  18  *
  19  * version 2.2
  20  */
  21
  22 #include <linux/types.h>
  23 #include <linux/sched.h>
  24 #include <linux/timer.h>
  25 #include <linux/netfilter.h>
  26 #include <linux/module.h>
  27 #include <linux/in.h>
  28 #include <linux/ip.h>
  29 #include <linux/tcp.h>
  30 #include <linux/spinlock.h>
  31
  32 #include <net/tcp.h>
  33
  34 #include <linux/netfilter_ipv4.h>
  35 #include <linux/netfilter_ipv4/ip_conntrack.h>
  36 #include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
  37
  38 #if 0
  39 #define DEBUGP printk
  40 #define DEBUGP_VARS
  41 #else
  42 #define DEBUGP(format, args...)
  43 #endif
  44
  45 /* Protects conntrack->proto.tcp */
  46 static DEFINE_RWLOCK(tcp_lock);
  47
  48 /* "Be conservative in what you do,
  49     be liberal in what you accept from others."
  50     If it's non-zero, we mark only out of window RST segments as INVALID. */
  51 int ip_ct_tcp_be_liberal = 0;
  52
  53 /* When connection is picked up from the middle, how many packets are required
  54    to pass in each direction when we assume we are in sync - if any side uses
  55    window scaling, we lost the game.
  56    If it is set to zero, we disable picking up already established
  57    connections. */
  58 int ip_ct_tcp_loose = 3;
  59
  60 /* Max number of the retransmitted packets without receiving an (acceptable)
  61    ACK from the destination. If this number is reached, a shorter timer
  62    will be started. */
  63 int ip_ct_tcp_max_retrans = 3;
  64
  65   /* FIXME: Examine ipfilter's timeouts and conntrack transitions more
  66      closely.  They're more complex. --RR */
  67
  68 static const char *tcp_conntrack_names[] = {
  69         "NONE",
  70         "SYN_SENT",
  71         "SYN_RECV",
  72         "ESTABLISHED",
  73         "FIN_WAIT",
  74         "CLOSE_WAIT",
  75         "LAST_ACK",
  76         "TIME_WAIT",
  77         "CLOSE",
  78         "LISTEN"
  79 };
  80
  81 #define SECS * HZ
  82 #define MINS * 60 SECS
  83 #define HOURS * 60 MINS
  84 #define DAYS * 24 HOURS
  85
  86 unsigned int ip_ct_tcp_timeout_syn_sent =      2 MINS;
  87 unsigned int ip_ct_tcp_timeout_syn_recv =     60 SECS;
  88 unsigned int ip_ct_tcp_timeout_established =   5 DAYS;
  89 unsigned int ip_ct_tcp_timeout_fin_wait =      2 MINS;
  90 unsigned int ip_ct_tcp_timeout_close_wait =   60 SECS;
  91 unsigned int ip_ct_tcp_timeout_last_ack =     30 SECS;
  92 unsigned int ip_ct_tcp_timeout_time_wait =     2 MINS;
  93 unsigned int ip_ct_tcp_timeout_close =        10 SECS;
  94
  95 /* RFC1122 says the R2 limit should be at least 100 seconds.
  96    Linux uses 15 packets as limit, which corresponds
  97    to ~13-30min depending on RTO. */
  98 unsigned int ip_ct_tcp_timeout_max_retrans =     5 MINS;
  99
 100 static const unsigned int * tcp_timeouts[]
 101 = { NULL,                              /*      TCP_CONNTRACK_NONE */
 102     &ip_ct_tcp_timeout_syn_sent,       /*      TCP_CONNTRACK_SYN_SENT, */
 103     &ip_ct_tcp_timeout_syn_recv,       /*      TCP_CONNTRACK_SYN_RECV, */
 104     &ip_ct_tcp_timeout_established,    /*      TCP_CONNTRACK_ESTABLISHED,      */
 105     &ip_ct_tcp_timeout_fin_wait,       /*      TCP_CONNTRACK_FIN_WAIT, */
 106     &ip_ct_tcp_timeout_close_wait,     /*      TCP_CONNTRACK_CLOSE_WAIT,       */
 107     &ip_ct_tcp_timeout_last_ack,       /*      TCP_CONNTRACK_LAST_ACK, */
 108     &ip_ct_tcp_timeout_time_wait,      /*      TCP_CONNTRACK_TIME_WAIT,        */
 109     &ip_ct_tcp_timeout_close,          /*      TCP_CONNTRACK_CLOSE,    */
 110     NULL,                              /*      TCP_CONNTRACK_LISTEN */
 111  };
 112
 113 #define sNO TCP_CONNTRACK_NONE
 114 #define sSS TCP_CONNTRACK_SYN_SENT
 115 #define sSR TCP_CONNTRACK_SYN_RECV
 116 #define sES TCP_CONNTRACK_ESTABLISHED
 117 #define sFW TCP_CONNTRACK_FIN_WAIT
 118 #define sCW TCP_CONNTRACK_CLOSE_WAIT
 119 #define sLA TCP_CONNTRACK_LAST_ACK
 120 #define sTW TCP_CONNTRACK_TIME_WAIT
 121 #define sCL TCP_CONNTRACK_CLOSE
 122 #define sLI TCP_CONNTRACK_LISTEN
 123 #define sIV TCP_CONNTRACK_MAX
 124 #define sIG TCP_CONNTRACK_IGNORE
 125
 126 /* What TCP flags are set from RST/SYN/FIN/ACK. */
 127 enum tcp_bit_set {
 128         TCP_SYN_SET,
 129         TCP_SYNACK_SET,
 130         TCP_FIN_SET,
 131         TCP_ACK_SET,
 132         TCP_RST_SET,
 133         TCP_NONE_SET,
 134 };
 135
 136 /*
 137  * The TCP state transition table needs a few words...
 138  *
 139  * We are the man in the middle. All the packets go through us
 140  * but might get lost in transit to the destination.
 141  * It is assumed that the destinations can't receive segments
 142  * we haven't seen.
 143  *
 144  * The checked segment is in window, but our windows are *not*
 145  * equivalent with the ones of the sender/receiver. We always
 146  * try to guess the state of the current sender.
 147  *
 148  * The meaning of the states are:
 149  *
 150  * NONE:        initial state
 151  * SYN_SENT:    SYN-only packet seen
 152  * SYN_RECV:    SYN-ACK packet seen
 153  * ESTABLISHED: ACK packet seen
 154  * FIN_WAIT:    FIN packet seen
 155  * CLOSE_WAIT:  ACK seen (after FIN)
 156  * LAST_ACK:    FIN seen (after FIN)
 157  * TIME_WAIT:   last ACK seen
 158  * CLOSE:       closed connection
 159  *
 160  * LISTEN state is not used.
 161  *
 162  * Packets marked as IGNORED (sIG):
 163  *      if they may be either invalid or valid
 164  *      and the receiver may send back a connection
 165  *      closing RST or a SYN/ACK.
 166  *
 167  * Packets marked as INVALID (sIV):
 168  *      if they are invalid
 169  *      or we do not support the request (simultaneous open)
 170  */
 171 static const enum tcp_conntrack tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
 172         {
 173 /* ORIGINAL */
 174 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 175 /*syn*/    { sSS, sSS, sIG, sIG, sIG, sIG, sIG, sSS, sSS, sIV },
 176 /*
 177  *      sNO -> sSS      Initialize a new connection
 178  *      sSS -> sSS      Retransmitted SYN
 179  *      sSR -> sIG      Late retransmitted SYN?
 180  *      sES -> sIG      Error: SYNs in window outside the SYN_SENT state
 181  *                      are errors. Receiver will reply with RST
 182  *                      and close the connection.
 183  *                      Or we are not in sync and hold a dead connection.
 184  *      sFW -> sIG
 185  *      sCW -> sIG
 186  *      sLA -> sIG
 187  *      sTW -> sSS      Reopened connection (RFC 1122).
 188  *      sCL -> sSS
 189  */
 190 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 191 /*synack*/ { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV },
 192 /*
 193  * A SYN/ACK from the client is always invalid:
 194  *      - either it tries to set up a simultaneous open, which is
 195  *        not supported;
 196  *      - or the firewall has just been inserted between the two hosts
 197  *        during the session set-up. The SYN will be retransmitted
 198  *        by the true client (or it'll time out).
 199  */
 200 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 201 /*fin*/    { sIV, sIV, sFW, sFW, sLA, sLA, sLA, sTW, sCL, sIV },
 202 /*
 203  *      sNO -> sIV      Too late and no reason to do anything...
 204  *      sSS -> sIV      Client migth not send FIN in this state:
 205  *                      we enforce waiting for a SYN/ACK reply first.
 206  *      sSR -> sFW      Close started.
 207  *      sES -> sFW
 208  *      sFW -> sLA      FIN seen in both directions, waiting for
 209  *                      the last ACK.
 210  *                      Migth be a retransmitted FIN as well...
 211  *      sCW -> sLA
 212  *      sLA -> sLA      Retransmitted FIN. Remain in the same state.
 213  *      sTW -> sTW
 214  *      sCL -> sCL
 215  */
 216 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 217 /*ack*/    { sES, sIV, sES, sES, sCW, sCW, sTW, sTW, sCL, sIV },
 218 /*
 219  *      sNO -> sES      Assumed.
 220  *      sSS -> sIV      ACK is invalid: we haven't seen a SYN/ACK yet.
 221  *      sSR -> sES      Established state is reached.
 222  *      sES -> sES      :-)
 223  *      sFW -> sCW      Normal close request answered by ACK.
 224  *      sCW -> sCW
 225  *      sLA -> sTW      Last ACK detected.
 226  *      sTW -> sTW      Retransmitted last ACK. Remain in the same state.
 227  *      sCL -> sCL
 228  */
 229 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 230 /*rst*/    { sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sIV },
 231 /*none*/   { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV }
 232         },
 233         {
 234 /* REPLY */
 235 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 236 /*syn*/    { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV },
 237 /*
 238  *      sNO -> sIV      Never reached.
 239  *      sSS -> sIV      Simultaneous open, not supported
 240  *      sSR -> sIV      Simultaneous open, not supported.
 241  *      sES -> sIV      Server may not initiate a connection.
 242  *      sFW -> sIV
 243  *      sCW -> sIV
 244  *      sLA -> sIV
 245  *      sTW -> sIV      Reopened connection, but server may not do it.
 246  *      sCL -> sIV
 247  */
 248 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 249 /*synack*/ { sIV, sSR, sSR, sIG, sIG, sIG, sIG, sIG, sIG, sIV },
 250 /*
 251  *      sSS -> sSR      Standard open.
 252  *      sSR -> sSR      Retransmitted SYN/ACK.
 253  *      sES -> sIG      Late retransmitted SYN/ACK?
 254  *      sFW -> sIG      Might be SYN/ACK answering ignored SYN
 255  *      sCW -> sIG
 256  *      sLA -> sIG
 257  *      sTW -> sIG
 258  *      sCL -> sIG
 259  */
 260 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 261 /*fin*/    { sIV, sIV, sFW, sFW, sLA, sLA, sLA, sTW, sCL, sIV },
 262 /*
 263  *      sSS -> sIV      Server might not send FIN in this state.
 264  *      sSR -> sFW      Close started.
 265  *      sES -> sFW
 266  *      sFW -> sLA      FIN seen in both directions.
 267  *      sCW -> sLA
 268  *      sLA -> sLA      Retransmitted FIN.
 269  *      sTW -> sTW
 270  *      sCL -> sCL
 271  */
 272 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 273 /*ack*/    { sIV, sIG, sSR, sES, sCW, sCW, sTW, sTW, sCL, sIV },
 274 /*
 275  *      sSS -> sIG      Might be a half-open connection.
 276  *      sSR -> sSR      Might answer late resent SYN.
 277  *      sES -> sES      :-)
 278  *      sFW -> sCW      Normal close request answered by ACK.
 279  *      sCW -> sCW
 280  *      sLA -> sTW      Last ACK detected.
 281  *      sTW -> sTW      Retransmitted last ACK.
 282  *      sCL -> sCL
 283  */
 284 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 285 /*rst*/    { sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sIV },
 286 /*none*/   { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV }
 287         }
 288 };
 289
 290 static int tcp_pkt_to_tuple(const struct sk_buff *skb,
 291                             unsigned int dataoff,
 292                             struct ip_conntrack_tuple *tuple)
 293 {
 294         struct tcphdr _hdr, *hp;
 295
 296         /* Actually only need first 8 bytes. */
 297         hp = skb_header_pointer(skb, dataoff, 8, &_hdr);
 298         if (hp == NULL)
 299                 return 0;
 300
 301         tuple->src.u.tcp.port = hp->source;
 302         tuple->dst.u.tcp.port = hp->dest;
 303
 304         return 1;
 305 }
 306
 307 static int tcp_invert_tuple(struct ip_conntrack_tuple *tuple,
 308                             const struct ip_conntrack_tuple *orig)
 309 {
 310         tuple->src.u.tcp.port = orig->dst.u.tcp.port;
 311         tuple->dst.u.tcp.port = orig->src.u.tcp.port;
 312         return 1;
 313 }
 314
 315 /* Print out the per-protocol part of the tuple. */
 316 static int tcp_print_tuple(struct seq_file *s,
 317                            const struct ip_conntrack_tuple *tuple)
 318 {
 319         return seq_printf(s, "sport=%hu dport=%hu ",
 320                           ntohs(tuple->src.u.tcp.port),
 321                           ntohs(tuple->dst.u.tcp.port));
 322 }
 323
 324 /* Print out the private part of the conntrack. */
 325 static int tcp_print_conntrack(struct seq_file *s,
 326                                const struct ip_conntrack *conntrack)
 327 {
 328         enum tcp_conntrack state;
 329
 330         read_lock_bh(&tcp_lock);
 331         state = conntrack->proto.tcp.state;
 332         read_unlock_bh(&tcp_lock);
 333
 334         return seq_printf(s, "%s ", tcp_conntrack_names[state]);
 335 }
 336
 337 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 338     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 339 static int tcp_to_nfattr(struct sk_buff *skb, struct nfattr *nfa,
 340                          const struct ip_conntrack *ct)
 341 {
 342         struct nfattr *nest_parms;
 343
 344         read_lock_bh(&tcp_lock);
 345         nest_parms = NFA_NEST(skb, CTA_PROTOINFO_TCP);
 346         NFA_PUT(skb, CTA_PROTOINFO_TCP_STATE, sizeof(u_int8_t),
 347                 &ct->proto.tcp.state);
 348         read_unlock_bh(&tcp_lock);
 349
 350         NFA_NEST_END(skb, nest_parms);
 351
 352         return 0;
 353
 354 nfattr_failure:
 355         read_unlock_bh(&tcp_lock);
 356         return -1;
 357 }
 358
 359 static const size_t cta_min_tcp[CTA_PROTOINFO_TCP_MAX] = {
 360         [CTA_PROTOINFO_TCP_STATE-1]     = sizeof(u_int8_t),
 361 };
 362
 363 static int nfattr_to_tcp(struct nfattr *cda[], struct ip_conntrack *ct)
 364 {
 365         struct nfattr *attr = cda[CTA_PROTOINFO_TCP-1];
 366         struct nfattr *tb[CTA_PROTOINFO_TCP_MAX];
 367
 368         /* updates could not contain anything about the private
 369          * protocol info, in that case skip the parsing */
 370         if (!attr)
 371                 return 0;
 372
 373         nfattr_parse_nested(tb, CTA_PROTOINFO_TCP_MAX, attr);
 374
 375         if (nfattr_bad_size(tb, CTA_PROTOINFO_TCP_MAX, cta_min_tcp))
 376                 return -EINVAL;
 377
 378         if (!tb[CTA_PROTOINFO_TCP_STATE-1])
 379                 return -EINVAL;
 380
 381         write_lock_bh(&tcp_lock);
 382         ct->proto.tcp.state =
 383                 *(u_int8_t *)NFA_DATA(tb[CTA_PROTOINFO_TCP_STATE-1]);
 384         write_unlock_bh(&tcp_lock);
 385
 386         return 0;
 387 }
 388 #endif
 389
 390 static unsigned int get_conntrack_index(const struct tcphdr *tcph)
 391 {
 392         if (tcph->rst) return TCP_RST_SET;
 393         else if (tcph->syn) return (tcph->ack ? TCP_SYNACK_SET : TCP_SYN_SET);
 394         else if (tcph->fin) return TCP_FIN_SET;
 395         else if (tcph->ack) return TCP_ACK_SET;
 396         else return TCP_NONE_SET;
 397 }
 398
 399 /* TCP connection tracking based on 'Real Stateful TCP Packet Filtering
 400    in IP Filter' by Guido van Rooij.
 401
 402    http://www.nluug.nl/events/sane2000/papers.html
 403    http://www.iae.nl/users/guido/papers/tcp_filtering.ps.gz
 404
 405    The boundaries and the conditions are changed according to RFC793:
 406    the packet must intersect the window (i.e. segments may be
 407    after the right or before the left edge) and thus receivers may ACK
 408    segments after the right edge of the window.
 409
 410         td_maxend = max(sack + max(win,1)) seen in reply packets
 411         td_maxwin = max(max(win, 1)) + (sack - ack) seen in sent packets
 412         td_maxwin += seq + len - sender.td_maxend
 413                         if seq + len > sender.td_maxend
 414         td_end    = max(seq + len) seen in sent packets
 415
 416    I.   Upper bound for valid data:     seq <= sender.td_maxend
 417    II.  Lower bound for valid data:     seq + len >= sender.td_end - receiver.td_maxwin
 418    III. Upper bound for valid ack:      sack <= receiver.td_end
 419    IV.  Lower bound for valid ack:      ack >= receiver.td_end - MAXACKWINDOW
 420
 421    where sack is the highest right edge of sack block found in the packet.
 422
 423    The upper bound limit for a valid ack is not ignored -
 424    we doesn't have to deal with fragments.
 425 */
 426
 427 static inline __u32 segment_seq_plus_len(__u32 seq,
 428                                          size_t len,
 429                                          struct iphdr *iph,
 430                                          struct tcphdr *tcph)
 431 {
 432         return (seq + len - (iph->ihl + tcph->doff)*4
 433                 + (tcph->syn ? 1 : 0) + (tcph->fin ? 1 : 0));
 434 }
 435
 436 /* Fixme: what about big packets? */
 437 #define MAXACKWINCONST                  66000
 438 #define MAXACKWINDOW(sender)                                            \
 439         ((sender)->td_maxwin > MAXACKWINCONST ? (sender)->td_maxwin     \
 440                                               : MAXACKWINCONST)
 441
 442 /*
 443  * Simplified tcp_parse_options routine from tcp_input.c
 444  */
 445 static void tcp_options(const struct sk_buff *skb,
 446                         struct iphdr *iph,
 447                         struct tcphdr *tcph,
 448                         struct ip_ct_tcp_state *state)
 449 {
 450         unsigned char buff[(15 * 4) - sizeof(struct tcphdr)];
 451         unsigned char *ptr;
 452         int length = (tcph->doff*4) - sizeof(struct tcphdr);
 453
 454         if (!length)
 455                 return;
 456
 457         ptr = skb_header_pointer(skb,
 458                                  (iph->ihl * 4) + sizeof(struct tcphdr),
 459                                  length, buff);
 460         BUG_ON(ptr == NULL);
 461
 462         state->td_scale =
 463         state->flags = 0;
 464
 465         while (length > 0) {
 466                 int opcode=*ptr++;
 467                 int opsize;
 468
 469                 switch (opcode) {
 470                 case TCPOPT_EOL:
 471                         return;
 472                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
 473                         length--;
 474                         continue;
 475                 default:
 476                         opsize=*ptr++;
 477                         if (opsize < 2) /* "silly options" */
 478                                 return;
 479                         if (opsize > length)
 480                                 break;  /* don't parse partial options */
 481
 482                         if (opcode == TCPOPT_SACK_PERM
 483                             && opsize == TCPOLEN_SACK_PERM)
 484                                 state->flags |= IP_CT_TCP_FLAG_SACK_PERM;
 485                         else if (opcode == TCPOPT_WINDOW
 486                                  && opsize == TCPOLEN_WINDOW) {
 487                                 state->td_scale = *(u_int8_t *)ptr;
 488
 489                                 if (state->td_scale > 14) {
 490                                         /* See RFC1323 */
 491                                         state->td_scale = 14;
 492                                 }
 493                                 state->flags |=
 494                                         IP_CT_TCP_FLAG_WINDOW_SCALE;
 495                         }
 496                         ptr += opsize - 2;
 497                         length -= opsize;
 498                 }
 499         }
 500 }
 501
 502 static void tcp_sack(const struct sk_buff *skb,
 503                      struct iphdr *iph,
 504                      struct tcphdr *tcph,
 505                      __u32 *sack)
 506 {
 507         unsigned char buff[(15 * 4) - sizeof(struct tcphdr)];
 508         unsigned char *ptr;
 509         int length = (tcph->doff*4) - sizeof(struct tcphdr);
 510         __u32 tmp;
 511
 512         if (!length)
 513                 return;
 514
 515         ptr = skb_header_pointer(skb,
 516                                  (iph->ihl * 4) + sizeof(struct tcphdr),
 517                                  length, buff);
 518         BUG_ON(ptr == NULL);
 519
 520         /* Fast path for timestamp-only option */
 521         if (length == TCPOLEN_TSTAMP_ALIGNED*4
 522             && *(__u32 *)ptr ==
 523                 __constant_ntohl((TCPOPT_NOP << 24)
 524                                  | (TCPOPT_NOP << 16)
 525                                  | (TCPOPT_TIMESTAMP << 8)
 526                                  | TCPOLEN_TIMESTAMP))
 527                 return;
 528
 529         while (length > 0) {
 530                 int opcode=*ptr++;
 531                 int opsize, i;
 532
 533                 switch (opcode) {
 534                 case TCPOPT_EOL:
 535                         return;
 536                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
 537                         length--;
 538                         continue;
 539                 default:
 540                         opsize=*ptr++;
 541                         if (opsize < 2) /* "silly options" */
 542                                 return;
 543                         if (opsize > length)
 544                                 break;  /* don't parse partial options */
 545
 546                         if (opcode == TCPOPT_SACK
 547                             && opsize >= (TCPOLEN_SACK_BASE
 548                                           + TCPOLEN_SACK_PERBLOCK)
 549                             && !((opsize - TCPOLEN_SACK_BASE)
 550                                  % TCPOLEN_SACK_PERBLOCK)) {
 551                                 for (i = 0;
 552                                      i < (opsize - TCPOLEN_SACK_BASE);
 553                                      i += TCPOLEN_SACK_PERBLOCK) {
 554                                         tmp = ntohl(*((u_int32_t *)(ptr+i)+1));
 555
 556                                         if (after(tmp, *sack))
 557                                                 *sack = tmp;
 558                                 }
 559                                 return;
 560                         }
 561                         ptr += opsize - 2;
 562                         length -= opsize;
 563                 }
 564         }
 565 }
 566
 567 static int tcp_in_window(struct ip_ct_tcp *state,
 568                          enum ip_conntrack_dir dir,
 569                          unsigned int index,
 570                          const struct sk_buff *skb,
 571                          struct iphdr *iph,
 572                          struct tcphdr *tcph)
 573 {
 574         struct ip_ct_tcp_state *sender = &state->seen[dir];
 575         struct ip_ct_tcp_state *receiver = &state->seen[!dir];
 576         __u32 seq, ack, sack, end, win, swin;
 577         int res;
 578
 579         /*
 580          * Get the required data from the packet.
 581          */
 582         seq = ntohl(tcph->seq);
 583         ack = sack = ntohl(tcph->ack_seq);
 584         win = ntohs(tcph->window);
 585         end = segment_seq_plus_len(seq, skb->len, iph, tcph);
 586
 587         if (receiver->flags & IP_CT_TCP_FLAG_SACK_PERM)
 588                 tcp_sack(skb, iph, tcph, &sack);
 589
 590         DEBUGP("tcp_in_window: START\n");
 591         DEBUGP("tcp_in_window: src=%u.%u.%u.%u:%hu dst=%u.%u.%u.%u:%hu "
 592                "seq=%u ack=%u sack=%u win=%u end=%u\n",
 593                 NIPQUAD(iph->saddr), ntohs(tcph->source),
 594                 NIPQUAD(iph->daddr), ntohs(tcph->dest),
 595                 seq, ack, sack, win, end);
 596         DEBUGP("tcp_in_window: sender end=%u maxend=%u maxwin=%u scale=%i "
 597                "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
 598                 sender->td_end, sender->td_maxend, sender->td_maxwin,
 599                 sender->td_scale,
 600                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
 601                 receiver->td_scale);
 602
 603         if (sender->td_end == 0) {
 604                 /*
 605                  * Initialize sender data.
 606                  */
 607                 if (tcph->syn && tcph->ack) {
 608                         /*
 609                          * Outgoing SYN-ACK in reply to a SYN.
 610                          */
 611                         sender->td_end =
 612                         sender->td_maxend = end;
 613                         sender->td_maxwin = (win == 0 ? 1 : win);
 614
 615                         tcp_options(skb, iph, tcph, sender);
 616                         /*
 617                          * RFC 1323:
 618                          * Both sides must send the Window Scale option
 619                          * to enable window scaling in either direction.
 620                          */
 621                         if (!(sender->flags & IP_CT_TCP_FLAG_WINDOW_SCALE
 622                               && receiver->flags & IP_CT_TCP_FLAG_WINDOW_SCALE))
 623                                 sender->td_scale =
 624                                 receiver->td_scale = 0;
 625                 } else {
 626                         /*
 627                          * We are in the middle of a connection,
 628                          * its history is lost for us.
 629                          * Let's try to use the data from the packet.
 630                          */
 631                         sender->td_end = end;
 632                         sender->td_maxwin = (win == 0 ? 1 : win);
 633                         sender->td_maxend = end + sender->td_maxwin;
 634                 }
 635         } else if (((state->state == TCP_CONNTRACK_SYN_SENT
 636                      && dir == IP_CT_DIR_ORIGINAL)
 637                     || (state->state == TCP_CONNTRACK_SYN_RECV
 638                         && dir == IP_CT_DIR_REPLY))
 639                     && after(end, sender->td_end)) {
 640                 /*
 641                  * RFC 793: "if a TCP is reinitialized ... then it need
 642                  * not wait at all; it must only be sure to use sequence
 643                  * numbers larger than those recently used."
 644                  */
 645                 sender->td_end =
 646                 sender->td_maxend = end;
 647                 sender->td_maxwin = (win == 0 ? 1 : win);
 648
 649                 tcp_options(skb, iph, tcph, sender);
 650         }
 651
 652         if (!(tcph->ack)) {
 653                 /*
 654                  * If there is no ACK, just pretend it was set and OK.
 655                  */
 656                 ack = sack = receiver->td_end;
 657         } else if (((tcp_flag_word(tcph) & (TCP_FLAG_ACK|TCP_FLAG_RST)) ==
 658                     (TCP_FLAG_ACK|TCP_FLAG_RST))
 659                    && (ack == 0)) {
 660                 /*
 661                  * Broken TCP stacks, that set ACK in RST packets as well
 662                  * with zero ack value.
 663                  */
 664                 ack = sack = receiver->td_end;
 665         }
 666
 667         if (seq == end
 668             && (!tcph->rst
 669                 || (seq == 0 && state->state == TCP_CONNTRACK_SYN_SENT)))
 670                 /*
 671                  * Packets contains no data: we assume it is valid
 672                  * and check the ack value only.
 673                  * However RST segments are always validated by their
 674                  * SEQ number, except when seq == 0 (reset sent answering
 675                  * SYN.
 676                  */
 677                 seq = end = sender->td_end;
 678
 679         DEBUGP("tcp_in_window: src=%u.%u.%u.%u:%hu dst=%u.%u.%u.%u:%hu "
 680                "seq=%u ack=%u sack =%u win=%u end=%u\n",
 681                 NIPQUAD(iph->saddr), ntohs(tcph->source),
 682                 NIPQUAD(iph->daddr), ntohs(tcph->dest),
 683                 seq, ack, sack, win, end);
 684         DEBUGP("tcp_in_window: sender end=%u maxend=%u maxwin=%u scale=%i "
 685                "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
 686                 sender->td_end, sender->td_maxend, sender->td_maxwin,
 687                 sender->td_scale,
 688                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
 689                 receiver->td_scale);
 690
 691         DEBUGP("tcp_in_window: I=%i II=%i III=%i IV=%i\n",
 692                 before(seq, sender->td_maxend + 1),
 693                 after(end, sender->td_end - receiver->td_maxwin - 1),
 694                 before(sack, receiver->td_end + 1),
 695                 after(ack, receiver->td_end - MAXACKWINDOW(sender)));
 696
 697         if (sender->loose || receiver->loose ||
 698             (before(seq, sender->td_maxend + 1) &&
 699              after(end, sender->td_end - receiver->td_maxwin - 1) &&
 700              before(sack, receiver->td_end + 1) &&
 701              after(ack, receiver->td_end - MAXACKWINDOW(sender)))) {
 702                 /*
 703                  * Take into account window scaling (RFC 1323).
 704                  */
 705                 if (!tcph->syn)
 706                         win <<= sender->td_scale;
 707
 708                 /*
 709                  * Update sender data.
 710                  */
 711                 swin = win + (sack - ack);
 712                 if (sender->td_maxwin < swin)
 713                         sender->td_maxwin = swin;
 714                 if (after(end, sender->td_end))
 715                         sender->td_end = end;
 716                 /*
 717                  * Update receiver data.
 718                  */
 719                 if (after(end, sender->td_maxend))
 720                         receiver->td_maxwin += end - sender->td_maxend;
 721                 if (after(sack + win, receiver->td_maxend - 1)) {
 722                         receiver->td_maxend = sack + win;
 723                         if (win == 0)
 724                                 receiver->td_maxend++;
 725                 }
 726
 727                 /*
 728                  * Check retransmissions.
 729                  */
 730                 if (index == TCP_ACK_SET) {
 731                         if (state->last_dir == dir
 732                             && state->last_seq == seq
 733                             && state->last_ack == ack
 734                             && state->last_end == end)
 735                                 state->retrans++;
 736                         else {
 737                                 state->last_dir = dir;
 738                                 state->last_seq = seq;
 739                                 state->last_ack = ack;
 740                                 state->last_end = end;
 741                                 state->retrans = 0;
 742                         }
 743                 }
 744                 /*
 745                  * Close the window of disabled window tracking :-)
 746                  */
 747                 if (sender->loose)
 748                         sender->loose--;
 749
 750                 res = 1;
 751         } else {
 752                 if (LOG_INVALID(IPPROTO_TCP))
 753                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 754                         "ip_ct_tcp: %s ",
 755                         before(seq, sender->td_maxend + 1) ?
 756                         after(end, sender->td_end - receiver->td_maxwin - 1) ?
 757                         before(sack, receiver->td_end + 1) ?
 758                         after(ack, receiver->td_end - MAXACKWINDOW(sender)) ? "BUG"
 759                         : "ACK is under the lower bound (possible overly delayed ACK)"
 760                         : "ACK is over the upper bound (ACKed data not seen yet)"
 761                         : "SEQ is under the lower bound (already ACKed data retransmitted)"
 762                         : "SEQ is over the upper bound (over the window of the receiver)");
 763
 764                 res = ip_ct_tcp_be_liberal;
 765         }
 766
 767         DEBUGP("tcp_in_window: res=%i sender end=%u maxend=%u maxwin=%u "
 768                "receiver end=%u maxend=%u maxwin=%u\n",
 769                 res, sender->td_end, sender->td_maxend, sender->td_maxwin,
 770                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin);
 771
 772         return res;
 773 }
 774
 775 #ifdef CONFIG_IP_NF_NAT_NEEDED
 776 /* Update sender->td_end after NAT successfully mangled the packet */
 777 void ip_conntrack_tcp_update(struct sk_buff *skb,
 778                              struct ip_conntrack *conntrack,
 779                              enum ip_conntrack_dir dir)
 780 {
 781         struct iphdr *iph = skb->nh.iph;
 782         struct tcphdr *tcph = (void *)skb->nh.iph + skb->nh.iph->ihl*4;
 783         __u32 end;
 784 #ifdef DEBUGP_VARS
 785         struct ip_ct_tcp_state *sender = &conntrack->proto.tcp.seen[dir];
 786         struct ip_ct_tcp_state *receiver = &conntrack->proto.tcp.seen[!dir];
 787 #endif
 788
 789         end = segment_seq_plus_len(ntohl(tcph->seq), skb->len, iph, tcph);
 790
 791         write_lock_bh(&tcp_lock);
 792         /*
 793          * We have to worry for the ack in the reply packet only...
 794          */
 795         if (after(end, conntrack->proto.tcp.seen[dir].td_end))
 796                 conntrack->proto.tcp.seen[dir].td_end = end;
 797         conntrack->proto.tcp.last_end = end;
 798         write_unlock_bh(&tcp_lock);
 799         DEBUGP("tcp_update: sender end=%u maxend=%u maxwin=%u scale=%i "
 800                "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
 801                 sender->td_end, sender->td_maxend, sender->td_maxwin,
 802                 sender->td_scale,
 803                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
 804                 receiver->td_scale);
 805 }
 806
 807 #endif
 808
 809 #define TH_FIN  0x01
 810 #define TH_SYN  0x02
 811 #define TH_RST  0x04
 812 #define TH_PUSH 0x08
 813 #define TH_ACK  0x10
 814 #define TH_URG  0x20
 815 #define TH_ECE  0x40
 816 #define TH_CWR  0x80
 817
 818 /* table of valid flag combinations - ECE and CWR are always valid */
 819 static const u8 tcp_valid_flags[(TH_FIN|TH_SYN|TH_RST|TH_PUSH|TH_ACK|TH_URG) + 1] =
 820 {
 821         [TH_SYN]                        = 1,
 822         [TH_SYN|TH_ACK]                 = 1,
 823         [TH_SYN|TH_PUSH]                = 1,
 824         [TH_SYN|TH_ACK|TH_PUSH]         = 1,
 825         [TH_RST]                        = 1,
 826         [TH_RST|TH_ACK]                 = 1,
 827         [TH_RST|TH_ACK|TH_PUSH]         = 1,
 828         [TH_FIN|TH_ACK]                 = 1,
 829         [TH_ACK]                        = 1,
 830         [TH_ACK|TH_PUSH]                = 1,
 831         [TH_ACK|TH_URG]                 = 1,
 832         [TH_ACK|TH_URG|TH_PUSH]         = 1,
 833         [TH_FIN|TH_ACK|TH_PUSH]         = 1,
 834         [TH_FIN|TH_ACK|TH_URG]          = 1,
 835         [TH_FIN|TH_ACK|TH_URG|TH_PUSH]  = 1,
 836 };
 837
 838 /* Protect conntrack agaist broken packets. Code taken from ipt_unclean.c.  */
 839 static int tcp_error(struct sk_buff *skb,
 840                      enum ip_conntrack_info *ctinfo,
 841                      unsigned int hooknum)
 842 {
 843         struct iphdr *iph = skb->nh.iph;
 844         struct tcphdr _tcph, *th;
 845         unsigned int tcplen = skb->len - iph->ihl * 4;
 846         u_int8_t tcpflags;
 847
 848         /* Smaller that minimal TCP header? */
 849         th = skb_header_pointer(skb, iph->ihl * 4,
 850                                 sizeof(_tcph), &_tcph);
 851         if (th == NULL) {
 852                 if (LOG_INVALID(IPPROTO_TCP))
 853                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 854                                 "ip_ct_tcp: short packet ");
 855                 return -NF_ACCEPT;
 856         }
 857
 858         /* Not whole TCP header or malformed packet */
 859         if (th->doff*4 < sizeof(struct tcphdr) || tcplen < th->doff*4) {
 860                 if (LOG_INVALID(IPPROTO_TCP))
 861                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 862                                 "ip_ct_tcp: truncated/malformed packet ");
 863                 return -NF_ACCEPT;
 864         }
 865
 866         /* Checksum invalid? Ignore.
 867          * We skip checking packets on the outgoing path
 868          * because the semantic of CHECKSUM_HW is different there
 869          * and moreover root might send raw packets.
 870          */
 871         /* FIXME: Source route IP option packets --RR */
 872         if (ip_conntrack_checksum && hooknum == NF_IP_PRE_ROUTING &&
 873             nf_ip_checksum(skb, hooknum, iph->ihl * 4, IPPROTO_TCP)) {
 874                 if (LOG_INVALID(IPPROTO_TCP))
 875                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 876                                   "ip_ct_tcp: bad TCP checksum ");
 877                 return -NF_ACCEPT;
 878         }
 879
 880         /* Check TCP flags. */
 881         tcpflags = (((u_int8_t *)th)[13] & ~(TH_ECE|TH_CWR));
 882         if (!tcp_valid_flags[tcpflags]) {
 883                 if (LOG_INVALID(IPPROTO_TCP))
 884                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 885                                   "ip_ct_tcp: invalid TCP flag combination ");
 886                 return -NF_ACCEPT;
 887         }
 888
 889         return NF_ACCEPT;
 890 }
 891
 892 /* Returns verdict for packet, or -1 for invalid. */
 893 static int tcp_packet(struct ip_conntrack *conntrack,
 894                       const struct sk_buff *skb,
 895                       enum ip_conntrack_info ctinfo)
 896 {
 897         enum tcp_conntrack new_state, old_state;
 898         enum ip_conntrack_dir dir;
 899         struct iphdr *iph = skb->nh.iph;
 900         struct tcphdr *th, _tcph;
 901         unsigned long timeout;
 902         unsigned int index;
 903
 904         th = skb_header_pointer(skb, iph->ihl * 4,
 905                                 sizeof(_tcph), &_tcph);
 906         BUG_ON(th == NULL);
 907
 908         write_lock_bh(&tcp_lock);
 909         old_state = conntrack->proto.tcp.state;
 910         dir = CTINFO2DIR(ctinfo);
 911         index = get_conntrack_index(th);
 912         new_state = tcp_conntracks[dir][index][old_state];
 913
 914         switch (new_state) {
 915         case TCP_CONNTRACK_IGNORE:
 916                 /* Ignored packets:
 917                  *
 918                  * a) SYN in ORIGINAL
 919                  * b) SYN/ACK in REPLY
 920                  * c) ACK in reply direction after initial SYN in original.
 921                  */
 922                 if (index == TCP_SYNACK_SET
 923                     && conntrack->proto.tcp.last_index == TCP_SYN_SET
 924                     && conntrack->proto.tcp.last_dir != dir
 925                     && ntohl(th->ack_seq) ==
 926                              conntrack->proto.tcp.last_end) {
 927                         /* This SYN/ACK acknowledges a SYN that we earlier
 928                          * ignored as invalid. This means that the client and
 929                          * the server are both in sync, while the firewall is
 930                          * not. We kill this session and block the SYN/ACK so
 931                          * that the client cannot but retransmit its SYN and
 932                          * thus initiate a clean new session.
 933                          */
 934                         write_unlock_bh(&tcp_lock);
 935                         if (LOG_INVALID(IPPROTO_TCP))
 936                                 nf_log_packet(PF_INET, 0, skb, NULL, NULL,
 937                                               NULL, "ip_ct_tcp: "
 938                                               "killing out of sync session ");
 939                         if (del_timer(&conntrack->timeout))
 940                                 conntrack->timeout.function((unsigned long)
 941                                                             conntrack);
 942                         return -NF_DROP;
 943                 }
 944                 conntrack->proto.tcp.last_index = index;
 945                 conntrack->proto.tcp.last_dir = dir;
 946                 conntrack->proto.tcp.last_seq = ntohl(th->seq);
 947                 conntrack->proto.tcp.last_end =
 948                     segment_seq_plus_len(ntohl(th->seq), skb->len, iph, th);
 949
 950                 write_unlock_bh(&tcp_lock);
 951                 if (LOG_INVALID(IPPROTO_TCP))
 952                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 953                                   "ip_ct_tcp: invalid packet ignored ");
 954                 return NF_ACCEPT;
 955         case TCP_CONNTRACK_MAX:
 956                 /* Invalid packet */
 957                 DEBUGP("ip_ct_tcp: Invalid dir=%i index=%u ostate=%u\n",
 958                        dir, get_conntrack_index(th),
 959                        old_state);
 960                 write_unlock_bh(&tcp_lock);
 961                 if (LOG_INVALID(IPPROTO_TCP))
 962                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 963                                   "ip_ct_tcp: invalid state ");
 964                 return -NF_ACCEPT;
 965         case TCP_CONNTRACK_SYN_SENT:
 966                 if (old_state < TCP_CONNTRACK_TIME_WAIT)
 967                         break;
 968                 if ((conntrack->proto.tcp.seen[dir].flags &
 969                          IP_CT_TCP_FLAG_CLOSE_INIT)
 970                     || after(ntohl(th->seq),
 971                              conntrack->proto.tcp.seen[dir].td_end)) {
 972                         /* Attempt to reopen a closed connection.
 973                         * Delete this connection and look up again. */
 974                         write_unlock_bh(&tcp_lock);
 975                         if (del_timer(&conntrack->timeout))
 976                                 conntrack->timeout.function((unsigned long)
 977                                                             conntrack);
 978                         return -NF_REPEAT;
 979                 } else {
 980                         write_unlock_bh(&tcp_lock);
 981                         if (LOG_INVALID(IPPROTO_TCP))
 982                                 nf_log_packet(PF_INET, 0, skb, NULL, NULL,
 983                                               NULL, "ip_ct_tcp: invalid SYN");
 984                         return -NF_ACCEPT;
 985                 }
 986         case TCP_CONNTRACK_CLOSE:
 987                 if (index == TCP_RST_SET
 988                     && ((test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)
 989                          && conntrack->proto.tcp.last_index == TCP_SYN_SET)
 990                         || (!test_bit(IPS_ASSURED_BIT, &conntrack->status)
 991                             && conntrack->proto.tcp.last_index == TCP_ACK_SET))
 992                     && ntohl(th->ack_seq) == conntrack->proto.tcp.last_end) {
 993                         /* RST sent to invalid SYN or ACK we had let through
 994                          * at a) and c) above:
 995                          *
 996                          * a) SYN was in window then
 997                          * c) we hold a half-open connection.
 998                          *
 999                          * Delete our connection entry.
1000                          * We skip window checking, because packet might ACK
1001                          * segments we ignored. */
1002                         goto in_window;
1003                 }
1004                 /* Just fall through */
1005         default:
1006                 /* Keep compilers happy. */
1007                 break;
1008         }
1009
1010         if (!tcp_in_window(&conntrack->proto.tcp, dir, index,
1011                            skb, iph, th)) {
1012                 write_unlock_bh(&tcp_lock);
1013                 return -NF_ACCEPT;
1014         }
1015     in_window:
1016         /* From now on we have got in-window packets */
1017         conntrack->proto.tcp.last_index = index;
1018
1019         DEBUGP("tcp_conntracks: src=%u.%u.%u.%u:%hu dst=%u.%u.%u.%u:%hu "
1020                "syn=%i ack=%i fin=%i rst=%i old=%i new=%i\n",
1021                 NIPQUAD(iph->saddr), ntohs(th->source),
1022                 NIPQUAD(iph->daddr), ntohs(th->dest),
1023                 (th->syn ? 1 : 0), (th->ack ? 1 : 0),
1024                 (th->fin ? 1 : 0), (th->rst ? 1 : 0),
1025                 old_state, new_state);
1026
1027         conntrack->proto.tcp.state = new_state;
1028         if (old_state != new_state
1029             && (new_state == TCP_CONNTRACK_FIN_WAIT
1030                 || new_state == TCP_CONNTRACK_CLOSE))
1031                 conntrack->proto.tcp.seen[dir].flags |= IP_CT_TCP_FLAG_CLOSE_INIT;
1032         timeout = conntrack->proto.tcp.retrans >= ip_ct_tcp_max_retrans
1033                   && *tcp_timeouts[new_state] > ip_ct_tcp_timeout_max_retrans
1034                   ? ip_ct_tcp_timeout_max_retrans : *tcp_timeouts[new_state];
1035         write_unlock_bh(&tcp_lock);
1036
1037         ip_conntrack_event_cache(IPCT_PROTOINFO_VOLATILE, skb);
1038         if (new_state != old_state)
1039                 ip_conntrack_event_cache(IPCT_PROTOINFO, skb);
1040
1041         if (!test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)) {
1042                 /* If only reply is a RST, we can consider ourselves not to
1043                    have an established connection: this is a fairly common
1044                    problem case, so we can delete the conntrack
1045                    immediately.  --RR */
1046                 if (th->rst) {
1047                         if (del_timer(&conntrack->timeout))
1048                                 conntrack->timeout.function((unsigned long)
1049                                                             conntrack);
1050                         return NF_ACCEPT;
1051                 }
1052         } else if (!test_bit(IPS_ASSURED_BIT, &conntrack->status)
1053                    && (old_state == TCP_CONNTRACK_SYN_RECV
1054                        || old_state == TCP_CONNTRACK_ESTABLISHED)
1055                    && new_state == TCP_CONNTRACK_ESTABLISHED) {
1056                 /* Set ASSURED if we see see valid ack in ESTABLISHED
1057                    after SYN_RECV or a valid answer for a picked up
1058                    connection. */
1059                 set_bit(IPS_ASSURED_BIT, &conntrack->status);
1060                 ip_conntrack_event_cache(IPCT_STATUS, skb);
1061         }
1062         ip_ct_refresh_acct(conntrack, ctinfo, skb, timeout);
1063
1064         return NF_ACCEPT;
1065 }
1066
1067 /* Called when a new connection for this protocol found. */
1068 static int tcp_new(struct ip_conntrack *conntrack,
1069                    const struct sk_buff *skb)
1070 {
1071         enum tcp_conntrack new_state;
1072         struct iphdr *iph = skb->nh.iph;
1073         struct tcphdr *th, _tcph;
1074 #ifdef DEBUGP_VARS
1075         struct ip_ct_tcp_state *sender = &conntrack->proto.tcp.seen[0];
1076         struct ip_ct_tcp_state *receiver = &conntrack->proto.tcp.seen[1];
1077 #endif
1078
1079         th = skb_header_pointer(skb, iph->ihl * 4,
1080                                 sizeof(_tcph), &_tcph);
1081         BUG_ON(th == NULL);
1082
1083         /* Don't need lock here: this conntrack not in circulation yet */
1084         new_state
1085                 = tcp_conntracks[0][get_conntrack_index(th)]
1086                 [TCP_CONNTRACK_NONE];
1087
1088         /* Invalid: delete conntrack */
1089         if (new_state >= TCP_CONNTRACK_MAX) {
1090                 DEBUGP("ip_ct_tcp: invalid new deleting.\n");
1091                 return 0;
1092         }
1093
1094         if (new_state == TCP_CONNTRACK_SYN_SENT) {
1095                 /* SYN packet */
1096                 conntrack->proto.tcp.seen[0].td_end =
1097                         segment_seq_plus_len(ntohl(th->seq), skb->len,
1098                                              iph, th);
1099                 conntrack->proto.tcp.seen[0].td_maxwin = ntohs(th->window);
1100                 if (conntrack->proto.tcp.seen[0].td_maxwin == 0)
1101                         conntrack->proto.tcp.seen[0].td_maxwin = 1;
1102                 conntrack->proto.tcp.seen[0].td_maxend =
1103                         conntrack->proto.tcp.seen[0].td_end;
1104
1105                 tcp_options(skb, iph, th, &conntrack->proto.tcp.seen[0]);
1106                 conntrack->proto.tcp.seen[1].flags = 0;
1107                 conntrack->proto.tcp.seen[0].loose =
1108                 conntrack->proto.tcp.seen[1].loose = 0;
1109         } else if (ip_ct_tcp_loose == 0) {
1110                 /* Don't try to pick up connections. */
1111                 return 0;
1112         } else {
1113                 /*
1114                  * We are in the middle of a connection,
1115                  * its history is lost for us.
1116                  * Let's try to use the data from the packet.
1117                  */
1118                 conntrack->proto.tcp.seen[0].td_end =
1119                         segment_seq_plus_len(ntohl(th->seq), skb->len,
1120                                              iph, th);
1121                 conntrack->proto.tcp.seen[0].td_maxwin = ntohs(th->window);
1122                 if (conntrack->proto.tcp.seen[0].td_maxwin == 0)
1123                         conntrack->proto.tcp.seen[0].td_maxwin = 1;
1124                 conntrack->proto.tcp.seen[0].td_maxend =
1125                         conntrack->proto.tcp.seen[0].td_end +
1126                         conntrack->proto.tcp.seen[0].td_maxwin;
1127                 conntrack->proto.tcp.seen[0].td_scale = 0;
1128
1129                 /* We assume SACK. Should we assume window scaling too? */
1130                 conntrack->proto.tcp.seen[0].flags =
1131                 conntrack->proto.tcp.seen[1].flags = IP_CT_TCP_FLAG_SACK_PERM;
1132                 conntrack->proto.tcp.seen[0].loose =
1133                 conntrack->proto.tcp.seen[1].loose = ip_ct_tcp_loose;
1134         }
1135
1136         conntrack->proto.tcp.seen[1].td_end = 0;
1137         conntrack->proto.tcp.seen[1].td_maxend = 0;
1138         conntrack->proto.tcp.seen[1].td_maxwin = 1;
1139         conntrack->proto.tcp.seen[1].td_scale = 0;
1140
1141         /* tcp_packet will set them */
1142         conntrack->proto.tcp.state = TCP_CONNTRACK_NONE;
1143         conntrack->proto.tcp.last_index = TCP_NONE_SET;
1144
1145         DEBUGP("tcp_new: sender end=%u maxend=%u maxwin=%u scale=%i "
1146                "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
1147                 sender->td_end, sender->td_maxend, sender->td_maxwin,
1148                 sender->td_scale,
1149                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
1150                 receiver->td_scale);
1151         return 1;
1152 }
1153
1154 struct ip_conntrack_protocol ip_conntrack_protocol_tcp =
1155 {
1156         .proto                  = IPPROTO_TCP,
1157         .name                   = "tcp",
1158         .pkt_to_tuple           = tcp_pkt_to_tuple,
1159         .invert_tuple           = tcp_invert_tuple,
1160         .print_tuple            = tcp_print_tuple,
1161         .print_conntrack        = tcp_print_conntrack,
1162         .packet                 = tcp_packet,
1163         .new                    = tcp_new,
1164         .error                  = tcp_error,
1165 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
1166     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
1167         .to_nfattr              = tcp_to_nfattr,
1168         .from_nfattr            = nfattr_to_tcp,
1169         .tuple_to_nfattr        = ip_ct_port_tuple_to_nfattr,
1170         .nfattr_to_tuple        = ip_ct_port_nfattr_to_tuple,
1171 #endif
1172 };