sys/netgraph/ng_tcpmss.c

   1 /*-
   2  * ng_tcpmss.c
   3  *
   4  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   5  *
   6  * Copyright (c) 2004, Alexey Popov <lollypop@flexuser.ru>
   7  * All rights reserved.
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  * 1. Redistributions of source code must retain the above copyright
  13  *    notice unmodified, this list of conditions, and the following
  14  *    disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  * This software includes fragments of the following programs:
  32  *      tcpmssd         Ruslan Ermilov <ru@FreeBSD.org>
  33  *
  34  * $FreeBSD$
  35  */
  36
  37 /*
  38  * This node is netgraph tool for workaround of PMTUD problem. It acts
  39  * like filter for IP packets. If configured, it reduces MSS of TCP SYN
  40  * packets.
  41  *
  42  * Configuration can be done by sending NGM_TCPMSS_CONFIG message. The
  43  * message sets filter for incoming packets on hook 'inHook'. Packet's
  44  * TCP MSS field is lowered to 'maxMSS' parameter and resulting packet
  45  * is sent to 'outHook'.
  46  *
  47  * XXX: statistics are updated not atomically, so they may broke on SMP.
  48  */
  49
  50 #include <sys/param.h>
  51 #include <sys/systm.h>
  52 #include <sys/endian.h>
  53 #include <sys/errno.h>
  54 #include <sys/kernel.h>
  55 #include <sys/malloc.h>
  56 #include <sys/mbuf.h>
  57
  58 #include <netinet/in.h>
  59 #include <netinet/in_systm.h>
  60 #include <netinet/ip.h>
  61 #include <netinet/tcp.h>
  62
  63 #include <netgraph/ng_message.h>
  64 #include <netgraph/netgraph.h>
  65 #include <netgraph/ng_parse.h>
  66 #include <netgraph/ng_tcpmss.h>
  67
  68 /* Per hook info. */
  69 typedef struct {
  70         hook_p                          outHook;
  71         struct ng_tcpmss_hookstat       stats;
  72 } *hpriv_p;
  73
  74 /* Netgraph methods. */
  75 static ng_constructor_t ng_tcpmss_constructor;
  76 static ng_rcvmsg_t      ng_tcpmss_rcvmsg;
  77 static ng_newhook_t     ng_tcpmss_newhook;
  78 static ng_rcvdata_t     ng_tcpmss_rcvdata;
  79 static ng_disconnect_t  ng_tcpmss_disconnect;
  80
  81 static int correct_mss(struct tcphdr *, int, uint16_t, int);
  82
  83 /* Parse type for struct ng_tcpmss_hookstat. */
  84 static const struct ng_parse_struct_field ng_tcpmss_hookstat_type_fields[]
  85         = NG_TCPMSS_HOOKSTAT_INFO;
  86 static const struct ng_parse_type ng_tcpmss_hookstat_type = {
  87         &ng_parse_struct_type,
  88         &ng_tcpmss_hookstat_type_fields
  89 };
  90
  91 /* Parse type for struct ng_tcpmss_config. */
  92 static const struct ng_parse_struct_field ng_tcpmss_config_type_fields[]
  93         = NG_TCPMSS_CONFIG_INFO;
  94 static const struct ng_parse_type ng_tcpmss_config_type = {
  95         &ng_parse_struct_type,
  96         ng_tcpmss_config_type_fields
  97 };
  98
  99 /* List of commands and how to convert arguments to/from ASCII. */
 100 static const struct ng_cmdlist ng_tcpmss_cmds[] = {
 101         {
 102           NGM_TCPMSS_COOKIE,
 103           NGM_TCPMSS_GET_STATS,
 104           "getstats",
 105           &ng_parse_hookbuf_type,
 106           &ng_tcpmss_hookstat_type
 107         },
 108         {
 109           NGM_TCPMSS_COOKIE,
 110           NGM_TCPMSS_CLR_STATS,
 111           "clrstats",
 112           &ng_parse_hookbuf_type,
 113           NULL
 114         },
 115         {
 116           NGM_TCPMSS_COOKIE,
 117           NGM_TCPMSS_GETCLR_STATS,
 118           "getclrstats",
 119           &ng_parse_hookbuf_type,
 120           &ng_tcpmss_hookstat_type
 121         },
 122         {
 123           NGM_TCPMSS_COOKIE,
 124           NGM_TCPMSS_CONFIG,
 125           "config",
 126           &ng_tcpmss_config_type,
 127           NULL
 128         },
 129         { 0 }
 130 };
 131
 132 /* Netgraph type descriptor. */
 133 static struct ng_type ng_tcpmss_typestruct = {
 134         .version =      NG_ABI_VERSION,
 135         .name =         NG_TCPMSS_NODE_TYPE,
 136         .constructor =  ng_tcpmss_constructor,
 137         .rcvmsg =       ng_tcpmss_rcvmsg,
 138         .newhook =      ng_tcpmss_newhook,
 139         .rcvdata =      ng_tcpmss_rcvdata,
 140         .disconnect =   ng_tcpmss_disconnect,
 141         .cmdlist =      ng_tcpmss_cmds,
 142 };
 143
 144 NETGRAPH_INIT(tcpmss, &ng_tcpmss_typestruct);
 145 #define ERROUT(x)       { error = (x); goto done; }
 146
 147 /*
 148  * Node constructor. No special actions required.
 149  */
 150 static int
 151 ng_tcpmss_constructor(node_p node)
 152 {
 153         return (0);
 154 }
 155
 156 /*
 157  * Add a hook. Any unique name is OK.
 158  */
 159 static int
 160 ng_tcpmss_newhook(node_p node, hook_p hook, const char *name)
 161 {
 162         hpriv_p priv;
 163
 164         priv = malloc(sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO);
 165         if (priv == NULL)
 166                 return (ENOMEM);
 167
 168         NG_HOOK_SET_PRIVATE(hook, priv);
 169
 170         return (0);
 171 }
 172
 173 /*
 174  * Receive a control message.
 175  */
 176 static int
 177 ng_tcpmss_rcvmsg
 178 (node_p node, item_p item, hook_p lasthook)
 179 {
 180         struct ng_mesg *msg, *resp = NULL;
 181         int error = 0;
 182
 183         NGI_GET_MSG(item, msg);
 184
 185         switch (msg->header.typecookie) {
 186         case NGM_TCPMSS_COOKIE:
 187                 switch (msg->header.cmd) {
 188                 case NGM_TCPMSS_GET_STATS:
 189                 case NGM_TCPMSS_CLR_STATS:
 190                 case NGM_TCPMSS_GETCLR_STATS:
 191                     {
 192                         hook_p hook;
 193                         hpriv_p priv;
 194
 195                         /* Check that message is long enough. */
 196                         if (msg->header.arglen != NG_HOOKSIZ)
 197                                 ERROUT(EINVAL);
 198
 199                         /* Find this hook. */
 200                         hook = ng_findhook(node, (char *)msg->data);
 201                         if (hook == NULL)
 202                                 ERROUT(ENOENT);
 203
 204                         priv = NG_HOOK_PRIVATE(hook);
 205
 206                         /* Create response. */
 207                         if (msg->header.cmd != NGM_TCPMSS_CLR_STATS) {
 208                                 NG_MKRESPONSE(resp, msg,
 209                                     sizeof(struct ng_tcpmss_hookstat), M_NOWAIT);
 210                                 if (resp == NULL)
 211                                         ERROUT(ENOMEM);
 212                                 bcopy(&priv->stats, resp->data,
 213                                     sizeof(struct ng_tcpmss_hookstat));
 214                         }
 215
 216                         if (msg->header.cmd != NGM_TCPMSS_GET_STATS)
 217                                 bzero(&priv->stats,
 218                                     sizeof(struct ng_tcpmss_hookstat));
 219                         break;
 220                     }
 221                 case NGM_TCPMSS_CONFIG:
 222                     {
 223                         struct ng_tcpmss_config *set;
 224                         hook_p in, out;
 225                         hpriv_p priv;
 226
 227                         /* Check that message is long enough. */
 228                         if (msg->header.arglen !=
 229                             sizeof(struct ng_tcpmss_config))
 230                                 ERROUT(EINVAL);
 231
 232                         set = (struct ng_tcpmss_config *)msg->data;
 233                         in = ng_findhook(node, set->inHook);
 234                         out = ng_findhook(node, set->outHook);
 235                         if (in == NULL || out == NULL)
 236                                 ERROUT(ENOENT);
 237
 238                         /* Configure MSS hack. */
 239                         priv = NG_HOOK_PRIVATE(in);
 240                         priv->outHook = out;
 241                         priv->stats.maxMSS = set->maxMSS;
 242
 243                         break;
 244                     }
 245                 default:
 246                         error = EINVAL;
 247                         break;
 248                 }
 249                 break;
 250         default:
 251                 error = EINVAL;
 252                 break;
 253         }
 254
 255 done:
 256         NG_RESPOND_MSG(error, node, item, resp);
 257         NG_FREE_MSG(msg);
 258
 259         return (error);
 260 }
 261
 262 /*
 263  * Receive data on a hook, and hack MSS.
 264  *
 265  */
 266 static int
 267 ng_tcpmss_rcvdata(hook_p hook, item_p item)
 268 {
 269         hpriv_p priv = NG_HOOK_PRIVATE(hook);
 270         struct mbuf *m = NULL;
 271         struct ip *ip;
 272         struct tcphdr *tcp;
 273         int iphlen, tcphlen, pktlen;
 274         int pullup_len = 0;
 275         int error = 0;
 276
 277         /* Drop packets if filter is not configured on this hook. */
 278         if (priv->outHook == NULL)
 279                 goto done;
 280
 281         NGI_GET_M(item, m);
 282
 283         /* Update stats on incoming hook. */
 284         pktlen = m->m_pkthdr.len;
 285         priv->stats.Octets += pktlen;
 286         priv->stats.Packets++;
 287
 288         /* Check whether we configured to fix MSS. */
 289         if (priv->stats.maxMSS == 0)
 290                 goto send;
 291
 292 #define M_CHECK(length) do {                                    \
 293         pullup_len += length;                                   \
 294         if ((m)->m_pkthdr.len < pullup_len)                     \
 295                 goto send;                                      \
 296         if ((m)->m_len < pullup_len &&                          \
 297            (((m) = m_pullup((m), pullup_len)) == NULL))         \
 298                 ERROUT(ENOBUFS);                                \
 299         } while (0)
 300
 301         /* Check mbuf packet size and arrange for IP header. */
 302         M_CHECK(sizeof(struct ip));
 303         ip = mtod(m, struct ip *);
 304
 305         /* Check IP version. */
 306         if (ip->ip_v != IPVERSION)
 307                 ERROUT(EINVAL);
 308
 309         /* Check IP header length. */
 310         iphlen = ip->ip_hl << 2;
 311         if (iphlen < sizeof(struct ip) || iphlen > pktlen )
 312                 ERROUT(EINVAL);
 313
 314         /* Check if it is TCP. */
 315         if (!(ip->ip_p == IPPROTO_TCP))
 316                 goto send;
 317
 318         /* Check mbuf packet size and arrange for IP+TCP header */
 319         M_CHECK(iphlen - sizeof(struct ip) + sizeof(struct tcphdr));
 320         ip = mtod(m, struct ip *);
 321         tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
 322
 323         /* Check TCP header length. */
 324         tcphlen = tcp->th_off << 2;
 325         if (tcphlen < sizeof(struct tcphdr) || tcphlen > pktlen - iphlen)
 326                 ERROUT(EINVAL);
 327
 328         /* Check SYN packet and has options. */
 329         if (!(tcp->th_flags & TH_SYN) || tcphlen == sizeof(struct tcphdr))
 330                 goto send;
 331
 332         /* Update SYN stats. */
 333         priv->stats.SYNPkts++;
 334
 335         M_CHECK(tcphlen - sizeof(struct tcphdr));
 336         ip = mtod(m, struct ip *);
 337         tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
 338
 339 #undef  M_CHECK
 340
 341         /* Fix MSS and update stats. */
 342         if (correct_mss(tcp, tcphlen, priv->stats.maxMSS,
 343             m->m_pkthdr.csum_flags))
 344                 priv->stats.FixedPkts++;
 345
 346 send:
 347         /* Deliver frame out destination hook. */
 348         NG_FWD_NEW_DATA(error, item, priv->outHook, m);
 349
 350         return (error);
 351
 352 done:
 353         NG_FREE_ITEM(item);
 354         NG_FREE_M(m);
 355
 356         return (error);
 357 }
 358
 359 /*
 360  * Hook disconnection.
 361  * We must check all hooks, since they may reference this one.
 362  */
 363 static int
 364 ng_tcpmss_disconnect(hook_p hook)
 365 {
 366         node_p node = NG_HOOK_NODE(hook);
 367         hook_p hook2;
 368
 369         LIST_FOREACH(hook2, &node->nd_hooks, hk_hooks) {
 370                 hpriv_p priv = NG_HOOK_PRIVATE(hook2);
 371
 372                 if (priv->outHook == hook)
 373                         priv->outHook = NULL;
 374         }
 375
 376         free(NG_HOOK_PRIVATE(hook), M_NETGRAPH);
 377
 378         if (NG_NODE_NUMHOOKS(NG_HOOK_NODE(hook)) == 0)
 379                 ng_rmnode_self(NG_HOOK_NODE(hook));
 380
 381         return (0);
 382 }
 383
 384 /*
 385  * Code from tcpmssd.
 386  */
 387
 388 /*-
 389  * The following macro is used to update an
 390  * internet checksum.  "acc" is a 32-bit
 391  * accumulation of all the changes to the
 392  * checksum (adding in old 16-bit words and
 393  * subtracting out new words), and "cksum"
 394  * is the checksum value to be updated.
 395  */
 396 #define TCPMSS_ADJUST_CHECKSUM(acc, cksum) do {         \
 397         acc += cksum;                                   \
 398         if (acc < 0) {                                  \
 399                 acc = -acc;                             \
 400                 acc = (acc >> 16) + (acc & 0xffff);     \
 401                 acc += acc >> 16;                       \
 402                 cksum = (u_short) ~acc;                 \
 403         } else {                                        \
 404                 acc = (acc >> 16) + (acc & 0xffff);     \
 405                 acc += acc >> 16;                       \
 406                 cksum = (u_short) acc;                  \
 407         }                                               \
 408 } while (0);
 409
 410 static int
 411 correct_mss(struct tcphdr *tc, int hlen, uint16_t maxmss, int flags)
 412 {
 413         int olen, optlen;
 414         u_char *opt;
 415         int accumulate;
 416         int res = 0;
 417         uint16_t sum;
 418
 419         for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
 420              olen > 0; olen -= optlen, opt += optlen) {
 421                 if (*opt == TCPOPT_EOL)
 422                         break;
 423                 else if (*opt == TCPOPT_NOP)
 424                         optlen = 1;
 425                 else {
 426                         optlen = *(opt + 1);
 427                         if (optlen <= 0 || optlen > olen)
 428                                 break;
 429                         if (*opt == TCPOPT_MAXSEG) {
 430                                 if (optlen != TCPOLEN_MAXSEG)
 431                                         continue;
 432                                 accumulate = be16dec(opt + 2);
 433                                 if (accumulate > maxmss) {
 434                                         if ((flags & CSUM_TCP) == 0) {
 435                                                 accumulate -= maxmss;
 436                                                 sum = be16dec(&tc->th_sum);
 437                                                 TCPMSS_ADJUST_CHECKSUM(accumulate, sum);
 438                                                 be16enc(&tc->th_sum, sum);
 439                                         }
 440                                         be16enc(opt + 2, maxmss);
 441                                         res = 1;
 442                                 }
 443                         }
 444                 }
 445         }
 446         return (res);
 447 }