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