/*- * ng_tcpmss.c * * Copyright (c) 2004, Alexey Popov * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice unmodified, this list of conditions, and the following * disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * This software includes fragments of the following programs: * tcpmssd Ruslan Ermilov * * $FreeBSD$ */ /* * This node is netgraph tool for workaround of PMTUD problem. It acts * like filter for IP packets. If configured, it reduces MSS of TCP SYN * packets. * * Configuration can be done by sending NGM_TCPMSS_CONFIG message. The * message sets filter for incoming packets on hook 'inHook'. Packet's * TCP MSS field is lowered to 'maxMSS' parameter and resulting packet * is sent to 'outHook'. * * XXX: statistics are updated not atomically, so they may broke on SMP. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* Per hook info. */ typedef struct { hook_p outHook; struct ng_tcpmss_hookstat stats; } *hpriv_p; /* Netgraph methods. */ static ng_constructor_t ng_tcpmss_constructor; static ng_rcvmsg_t ng_tcpmss_rcvmsg; static ng_newhook_t ng_tcpmss_newhook; static ng_rcvdata_t ng_tcpmss_rcvdata; static ng_disconnect_t ng_tcpmss_disconnect; static int correct_mss(struct tcphdr *, int, uint16_t, int); /* Parse type for struct ng_tcpmss_hookstat. */ static const struct ng_parse_struct_field ng_tcpmss_hookstat_type_fields[] = NG_TCPMSS_HOOKSTAT_INFO; static const struct ng_parse_type ng_tcpmss_hookstat_type = { &ng_parse_struct_type, &ng_tcpmss_hookstat_type_fields }; /* Parse type for struct ng_tcpmss_config. */ static const struct ng_parse_struct_field ng_tcpmss_config_type_fields[] = NG_TCPMSS_CONFIG_INFO; static const struct ng_parse_type ng_tcpmss_config_type = { &ng_parse_struct_type, ng_tcpmss_config_type_fields }; /* List of commands and how to convert arguments to/from ASCII. */ static const struct ng_cmdlist ng_tcpmss_cmds[] = { { NGM_TCPMSS_COOKIE, NGM_TCPMSS_GET_STATS, "getstats", &ng_parse_hookbuf_type, &ng_tcpmss_hookstat_type }, { NGM_TCPMSS_COOKIE, NGM_TCPMSS_CLR_STATS, "clrstats", &ng_parse_hookbuf_type, NULL }, { NGM_TCPMSS_COOKIE, NGM_TCPMSS_GETCLR_STATS, "getclrstats", &ng_parse_hookbuf_type, &ng_tcpmss_hookstat_type }, { NGM_TCPMSS_COOKIE, NGM_TCPMSS_CONFIG, "config", &ng_tcpmss_config_type, NULL }, { 0 } }; /* Netgraph type descriptor. */ static struct ng_type ng_tcpmss_typestruct = { .version = NG_ABI_VERSION, .name = NG_TCPMSS_NODE_TYPE, .constructor = ng_tcpmss_constructor, .rcvmsg = ng_tcpmss_rcvmsg, .newhook = ng_tcpmss_newhook, .rcvdata = ng_tcpmss_rcvdata, .disconnect = ng_tcpmss_disconnect, .cmdlist = ng_tcpmss_cmds, }; NETGRAPH_INIT(tcpmss, &ng_tcpmss_typestruct); #define ERROUT(x) { error = (x); goto done; } /* * Node constructor. No special actions required. */ static int ng_tcpmss_constructor(node_p node) { return (0); } /* * Add a hook. Any unique name is OK. */ static int ng_tcpmss_newhook(node_p node, hook_p hook, const char *name) { hpriv_p priv; priv = malloc(sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO); if (priv == NULL) return (ENOMEM); NG_HOOK_SET_PRIVATE(hook, priv); return (0); } /* * Receive a control message. */ static int ng_tcpmss_rcvmsg (node_p node, item_p item, hook_p lasthook) { struct ng_mesg *msg, *resp = NULL; int error = 0; NGI_GET_MSG(item, msg); switch (msg->header.typecookie) { case NGM_TCPMSS_COOKIE: switch (msg->header.cmd) { case NGM_TCPMSS_GET_STATS: case NGM_TCPMSS_CLR_STATS: case NGM_TCPMSS_GETCLR_STATS: { hook_p hook; hpriv_p priv; /* Check that message is long enough. */ if (msg->header.arglen != NG_HOOKSIZ) ERROUT(EINVAL); /* Find this hook. */ hook = ng_findhook(node, (char *)msg->data); if (hook == NULL) ERROUT(ENOENT); priv = NG_HOOK_PRIVATE(hook); /* Create response. */ if (msg->header.cmd != NGM_TCPMSS_CLR_STATS) { NG_MKRESPONSE(resp, msg, sizeof(struct ng_tcpmss_hookstat), M_NOWAIT); if (resp == NULL) ERROUT(ENOMEM); bcopy(&priv->stats, resp->data, sizeof(struct ng_tcpmss_hookstat)); } if (msg->header.cmd != NGM_TCPMSS_GET_STATS) bzero(&priv->stats, sizeof(struct ng_tcpmss_hookstat)); break; } case NGM_TCPMSS_CONFIG: { struct ng_tcpmss_config *set; hook_p in, out; hpriv_p priv; /* Check that message is long enough. */ if (msg->header.arglen != sizeof(struct ng_tcpmss_config)) ERROUT(EINVAL); set = (struct ng_tcpmss_config *)msg->data; in = ng_findhook(node, set->inHook); out = ng_findhook(node, set->outHook); if (in == NULL || out == NULL) ERROUT(ENOENT); /* Configure MSS hack. */ priv = NG_HOOK_PRIVATE(in); priv->outHook = out; priv->stats.maxMSS = set->maxMSS; break; } default: error = EINVAL; break; } break; default: error = EINVAL; break; } done: NG_RESPOND_MSG(error, node, item, resp); NG_FREE_MSG(msg); return (error); } /* * Receive data on a hook, and hack MSS. * */ static int ng_tcpmss_rcvdata(hook_p hook, item_p item) { hpriv_p priv = NG_HOOK_PRIVATE(hook); struct mbuf *m = NULL; struct ip *ip; struct tcphdr *tcp; int iphlen, tcphlen, pktlen; int pullup_len = 0; int error = 0; /* Drop packets if filter is not configured on this hook. */ if (priv->outHook == NULL) goto done; NGI_GET_M(item, m); /* Update stats on incoming hook. */ pktlen = m->m_pkthdr.len; priv->stats.Octets += pktlen; priv->stats.Packets++; /* Check whether we configured to fix MSS. */ if (priv->stats.maxMSS == 0) goto send; #define M_CHECK(length) do { \ pullup_len += length; \ if ((m)->m_pkthdr.len < pullup_len) \ goto send; \ if ((m)->m_len < pullup_len && \ (((m) = m_pullup((m), pullup_len)) == NULL)) \ ERROUT(ENOBUFS); \ } while (0) /* Check mbuf packet size and arrange for IP header. */ M_CHECK(sizeof(struct ip)); ip = mtod(m, struct ip *); /* Check IP version. */ if (ip->ip_v != IPVERSION) ERROUT(EINVAL); /* Check IP header length. */ iphlen = ip->ip_hl << 2; if (iphlen < sizeof(struct ip) || iphlen > pktlen ) ERROUT(EINVAL); /* Check if it is TCP. */ if (!(ip->ip_p == IPPROTO_TCP)) goto send; /* Check mbuf packet size and arrange for IP+TCP header */ M_CHECK(iphlen - sizeof(struct ip) + sizeof(struct tcphdr)); ip = mtod(m, struct ip *); tcp = (struct tcphdr *)((caddr_t )ip + iphlen); /* Check TCP header length. */ tcphlen = tcp->th_off << 2; if (tcphlen < sizeof(struct tcphdr) || tcphlen > pktlen - iphlen) ERROUT(EINVAL); /* Check SYN packet and has options. */ if (!(tcp->th_flags & TH_SYN) || tcphlen == sizeof(struct tcphdr)) goto send; /* Update SYN stats. */ priv->stats.SYNPkts++; M_CHECK(tcphlen - sizeof(struct tcphdr)); ip = mtod(m, struct ip *); tcp = (struct tcphdr *)((caddr_t )ip + iphlen); #undef M_CHECK /* Fix MSS and update stats. */ if (correct_mss(tcp, tcphlen, priv->stats.maxMSS, m->m_pkthdr.csum_flags)) priv->stats.FixedPkts++; send: /* Deliver frame out destination hook. */ NG_FWD_NEW_DATA(error, item, priv->outHook, m); return (error); done: NG_FREE_ITEM(item); NG_FREE_M(m); return (error); } /* * Hook disconnection. * We must check all hooks, since they may reference this one. */ static int ng_tcpmss_disconnect(hook_p hook) { node_p node = NG_HOOK_NODE(hook); hook_p hook2; LIST_FOREACH(hook2, &node->nd_hooks, hk_hooks) { hpriv_p priv = NG_HOOK_PRIVATE(hook2); if (priv->outHook == hook) priv->outHook = NULL; } free(NG_HOOK_PRIVATE(hook), M_NETGRAPH); if (NG_NODE_NUMHOOKS(NG_HOOK_NODE(hook)) == 0) ng_rmnode_self(NG_HOOK_NODE(hook)); return (0); } /* * Code from tcpmssd. */ /*- * The following macro is used to update an * internet checksum. "acc" is a 32-bit * accumulation of all the changes to the * checksum (adding in old 16-bit words and * subtracting out new words), and "cksum" * is the checksum value to be updated. */ #define TCPMSS_ADJUST_CHECKSUM(acc, cksum) do { \ acc += cksum; \ if (acc < 0) { \ acc = -acc; \ acc = (acc >> 16) + (acc & 0xffff); \ acc += acc >> 16; \ cksum = (u_short) ~acc; \ } else { \ acc = (acc >> 16) + (acc & 0xffff); \ acc += acc >> 16; \ cksum = (u_short) acc; \ } \ } while (0); static int correct_mss(struct tcphdr *tc, int hlen, uint16_t maxmss, int flags) { int olen, optlen; u_char *opt; int accumulate; int res = 0; uint16_t sum; for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1); olen > 0; olen -= optlen, opt += optlen) { if (*opt == TCPOPT_EOL) break; else if (*opt == TCPOPT_NOP) optlen = 1; else { optlen = *(opt + 1); if (optlen <= 0 || optlen > olen) break; if (*opt == TCPOPT_MAXSEG) { if (optlen != TCPOLEN_MAXSEG) continue; accumulate = be16dec(opt + 2); if (accumulate > maxmss) { if ((flags & CSUM_TCP) == 0) { accumulate -= maxmss; sum = be16dec(&tc->th_sum); TCPMSS_ADJUST_CHECKSUM(accumulate, sum); be16enc(&tc->th_sum, sum); } be16enc(opt + 2, maxmss); res = 1; } } } } return (res); }