Date: Mon, 3 Apr 2017 22:12:11 +0800 From: Julian Elischer <julian@freebsd.org> To: "Andrey V. Elsukov" <ae@FreeBSD.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r316435 - in head: sbin/ipfw sys/conf sys/modules sys/modules/ipfw_pmod sys/netpfil/ipfw/pmod Message-ID: <2fb0e146-8486-09c3-0c44-75c71a74fc2f@freebsd.org> In-Reply-To: <201704030307.v3337mfs039014@repo.freebsd.org> References: <201704030307.v3337mfs039014@repo.freebsd.org>
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On 3/4/17 11:07 am, Andrey V. Elsukov wrote: > Author: ae > Date: Mon Apr 3 03:07:48 2017 > New Revision: 316435 > URL: https://svnweb.freebsd.org/changeset/base/316435 it was always my intention to hook netgraph modules into ipfw in this way > > Log: > Add ipfw_pmod kernel module. > > The module is designed for modification of a packets of any protocols. > For now it implements only TCP MSS modification. It adds the external > action handler for "tcp-setmss" action. > > A rule with tcp-setmss action does additional check for protocol and > TCP flags. If SYN flag is present, it parses TCP options and modifies > MSS option if its value is greater than configured value in the rule. > Then it adjustes TCP checksum if needed. After handling the search > continues with the next rule. > > Obtained from: Yandex LLC > MFC after: 2 weeks > Relnotes: yes > Sponsored by: Yandex LLC > No objection from: #network > Differential Revision: https://reviews.freebsd.org/D10150 > > Added: > head/sys/modules/ipfw_pmod/ > head/sys/modules/ipfw_pmod/Makefile (contents, props changed) > head/sys/netpfil/ipfw/pmod/ > head/sys/netpfil/ipfw/pmod/ip_fw_pmod.c (contents, props changed) > head/sys/netpfil/ipfw/pmod/pmod.h (contents, props changed) > head/sys/netpfil/ipfw/pmod/tcpmod.c (contents, props changed) > Modified: > head/sbin/ipfw/ipfw.8 > head/sbin/ipfw/ipfw2.c > head/sbin/ipfw/ipfw2.h > head/sys/conf/NOTES > head/sys/conf/files > head/sys/conf/options > head/sys/modules/Makefile > > Modified: head/sbin/ipfw/ipfw.8 > ============================================================================== > --- head/sbin/ipfw/ipfw.8 Mon Apr 3 02:44:40 2017 (r316434) > +++ head/sbin/ipfw/ipfw.8 Mon Apr 3 03:07:48 2017 (r316435) > @@ -1,7 +1,7 @@ > .\" > .\" $FreeBSD$ > .\" > -.Dd March 15, 2017 > +.Dd April 3, 2017 > .Dt IPFW 8 > .Os > .Sh NAME > @@ -1118,6 +1118,20 @@ It is also possible to use the > keyword with setdscp. > If the tablearg value is not within the 0..64 range, lower 6 bits of supplied > value are used. > +.It Cm tcp-setmss Ar mss > +Set the Maximum Segment Size (MSS) in the TCP segment to value > +.Ar mss . > +The kernel module > +.Cm ipfw_pmod > +should be loaded or kernel should have > +.Cm options IPFIREWALL_PMOD > +to be able use this action. > +This command does not change a packet if original MSS value is lower than > +specified value. > +Both TCP over IPv4 and over IPv6 are supported. > +Regardless of matched a packet or not by the > +.Cm tcp-setmss > +rule, the search continues with the next rule. > .It Cm reass > Queue and reassemble IP fragments. > If the packet is not fragmented, counters are updated and > > Modified: head/sbin/ipfw/ipfw2.c > ============================================================================== > --- head/sbin/ipfw/ipfw2.c Mon Apr 3 02:44:40 2017 (r316434) > +++ head/sbin/ipfw/ipfw2.c Mon Apr 3 03:07:48 2017 (r316435) > @@ -36,6 +36,7 @@ > #include <pwd.h> > #include <stdio.h> > #include <stdarg.h> > +#include <stdint.h> > #include <stdlib.h> > #include <string.h> > #include <sysexits.h> > @@ -238,6 +239,7 @@ static struct _s_x rule_eactions[] = { > { "nat64lsn", TOK_NAT64LSN }, > { "nat64stl", TOK_NAT64STL }, > { "nptv6", TOK_NPTV6 }, > + { "tcp-setmss", TOK_TCPSETMSS }, > { NULL, 0 } /* terminator */ > }; > > @@ -272,6 +274,7 @@ static struct _s_x rule_actions[] = { > { "call", TOK_CALL }, > { "return", TOK_RETURN }, > { "eaction", TOK_EACTION }, > + { "tcp-setmss", TOK_TCPSETMSS }, > { NULL, 0 } /* terminator */ > }; > > @@ -4007,6 +4010,26 @@ chkarg: > fill_cmd(action, O_CALLRETURN, F_NOT, 0); > break; > > + case TOK_TCPSETMSS: { > + u_long mss; > + uint16_t idx; > + > + idx = pack_object(tstate, "tcp-setmss", IPFW_TLV_EACTION); > + if (idx == 0) > + errx(EX_DATAERR, "pack_object failed"); > + fill_cmd(action, O_EXTERNAL_ACTION, 0, idx); > + NEED1("Missing MSS value"); > + action = next_cmd(action, &ablen); > + action->len = 1; > + CHECK_ACTLEN; > + mss = strtoul(*av, NULL, 10); > + if (mss == 0 || mss > UINT16_MAX) > + errx(EX_USAGE, "invalid MSS value %s", *av); > + fill_cmd(action, O_EXTERNAL_DATA, 0, (uint16_t)mss); > + av++; > + break; > + } > + > default: > av--; > if (match_token(rule_eactions, *av) == -1) > > Modified: head/sbin/ipfw/ipfw2.h > ============================================================================== > --- head/sbin/ipfw/ipfw2.h Mon Apr 3 02:44:40 2017 (r316434) > +++ head/sbin/ipfw/ipfw2.h Mon Apr 3 03:07:48 2017 (r316435) > @@ -284,6 +284,8 @@ enum tokens { > TOK_INTPREFIX, > TOK_EXTPREFIX, > TOK_PREFIXLEN, > + > + TOK_TCPSETMSS, > }; > > /* > > Modified: head/sys/conf/NOTES > ============================================================================== > --- head/sys/conf/NOTES Mon Apr 3 02:44:40 2017 (r316434) > +++ head/sys/conf/NOTES Mon Apr 3 03:07:48 2017 (r316435) > @@ -971,6 +971,9 @@ device lagg > # > # IPFIREWALL_NPTV6 adds support for in kernel NPTv6 in ipfw. > # > +# IPFIREWALL_PMOD adds support for protocols modification module. Currently > +# it supports only TCP MSS modification. > +# > # IPSTEALTH enables code to support stealth forwarding (i.e., forwarding > # packets without touching the TTL). This can be useful to hide firewalls > # from traceroute and similar tools. > > Modified: head/sys/conf/files > ============================================================================== > --- head/sys/conf/files Mon Apr 3 02:44:40 2017 (r316434) > +++ head/sys/conf/files Mon Apr 3 03:07:48 2017 (r316435) > @@ -4230,6 +4230,8 @@ netpfil/ipfw/nptv6/ip_fw_nptv6.c optiona > ipfirewall_nptv6 > netpfil/ipfw/nptv6/nptv6.c optional inet inet6 ipfirewall \ > ipfirewall_nptv6 > +netpfil/ipfw/pmod/ip_fw_pmod.c optional inet ipfirewall_pmod > +netpfil/ipfw/pmod/tcpmod.c optional inet ipfirewall_pmod > netpfil/pf/if_pflog.c optional pflog pf inet > netpfil/pf/if_pfsync.c optional pfsync pf inet > netpfil/pf/pf.c optional pf inet > > Modified: head/sys/conf/options > ============================================================================== > --- head/sys/conf/options Mon Apr 3 02:44:40 2017 (r316434) > +++ head/sys/conf/options Mon Apr 3 03:07:48 2017 (r316435) > @@ -426,6 +426,7 @@ IPFIREWALL_NAT64_DIRECT_OUTPUT opt_ipfw. > IPFIREWALL_NPTV6 opt_ipfw.h > IPFIREWALL_VERBOSE opt_ipfw.h > IPFIREWALL_VERBOSE_LIMIT opt_ipfw.h > +IPFIREWALL_PMOD opt_ipfw.h > IPSEC opt_ipsec.h > IPSEC_DEBUG opt_ipsec.h > IPSEC_SUPPORT opt_ipsec.h > > Modified: head/sys/modules/Makefile > ============================================================================== > --- head/sys/modules/Makefile Mon Apr 3 02:44:40 2017 (r316434) > +++ head/sys/modules/Makefile Mon Apr 3 03:07:48 2017 (r316435) > @@ -173,6 +173,7 @@ SUBDIR= \ > ipfw_nat \ > ${_ipfw_nat64} \ > ${_ipfw_nptv6} \ > + ${_ipfw_pmod} \ > ${_ipmi} \ > ip6_mroute_mod \ > ip_mroute_mod \ > @@ -443,6 +444,7 @@ _toecore= toecore > _if_enc= if_enc > _if_gif= if_gif > _if_gre= if_gre > +_ipfw_pmod= ipfw_pmod > .if ${MK_IPSEC_SUPPORT} != "no" > _ipsec= ipsec > .endif > > Added: head/sys/modules/ipfw_pmod/Makefile > ============================================================================== > --- /dev/null 00:00:00 1970 (empty, because file is newly added) > +++ head/sys/modules/ipfw_pmod/Makefile Mon Apr 3 03:07:48 2017 (r316435) > @@ -0,0 +1,8 @@ > +# $FreeBSD$ > + > +.PATH: ${SRCTOP}/sys/netpfil/ipfw/pmod > + > +KMOD= ipfw_pmod > +SRCS= ip_fw_pmod.c tcpmod.c opt_inet.h opt_inet6.h > + > +.include <bsd.kmod.mk> > > Added: head/sys/netpfil/ipfw/pmod/ip_fw_pmod.c > ============================================================================== > --- /dev/null 00:00:00 1970 (empty, because file is newly added) > +++ head/sys/netpfil/ipfw/pmod/ip_fw_pmod.c Mon Apr 3 03:07:48 2017 (r316435) > @@ -0,0 +1,101 @@ > +/*- > + * Copyright (c) 2017 Yandex LLC > + * Copyright (c) 2017 Andrey V. Elsukov <ae@FreeBSD.org> > + * All rights reserved. > + * > + * Redistribution and use in source and binary forms, with or without > + * modification, are permitted provided that the following conditions > + * are met: > + * > + * 1. Redistributions of source code must retain the above copyright > + * notice, this list of conditions and the following disclaimer. > + * 2. Redistributions in binary form must reproduce the above copyright > + * notice, this list of conditions and the following disclaimer in the > + * documentation and/or other materials provided with the distribution. > + * > + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR > + * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES > + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. > + * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, > + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT > + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, > + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY > + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT > + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF > + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. > + */ > + > +#include <sys/cdefs.h> > +__FBSDID("$FreeBSD$"); > + > +#include <sys/param.h> > +#include <sys/systm.h> > +#include <sys/kernel.h> > +#include <sys/lock.h> > +#include <sys/malloc.h> > +#include <sys/module.h> > +#include <sys/rwlock.h> > +#include <sys/socket.h> > + > +#include <net/if.h> > +#include <net/vnet.h> > + > +#include <netinet/in.h> > +#include <netinet/ip_var.h> > +#include <netinet/ip_fw.h> > + > +#include <netpfil/ipfw/ip_fw_private.h> > +#include <netpfil/ipfw/pmod/pmod.h> > + > +static int > +vnet_ipfw_pmod_init(const void *arg __unused) > +{ > + int error; > + > + error = tcpmod_init(&V_layer3_chain, IS_DEFAULT_VNET(curvnet)); > + return (error); > +} > + > +static int > +vnet_ipfw_pmod_uninit(const void *arg __unused) > +{ > + > + tcpmod_uninit(&V_layer3_chain, IS_DEFAULT_VNET(curvnet)); > + return (0); > +} > + > +static int > +ipfw_pmod_modevent(module_t mod, int type, void *unused) > +{ > + > + switch (type) { > + case MOD_LOAD: > + case MOD_UNLOAD: > + break; > + default: > + return (EOPNOTSUPP); > + } > + return (0); > +} > + > +static moduledata_t ipfw_pmod_mod = { > + "ipfw_pmod", > + ipfw_pmod_modevent, > + 0 > +}; > + > +/* Define startup order. */ > +#define IPFW_PMOD_SI_SUB_FIREWALL SI_SUB_PROTO_IFATTACHDOMAIN > +#define IPFW_PMOD_MODEVENT_ORDER (SI_ORDER_ANY - 128) /* after ipfw */ > +#define IPFW_PMOD_MODULE_ORDER (IPFW_PMOD_MODEVENT_ORDER + 1) > +#define IPFW_PMOD_VNET_ORDER (IPFW_PMOD_MODEVENT_ORDER + 2) > + > +DECLARE_MODULE(ipfw_pmod, ipfw_pmod_mod, IPFW_PMOD_SI_SUB_FIREWALL, > + IPFW_PMOD_MODULE_ORDER); > +MODULE_DEPEND(ipfw_pmod, ipfw, 3, 3, 3); > +MODULE_VERSION(ipfw_pmod, 1); > + > +VNET_SYSINIT(vnet_ipfw_pmod_init, IPFW_PMOD_SI_SUB_FIREWALL, > + IPFW_PMOD_VNET_ORDER, vnet_ipfw_pmod_init, NULL); > +VNET_SYSUNINIT(vnet_ipfw_pmod_uninit, IPFW_PMOD_SI_SUB_FIREWALL, > + IPFW_PMOD_VNET_ORDER, vnet_ipfw_pmod_uninit, NULL); > > Added: head/sys/netpfil/ipfw/pmod/pmod.h > ============================================================================== > --- /dev/null 00:00:00 1970 (empty, because file is newly added) > +++ head/sys/netpfil/ipfw/pmod/pmod.h Mon Apr 3 03:07:48 2017 (r316435) > @@ -0,0 +1,36 @@ > +/*- > + * Copyright (c) 2017 Yandex LLC > + * Copyright (c) 2017 Andrey V. Elsukov <ae@FreeBSD.org> > + * 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, 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 ``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 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. > + * > + * $FreeBSD$ > + */ > + > +#ifndef _IP_FW_PMOD_H_ > +#define _IP_FW_PMOD_H_ > + > +int tcpmod_init(struct ip_fw_chain *ch, int first); > +void tcpmod_uninit(struct ip_fw_chain *ch, int last); > +#endif /* _IP_FW_PMOD_H_ */ > + > > Added: head/sys/netpfil/ipfw/pmod/tcpmod.c > ============================================================================== > --- /dev/null 00:00:00 1970 (empty, because file is newly added) > +++ head/sys/netpfil/ipfw/pmod/tcpmod.c Mon Apr 3 03:07:48 2017 (r316435) > @@ -0,0 +1,246 @@ > +/*- > + * Copyright (c) 2017 Yandex LLC > + * Copyright (c) 2017 Andrey V. Elsukov <ae@FreeBSD.org> > + * 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, 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 ``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 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. > + */ > + > +#include "opt_inet.h" > +#include "opt_inet6.h" > + > +#include <sys/cdefs.h> > +__FBSDID("$FreeBSD$"); > + > +#include <sys/param.h> > +#include <sys/systm.h> > +#include <sys/errno.h> > +#include <sys/kernel.h> > +#include <sys/mbuf.h> > +#include <sys/module.h> > +#include <sys/socket.h> > + > +#include <net/if.h> > +#include <net/if_var.h> > +#include <net/pfil.h> > +#include <net/vnet.h> > + > +#include <netinet/in.h> > +#include <netinet/ip.h> > +#include <netinet/ip_var.h> > +#include <netinet/tcp.h> > +#include <netinet/ip_fw.h> > +#include <netinet/ip6.h> > + > +#include <netpfil/ipfw/ip_fw_private.h> > +#include <netpfil/ipfw/pmod/pmod.h> > + > +#include <machine/in_cksum.h> > + > +static VNET_DEFINE(uint16_t, tcpmod_setmss_eid) = 0; > +#define V_tcpmod_setmss_eid VNET(tcpmod_setmss_eid) > + > +static int > +tcpmod_setmss(struct mbuf **mp, struct tcphdr *tcp, int tlen, uint16_t mss) > +{ > + struct mbuf *m; > + u_char *cp; > + int optlen, ret; > + uint16_t oldmss, csum; > + > + m = *mp; > + ret = IP_FW_DENY; > + if (m->m_len < m->m_pkthdr.len) { > + /* > + * We shouldn't have any data, IP packet contains only > + * TCP header with options. > + */ > + *mp = m = m_pullup(m, m->m_pkthdr.len); > + if (m == NULL) > + return (ret); > + } > + /* Parse TCP options. */ > + for (tlen -= sizeof(struct tcphdr), cp = (u_char *)(tcp + 1); > + tlen > 0; tlen -= optlen, cp += optlen) { > + if (cp[0] == TCPOPT_EOL) > + break; > + if (cp[0] == TCPOPT_NOP) { > + optlen = 1; > + continue; > + } > + if (tlen < 2) > + break; > + optlen = cp[1]; > + if (optlen < 2 || optlen > tlen) > + break; > + if (cp[0] == TCPOPT_MAXSEG) { > + if (optlen != TCPOLEN_MAXSEG) > + break; > + ret = 0; /* report success */ > + bcopy(cp + 2, &oldmss, sizeof(oldmss)); > + /* Do not update lower MSS value */ > + if (oldmss <= mss) > + break; > + bcopy(&mss, cp + 2, sizeof(mss)); > + /* Update checksum if it is not delayed. */ > + if ((m->m_pkthdr.csum_flags & > + (CSUM_TCP | CSUM_TCP_IPV6)) == 0) { > + bcopy(&tcp->th_sum, &csum, sizeof(csum)); > + csum = cksum_adjust(csum, oldmss, mss); > + bcopy(&csum, &tcp->th_sum, sizeof(csum)); > + } > + break; > + } > + } > + > + return (ret); > +} > + > +#ifdef INET6 > +static int > +tcpmod_ipv6_setmss(struct mbuf **mp, uint16_t mss) > +{ > + struct ip6_hdr *ip6; > + struct ip6_hbh *hbh; > + struct tcphdr *tcp; > + int hlen, plen, proto; > + > + ip6 = mtod(*mp, struct ip6_hdr *); > + hlen = sizeof(*ip6); > + proto = ip6->ip6_nxt; > + /* > + * Skip IPv6 extension headers and get the TCP header. > + * ipfw_chk() has already done this work. So we are sure that > + * we will not do an access to the out of bounds. For this > + * reason we skip some checks here. > + */ > + while (proto == IPPROTO_HOPOPTS || proto == IPPROTO_ROUTING || > + proto == IPPROTO_DSTOPTS) { > + hbh = mtodo(*mp, hlen); > + proto = hbh->ip6h_nxt; > + hlen += hbh->ip6h_len << 3; > + } > + tcp = mtodo(*mp, hlen); > + plen = (*mp)->m_pkthdr.len - hlen; > + hlen = tcp->th_off << 2; > + /* We must have TCP options and enough data in a packet. */ > + if (hlen <= sizeof(struct tcphdr) || hlen > plen) > + return (IP_FW_DENY); > + return (tcpmod_setmss(mp, tcp, hlen, mss)); > +} > +#endif /* INET6 */ > + > +#ifdef INET > +static int > +tcpmod_ipv4_setmss(struct mbuf **mp, uint16_t mss) > +{ > + struct tcphdr *tcp; > + struct ip *ip; > + int hlen, plen; > + > + ip = mtod(*mp, struct ip *); > + hlen = ip->ip_hl << 2; > + tcp = mtodo(*mp, hlen); > + plen = (*mp)->m_pkthdr.len - hlen; > + hlen = tcp->th_off << 2; > + /* We must have TCP options and enough data in a packet. */ > + if (hlen <= sizeof(struct tcphdr) || hlen > plen) > + return (IP_FW_DENY); > + return (tcpmod_setmss(mp, tcp, hlen, mss)); > +} > +#endif /* INET */ > + > +/* > + * ipfw external action handler. > + */ > +static int > +ipfw_tcpmod(struct ip_fw_chain *chain, struct ip_fw_args *args, > + ipfw_insn *cmd, int *done) > +{ > + ipfw_insn *icmd; > + int ret; > + > + *done = 0; /* try next rule if not matched */ > + ret = IP_FW_DENY; > + icmd = cmd + 1; > + if (cmd->opcode != O_EXTERNAL_ACTION || > + cmd->arg1 != V_tcpmod_setmss_eid || > + icmd->opcode != O_EXTERNAL_DATA || > + icmd->len != F_INSN_SIZE(ipfw_insn)) > + return (ret); > + > + /* > + * NOTE: ipfw_chk() can set f_id.proto from IPv6 fragment header, > + * but f_id._flags can be filled only from real TCP header. > + * > + * NOTE: ipfw_chk() drops very short packets in the PULLUP_TO() > + * macro. But we need to check that mbuf is contiguous more than > + * IP+IP_options/IP_extensions+tcphdr length, because TCP header > + * must have TCP options, and ipfw_chk() does PULLUP_TO() size of > + * struct tcphdr. > + * > + * NOTE: we require only the presence of SYN flag. User should > + * properly configure the rule to select the direction of packets, > + * that should be modified. > + */ > + if (args->f_id.proto != IPPROTO_TCP || > + (args->f_id._flags & TH_SYN) == 0) > + return (ret); > + > + switch (args->f_id.addr_type) { > +#ifdef INET > + case 4: > + ret = tcpmod_ipv4_setmss(&args->m, htons(icmd->arg1)); > + break; > +#endif > +#ifdef INET6 > + case 6: > + ret = tcpmod_ipv6_setmss(&args->m, htons(icmd->arg1)); > + break; > +#endif > + } > + /* > + * We return zero in both @ret and @done on success, and ipfw_chk() > + * will update rule counters. Otherwise a packet will not be matched > + * by rule. > + */ > + return (ret); > +} > + > +int > +tcpmod_init(struct ip_fw_chain *ch, int first) > +{ > + > + V_tcpmod_setmss_eid = ipfw_add_eaction(ch, ipfw_tcpmod, "tcp-setmss"); > + if (V_tcpmod_setmss_eid == 0) > + return (ENXIO); > + return (0); > +} > + > +void > +tcpmod_uninit(struct ip_fw_chain *ch, int last) > +{ > + > + ipfw_del_eaction(ch, V_tcpmod_setmss_eid); > + V_tcpmod_setmss_eid = 0; > +} > + > >
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