svn commit: r316435 - in head: sbin/ipfw sys/conf sys/modules sys/modules/ipfw_pmod sys/netpfil/ipfw/pmod
Julian Elischer
julian at freebsd.org
Mon Apr 3 14:12:31 UTC 2017
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: ${SRCTOP}/sys/netpfil/ipfw/pmod
> +
> +KMOD= ipfw_pmod
> +SRCS= ip_fw_pmod.c tcpmod.c opt_inet.h opt_inet6.h
> +
> +.include <bsd.kmod.mk>
>
> Added: head/sys/netpfil/ipfw/pmod/ip_fw_pmod.c
> ==============================================================================
> --- /dev/null 00:00:00 1970 (empty, because file is newly added)
> +++ head/sys/netpfil/ipfw/pmod/ip_fw_pmod.c Mon Apr 3 03:07:48 2017 (r316435)
> @@ -0,0 +1,101 @@
> +/*-
> + * Copyright (c) 2017 Yandex LLC
> + * Copyright (c) 2017 Andrey V. Elsukov <ae at FreeBSD.org>
> + * All rights reserved.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + *
> + * 1. Redistributions of source code must retain the above copyright
> + * notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + * notice, this list of conditions and the following disclaimer in the
> + * documentation and/or other materials provided with the distribution.
> + *
> + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
> + * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
> + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
> + * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
> + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
> + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
> + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
> + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
> + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> + */
> +
> +#include <sys/cdefs.h>
> +__FBSDID("$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 at 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 at 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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