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head/sys/netpfil/ipfw/pmod/tcpmod.c

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/*-
* 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;
}