2 * Copyright (c) 2000 Ruslan Ermilov and Brian Somers <brian@Awfulhak.org>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 #include <sys/param.h>
31 #include <sys/socket.h>
32 #include <net/route.h>
33 #include <netinet/in_systm.h>
34 #include <netinet/in.h>
35 #include <netinet/ip.h>
36 #include <netinet/tcp.h>
47 #include "throughput.h"
54 #include "slcompress.h"
58 #include "descriptor.h"
70 * We are in a liberal position about MSS
71 * (RFC 879, section 7).
73 #define MAXMSS(mtu) (mtu - sizeof(struct ip) - sizeof(struct tcphdr))
77 * The following macro is used to update an
78 * internet checksum. "acc" is a 32-bit
79 * accumulation of all the changes to the
80 * checksum (adding in old 16-bit words and
81 * subtracting out new words), and "cksum"
82 * is the checksum value to be updated.
84 #define ADJUST_CHECKSUM(acc, cksum) { \
88 acc = (acc >> 16) + (acc & 0xffff); \
90 cksum = (u_short) ~acc; \
92 acc = (acc >> 16) + (acc & 0xffff); \
94 cksum = (u_short) acc; \
99 MSSFixup(struct tcphdr *tc, ssize_t pktlen, u_int16_t maxmss)
101 int hlen, olen, optlen;
106 hlen = tc->th_off << 2;
108 /* Invalid header length or header without options. */
109 if (hlen <= sizeof(struct tcphdr) || hlen > pktlen)
112 /* MSS option only allowed within SYN packets. */
113 if (!(tc->th_flags & TH_SYN))
116 for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
117 olen > 0; olen -= optlen, opt += optlen) {
118 if (*opt == TCPOPT_EOL)
120 else if (*opt == TCPOPT_NOP)
124 if (optlen <= 0 || optlen > olen)
126 if (*opt == TCPOPT_MAXSEG) {
127 if (optlen != TCPOLEN_MAXSEG)
129 mss = (u_int16_t *)(opt + 2);
130 if (ntohs(*mss) > maxmss) {
131 log_Printf(LogDEBUG, "MSS: %u -> %u\n",
132 ntohs(*mss), maxmss);
134 *mss = htons(maxmss);
136 ADJUST_CHECKSUM(accumulate, tc->th_sum);
144 tcpmss_Check(struct bundle *bundle, struct mbuf *bp)
149 if (!Enabled(bundle, OPT_TCPMSSFIXUP))
154 pip = (struct ip *)MBUF_CTOP(bp);
155 hlen = pip->ip_hl << 2;
158 * Check for MSS option only for TCP packets with zero fragment offsets
159 * and correct total and header lengths.
161 if (pip->ip_p == IPPROTO_TCP && (ntohs(pip->ip_off) & IP_OFFMASK) == 0 &&
162 ntohs(pip->ip_len) == plen && hlen <= plen &&
163 plen - hlen >= sizeof(struct tcphdr))
164 MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
165 MAXMSS(bundle->iface->mtu));
171 tcpmss_LayerPush(struct bundle *bundle, struct link *l, struct mbuf *bp,
172 int pri, u_short *proto)
174 return tcpmss_Check(bundle, bp);
178 tcpmss_LayerPull(struct bundle *bundle, struct link *l, struct mbuf *bp,
181 return tcpmss_Check(bundle, bp);
184 struct layer tcpmsslayer =
185 { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, tcpmss_LayerPull };