169 lines
4.6 KiB
C
169 lines
4.6 KiB
C
/*-
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* Copyright (c) 2000 Ruslan Ermilov and Brian Somers <brian@Awfulhak.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#include <sys/param.h>
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#include <netinet/in_systm.h>
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#include <netinet/in.h>
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#include <netinet/ip.h>
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#include <netinet/tcp.h>
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#include <sys/un.h>
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#include <termios.h>
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#include "layer.h"
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#include "defs.h"
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#include "log.h"
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#include "timer.h"
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#include "fsm.h"
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#include "mbuf.h"
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#include "throughput.h"
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#include "lqr.h"
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#include "hdlc.h"
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#include "lcp.h"
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#include "ccp.h"
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#include "link.h"
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#include "iplist.h"
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#include "slcompress.h"
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#include "ipcp.h"
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#include "filter.h"
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#include "descriptor.h"
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#include "mp.h"
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#ifndef NORADIUS
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#include "radius.h"
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#endif
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#include "bundle.h"
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/*-
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* We are in a liberal position about MSS
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* (RFC 879, section 7).
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*/
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#define MAXMSS(mtu) (mtu - sizeof(struct ip) - sizeof(struct tcphdr))
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static void MSSFixup(struct tcphdr *, ssize_t, u_int16_t);
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static struct mbuf *
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tcpmss_LayerPush(struct bundle *bundle, struct link *l, struct mbuf *bp,
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int pri, u_short *proto)
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{
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struct ip *pip;
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int hlen, plen;
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if (!Enabled(bundle, OPT_TCPMSSFIXUP))
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return bp;
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bp = m_pullup(bp);
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plen = m_length(bp);
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pip = (struct ip *)MBUF_CTOP(bp);
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hlen = pip->ip_hl << 2;
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/*
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* Check for MSS option only for TCP packets with zero fragment offsets
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* and correct total and header lengths.
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*/
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if (pip->ip_p == IPPROTO_TCP && (ntohs(pip->ip_off) & IP_OFFMASK) == 0 &&
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ntohs(pip->ip_len) == plen && hlen <= plen &&
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plen - hlen >= sizeof(struct tcphdr))
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MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
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MAXMSS(bundle->mtu));
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return bp;
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}
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/*-
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* The following macro is used to update an
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* internet checksum. "acc" is a 32-bit
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* accumulation of all the changes to the
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* checksum (adding in old 16-bit words and
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* subtracting out new words), and "cksum"
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* is the checksum value to be updated.
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*/
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#define ADJUST_CHECKSUM(acc, cksum) { \
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acc += cksum; \
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if (acc < 0) { \
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acc = -acc; \
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acc = (acc >> 16) + (acc & 0xffff); \
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acc += acc >> 16; \
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cksum = (u_short) ~acc; \
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} else { \
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acc = (acc >> 16) + (acc & 0xffff); \
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acc += acc >> 16; \
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cksum = (u_short) acc; \
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} \
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}
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static void
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MSSFixup(struct tcphdr *tc, ssize_t pktlen, u_int16_t maxmss)
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{
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int hlen, olen, optlen;
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u_char *opt;
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u_int16_t *mss;
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int accumulate;
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hlen = tc->th_off << 2;
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/* Invalid header length or header without options. */
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if (hlen <= sizeof(struct tcphdr) || hlen > pktlen)
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return;
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/* MSS option only allowed within SYN packets. */
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if (!(tc->th_flags & TH_SYN))
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return;
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for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
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olen > 0; olen -= optlen, opt += optlen) {
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if (*opt == TCPOPT_EOL)
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break;
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else if (*opt == TCPOPT_NOP)
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optlen = 1;
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else {
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optlen = *(opt + 1);
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if (optlen <= 0 || optlen > olen)
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break;
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if (*opt == TCPOPT_MAXSEG) {
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if (optlen != TCPOLEN_MAXSEG)
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continue;
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mss = (u_int16_t *)(opt + 2);
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if (ntohs(*mss) > maxmss) {
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log_Printf(LogDEBUG, "MSS: %u -> %u\n",
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ntohs(*mss), maxmss);
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accumulate = *mss;
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*mss = htons(maxmss);
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accumulate -= *mss;
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ADJUST_CHECKSUM(accumulate, tc->th_sum);
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}
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}
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}
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}
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}
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struct layer tcpmsslayer = { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, NULL };
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