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Diffstat (limited to 'src/tcpmss.c')
| -rw-r--r-- | src/tcpmss.c | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/src/tcpmss.c b/src/tcpmss.c new file mode 100644 index 0000000..faa76da --- /dev/null +++ b/src/tcpmss.c @@ -0,0 +1,185 @@ +/*- + * Copyright (c) 2000 Ruslan Ermilov and Brian Somers <brian@Awfulhak.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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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: src/usr.sbin/ppp/tcpmss.c,v 1.8.26.1 2010/12/21 17:10:29 kensmith Exp $ + */ + +#include <sys/param.h> + +#include <sys/socket.h> +#include <net/route.h> +#include <netinet/in_systm.h> +#include <netinet/in.h> +#include <netinet/ip.h> +#include <netinet/tcp.h> +#include <sys/un.h> + +#include <termios.h> + +#include "layer.h" +#include "defs.h" +#include "log.h" +#include "timer.h" +#include "fsm.h" +#include "mbuf.h" +#include "throughput.h" +#include "lqr.h" +#include "hdlc.h" +#include "lcp.h" +#include "ccp.h" +#include "link.h" +#include "iplist.h" +#include "slcompress.h" +#include "ncpaddr.h" +#include "ipcp.h" +#include "filter.h" +#include "descriptor.h" +#include "mp.h" +#include "iface.h" +#ifndef NORADIUS +#include "radius.h" +#endif +#include "ipv6cp.h" +#include "ncp.h" +#include "bundle.h" + + +/*- + * We are in a liberal position about MSS + * (RFC 879, section 7). + */ +#define MAXMSS(mtu) ((mtu) - sizeof(struct ip) - sizeof(struct tcphdr) - 12) + + +/*- + * The following macro is used to update an + * internet checksum. "acc" is a 32-bit + * accumulation of all the changes to the + * checksum (adding in old 16-bit words and + * subtracting out new words), and "cksum" + * is the checksum value to be updated. + */ +#define ADJUST_CHECKSUM(acc, cksum) { \ + acc += cksum; \ + if (acc < 0) { \ + acc = -acc; \ + acc = (acc >> 16) + (acc & 0xffff); \ + acc += acc >> 16; \ + cksum = (u_short) ~acc; \ + } else { \ + acc = (acc >> 16) + (acc & 0xffff); \ + acc += acc >> 16; \ + cksum = (u_short) acc; \ + } \ +} + +static void +MSSFixup(struct tcphdr *tc, size_t pktlen, u_int16_t maxmss) +{ + size_t hlen, olen, optlen; + u_char *opt; + u_int16_t *mss; + int accumulate; + + hlen = tc->th_off << 2; + + /* Invalid header length or header without options. */ + if (hlen <= sizeof(struct tcphdr) || hlen > pktlen) + return; + + /* MSS option only allowed within SYN packets. */ + if (!(tc->th_flags & TH_SYN)) + return; + + for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1); + olen > 0; olen -= optlen, opt += optlen) { + if (*opt == TCPOPT_EOL) + break; + else if (*opt == TCPOPT_NOP) + optlen = 1; + else { + optlen = *(opt + 1); + if (optlen <= 0 || optlen > olen) + break; + if (*opt == TCPOPT_MAXSEG) { + if (optlen != TCPOLEN_MAXSEG) + continue; + mss = (u_int16_t *)(opt + 2); + if (ntohs(*mss) > maxmss) { + log_Printf(LogDEBUG, "MSS: %u -> %u\n", + ntohs(*mss), maxmss); + accumulate = *mss; + *mss = htons(maxmss); + accumulate -= *mss; + ADJUST_CHECKSUM(accumulate, tc->th_sum); + } + } + } + } +} + +static struct mbuf * +tcpmss_Check(struct bundle *bundle, struct mbuf *bp) +{ + struct ip *pip; + size_t hlen, plen; + + if (!Enabled(bundle, OPT_TCPMSSFIXUP)) + return bp; + + bp = m_pullup(bp); + plen = m_length(bp); + pip = (struct ip *)MBUF_CTOP(bp); + hlen = pip->ip_hl << 2; + + /* + * Check for MSS option only for TCP packets with zero fragment offsets + * and correct total and header lengths. + */ + if (pip->ip_p == IPPROTO_TCP && (ntohs(pip->ip_off) & IP_OFFMASK) == 0 && + ntohs(pip->ip_len) == plen && hlen <= plen && + plen >= sizeof(struct tcphdr) + hlen) + MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen, + MAXMSS(bundle->iface->mtu)); + + return bp; +} + +static struct mbuf * +tcpmss_LayerPush(struct bundle *bundle, struct link *l __unused, + struct mbuf *bp, int pri __unused, u_short *proto __unused) +{ + return tcpmss_Check(bundle, bp); +} + +static struct mbuf * +tcpmss_LayerPull(struct bundle *bundle, struct link *l __unused, + struct mbuf *bp, u_short *proto __unused) +{ + return tcpmss_Check(bundle, bp); +} + +struct layer tcpmsslayer = + { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, tcpmss_LayerPull }; |