Add ``enable/disable tcpmssfixup'', defaulting to enabled.

Suggested by:	julian
Hijacked from:	ru (ports/net/tcpmssd)

usr.sbin/ppp/Makefile

@@ -5,8 +5,8 @@ SRCS=	acf.c arp.c async.c auth.c bundle.c cbcp.c ccp.c chap.c chat.c \
 	command.c datalink.c deflate.c defs.c exec.c filter.c fsm.c hdlc.c \
 	iface.c ip.c ipcp.c iplist.c lcp.c link.c log.c lqr.c main.c \
 	mbuf.c mp.c pap.c physical.c pred.c probe.c prompt.c proto.c route.c \
-	server.c sig.c slcompress.c sync.c systems.c tcp.c throughput.c \
-	timer.c tty.c tun.c udp.c vjcomp.c
+	server.c sig.c slcompress.c sync.c systems.c tcp.c tcpmss.c \
+	throughput.c timer.c tty.c tun.c udp.c vjcomp.c
 CFLAGS+=-Wall
 LDADD+= -lcrypt -lmd -lutil -lz
 DPADD+=	${LIBCRYPT} ${LIBMD} ${LIBUTIL} ${LIBZ}

usr.sbin/ppp/bundle.c

@@ -797,6 +797,7 @@ bundle_Create(const char *prefix, int type, int unit)
   log_Printf(LogPHASE, "Using interface: %s\n", ifname);
 
   bundle.bandwidth = 0;
+  bundle.mtu = 1500;
   bundle.routing_seq = 0;
   bundle.phase = PHASE_DEAD;
   bundle.CleaningUp = 0;
@@ -812,7 +813,7 @@ bundle_Create(const char *prefix, int type, int unit)
   bundle.cfg.idle.min_timeout = 0;
   *bundle.cfg.auth.name = '\0';
   *bundle.cfg.auth.key = '\0';
-  bundle.cfg.opt = OPT_SROUTES | OPT_IDCHECK | OPT_LOOPBACK |
+  bundle.cfg.opt = OPT_SROUTES | OPT_IDCHECK | OPT_LOOPBACK | OPT_TCPMSSFIXUP |
                    OPT_THROUGHPUT | OPT_UTMP;
   *bundle.cfg.label = '\0';
   bundle.cfg.mtu = DEF_MTU;
@@ -1232,9 +1233,11 @@ bundle_ShowStatus(struct cmdargs const *arg)
                 optval(arg->bundle, OPT_PROXY));
   prompt_Printf(arg->prompt, " Proxyall:      %s\n",
                 optval(arg->bundle, OPT_PROXYALL));
-  prompt_Printf(arg->prompt, " Throughput:    %-20.20s",
+  prompt_Printf(arg->prompt, " TCPMSS Fixup:  %-20.20s",
+                optval(arg->bundle, OPT_TCPMSSFIXUP));
+  prompt_Printf(arg->prompt, " Throughput:    %s\n",
                 optval(arg->bundle, OPT_THROUGHPUT));
-  prompt_Printf(arg->prompt, " Utmp Logging:  %s\n",
+  prompt_Printf(arg->prompt, " Utmp Logging:  %-20.20s",
                 optval(arg->bundle, OPT_UTMP));
   prompt_Printf(arg->prompt, " Iface-Alias:   %s\n",
                 optval(arg->bundle, OPT_IFACEALIAS));
@@ -1924,10 +1927,10 @@ void
 bundle_CalculateBandwidth(struct bundle *bundle)
 {
   struct datalink *dl;
-  int mtu, sp;
+  int sp;
 
   bundle->bandwidth = 0;
-  mtu = 0;
+  bundle->mtu = 0;
   for (dl = bundle->links; dl; dl = dl->next)
     if (dl->state == DATALINK_OPEN) {
       if ((sp = dl->mp.bandwidth) == 0 &&
@@ -1937,7 +1940,7 @@ bundle_CalculateBandwidth(struct bundle *bundle)
       else
         bundle->bandwidth += sp;
       if (!bundle->ncp.mp.active) {
-        mtu = dl->physical->link.lcp.his_mru;
+        bundle->mtu = dl->physical->link.lcp.his_mru;
         break;
       }
     }
@@ -1946,19 +1949,20 @@ bundle_CalculateBandwidth(struct bundle *bundle)
     bundle->bandwidth = 115200;		/* Shrug */
 
   if (bundle->ncp.mp.active)
-    mtu = bundle->ncp.mp.peer_mrru;
-  else if (!mtu)
-    mtu = 1500;
+    bundle->mtu = bundle->ncp.mp.peer_mrru;
+  else if (!bundle->mtu)
+    bundle->mtu = 1500;
 
 #ifndef NORADIUS
-  if (bundle->radius.valid && bundle->radius.mtu && bundle->radius.mtu < mtu) {
+  if (bundle->radius.valid && bundle->radius.mtu &&
+      bundle->radius.mtu < bundle->mtu) {
     log_Printf(LogLCP, "Reducing MTU to radius value %lu\n",
                bundle->radius.mtu);
-    mtu = bundle->radius.mtu;
+    bundle->mtu = bundle->radius.mtu;
   }
 #endif
 
-  tun_configure(bundle, mtu);
+  tun_configure(bundle);
 }
 
 void

usr.sbin/ppp/bundle.h

@@ -42,8 +42,9 @@
 #define OPT_PROXY	0x0040
 #define OPT_PROXYALL	0x0080
 #define OPT_SROUTES	0x0100
-#define OPT_THROUGHPUT	0x0200
-#define OPT_UTMP	0x0400
+#define OPT_TCPMSSFIXUP	0x0200
+#define OPT_THROUGHPUT	0x0400
+#define OPT_UTMP	0x0800
 
 #define MAX_ENDDISC_CLASS 5
 
@@ -72,6 +73,7 @@ struct bundle {
   } dev;
 
   u_long bandwidth;           /* struct tuninfo speed */
+  int mtu;                    /* struct tuninfo MTU */
   struct iface *iface;        /* Interface information */
 
   int routing_seq;            /* The current routing sequence number */
@@ -101,7 +103,7 @@ struct bundle {
     } auth;
     unsigned opt;             /* Uses OPT_ bits from above */
     char label[50];           /* last thing `load'ed */
-    u_short mtu;              /* Interface mtu */
+    u_short mtu;              /* Required interface MTU */
     u_short ifqueue;          /* Interface queue size */
 
     struct {

usr.sbin/ppp/command.c

@@ -2531,12 +2531,14 @@ static struct cmdtab const NegotiateCommands[] = {
   "disable|enable", (const void *)OPT_PROXYALL},
   {"sroutes", NULL, OptSet, LOCAL_AUTH, "Use sticky routes",
   "disable|enable", (const void *)OPT_SROUTES},
+  {"tcpmssfixup", "mssfixup", OptSet, LOCAL_AUTH, "Modify MSS options",
+  "disable|enable", (const void *)OPT_TCPMSSFIXUP},
   {"throughput", NULL, OptSet, LOCAL_AUTH, "Rolling throughput",
   "disable|enable", (const void *)OPT_THROUGHPUT},
   {"utmp", NULL, OptSet, LOCAL_AUTH, "Log connections in utmp",
   "disable|enable", (const void *)OPT_UTMP},
 
-#define OPT_MAX 10	/* accept/deny allowed below and not above */
+#define OPT_MAX 11	/* accept/deny allowed below and not above */
 
   {"acfcomp", NULL, NegotiateSet, LOCAL_AUTH | LOCAL_CX,
   "Address & Control field compression", "accept|deny|disable|enable",

usr.sbin/ppp/physical.c

@@ -99,6 +99,7 @@
 #ifndef NOATM
 #include "atm.h"
 #endif
+#include "tcpmss.h"
 
 #define PPPOTCPLINE "ppp"
 
@@ -1052,6 +1053,7 @@ physical_SetupStack(struct physical *p, const char *who, int how)
   link_Stack(&p->link, &lqrlayer);
   link_Stack(&p->link, &ccplayer);
   link_Stack(&p->link, &vjlayer);
+  link_Stack(&p->link, &tcpmsslayer);
 #ifndef NONAT
   link_Stack(&p->link, &natlayer);
 #endif

usr.sbin/ppp/ppp.8

@@ -3007,6 +3007,14 @@ Disabling this option will prevent the re-application of sticky routes,
 although the
 .Sq stick route
 list will still be maintained.
+.It Op tcp Ns Xo
+.No mssfixup
+.Xc
+Default: Enabled.
+This option tells
+.Nm
+to adjust outgoing TCP SYN packets so that the maximum receive segment
+size is not greater than the amount allowed by the interface MTU.
 .It throughput
 Default: Enabled.
 This option tells

usr.sbin/ppp/ppp.8.m4

@@ -3007,6 +3007,14 @@ Disabling this option will prevent the re-application of sticky routes,
 although the
 .Sq stick route
 list will still be maintained.
+.It Op tcp Ns Xo
+.No mssfixup
+.Xc
+Default: Enabled.
+This option tells
+.Nm
+to adjust outgoing TCP SYN packets so that the maximum receive segment
+size is not greater than the amount allowed by the interface MTU.
 .It throughput
 Default: Enabled.
 This option tells

usr.sbin/ppp/tcpmss.c

@@ -0,0 +1,168 @@
+/*-
+ * 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.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/param.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 "ipcp.h"
+#include "filter.h"
+#include "descriptor.h"
+#include "mp.h"
+#ifndef NORADIUS
+#include "radius.h"
+#endif
+#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)) 
+
+
+static void MSSFixup(struct tcphdr *, ssize_t, u_int16_t);
+
+
+static struct mbuf *
+tcpmss_LayerPush(struct bundle *bundle, struct link *l, struct mbuf *bp,
+                 int pri, u_short *proto)
+{
+  struct ip *pip;
+  int 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 - hlen >= sizeof(struct tcphdr))
+    MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
+             MAXMSS(bundle->mtu));
+
+  return bp;
+}
+
+/*-
+ * 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, ssize_t pktlen, u_int16_t maxmss)
+{
+  int 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);
+        }
+      }
+    }
+  }
+}
+
+struct layer tcpmsslayer = { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, NULL };

usr.sbin/ppp/tcpmss.h

@@ -0,0 +1,29 @@
+/*-
+ * Copyright (c) 2000 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.
+ *
+ * $FreeBSD$
+ */
+
+extern struct layer tcpmsslayer;

usr.sbin/ppp/tun.c

@@ -74,7 +74,7 @@
 #include "tun.h"
 
 void
-tun_configure(struct bundle *bundle, int mtu)
+tun_configure(struct bundle *bundle)
 {
 #ifdef __NetBSD__
   struct ifreq ifr;
@@ -88,7 +88,7 @@ tun_configure(struct bundle *bundle, int mtu)
   }
 
   sprintf(ifr.ifr_name, "tun%d", bundle->unit);
-  ifr.ifr_mtu = mtu;
+  ifr.ifr_mtu = bundle->mtu;
   if (ioctl(s, SIOCSIFMTU, &ifr) < 0)
       log_Printf(LogERROR, "tun_configure: ioctl(SIOCSIFMTU): %s\n",
              strerror(errno));
@@ -99,7 +99,7 @@ tun_configure(struct bundle *bundle, int mtu)
 
   memset(&info, '\0', sizeof info);
   info.type = IFT_PPP;
-  info.mtu = mtu;
+  info.mtu = bundle->mtu;
   
   info.baudrate = bundle->bandwidth;
 #ifdef __OpenBSD__

usr.sbin/ppp/tun.h

@@ -36,4 +36,4 @@ struct tun_data {
 
 struct bundle;
 
-extern void tun_configure(struct bundle *, int);
+extern void tun_configure(struct bundle *);