The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netgraph/ng_tcpmss.c

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    1 /*-
    2  * ng_tcpmss.c
    3  *
    4  * Copyright (c) 2004, Alexey Popov <lollypop@flexuser.ru>
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice unmodified, this list of conditions, and the following
   12  *    disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  * This software includes fragments of the following programs:
   30  *      tcpmssd         Ruslan Ermilov <ru@FreeBSD.org>
   31  *
   32  * $FreeBSD: releng/11.1/sys/netgraph/ng_tcpmss.c 206032 2010-04-01 10:41:01Z mav $
   33  */
   34 
   35 /*
   36  * This node is netgraph tool for workaround of PMTUD problem. It acts
   37  * like filter for IP packets. If configured, it reduces MSS of TCP SYN
   38  * packets.
   39  *
   40  * Configuration can be done by sending NGM_TCPMSS_CONFIG message. The
   41  * message sets filter for incoming packets on hook 'inHook'. Packet's
   42  * TCP MSS field is lowered to 'maxMSS' parameter and resulting packet
   43  * is sent to 'outHook'.
   44  *
   45  * XXX: statistics are updated not atomically, so they may broke on SMP.
   46  */
   47 
   48 #include <sys/param.h>
   49 #include <sys/systm.h>
   50 #include <sys/endian.h>
   51 #include <sys/errno.h>
   52 #include <sys/kernel.h>
   53 #include <sys/malloc.h>
   54 #include <sys/mbuf.h>
   55 
   56 #include <netinet/in.h>
   57 #include <netinet/in_systm.h>
   58 #include <netinet/ip.h>
   59 #include <netinet/tcp.h>
   60 
   61 #include <netgraph/ng_message.h>
   62 #include <netgraph/netgraph.h>
   63 #include <netgraph/ng_parse.h>
   64 #include <netgraph/ng_tcpmss.h>
   65 
   66 /* Per hook info. */
   67 typedef struct {
   68         hook_p                          outHook;
   69         struct ng_tcpmss_hookstat       stats;
   70 } *hpriv_p;
   71 
   72 /* Netgraph methods. */
   73 static ng_constructor_t ng_tcpmss_constructor;
   74 static ng_rcvmsg_t      ng_tcpmss_rcvmsg;
   75 static ng_newhook_t     ng_tcpmss_newhook;
   76 static ng_rcvdata_t     ng_tcpmss_rcvdata;
   77 static ng_disconnect_t  ng_tcpmss_disconnect;
   78 
   79 static int correct_mss(struct tcphdr *, int, uint16_t, int);
   80 
   81 /* Parse type for struct ng_tcpmss_hookstat. */
   82 static const struct ng_parse_struct_field ng_tcpmss_hookstat_type_fields[]
   83         = NG_TCPMSS_HOOKSTAT_INFO;
   84 static const struct ng_parse_type ng_tcpmss_hookstat_type = {
   85         &ng_parse_struct_type,
   86         &ng_tcpmss_hookstat_type_fields
   87 };
   88 
   89 /* Parse type for struct ng_tcpmss_config. */
   90 static const struct ng_parse_struct_field ng_tcpmss_config_type_fields[]
   91         = NG_TCPMSS_CONFIG_INFO;
   92 static const struct ng_parse_type ng_tcpmss_config_type = {
   93         &ng_parse_struct_type,
   94         ng_tcpmss_config_type_fields
   95 };
   96 
   97 /* List of commands and how to convert arguments to/from ASCII. */
   98 static const struct ng_cmdlist ng_tcpmss_cmds[] = {
   99         {
  100           NGM_TCPMSS_COOKIE,
  101           NGM_TCPMSS_GET_STATS,
  102           "getstats",
  103           &ng_parse_hookbuf_type,
  104           &ng_tcpmss_hookstat_type
  105         },
  106         {
  107           NGM_TCPMSS_COOKIE,
  108           NGM_TCPMSS_CLR_STATS,
  109           "clrstats",
  110           &ng_parse_hookbuf_type,
  111           NULL
  112         },
  113         {
  114           NGM_TCPMSS_COOKIE,
  115           NGM_TCPMSS_GETCLR_STATS,
  116           "getclrstats",
  117           &ng_parse_hookbuf_type,
  118           &ng_tcpmss_hookstat_type
  119         },
  120         {
  121           NGM_TCPMSS_COOKIE,
  122           NGM_TCPMSS_CONFIG,
  123           "config",
  124           &ng_tcpmss_config_type,
  125           NULL
  126         },
  127         { 0 }
  128 };
  129 
  130 /* Netgraph type descriptor. */
  131 static struct ng_type ng_tcpmss_typestruct = {
  132         .version =      NG_ABI_VERSION,
  133         .name =         NG_TCPMSS_NODE_TYPE,
  134         .constructor =  ng_tcpmss_constructor,
  135         .rcvmsg =       ng_tcpmss_rcvmsg,
  136         .newhook =      ng_tcpmss_newhook,
  137         .rcvdata =      ng_tcpmss_rcvdata,
  138         .disconnect =   ng_tcpmss_disconnect,
  139         .cmdlist =      ng_tcpmss_cmds,
  140 };
  141 
  142 NETGRAPH_INIT(tcpmss, &ng_tcpmss_typestruct);
  143 
  144 #define ERROUT(x)       { error = (x); goto done; }
  145 
  146 /*
  147  * Node constructor. No special actions required.
  148  */
  149 static int
  150 ng_tcpmss_constructor(node_p node)
  151 {
  152         return (0);
  153 }
  154 
  155 /*
  156  * Add a hook. Any unique name is OK.
  157  */
  158 static int
  159 ng_tcpmss_newhook(node_p node, hook_p hook, const char *name)
  160 {
  161         hpriv_p priv;
  162 
  163         priv = malloc(sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO);
  164         if (priv == NULL)
  165                 return (ENOMEM);
  166 
  167         NG_HOOK_SET_PRIVATE(hook, priv);
  168 
  169         return (0);
  170 }
  171 
  172 /*
  173  * Receive a control message.
  174  */
  175 static int
  176 ng_tcpmss_rcvmsg
  177 (node_p node, item_p item, hook_p lasthook)
  178 {
  179         struct ng_mesg *msg, *resp = NULL;
  180         int error = 0;
  181 
  182         NGI_GET_MSG(item, msg);
  183 
  184         switch (msg->header.typecookie) {
  185         case NGM_TCPMSS_COOKIE:
  186                 switch (msg->header.cmd) {
  187                 case NGM_TCPMSS_GET_STATS:
  188                 case NGM_TCPMSS_CLR_STATS:
  189                 case NGM_TCPMSS_GETCLR_STATS:
  190                     {
  191                         hook_p hook;
  192                         hpriv_p priv;
  193 
  194                         /* Check that message is long enough. */
  195                         if (msg->header.arglen != NG_HOOKSIZ)
  196                                 ERROUT(EINVAL);
  197 
  198                         /* Find this hook. */
  199                         hook = ng_findhook(node, (char *)msg->data);
  200                         if (hook == NULL)
  201                                 ERROUT(ENOENT);
  202 
  203                         priv = NG_HOOK_PRIVATE(hook);
  204 
  205                         /* Create response. */
  206                         if (msg->header.cmd != NGM_TCPMSS_CLR_STATS) {
  207                                 NG_MKRESPONSE(resp, msg,
  208                                     sizeof(struct ng_tcpmss_hookstat), M_NOWAIT);
  209                                 if (resp == NULL)
  210                                         ERROUT(ENOMEM);
  211                                 bcopy(&priv->stats, resp->data,
  212                                     sizeof(struct ng_tcpmss_hookstat)); 
  213                         }
  214 
  215                         if (msg->header.cmd != NGM_TCPMSS_GET_STATS)
  216                                 bzero(&priv->stats,
  217                                     sizeof(struct ng_tcpmss_hookstat));
  218                         break;
  219                     }
  220                 case NGM_TCPMSS_CONFIG:
  221                     {
  222                         struct ng_tcpmss_config *set;
  223                         hook_p in, out;
  224                         hpriv_p priv;
  225 
  226                         /* Check that message is long enough. */
  227                         if (msg->header.arglen !=
  228                             sizeof(struct ng_tcpmss_config))
  229                                 ERROUT(EINVAL);
  230 
  231                         set = (struct ng_tcpmss_config *)msg->data;
  232                         in = ng_findhook(node, set->inHook);
  233                         out = ng_findhook(node, set->outHook);
  234                         if (in == NULL || out == NULL)
  235                                 ERROUT(ENOENT);
  236 
  237                         /* Configure MSS hack. */
  238                         priv = NG_HOOK_PRIVATE(in);
  239                         priv->outHook = out;
  240                         priv->stats.maxMSS = set->maxMSS;
  241 
  242                         break;
  243                     }
  244                 default:
  245                         error = EINVAL;
  246                         break;
  247                 }
  248                 break;
  249         default:
  250                 error = EINVAL;
  251                 break;
  252         }
  253 
  254 done:
  255         NG_RESPOND_MSG(error, node, item, resp);
  256         NG_FREE_MSG(msg);
  257 
  258         return (error);
  259 }
  260 
  261 /*
  262  * Receive data on a hook, and hack MSS.
  263  *
  264  */
  265 static int
  266 ng_tcpmss_rcvdata(hook_p hook, item_p item)
  267 {
  268         hpriv_p priv = NG_HOOK_PRIVATE(hook);
  269         struct mbuf *m = NULL;
  270         struct ip *ip;
  271         struct tcphdr *tcp;
  272         int iphlen, tcphlen, pktlen;
  273         int pullup_len = 0;
  274         int error = 0;
  275 
  276         /* Drop packets if filter is not configured on this hook. */
  277         if (priv->outHook == NULL)
  278                 goto done;
  279 
  280         NGI_GET_M(item, m);
  281 
  282         /* Update stats on incoming hook. */
  283         pktlen = m->m_pkthdr.len;
  284         priv->stats.Octets += pktlen;
  285         priv->stats.Packets++;
  286 
  287         /* Check whether we configured to fix MSS. */
  288         if (priv->stats.maxMSS == 0)
  289                 goto send;
  290 
  291 #define M_CHECK(length) do {                                    \
  292         pullup_len += length;                                   \
  293         if ((m)->m_pkthdr.len < pullup_len)                     \
  294                 goto send;                                      \
  295         if ((m)->m_len < pullup_len &&                          \
  296            (((m) = m_pullup((m), pullup_len)) == NULL))         \
  297                 ERROUT(ENOBUFS);                                \
  298         } while (0)
  299 
  300         /* Check mbuf packet size and arrange for IP header. */
  301         M_CHECK(sizeof(struct ip));
  302         ip = mtod(m, struct ip *);
  303 
  304         /* Check IP version. */
  305         if (ip->ip_v != IPVERSION)
  306                 ERROUT(EINVAL);
  307 
  308         /* Check IP header length. */
  309         iphlen = ip->ip_hl << 2;
  310         if (iphlen < sizeof(struct ip) || iphlen > pktlen )
  311                 ERROUT(EINVAL);
  312 
  313         /* Check if it is TCP. */
  314         if (!(ip->ip_p == IPPROTO_TCP))
  315                 goto send;
  316 
  317         /* Check mbuf packet size and arrange for IP+TCP header */
  318         M_CHECK(iphlen - sizeof(struct ip) + sizeof(struct tcphdr));
  319         ip = mtod(m, struct ip *);
  320         tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
  321 
  322         /* Check TCP header length. */
  323         tcphlen = tcp->th_off << 2;
  324         if (tcphlen < sizeof(struct tcphdr) || tcphlen > pktlen - iphlen)
  325                 ERROUT(EINVAL);
  326 
  327         /* Check SYN packet and has options. */
  328         if (!(tcp->th_flags & TH_SYN) || tcphlen == sizeof(struct tcphdr))
  329                 goto send;
  330         
  331         /* Update SYN stats. */
  332         priv->stats.SYNPkts++;
  333 
  334         M_CHECK(tcphlen - sizeof(struct tcphdr));
  335         ip = mtod(m, struct ip *);
  336         tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
  337 
  338 #undef  M_CHECK
  339 
  340         /* Fix MSS and update stats. */
  341         if (correct_mss(tcp, tcphlen, priv->stats.maxMSS,
  342             m->m_pkthdr.csum_flags))
  343                 priv->stats.FixedPkts++;
  344 
  345 send:
  346         /* Deliver frame out destination hook. */
  347         NG_FWD_NEW_DATA(error, item, priv->outHook, m);
  348 
  349         return (error);
  350 
  351 done:
  352         NG_FREE_ITEM(item);
  353         NG_FREE_M(m);
  354 
  355         return (error);
  356 }
  357 
  358 /*
  359  * Hook disconnection.
  360  * We must check all hooks, since they may reference this one.
  361  */
  362 static int
  363 ng_tcpmss_disconnect(hook_p hook)
  364 {
  365         node_p node = NG_HOOK_NODE(hook);
  366         hook_p hook2;
  367 
  368         LIST_FOREACH(hook2, &node->nd_hooks, hk_hooks) {
  369                 hpriv_p priv = NG_HOOK_PRIVATE(hook2);
  370 
  371                 if (priv->outHook == hook)
  372                         priv->outHook = NULL;
  373         }
  374 
  375         free(NG_HOOK_PRIVATE(hook), M_NETGRAPH);
  376 
  377         if (NG_NODE_NUMHOOKS(NG_HOOK_NODE(hook)) == 0)
  378                 ng_rmnode_self(NG_HOOK_NODE(hook));
  379 
  380         return (0);
  381 }
  382 
  383 /*
  384  * Code from tcpmssd.
  385  */
  386 
  387 /*-
  388  * The following macro is used to update an
  389  * internet checksum.  "acc" is a 32-bit
  390  * accumulation of all the changes to the
  391  * checksum (adding in old 16-bit words and
  392  * subtracting out new words), and "cksum"
  393  * is the checksum value to be updated.
  394  */
  395 #define TCPMSS_ADJUST_CHECKSUM(acc, cksum) do {         \
  396         acc += cksum;                                   \
  397         if (acc < 0) {                                  \
  398                 acc = -acc;                             \
  399                 acc = (acc >> 16) + (acc & 0xffff);     \
  400                 acc += acc >> 16;                       \
  401                 cksum = (u_short) ~acc;                 \
  402         } else {                                        \
  403                 acc = (acc >> 16) + (acc & 0xffff);     \
  404                 acc += acc >> 16;                       \
  405                 cksum = (u_short) acc;                  \
  406         }                                               \
  407 } while (0);
  408 
  409 static int
  410 correct_mss(struct tcphdr *tc, int hlen, uint16_t maxmss, int flags)
  411 {
  412         int olen, optlen;
  413         u_char *opt;
  414         int accumulate;
  415         int res = 0;
  416         uint16_t sum;
  417 
  418         for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
  419              olen > 0; olen -= optlen, opt += optlen) {
  420                 if (*opt == TCPOPT_EOL)
  421                         break;
  422                 else if (*opt == TCPOPT_NOP)
  423                         optlen = 1;
  424                 else {
  425                         optlen = *(opt + 1);
  426                         if (optlen <= 0 || optlen > olen)
  427                                 break;
  428                         if (*opt == TCPOPT_MAXSEG) {
  429                                 if (optlen != TCPOLEN_MAXSEG)
  430                                         continue;
  431                                 accumulate = be16dec(opt + 2);
  432                                 if (accumulate > maxmss) {
  433                                         if ((flags & CSUM_TCP) == 0) {
  434                                                 accumulate -= maxmss;
  435                                                 sum = be16dec(&tc->th_sum);
  436                                                 TCPMSS_ADJUST_CHECKSUM(accumulate, sum);
  437                                                 be16enc(&tc->th_sum, sum);
  438                                         }
  439                                         be16enc(opt + 2, maxmss);
  440                                         res = 1;
  441                                 }
  442                         }
  443                 }
  444         }
  445         return (res);
  446 }

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