The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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  * $FreeBSD$
   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/errno.h>
   51 #include <sys/kernel.h>
   52 #include <sys/malloc.h>
   53 #include <sys/mbuf.h>
   54 
   55 #include <netinet/in.h>
   56 #include <netinet/in_systm.h>
   57 #include <netinet/ip.h>
   58 #include <netinet/tcp.h>
   59 
   60 #include <netgraph/ng_message.h>
   61 #include <netgraph/netgraph.h>
   62 #include <netgraph/ng_parse.h>
   63 #include <netgraph/ng_tcpmss.h>
   64 
   65 /* Per hook info. */
   66 typedef struct {
   67         hook_p                          outHook;
   68         struct ng_tcpmss_hookstat       stats;
   69 } *hpriv_p;
   70 
   71 /* Netgraph methods. */
   72 static ng_constructor_t ng_tcpmss_constructor;
   73 static ng_rcvmsg_t      ng_tcpmss_rcvmsg;
   74 static ng_newhook_t     ng_tcpmss_newhook;
   75 static ng_rcvdata_t     ng_tcpmss_rcvdata;
   76 static ng_disconnect_t  ng_tcpmss_disconnect;
   77 
   78 static int correct_mss(struct tcphdr *, int, uint16_t, int);
   79 
   80 /* Parse type for struct ng_tcpmss_hookstat. */
   81 static const struct ng_parse_struct_field ng_tcpmss_hookstat_type_fields[]
   82         = NG_TCPMSS_HOOKSTAT_INFO;
   83 static const struct ng_parse_type ng_tcpmss_hookstat_type = {
   84         &ng_parse_struct_type,
   85         &ng_tcpmss_hookstat_type_fields
   86 };
   87 
   88 /* Parse type for struct ng_tcpmss_config. */
   89 static const struct ng_parse_struct_field ng_tcpmss_config_type_fields[]
   90         = NG_TCPMSS_CONFIG_INFO;
   91 static const struct ng_parse_type ng_tcpmss_config_type = {
   92         &ng_parse_struct_type,
   93         ng_tcpmss_config_type_fields
   94 };
   95 
   96 /* List of commands and how to convert arguments to/from ASCII. */
   97 static const struct ng_cmdlist ng_tcpmss_cmds[] = {
   98         {
   99           NGM_TCPMSS_COOKIE,
  100           NGM_TCPMSS_GET_STATS,
  101           "getstats",
  102           &ng_parse_hookbuf_type,
  103           &ng_tcpmss_hookstat_type
  104         },
  105         {
  106           NGM_TCPMSS_COOKIE,
  107           NGM_TCPMSS_CLR_STATS,
  108           "clrstats",
  109           &ng_parse_hookbuf_type,
  110           NULL
  111         },
  112         {
  113           NGM_TCPMSS_COOKIE,
  114           NGM_TCPMSS_GETCLR_STATS,
  115           "getclrstats",
  116           &ng_parse_hookbuf_type,
  117           &ng_tcpmss_hookstat_type
  118         },
  119         {
  120           NGM_TCPMSS_COOKIE,
  121           NGM_TCPMSS_CONFIG,
  122           "config",
  123           &ng_tcpmss_config_type,
  124           NULL
  125         },
  126         { 0 }
  127 };
  128 
  129 /* Netgraph type descriptor. */
  130 static struct ng_type ng_tcpmss_typestruct = {
  131         .version =      NG_ABI_VERSION,
  132         .name =         NG_TCPMSS_NODE_TYPE,
  133         .constructor =  ng_tcpmss_constructor,
  134         .rcvmsg =       ng_tcpmss_rcvmsg,
  135         .newhook =      ng_tcpmss_newhook,
  136         .rcvdata =      ng_tcpmss_rcvdata,
  137         .disconnect =   ng_tcpmss_disconnect,
  138         .cmdlist =      ng_tcpmss_cmds,
  139 };
  140 
  141 NETGRAPH_INIT(tcpmss, &ng_tcpmss_typestruct);
  142 
  143 #define ERROUT(x)       { error = (x); goto done; }
  144 
  145 /*
  146  * Node constructor. No special actions required.
  147  */
  148 static int
  149 ng_tcpmss_constructor(node_p node)
  150 {
  151         return (0);
  152 }
  153 
  154 /*
  155  * Add a hook. Any unique name is OK.
  156  */
  157 static int
  158 ng_tcpmss_newhook(node_p node, hook_p hook, const char *name)
  159 {
  160         hpriv_p priv;
  161 
  162         MALLOC(priv, hpriv_p, sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO);
  163         if (priv == NULL)
  164                 return (ENOMEM);
  165 
  166         NG_HOOK_SET_PRIVATE(hook, priv);
  167 
  168         return (0);
  169 }
  170 
  171 /*
  172  * Receive a control message.
  173  */
  174 static int
  175 ng_tcpmss_rcvmsg
  176 (node_p node, item_p item, hook_p lasthook)
  177 {
  178         struct ng_mesg *msg, *resp = NULL;
  179         int error = 0;
  180 
  181         NGI_GET_MSG(item, msg);
  182 
  183         switch (msg->header.typecookie) {
  184         case NGM_TCPMSS_COOKIE:
  185                 switch (msg->header.cmd) {
  186                 case NGM_TCPMSS_GET_STATS:
  187                 case NGM_TCPMSS_CLR_STATS:
  188                 case NGM_TCPMSS_GETCLR_STATS:
  189                     {
  190                         hook_p hook;
  191                         hpriv_p priv;
  192 
  193                         /* Check that message is long enough. */
  194                         if (msg->header.arglen != NG_HOOKSIZ)
  195                                 ERROUT(EINVAL);
  196 
  197                         /* Find this hook. */
  198                         hook = ng_findhook(node, (char *)msg->data);
  199                         if (hook == NULL)
  200                                 ERROUT(ENOENT);
  201 
  202                         priv = NG_HOOK_PRIVATE(hook);
  203 
  204                         /* Create response. */
  205                         if (msg->header.cmd != NGM_TCPMSS_CLR_STATS) {
  206                                 NG_MKRESPONSE(resp, msg,
  207                                     sizeof(struct ng_tcpmss_hookstat), M_NOWAIT);
  208                                 if (resp == NULL)
  209                                         ERROUT(ENOMEM);
  210                                 bcopy(&priv->stats, resp->data,
  211                                     sizeof(struct ng_tcpmss_hookstat)); 
  212                         }
  213 
  214                         if (msg->header.cmd != NGM_TCPMSS_GET_STATS)
  215                                 bzero(&priv->stats,
  216                                     sizeof(struct ng_tcpmss_hookstat));
  217                         break;
  218                     }
  219                 case NGM_TCPMSS_CONFIG:
  220                     {
  221                         struct ng_tcpmss_config *set;
  222                         hook_p in, out;
  223                         hpriv_p priv;
  224 
  225                         /* Check that message is long enough. */
  226                         if (msg->header.arglen !=
  227                             sizeof(struct ng_tcpmss_config))
  228                                 ERROUT(EINVAL);
  229 
  230                         set = (struct ng_tcpmss_config *)msg->data;
  231                         in = ng_findhook(node, set->inHook);
  232                         out = ng_findhook(node, set->outHook);
  233                         if (in == NULL || out == NULL)
  234                                 ERROUT(ENOENT);
  235 
  236                         /* Configure MSS hack. */
  237                         priv = NG_HOOK_PRIVATE(in);
  238                         priv->outHook = out;
  239                         priv->stats.maxMSS = set->maxMSS;
  240 
  241                         break;
  242                     }
  243                 default:
  244                         error = EINVAL;
  245                         break;
  246                 }
  247                 break;
  248         default:
  249                 error = EINVAL;
  250                 break;
  251         }
  252 
  253 done:
  254         NG_RESPOND_MSG(error, node, item, resp);
  255         NG_FREE_MSG(msg);
  256 
  257         return (error);
  258 }
  259 
  260 /*
  261  * Receive data on a hook, and hack MSS.
  262  *
  263  */
  264 static int
  265 ng_tcpmss_rcvdata(hook_p hook, item_p item)
  266 {
  267         hpriv_p priv = NG_HOOK_PRIVATE(hook);
  268         struct mbuf *m = NULL;
  269         struct ip *ip;
  270         struct tcphdr *tcp;
  271         int iphlen, tcphlen, pktlen;
  272         int pullup_len = 0;
  273         int error = 0;
  274 
  275         /* Drop packets if filter is not configured on this hook. */
  276         if (priv->outHook == NULL)
  277                 goto done;
  278 
  279         NGI_GET_M(item, m);
  280 
  281         /* Update stats on incoming hook. */
  282         pktlen = m->m_pkthdr.len;
  283         priv->stats.Octets += pktlen;
  284         priv->stats.Packets++;
  285 
  286         /* Check whether we configured to fix MSS. */
  287         if (priv->stats.maxMSS == 0)
  288                 goto send;
  289 
  290 #define M_CHECK(length) do {                                    \
  291         pullup_len += length;                                   \
  292         if ((m)->m_pkthdr.len < pullup_len)                     \
  293                 goto send;                                      \
  294         if ((m)->m_len < pullup_len &&                          \
  295            (((m) = m_pullup((m), pullup_len)) == NULL))         \
  296                 ERROUT(ENOBUFS);                                \
  297         } while (0)
  298 
  299         /* Check mbuf packet size and arrange for IP header. */
  300         M_CHECK(sizeof(struct ip));
  301         ip = mtod(m, struct ip *);
  302 
  303         /* Check IP version. */
  304         if (ip->ip_v != IPVERSION)
  305                 ERROUT(EINVAL);
  306 
  307         /* Check IP header length. */
  308         iphlen = ip->ip_hl << 2;
  309         if (iphlen < sizeof(struct ip) || iphlen > pktlen )
  310                 ERROUT(EINVAL);
  311 
  312         /* Check if it is TCP. */
  313         if (!(ip->ip_p == IPPROTO_TCP))
  314                 goto send;
  315 
  316         /* Check mbuf packet size and arrange for IP+TCP header */
  317         M_CHECK(iphlen - sizeof(struct ip) + sizeof(struct tcphdr));
  318         ip = mtod(m, struct ip *);
  319         tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
  320 
  321         /* Check TCP header length. */
  322         tcphlen = tcp->th_off << 2;
  323         if (tcphlen < sizeof(struct tcphdr) || tcphlen > pktlen - iphlen)
  324                 ERROUT(EINVAL);
  325 
  326         /* Check SYN packet and has options. */
  327         if (!(tcp->th_flags & TH_SYN) || tcphlen == sizeof(struct tcphdr))
  328                 goto send;
  329         
  330         /* Update SYN stats. */
  331         priv->stats.SYNPkts++;
  332 
  333         M_CHECK(tcphlen - sizeof(struct tcphdr));
  334         ip = mtod(m, struct ip *);
  335         tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
  336 
  337 #undef  M_CHECK
  338 
  339         /* Fix MSS and update stats. */
  340         if (correct_mss(tcp, tcphlen, priv->stats.maxMSS,
  341             m->m_pkthdr.csum_flags))
  342                 priv->stats.FixedPkts++;
  343 
  344 send:
  345         /* Deliver frame out destination hook. */
  346         NG_FWD_NEW_DATA(error, item, priv->outHook, m);
  347 
  348         return (error);
  349 
  350 done:
  351         NG_FREE_ITEM(item);
  352         NG_FREE_M(m);
  353 
  354         return (error);
  355 }
  356 
  357 /*
  358  * Hook disconnection.
  359  * We must check all hooks, since they may reference this one.
  360  */
  361 static int
  362 ng_tcpmss_disconnect(hook_p hook)
  363 {
  364         node_p node = NG_HOOK_NODE(hook);
  365         hook_p hook2;
  366 
  367         LIST_FOREACH(hook2, &node->nd_hooks, hk_hooks) {
  368                 hpriv_p priv = NG_HOOK_PRIVATE(hook2);
  369 
  370                 if (priv->outHook == hook)
  371                         priv->outHook = NULL;
  372         }
  373 
  374         FREE(NG_HOOK_PRIVATE(hook), M_NETGRAPH);
  375 
  376         if (NG_NODE_NUMHOOKS(NG_HOOK_NODE(hook)) == 0)
  377                 ng_rmnode_self(NG_HOOK_NODE(hook));
  378 
  379         return (0);
  380 }
  381 
  382 /*
  383  * Code from tcpmssd.
  384  */
  385 
  386 /*-
  387  * The following macro is used to update an
  388  * internet checksum.  "acc" is a 32-bit
  389  * accumulation of all the changes to the
  390  * checksum (adding in old 16-bit words and
  391  * subtracting out new words), and "cksum"
  392  * is the checksum value to be updated.
  393  */
  394 #define TCPMSS_ADJUST_CHECKSUM(acc, cksum) do {         \
  395         acc += cksum;                                   \
  396         if (acc < 0) {                                  \
  397                 acc = -acc;                             \
  398                 acc = (acc >> 16) + (acc & 0xffff);     \
  399                 acc += acc >> 16;                       \
  400                 cksum = (u_short) ~acc;                 \
  401         } else {                                        \
  402                 acc = (acc >> 16) + (acc & 0xffff);     \
  403                 acc += acc >> 16;                       \
  404                 cksum = (u_short) acc;                  \
  405         }                                               \
  406 } while (0);
  407 
  408 static int
  409 correct_mss(struct tcphdr *tc, int hlen, uint16_t maxmss, int flags)
  410 {
  411         int olen, optlen;
  412         u_char *opt;
  413         uint16_t *mss;
  414         int accumulate;
  415         int res = 0;
  416 
  417         for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
  418              olen > 0; olen -= optlen, opt += optlen) {
  419                 if (*opt == TCPOPT_EOL)
  420                         break;
  421                 else if (*opt == TCPOPT_NOP)
  422                         optlen = 1;
  423                 else {
  424                         optlen = *(opt + 1);
  425                         if (optlen <= 0 || optlen > olen)
  426                                 break;
  427                         if (*opt == TCPOPT_MAXSEG) {
  428                                 if (optlen != TCPOLEN_MAXSEG)
  429                                         continue;
  430                                 mss = (uint16_t *)(opt + 2);
  431                                 if (ntohs(*mss) > maxmss) {
  432                                         accumulate = *mss;
  433                                         *mss = htons(maxmss);
  434                                         accumulate -= *mss;
  435                                         if ((flags & CSUM_TCP) == 0)
  436                                                 TCPMSS_ADJUST_CHECKSUM(accumulate, tc->th_sum);
  437                                         res = 1;
  438                                 }
  439                         }
  440                 }
  441         }
  442         return (res);
  443 }

Cache object: 3c23d8d0d56bd76b9d723ff3320af0cf


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