ng_tcpmss.c

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    1 /*-
    2  * ng_tcpmss.c
    3  *
    4  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    5  *
    6  * Copyright (c) 2004, Alexey Popov <lollypop@flexuser.ru>
    7  * All rights reserved.
    8  *
    9  * Redistribution and use in source and binary forms, with or without
   10  * modification, are permitted provided that the following conditions
   11  * are met:
   12  * 1. Redistributions of source code must retain the above copyright
   13  *    notice unmodified, this list of conditions, and the following
   14  *    disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  *
   19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  *
   31  * This software includes fragments of the following programs:
   32  *      tcpmssd         Ruslan Ermilov <ru@FreeBSD.org>
   33  *
   34  * $FreeBSD$
   35  */
   36 
   37 /*
   38  * This node is netgraph tool for workaround of PMTUD problem. It acts
   39  * like filter for IP packets. If configured, it reduces MSS of TCP SYN
   40  * packets.
   41  *
   42  * Configuration can be done by sending NGM_TCPMSS_CONFIG message. The
   43  * message sets filter for incoming packets on hook 'inHook'. Packet's
   44  * TCP MSS field is lowered to 'maxMSS' parameter and resulting packet
   45  * is sent to 'outHook'.
   46  *
   47  * XXX: statistics are updated not atomically, so they may broke on SMP.
   48  */
   49 
   50 #include <sys/param.h>
   51 #include <sys/systm.h>
   52 #include <sys/endian.h>
   53 #include <sys/errno.h>
   54 #include <sys/kernel.h>
   55 #include <sys/malloc.h>
   56 #include <sys/mbuf.h>
   57 
   58 #include <netinet/in.h>
   59 #include <netinet/in_systm.h>
   60 #include <netinet/ip.h>
   61 #include <netinet/tcp.h>
   62 
   63 #include <netgraph/ng_message.h>
   64 #include <netgraph/netgraph.h>
   65 #include <netgraph/ng_parse.h>
   66 #include <netgraph/ng_tcpmss.h>
   67 
   68 /* Per hook info. */
   69 typedef struct {
   70         hook_p                          outHook;
   71         struct ng_tcpmss_hookstat       stats;
   72 } *hpriv_p;
   73 
   74 /* Netgraph methods. */
   75 static ng_constructor_t ng_tcpmss_constructor;
   76 static ng_rcvmsg_t      ng_tcpmss_rcvmsg;
   77 static ng_newhook_t     ng_tcpmss_newhook;
   78 static ng_rcvdata_t     ng_tcpmss_rcvdata;
   79 static ng_disconnect_t  ng_tcpmss_disconnect;
   80 
   81 static int correct_mss(struct tcphdr *, int, uint16_t, int);
   82 
   83 /* Parse type for struct ng_tcpmss_hookstat. */
   84 static const struct ng_parse_struct_field ng_tcpmss_hookstat_type_fields[]
   85         = NG_TCPMSS_HOOKSTAT_INFO;
   86 static const struct ng_parse_type ng_tcpmss_hookstat_type = {
   87         &ng_parse_struct_type,
   88         &ng_tcpmss_hookstat_type_fields
   89 };
   90 
   91 /* Parse type for struct ng_tcpmss_config. */
   92 static const struct ng_parse_struct_field ng_tcpmss_config_type_fields[]
   93         = NG_TCPMSS_CONFIG_INFO;
   94 static const struct ng_parse_type ng_tcpmss_config_type = {
   95         &ng_parse_struct_type,
   96         ng_tcpmss_config_type_fields
   97 };
   98 
   99 /* List of commands and how to convert arguments to/from ASCII. */
  100 static const struct ng_cmdlist ng_tcpmss_cmds[] = {
  101         {
  102           NGM_TCPMSS_COOKIE,
  103           NGM_TCPMSS_GET_STATS,
  104           "getstats",
  105           &ng_parse_hookbuf_type,
  106           &ng_tcpmss_hookstat_type
  107         },
  108         {
  109           NGM_TCPMSS_COOKIE,
  110           NGM_TCPMSS_CLR_STATS,
  111           "clrstats",
  112           &ng_parse_hookbuf_type,
  113           NULL
  114         },
  115         {
  116           NGM_TCPMSS_COOKIE,
  117           NGM_TCPMSS_GETCLR_STATS,
  118           "getclrstats",
  119           &ng_parse_hookbuf_type,
  120           &ng_tcpmss_hookstat_type
  121         },
  122         {
  123           NGM_TCPMSS_COOKIE,
  124           NGM_TCPMSS_CONFIG,
  125           "config",
  126           &ng_tcpmss_config_type,
  127           NULL
  128         },
  129         { 0 }
  130 };
  131 
  132 /* Netgraph type descriptor. */
  133 static struct ng_type ng_tcpmss_typestruct = {
  134         .version =      NG_ABI_VERSION,
  135         .name =         NG_TCPMSS_NODE_TYPE,
  136         .constructor =  ng_tcpmss_constructor,
  137         .rcvmsg =       ng_tcpmss_rcvmsg,
  138         .newhook =      ng_tcpmss_newhook,
  139         .rcvdata =      ng_tcpmss_rcvdata,
  140         .disconnect =   ng_tcpmss_disconnect,
  141         .cmdlist =      ng_tcpmss_cmds,
  142 };
  143 
  144 NETGRAPH_INIT(tcpmss, &ng_tcpmss_typestruct);
  145 #define ERROUT(x)       { error = (x); goto done; }
  146 
  147 /*
  148  * Node constructor. No special actions required.
  149  */
  150 static int
  151 ng_tcpmss_constructor(node_p node)
  152 {
  153         return (0);
  154 }
  155 
  156 /*
  157  * Add a hook. Any unique name is OK.
  158  */
  159 static int
  160 ng_tcpmss_newhook(node_p node, hook_p hook, const char *name)
  161 {
  162         hpriv_p priv;
  163 
  164         priv = malloc(sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO);
  165         if (priv == NULL)
  166                 return (ENOMEM);
  167 
  168         NG_HOOK_SET_PRIVATE(hook, priv);
  169 
  170         return (0);
  171 }
  172 
  173 /*
  174  * Receive a control message.
  175  */
  176 static int
  177 ng_tcpmss_rcvmsg
  178 (node_p node, item_p item, hook_p lasthook)
  179 {
  180         struct ng_mesg *msg, *resp = NULL;
  181         int error = 0;
  182 
  183         NGI_GET_MSG(item, msg);
  184 
  185         switch (msg->header.typecookie) {
  186         case NGM_TCPMSS_COOKIE:
  187                 switch (msg->header.cmd) {
  188                 case NGM_TCPMSS_GET_STATS:
  189                 case NGM_TCPMSS_CLR_STATS:
  190                 case NGM_TCPMSS_GETCLR_STATS:
  191                     {
  192                         hook_p hook;
  193                         hpriv_p priv;
  194 
  195                         /* Check that message is long enough. */
  196                         if (msg->header.arglen != NG_HOOKSIZ)
  197                                 ERROUT(EINVAL);
  198 
  199                         /* Find this hook. */
  200                         hook = ng_findhook(node, (char *)msg->data);
  201                         if (hook == NULL)
  202                                 ERROUT(ENOENT);
  203 
  204                         priv = NG_HOOK_PRIVATE(hook);
  205 
  206                         /* Create response. */
  207                         if (msg->header.cmd != NGM_TCPMSS_CLR_STATS) {
  208                                 NG_MKRESPONSE(resp, msg,
  209                                     sizeof(struct ng_tcpmss_hookstat), M_NOWAIT);
  210                                 if (resp == NULL)
  211                                         ERROUT(ENOMEM);
  212                                 bcopy(&priv->stats, resp->data,
  213                                     sizeof(struct ng_tcpmss_hookstat)); 
  214                         }
  215 
  216                         if (msg->header.cmd != NGM_TCPMSS_GET_STATS)
  217                                 bzero(&priv->stats,
  218                                     sizeof(struct ng_tcpmss_hookstat));
  219                         break;
  220                     }
  221                 case NGM_TCPMSS_CONFIG:
  222                     {
  223                         struct ng_tcpmss_config *set;
  224                         hook_p in, out;
  225                         hpriv_p priv;
  226 
  227                         /* Check that message is long enough. */
  228                         if (msg->header.arglen !=
  229                             sizeof(struct ng_tcpmss_config))
  230                                 ERROUT(EINVAL);
  231 
  232                         set = (struct ng_tcpmss_config *)msg->data;
  233                         in = ng_findhook(node, set->inHook);
  234                         out = ng_findhook(node, set->outHook);
  235                         if (in == NULL || out == NULL)
  236                                 ERROUT(ENOENT);
  237 
  238                         /* Configure MSS hack. */
  239                         priv = NG_HOOK_PRIVATE(in);
  240                         priv->outHook = out;
  241                         priv->stats.maxMSS = set->maxMSS;
  242 
  243                         break;
  244                     }
  245                 default:
  246                         error = EINVAL;
  247                         break;
  248                 }
  249                 break;
  250         default:
  251                 error = EINVAL;
  252                 break;
  253         }
  254 
  255 done:
  256         NG_RESPOND_MSG(error, node, item, resp);
  257         NG_FREE_MSG(msg);
  258 
  259         return (error);
  260 }
  261 
  262 /*
  263  * Receive data on a hook, and hack MSS.
  264  *
  265  */
  266 static int
  267 ng_tcpmss_rcvdata(hook_p hook, item_p item)
  268 {
  269         hpriv_p priv = NG_HOOK_PRIVATE(hook);
  270         struct mbuf *m = NULL;
  271         struct ip *ip;
  272         struct tcphdr *tcp;
  273         int iphlen, tcphlen, pktlen;
  274         int pullup_len = 0;
  275         int error = 0;
  276 
  277         /* Drop packets if filter is not configured on this hook. */
  278         if (priv->outHook == NULL)
  279                 goto done;
  280 
  281         NGI_GET_M(item, m);
  282 
  283         /* Update stats on incoming hook. */
  284         pktlen = m->m_pkthdr.len;
  285         priv->stats.Octets += pktlen;
  286         priv->stats.Packets++;
  287 
  288         /* Check whether we configured to fix MSS. */
  289         if (priv->stats.maxMSS == 0)
  290                 goto send;
  291 
  292 #define M_CHECK(length) do {                                    \
  293         pullup_len += length;                                   \
  294         if ((m)->m_pkthdr.len < pullup_len)                     \
  295                 goto send;                                      \
  296         if ((m)->m_len < pullup_len &&                          \
  297            (((m) = m_pullup((m), pullup_len)) == NULL))         \
  298                 ERROUT(ENOBUFS);                                \
  299         } while (0)
  300 
  301         /* Check mbuf packet size and arrange for IP header. */
  302         M_CHECK(sizeof(struct ip));
  303         ip = mtod(m, struct ip *);
  304 
  305         /* Check IP version. */
  306         if (ip->ip_v != IPVERSION)
  307                 ERROUT(EINVAL);
  308 
  309         /* Check IP header length. */
  310         iphlen = ip->ip_hl << 2;
  311         if (iphlen < sizeof(struct ip) || iphlen > pktlen )
  312                 ERROUT(EINVAL);
  313 
  314         /* Check if it is TCP. */
  315         if (!(ip->ip_p == IPPROTO_TCP))
  316                 goto send;
  317 
  318         /* Check mbuf packet size and arrange for IP+TCP header */
  319         M_CHECK(iphlen - sizeof(struct ip) + sizeof(struct tcphdr));
  320         ip = mtod(m, struct ip *);
  321         tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
  322 
  323         /* Check TCP header length. */
  324         tcphlen = tcp->th_off << 2;
  325         if (tcphlen < sizeof(struct tcphdr) || tcphlen > pktlen - iphlen)
  326                 ERROUT(EINVAL);
  327 
  328         /* Check SYN packet and has options. */
  329         if (!(tcp->th_flags & TH_SYN) || tcphlen == sizeof(struct tcphdr))
  330                 goto send;
  331 
  332         /* Update SYN stats. */
  333         priv->stats.SYNPkts++;
  334 
  335         M_CHECK(tcphlen - sizeof(struct tcphdr));
  336         ip = mtod(m, struct ip *);
  337         tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
  338 
  339 #undef  M_CHECK
  340 
  341         /* Fix MSS and update stats. */
  342         if (correct_mss(tcp, tcphlen, priv->stats.maxMSS,
  343             m->m_pkthdr.csum_flags))
  344                 priv->stats.FixedPkts++;
  345 
  346 send:
  347         /* Deliver frame out destination hook. */
  348         NG_FWD_NEW_DATA(error, item, priv->outHook, m);
  349 
  350         return (error);
  351 
  352 done:
  353         NG_FREE_ITEM(item);
  354         NG_FREE_M(m);
  355 
  356         return (error);
  357 }
  358 
  359 /*
  360  * Hook disconnection.
  361  * We must check all hooks, since they may reference this one.
  362  */
  363 static int
  364 ng_tcpmss_disconnect(hook_p hook)
  365 {
  366         node_p node = NG_HOOK_NODE(hook);
  367         hook_p hook2;
  368 
  369         LIST_FOREACH(hook2, &node->nd_hooks, hk_hooks) {
  370                 hpriv_p priv = NG_HOOK_PRIVATE(hook2);
  371 
  372                 if (priv->outHook == hook)
  373                         priv->outHook = NULL;
  374         }
  375 
  376         free(NG_HOOK_PRIVATE(hook), M_NETGRAPH);
  377 
  378         if (NG_NODE_NUMHOOKS(NG_HOOK_NODE(hook)) == 0)
  379                 ng_rmnode_self(NG_HOOK_NODE(hook));
  380 
  381         return (0);
  382 }
  383 
  384 /*
  385  * Code from tcpmssd.
  386  */
  387 
  388 /*-
  389  * The following macro is used to update an
  390  * internet checksum.  "acc" is a 32-bit
  391  * accumulation of all the changes to the
  392  * checksum (adding in old 16-bit words and
  393  * subtracting out new words), and "cksum"
  394  * is the checksum value to be updated.
  395  */
  396 #define TCPMSS_ADJUST_CHECKSUM(acc, cksum) do {         \
  397         acc += cksum;                                   \
  398         if (acc < 0) {                                  \
  399                 acc = -acc;                             \
  400                 acc = (acc >> 16) + (acc & 0xffff);     \
  401                 acc += acc >> 16;                       \
  402                 cksum = (u_short) ~acc;                 \
  403         } else {                                        \
  404                 acc = (acc >> 16) + (acc & 0xffff);     \
  405                 acc += acc >> 16;                       \
  406                 cksum = (u_short) acc;                  \
  407         }                                               \
  408 } while (0);
  409 
  410 static int
  411 correct_mss(struct tcphdr *tc, int hlen, uint16_t maxmss, int flags)
  412 {
  413         int olen, optlen;
  414         u_char *opt;
  415         int accumulate;
  416         int res = 0;
  417         uint16_t sum;
  418 
  419         for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
  420              olen > 0; olen -= optlen, opt += optlen) {
  421                 if (*opt == TCPOPT_EOL)
  422                         break;
  423                 else if (*opt == TCPOPT_NOP)
  424                         optlen = 1;
  425                 else {
  426                         optlen = *(opt + 1);
  427                         if (optlen <= 0 || optlen > olen)
  428                                 break;
  429                         if (*opt == TCPOPT_MAXSEG) {
  430                                 if (optlen != TCPOLEN_MAXSEG)
  431                                         continue;
  432                                 accumulate = be16dec(opt + 2);
  433                                 if (accumulate > maxmss) {
  434                                         if ((flags & CSUM_TCP) == 0) {
  435                                                 accumulate -= maxmss;
  436                                                 sum = be16dec(&tc->th_sum);
  437                                                 TCPMSS_ADJUST_CHECKSUM(accumulate, sum);
  438                                                 be16enc(&tc->th_sum, sum);
  439                                         }
  440                                         be16enc(opt + 2, maxmss);
  441                                         res = 1;
  442                                 }
  443                         }
  444                 }
  445         }
  446         return (res);
  447 }
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FreeBSD/Linux Kernel Cross Reference sys/netgraph/ng_tcpmss.c

FreeBSD/Linux Kernel Cross Reference
sys/netgraph/ng_tcpmss.c
