The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netgraph/ng_l2tp.c

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    1 
    2 /*
    3  * Copyright (c) 2001-2002 Packet Design, LLC.
    4  * All rights reserved.
    5  * 
    6  * Subject to the following obligations and disclaimer of warranty,
    7  * use and redistribution of this software, in source or object code
    8  * forms, with or without modifications are expressly permitted by
    9  * Packet Design; provided, however, that:
   10  * 
   11  *    (i)  Any and all reproductions of the source or object code
   12  *         must include the copyright notice above and the following
   13  *         disclaimer of warranties; and
   14  *    (ii) No rights are granted, in any manner or form, to use
   15  *         Packet Design trademarks, including the mark "PACKET DESIGN"
   16  *         on advertising, endorsements, or otherwise except as such
   17  *         appears in the above copyright notice or in the software.
   18  * 
   19  * THIS SOFTWARE IS BEING PROVIDED BY PACKET DESIGN "AS IS", AND
   20  * TO THE MAXIMUM EXTENT PERMITTED BY LAW, PACKET DESIGN MAKES NO
   21  * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING
   22  * THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED
   23  * WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
   24  * OR NON-INFRINGEMENT.  PACKET DESIGN DOES NOT WARRANT, GUARANTEE,
   25  * OR MAKE ANY REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS
   26  * OF THE USE OF THIS SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY,
   27  * RELIABILITY OR OTHERWISE.  IN NO EVENT SHALL PACKET DESIGN BE
   28  * LIABLE FOR ANY DAMAGES RESULTING FROM OR ARISING OUT OF ANY USE
   29  * OF THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY DIRECT,
   30  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, PUNITIVE, OR CONSEQUENTIAL
   31  * DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, LOSS OF
   32  * USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY THEORY OF
   33  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
   35  * THE USE OF THIS SOFTWARE, EVEN IF PACKET DESIGN IS ADVISED OF
   36  * THE POSSIBILITY OF SUCH DAMAGE.
   37  * 
   38  * Author: Archie Cobbs <archie@freebsd.org>
   39  *
   40  * $FreeBSD: releng/5.1/sys/netgraph/ng_l2tp.c 113073 2003-04-04 12:12:34Z des $
   41  */
   42 
   43 /*
   44  * L2TP netgraph node type.
   45  *
   46  * This node type implements the lower layer of the
   47  * L2TP protocol as specified in RFC 2661.
   48  */
   49 
   50 #include <sys/param.h>
   51 #include <sys/systm.h>
   52 #include <sys/kernel.h>
   53 #include <sys/time.h>
   54 #include <sys/conf.h>
   55 #include <sys/mbuf.h>
   56 #include <sys/malloc.h>
   57 #include <sys/errno.h>
   58 #include <sys/libkern.h>
   59 
   60 #include <netgraph/ng_message.h>
   61 #include <netgraph/netgraph.h>
   62 #include <netgraph/ng_parse.h>
   63 #include <netgraph/ng_l2tp.h>
   64 
   65 #ifdef NG_SEPARATE_MALLOC
   66 MALLOC_DEFINE(M_NETGRAPH_L2TP, "netgraph_l2tp", "netgraph l2tp node");
   67 #else
   68 #define M_NETGRAPH_L2TP M_NETGRAPH
   69 #endif
   70 
   71 /* L2TP header format (first 2 bytes only) */
   72 #define L2TP_HDR_CTRL           0x8000                  /* control packet */
   73 #define L2TP_HDR_LEN            0x4000                  /* has length field */
   74 #define L2TP_HDR_SEQ            0x0800                  /* has ns, nr fields */
   75 #define L2TP_HDR_OFF            0x0200                  /* has offset field */
   76 #define L2TP_HDR_PRIO           0x0100                  /* give priority */
   77 #define L2TP_HDR_VERS_MASK      0x000f                  /* version field mask */
   78 #define L2TP_HDR_VERSION        0x0002                  /* version field */
   79 
   80 /* Bits that must be zero or one in first two bytes of header */
   81 #define L2TP_CTRL_0BITS         0x030d                  /* ctrl: must be 0 */
   82 #define L2TP_CTRL_1BITS         0xc802                  /* ctrl: must be 1 */
   83 #define L2TP_DATA_0BITS         0x800d                  /* data: must be 0 */
   84 #define L2TP_DATA_1BITS         0x0002                  /* data: must be 1 */
   85 
   86 /* Standard xmit ctrl and data header bits */
   87 #define L2TP_CTRL_HDR           (L2TP_HDR_CTRL | L2TP_HDR_LEN \
   88                                     | L2TP_HDR_SEQ | L2TP_HDR_VERSION)
   89 #define L2TP_DATA_HDR           (L2TP_HDR_VERSION)      /* optional: len, seq */
   90 
   91 /* Some hard coded values */
   92 #define L2TP_MAX_XWIN           16                      /* my max xmit window */
   93 #define L2TP_MAX_REXMIT         5                       /* default max rexmit */
   94 #define L2TP_MAX_REXMIT_TO      30                      /* default rexmit to */
   95 #define L2TP_DELAYED_ACK        ((hz + 19) / 20)        /* delayed ack: 50 ms */
   96 
   97 /* Default data sequence number configuration for new sessions */
   98 #define L2TP_CONTROL_DSEQ       1                       /* we are the lns */
   99 #define L2TP_ENABLE_DSEQ        1                       /* enable data seq # */
  100 
  101 /* Compare sequence numbers using circular math */
  102 #define L2TP_SEQ_DIFF(x, y)     ((int)((int16_t)(x) - (int16_t)(y)))
  103 
  104 /*
  105  * Sequence number state
  106  *
  107  * Invariants:
  108  *    - If cwnd < ssth, we're doing slow start, otherwise congestion avoidance
  109  *    - The number of unacknowledged xmit packets is (ns - rack) <= seq->wmax
  110  *    - The first (ns - rack) mbuf's in xwin[] array are copies of these
  111  *      unacknowledged packets; the remainder of xwin[] consists first of
  112  *      zero or more further untransmitted packets in the transmit queue
  113  *    - We try to keep the peer's receive window as full as possible.
  114  *      Therefore, (i < cwnd && xwin[i] != NULL) implies (ns - rack) > i.
  115  *    - rack_timer is running iff (ns - rack) > 0 (unack'd xmit'd pkts)
  116  *    - If xack != nr, there are unacknowledged recv packet(s) (delayed ack)
  117  *    - xack_timer is running iff xack != nr (unack'd rec'd pkts)
  118  */
  119 struct l2tp_seq {
  120         u_int16_t               ns;             /* next xmit seq we send */
  121         u_int16_t               nr;             /* next recv seq we expect */
  122         u_int16_t               rack;           /* last 'nr' we rec'd */
  123         u_int16_t               xack;           /* last 'nr' we sent */
  124         u_int16_t               wmax;           /* peer's max recv window */
  125         u_int16_t               cwnd;           /* current congestion window */
  126         u_int16_t               ssth;           /* slow start threshold */
  127         u_int16_t               acks;           /* # consecutive acks rec'd */
  128         u_int16_t               rexmits;        /* # retransmits sent */
  129         u_int16_t               max_rexmits;    /* max # retransmits sent */
  130         u_int16_t               max_rexmit_to;  /* max retransmit timeout */
  131         struct callout          rack_timer;     /* retransmit timer */
  132         struct callout          xack_timer;     /* delayed ack timer */
  133         u_char                  rack_timer_running;     /* xmit timer running */
  134         u_char                  xack_timer_running;     /* ack timer running */
  135         struct mbuf             *xwin[L2TP_MAX_XWIN];   /* transmit window */
  136 };
  137 
  138 /* Node private data */
  139 struct ng_l2tp_private {
  140         node_p                  node;           /* back pointer to node */
  141         hook_p                  ctrl;           /* hook to upper layers */
  142         hook_p                  lower;          /* hook to lower layers */
  143         struct ng_l2tp_config   conf;           /* node configuration */
  144         struct ng_l2tp_stats    stats;          /* node statistics */
  145         struct l2tp_seq         seq;            /* ctrl sequence number state */
  146         ng_ID_t                 ftarget;        /* failure message target */
  147 };
  148 typedef struct ng_l2tp_private *priv_p;
  149 
  150 /* Hook private data (data session hooks only) */
  151 struct ng_l2tp_hook_private {
  152         struct ng_l2tp_sess_config      conf;   /* hook/session config */
  153         u_int16_t                       ns;     /* data ns sequence number */
  154         u_int16_t                       nr;     /* data nr sequence number */
  155 };
  156 typedef struct ng_l2tp_hook_private *hookpriv_p;
  157 
  158 /* Netgraph node methods */
  159 static ng_constructor_t ng_l2tp_constructor;
  160 static ng_rcvmsg_t      ng_l2tp_rcvmsg;
  161 static ng_shutdown_t    ng_l2tp_shutdown;
  162 static ng_newhook_t     ng_l2tp_newhook;
  163 static ng_rcvdata_t     ng_l2tp_rcvdata;
  164 static ng_disconnect_t  ng_l2tp_disconnect;
  165 
  166 /* Internal functions */
  167 static int      ng_l2tp_recv_lower(node_p node, item_p item);
  168 static int      ng_l2tp_recv_ctrl(node_p node, item_p item);
  169 static int      ng_l2tp_recv_data(node_p node, item_p item, hookpriv_p hpriv);
  170 
  171 static int      ng_l2tp_xmit_ctrl(priv_p priv, struct mbuf *m, u_int16_t ns);
  172 
  173 static void     ng_l2tp_seq_init(priv_p priv);
  174 static int      ng_l2tp_seq_adjust(priv_p priv,
  175                         const struct ng_l2tp_config *conf);
  176 static void     ng_l2tp_seq_reset(priv_p priv);
  177 static void     ng_l2tp_seq_failure(priv_p priv);
  178 static void     ng_l2tp_seq_recv_nr(priv_p priv, u_int16_t nr);
  179 static int      ng_l2tp_seq_recv_ns(priv_p priv, u_int16_t ns);
  180 static void     ng_l2tp_seq_xack_timeout(void *arg);
  181 static void     ng_l2tp_seq_rack_timeout(void *arg);
  182 
  183 static ng_fn_eachhook   ng_l2tp_find_session;
  184 static ng_fn_eachhook   ng_l2tp_reset_session;
  185 
  186 #ifdef INVARIANTS
  187 static void     ng_l2tp_seq_check(struct l2tp_seq *seq);
  188 #endif
  189 
  190 /* Parse type for struct ng_l2tp_config */
  191 static const struct ng_parse_struct_field
  192         ng_l2tp_config_type_fields[] = NG_L2TP_CONFIG_TYPE_INFO;
  193 static const struct ng_parse_type ng_l2tp_config_type = {
  194         &ng_parse_struct_type,
  195         &ng_l2tp_config_type_fields,
  196 };
  197 
  198 /* Parse type for struct ng_l2tp_sess_config */
  199 static const struct ng_parse_struct_field
  200         ng_l2tp_sess_config_type_fields[] = NG_L2TP_SESS_CONFIG_TYPE_INFO;
  201 static const struct ng_parse_type ng_l2tp_sess_config_type = {
  202         &ng_parse_struct_type,
  203         &ng_l2tp_sess_config_type_fields,
  204 };
  205 
  206 /* Parse type for struct ng_l2tp_stats */
  207 static const struct ng_parse_struct_field
  208         ng_l2tp_stats_type_fields[] = NG_L2TP_STATS_TYPE_INFO;
  209 static const struct ng_parse_type ng_pptp_stats_type = {
  210         &ng_parse_struct_type,
  211         &ng_l2tp_stats_type_fields
  212 };
  213 
  214 /* List of commands and how to convert arguments to/from ASCII */
  215 static const struct ng_cmdlist ng_l2tp_cmdlist[] = {
  216         {
  217           NGM_L2TP_COOKIE,
  218           NGM_L2TP_SET_CONFIG,
  219           "setconfig",
  220           &ng_l2tp_config_type,
  221           NULL
  222         },
  223         {
  224           NGM_L2TP_COOKIE,
  225           NGM_L2TP_GET_CONFIG,
  226           "getconfig",
  227           NULL,
  228           &ng_l2tp_config_type
  229         },
  230         {
  231           NGM_L2TP_COOKIE,
  232           NGM_L2TP_SET_SESS_CONFIG,
  233           "setsessconfig",
  234           &ng_l2tp_sess_config_type,
  235           NULL
  236         },
  237         {
  238           NGM_L2TP_COOKIE,
  239           NGM_L2TP_GET_SESS_CONFIG,
  240           "getsessconfig",
  241           &ng_parse_hint16_type,
  242           &ng_l2tp_sess_config_type
  243         },
  244         {
  245           NGM_L2TP_COOKIE,
  246           NGM_L2TP_GET_STATS,
  247           "getstats",
  248           NULL,
  249           &ng_pptp_stats_type
  250         },
  251         {
  252           NGM_L2TP_COOKIE,
  253           NGM_L2TP_CLR_STATS,
  254           "clrstats",
  255           NULL,
  256           NULL
  257         },
  258         {
  259           NGM_L2TP_COOKIE,
  260           NGM_L2TP_GETCLR_STATS,
  261           "getclrstats",
  262           NULL,
  263           &ng_pptp_stats_type
  264         },
  265         {
  266           NGM_L2TP_COOKIE,
  267           NGM_L2TP_ACK_FAILURE,
  268           "ackfailure",
  269           NULL,
  270           NULL
  271         },
  272         { 0 }
  273 };
  274 
  275 /* Node type descriptor */
  276 static struct ng_type ng_l2tp_typestruct = {
  277         NG_ABI_VERSION,
  278         NG_L2TP_NODE_TYPE,
  279         NULL,
  280         ng_l2tp_constructor,
  281         ng_l2tp_rcvmsg,
  282         ng_l2tp_shutdown,
  283         ng_l2tp_newhook,
  284         NULL,
  285         NULL,
  286         ng_l2tp_rcvdata,
  287         ng_l2tp_disconnect,
  288         ng_l2tp_cmdlist
  289 };
  290 NETGRAPH_INIT(l2tp, &ng_l2tp_typestruct);
  291 
  292 /* Sequence number state sanity checking */
  293 #ifdef INVARIANTS
  294 #define L2TP_SEQ_CHECK(seq)     ng_l2tp_seq_check(seq)
  295 #else
  296 #define L2TP_SEQ_CHECK(x)       do { } while (0)
  297 #endif
  298 
  299 /* memmove macro */
  300 #define memmove(d, s, l)        bcopy(s, d, l)
  301 
  302 /* Whether to use m_copypacket() or m_dup() */
  303 #define L2TP_COPY_MBUF          m_copypacket
  304 
  305 /************************************************************************
  306                         NETGRAPH NODE STUFF
  307 ************************************************************************/
  308 
  309 /*
  310  * Node type constructor
  311  */
  312 static int
  313 ng_l2tp_constructor(node_p node)
  314 {
  315         priv_p priv;
  316 
  317         /* Allocate private structure */
  318         MALLOC(priv, priv_p, sizeof(*priv), M_NETGRAPH_L2TP, M_NOWAIT | M_ZERO);
  319         if (priv == NULL)
  320                 return (ENOMEM);
  321         NG_NODE_SET_PRIVATE(node, priv);
  322         priv->node = node;
  323 
  324         /* Apply a semi-reasonable default configuration */
  325         priv->conf.peer_win = 1;
  326         priv->conf.rexmit_max = L2TP_MAX_REXMIT;
  327         priv->conf.rexmit_max_to = L2TP_MAX_REXMIT_TO;
  328 
  329         /* Initialize sequence number state */
  330         ng_l2tp_seq_init(priv);
  331 
  332         /* Done */
  333         return (0);
  334 }
  335 
  336 /*
  337  * Give our OK for a hook to be added.
  338  */
  339 static int
  340 ng_l2tp_newhook(node_p node, hook_p hook, const char *name)
  341 {
  342         const priv_p priv = NG_NODE_PRIVATE(node);
  343 
  344         /* Check hook name */
  345         if (strcmp(name, NG_L2TP_HOOK_CTRL) == 0) {
  346                 if (priv->ctrl != NULL)
  347                         return (EISCONN);
  348                 priv->ctrl = hook;
  349         } else if (strcmp(name, NG_L2TP_HOOK_LOWER) == 0) {
  350                 if (priv->lower != NULL)
  351                         return (EISCONN);
  352                 priv->lower = hook;
  353         } else {
  354                 static const char hexdig[16] = "0123456789abcdef";
  355                 u_int16_t session_id;
  356                 hookpriv_p hpriv;
  357                 const char *hex;
  358                 int i;
  359                 int j;
  360 
  361                 /* Parse hook name to get session ID */
  362                 if (strncmp(name, NG_L2TP_HOOK_SESSION_P,
  363                     sizeof(NG_L2TP_HOOK_SESSION_P) - 1) != 0)
  364                         return (EINVAL);
  365                 hex = name + sizeof(NG_L2TP_HOOK_SESSION_P) - 1;
  366                 for (session_id = i = 0; i < 4; i++) {
  367                         for (j = 0; j < 16 && hex[i] != hexdig[j]; j++);
  368                         if (j == 16)
  369                                 return (EINVAL);
  370                         session_id = (session_id << 4) | j;
  371                 }
  372                 if (hex[i] != '\0')
  373                         return (EINVAL);
  374 
  375                 /* Create hook private structure */
  376                 MALLOC(hpriv, hookpriv_p,
  377                     sizeof(*hpriv), M_NETGRAPH_L2TP, M_NOWAIT | M_ZERO);
  378                 if (hpriv == NULL)
  379                         return (ENOMEM);
  380                 hpriv->conf.session_id = htons(session_id);
  381                 hpriv->conf.control_dseq = L2TP_CONTROL_DSEQ;
  382                 hpriv->conf.enable_dseq = L2TP_ENABLE_DSEQ;
  383                 NG_HOOK_SET_PRIVATE(hook, hpriv);
  384         }
  385 
  386         /* Done */
  387         return (0);
  388 }
  389 
  390 /*
  391  * Receive a control message.
  392  */
  393 static int
  394 ng_l2tp_rcvmsg(node_p node, item_p item, hook_p lasthook)
  395 {
  396         const priv_p priv = NG_NODE_PRIVATE(node);
  397         struct ng_mesg *resp = NULL;
  398         struct ng_mesg *msg;
  399         int error = 0;
  400 
  401         NGI_GET_MSG(item, msg);
  402         switch (msg->header.typecookie) {
  403         case NGM_L2TP_COOKIE:
  404                 switch (msg->header.cmd) {
  405                 case NGM_L2TP_SET_CONFIG:
  406                     {
  407                         struct ng_l2tp_config *const conf =
  408                                 (struct ng_l2tp_config *)msg->data;
  409 
  410                         /* Check for invalid or illegal config */
  411                         if (msg->header.arglen != sizeof(*conf)) {
  412                                 error = EINVAL;
  413                                 break;
  414                         }
  415                         conf->enabled = !!conf->enabled;
  416                         conf->match_id = !!conf->match_id;
  417                         conf->tunnel_id = htons(conf->tunnel_id);
  418                         conf->peer_id = htons(conf->peer_id);
  419                         if (priv->conf.enabled
  420                             && ((priv->conf.tunnel_id != 0
  421                                && conf->tunnel_id != priv->conf.tunnel_id)
  422                               || ((priv->conf.peer_id != 0
  423                                && conf->peer_id != priv->conf.peer_id)))) {
  424                                 error = EBUSY;
  425                                 break;
  426                         }
  427 
  428                         /* Save calling node as failure target */
  429                         priv->ftarget = NGI_RETADDR(item);
  430 
  431                         /* Adjust sequence number state */
  432                         if ((error = ng_l2tp_seq_adjust(priv, conf)) != 0)
  433                                 break;
  434 
  435                         /* Update node's config */
  436                         priv->conf = *conf;
  437                         break;
  438                     }
  439                 case NGM_L2TP_GET_CONFIG:
  440                     {
  441                         struct ng_l2tp_config *conf;
  442 
  443                         NG_MKRESPONSE(resp, msg, sizeof(*conf), M_NOWAIT);
  444                         if (resp == NULL) {
  445                                 error = ENOMEM;
  446                                 break;
  447                         }
  448                         conf = (struct ng_l2tp_config *)resp->data;
  449                         *conf = priv->conf;
  450 
  451                         /* Put ID's in host order */
  452                         conf->tunnel_id = ntohs(conf->tunnel_id);
  453                         conf->peer_id = ntohs(conf->peer_id);
  454                         break;
  455                     }
  456                 case NGM_L2TP_SET_SESS_CONFIG:
  457                     {
  458                         struct ng_l2tp_sess_config *const conf =
  459                             (struct ng_l2tp_sess_config *)msg->data;
  460                         hookpriv_p hpriv;
  461                         hook_p hook;
  462 
  463                         /* Check for invalid or illegal config */
  464                         if (msg->header.arglen != sizeof(*conf)) {
  465                                 error = EINVAL;
  466                                 break;
  467                         }
  468 
  469                         /* Put ID's in network order */
  470                         conf->session_id = htons(conf->session_id);
  471                         conf->peer_id = htons(conf->peer_id);
  472 
  473                         /* Find matching hook */
  474                         NG_NODE_FOREACH_HOOK(node, ng_l2tp_find_session,
  475                             (void *)(uintptr_t)conf->session_id, hook);
  476                         if (hook == NULL) {
  477                                 error = ENOENT;
  478                                 break;
  479                         }
  480                         hpriv = NG_HOOK_PRIVATE(hook);
  481 
  482                         /* Update hook's config */
  483                         hpriv->conf = *conf;
  484                         break;
  485                     }
  486                 case NGM_L2TP_GET_SESS_CONFIG:
  487                     {
  488                         struct ng_l2tp_sess_config *conf;
  489                         u_int16_t session_id;
  490                         hookpriv_p hpriv;
  491                         hook_p hook;
  492 
  493                         /* Get session ID */
  494                         if (msg->header.arglen != sizeof(session_id)) {
  495                                 error = EINVAL;
  496                                 break;
  497                         }
  498                         memcpy(&session_id, msg->data, 2);
  499                         session_id = htons(session_id);
  500 
  501                         /* Find matching hook */
  502                         NG_NODE_FOREACH_HOOK(node, ng_l2tp_find_session,
  503                             (void *)(uintptr_t)session_id, hook);
  504                         if (hook == NULL) {
  505                                 error = ENOENT;
  506                                 break;
  507                         }
  508                         hpriv = NG_HOOK_PRIVATE(hook);
  509 
  510                         /* Send response */
  511                         NG_MKRESPONSE(resp, msg, sizeof(hpriv->conf), M_NOWAIT);
  512                         if (resp == NULL) {
  513                                 error = ENOMEM;
  514                                 break;
  515                         }
  516                         conf = (struct ng_l2tp_sess_config *)resp->data;
  517                         *conf = hpriv->conf;
  518 
  519                         /* Put ID's in host order */
  520                         conf->session_id = ntohs(conf->session_id);
  521                         conf->peer_id = ntohs(conf->peer_id);
  522                         break;
  523                     }
  524                 case NGM_L2TP_GET_STATS:
  525                 case NGM_L2TP_CLR_STATS:
  526                 case NGM_L2TP_GETCLR_STATS:
  527                     {
  528                         if (msg->header.cmd != NGM_L2TP_CLR_STATS) {
  529                                 NG_MKRESPONSE(resp, msg,
  530                                     sizeof(priv->stats), M_NOWAIT);
  531                                 if (resp == NULL) {
  532                                         error = ENOMEM;
  533                                         break;
  534                                 }
  535                                 memcpy(resp->data,
  536                                     &priv->stats, sizeof(priv->stats));
  537                         }
  538                         if (msg->header.cmd != NGM_L2TP_GET_STATS)
  539                                 memset(&priv->stats, 0, sizeof(priv->stats));
  540                         break;
  541                     }
  542                 default:
  543                         error = EINVAL;
  544                         break;
  545                 }
  546                 break;
  547         default:
  548                 error = EINVAL;
  549                 break;
  550         }
  551 
  552         /* Done */
  553         NG_RESPOND_MSG(error, node, item, resp);
  554         NG_FREE_MSG(msg);
  555         return (error);
  556 }
  557 
  558 /*
  559  * Receive incoming data on a hook.
  560  */
  561 static int
  562 ng_l2tp_rcvdata(hook_p hook, item_p item)
  563 {
  564         const node_p node = NG_HOOK_NODE(hook);
  565         const priv_p priv = NG_NODE_PRIVATE(node);
  566         int error;
  567 
  568         /* Sanity check */
  569         L2TP_SEQ_CHECK(&priv->seq);
  570 
  571         /* If not configured, reject */
  572         if (!priv->conf.enabled) {
  573                 NG_FREE_ITEM(item);
  574                 return (ENXIO);
  575         }
  576 
  577         /* Handle incoming frame from below */
  578         if (hook == priv->lower) {
  579                 error = ng_l2tp_recv_lower(node, item);
  580                 goto done;
  581         }
  582 
  583         /* Handle outgoing control frame */
  584         if (hook == priv->ctrl) {
  585                 error = ng_l2tp_recv_ctrl(node, item);
  586                 goto done;
  587         }
  588 
  589         /* Handle outgoing data frame */
  590         error = ng_l2tp_recv_data(node, item, NG_HOOK_PRIVATE(hook));
  591 
  592 done:
  593         /* Done */
  594         L2TP_SEQ_CHECK(&priv->seq);
  595         return (error);
  596 }
  597 
  598 /*
  599  * Destroy node
  600  */
  601 static int
  602 ng_l2tp_shutdown(node_p node)
  603 {
  604         const priv_p priv = NG_NODE_PRIVATE(node);
  605         struct l2tp_seq *const seq = &priv->seq;
  606 
  607         /* Sanity check */
  608         L2TP_SEQ_CHECK(seq);
  609 
  610         /* Reset sequence number state */
  611         ng_l2tp_seq_reset(priv);
  612 
  613         /* Free private data if neither timer is running */
  614         if (!seq->rack_timer_running && !seq->xack_timer_running) {
  615                 FREE(priv, M_NETGRAPH_L2TP);
  616                 NG_NODE_SET_PRIVATE(node, NULL);
  617         }
  618 
  619         /* Unref node */
  620         NG_NODE_UNREF(node);
  621         return (0);
  622 }
  623 
  624 /*
  625  * Hook disconnection
  626  */
  627 static int
  628 ng_l2tp_disconnect(hook_p hook)
  629 {
  630         const node_p node = NG_HOOK_NODE(hook);
  631         const priv_p priv = NG_NODE_PRIVATE(node);
  632 
  633         /* Zero out hook pointer */
  634         if (hook == priv->ctrl)
  635                 priv->ctrl = NULL;
  636         else if (hook == priv->lower)
  637                 priv->lower = NULL;
  638         else {
  639                 FREE(NG_HOOK_PRIVATE(hook), M_NETGRAPH_L2TP);
  640                 NG_HOOK_SET_PRIVATE(hook, NULL);
  641         }
  642 
  643         /* Go away if no longer connected to anything */
  644         if (NG_NODE_NUMHOOKS(node) == 0 && NG_NODE_IS_VALID(node))
  645                 ng_rmnode_self(node);
  646         return (0);
  647 }
  648 
  649 /*************************************************************************
  650                         INTERNAL FUNCTIONS
  651 *************************************************************************/
  652 
  653 /*
  654  * Find the hook with a given session ID.
  655  */
  656 static int
  657 ng_l2tp_find_session(hook_p hook, void *arg)
  658 {
  659         const hookpriv_p hpriv = NG_HOOK_PRIVATE(hook);
  660         const u_int16_t sid = (u_int16_t)(uintptr_t)arg;
  661 
  662         if (hpriv == NULL || hpriv->conf.session_id != sid)
  663                 return (-1);
  664         return (0);
  665 }
  666 
  667 /*
  668  * Reset a hook's session state.
  669  */
  670 static int
  671 ng_l2tp_reset_session(hook_p hook, void *arg)
  672 {
  673         const hookpriv_p hpriv = NG_HOOK_PRIVATE(hook);
  674 
  675         if (hpriv != NULL) {
  676                 hpriv->conf.control_dseq = 0;
  677                 hpriv->conf.enable_dseq = 0;
  678                 hpriv->nr = 0;
  679                 hpriv->ns = 0;
  680         }
  681         return (-1);
  682 }
  683 
  684 /*
  685  * Handle an incoming frame from below.
  686  */
  687 static int
  688 ng_l2tp_recv_lower(node_p node, item_p item)
  689 {
  690         static const u_int16_t req_bits[2][2] = {
  691                 { L2TP_DATA_0BITS, L2TP_DATA_1BITS },
  692                 { L2TP_CTRL_0BITS, L2TP_CTRL_1BITS },
  693         };
  694         const priv_p priv = NG_NODE_PRIVATE(node);
  695         hookpriv_p hpriv = NULL;
  696         hook_p hook = NULL;
  697         u_int16_t ids[2];
  698         struct mbuf *m;
  699         u_int16_t hdr;
  700         u_int16_t ns;
  701         u_int16_t nr;
  702         int is_ctrl;
  703         int error;
  704         int len;
  705 
  706         /* Grab mbuf */
  707         NGI_GET_M(item, m);
  708 
  709         /* Update stats */
  710         priv->stats.recvPackets++;
  711         priv->stats.recvOctets += m->m_pkthdr.len;
  712 
  713         /* Get initial header */
  714         if (m->m_pkthdr.len < 6) {
  715                 priv->stats.recvRunts++;
  716                 NG_FREE_ITEM(item);
  717                 NG_FREE_M(m);
  718                 return (EINVAL);
  719         }
  720         if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
  721                 priv->stats.memoryFailures++;
  722                 NG_FREE_ITEM(item);
  723                 return (EINVAL);
  724         }
  725         hdr = ntohs(*mtod(m, u_int16_t *));
  726         m_adj(m, 2);
  727 
  728         /* Check required header bits and minimum length */
  729         is_ctrl = (hdr & L2TP_HDR_CTRL) != 0;
  730         if ((hdr & req_bits[is_ctrl][0]) != 0
  731             || (~hdr & req_bits[is_ctrl][1]) != 0) {
  732                 priv->stats.recvInvalid++;
  733                 NG_FREE_ITEM(item);
  734                 NG_FREE_M(m);
  735                 return (EINVAL);
  736         }
  737         if (m->m_pkthdr.len < 4                         /* tunnel, session id */
  738             + (2 * ((hdr & L2TP_HDR_LEN) != 0))         /* length field */
  739             + (4 * ((hdr & L2TP_HDR_SEQ) != 0))         /* seq # fields */
  740             + (2 * ((hdr & L2TP_HDR_OFF) != 0))) {      /* offset field */
  741                 priv->stats.recvRunts++;
  742                 NG_FREE_ITEM(item);
  743                 NG_FREE_M(m);
  744                 return (EINVAL);
  745         }
  746 
  747         /* Get and validate length field if present */
  748         if ((hdr & L2TP_HDR_LEN) != 0) {
  749                 if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
  750                         priv->stats.memoryFailures++;
  751                         NG_FREE_ITEM(item);
  752                         return (EINVAL);
  753                 }
  754                 len = (u_int16_t)ntohs(*mtod(m, u_int16_t *)) - 4;
  755                 m_adj(m, 2);
  756                 if (len < 0 || len > m->m_pkthdr.len) {
  757                         priv->stats.recvInvalid++;
  758                         NG_FREE_ITEM(item);
  759                         NG_FREE_M(m);
  760                         return (EINVAL);
  761                 }
  762                 if (len < m->m_pkthdr.len)              /* trim extra bytes */
  763                         m_adj(m, -(m->m_pkthdr.len - len));
  764         }
  765 
  766         /* Get tunnel ID and session ID */
  767         if (m->m_len < 4 && (m = m_pullup(m, 4)) == NULL) {
  768                 priv->stats.memoryFailures++;
  769                 NG_FREE_ITEM(item);
  770                 return (EINVAL);
  771         }
  772         memcpy(ids, mtod(m, u_int16_t *), 4);
  773         m_adj(m, 4);
  774 
  775         /* Check tunnel ID */
  776         if (ids[0] != priv->conf.tunnel_id
  777             && (priv->conf.match_id || ids[0] != 0)) {
  778                 priv->stats.recvWrongTunnel++;
  779                 NG_FREE_ITEM(item);
  780                 NG_FREE_M(m);
  781                 return (EADDRNOTAVAIL);
  782         }
  783 
  784         /* Check session ID (for data packets only) */
  785         if ((hdr & L2TP_HDR_CTRL) == 0) {
  786                 NG_NODE_FOREACH_HOOK(node, ng_l2tp_find_session,
  787                     (void *)(uintptr_t)ids[1], hook);
  788                 if (hook == NULL) {
  789                         priv->stats.recvUnknownSID++;
  790                         NG_FREE_ITEM(item);
  791                         NG_FREE_M(m);
  792                         return (ENOTCONN);
  793                 }
  794                 hpriv = NG_HOOK_PRIVATE(hook);
  795         }
  796 
  797         /* Get Ns, Nr fields if present */
  798         if ((hdr & L2TP_HDR_SEQ) != 0) {
  799                 if (m->m_len < 4 && (m = m_pullup(m, 4)) == NULL) {
  800                         priv->stats.memoryFailures++;
  801                         NG_FREE_ITEM(item);
  802                         return (EINVAL);
  803                 }
  804                 memcpy(&ns, &mtod(m, u_int16_t *)[0], 2);
  805                 ns = ntohs(ns);
  806                 memcpy(&nr, &mtod(m, u_int16_t *)[1], 2);
  807                 nr = ntohs(nr);
  808                 m_adj(m, 4);
  809         }
  810 
  811         /* Strip offset padding if present */
  812         if ((hdr & L2TP_HDR_OFF) != 0) {
  813                 u_int16_t offset;
  814 
  815                 /* Get length of offset padding */
  816                 if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
  817                         priv->stats.memoryFailures++;
  818                         NG_FREE_ITEM(item);
  819                         return (EINVAL);
  820                 }
  821                 memcpy(&offset, mtod(m, u_int16_t *), 2);
  822                 offset = ntohs(offset);
  823 
  824                 /* Trim offset padding */
  825                 if (offset <= 2 || offset > m->m_pkthdr.len) {
  826                         priv->stats.recvInvalid++;
  827                         NG_FREE_ITEM(item);
  828                         NG_FREE_M(m);
  829                         return (EINVAL);
  830                 }
  831                 m_adj(m, offset);
  832         }
  833 
  834         /* Handle control packets */
  835         if ((hdr & L2TP_HDR_CTRL) != 0) {
  836 
  837                 /* Handle receive ack sequence number Nr */
  838                 ng_l2tp_seq_recv_nr(priv, nr);
  839 
  840                 /* Discard ZLB packets */
  841                 if (m->m_pkthdr.len == 0) {
  842                         priv->stats.recvZLBs++;
  843                         NG_FREE_ITEM(item);
  844                         NG_FREE_M(m);
  845                         return (0);
  846                 }
  847 
  848                 /*
  849                  * Prepend session ID to packet here: we don't want to accept
  850                  * the send sequence number Ns if we have to drop the packet
  851                  * later because of a memory error, because then the upper
  852                  * layer would never get the packet.
  853                  */
  854                 M_PREPEND(m, 2, M_DONTWAIT);
  855                 if (m == NULL) {
  856                         priv->stats.memoryFailures++;
  857                         NG_FREE_ITEM(item);
  858                         return (ENOBUFS);
  859                 }
  860                 memcpy(mtod(m, u_int16_t *), &ids[1], 2);
  861 
  862                 /* Now handle send sequence number */
  863                 if (ng_l2tp_seq_recv_ns(priv, ns) == -1) {
  864                         NG_FREE_ITEM(item);
  865                         NG_FREE_M(m);
  866                         return (0);
  867                 }
  868 
  869                 /* Deliver packet to upper layers */
  870                 NG_FWD_NEW_DATA(error, item, priv->ctrl, m);
  871                 return (error);
  872         }
  873 
  874         /* Follow peer's lead in data sequencing, if configured to do so */
  875         if (!hpriv->conf.control_dseq)
  876                 hpriv->conf.enable_dseq = ((hdr & L2TP_HDR_SEQ) != 0);
  877 
  878         /* Handle data sequence numbers if present and enabled */
  879         if ((hdr & L2TP_HDR_SEQ) != 0) {
  880                 if (hpriv->conf.enable_dseq
  881                     && L2TP_SEQ_DIFF(ns, hpriv->nr) < 0) {
  882                         NG_FREE_ITEM(item);     /* duplicate or out of order */
  883                         NG_FREE_M(m);
  884                         priv->stats.recvDataDrops++;
  885                         return (0);
  886                 }
  887                 hpriv->nr = ns + 1;
  888         }
  889 
  890         /* Drop empty data packets */
  891         if (m->m_pkthdr.len == 0) {
  892                 NG_FREE_ITEM(item);
  893                 NG_FREE_M(m);
  894                 return (0);
  895         }
  896 
  897         /* Deliver data */
  898         NG_FWD_NEW_DATA(error, item, hook, m);
  899         return (error);
  900 }
  901 
  902 /*
  903  * Handle an outgoing control frame.
  904  */
  905 static int
  906 ng_l2tp_recv_ctrl(node_p node, item_p item)
  907 {
  908         const priv_p priv = NG_NODE_PRIVATE(node);
  909         struct l2tp_seq *const seq = &priv->seq;
  910         struct mbuf *m;
  911         int i;
  912 
  913         /* Grab mbuf and discard other stuff XXX */
  914         NGI_GET_M(item, m);
  915         NG_FREE_ITEM(item);
  916 
  917         /* Packet should have session ID prepended */
  918         if (m->m_pkthdr.len < 2) {
  919                 priv->stats.xmitInvalid++;
  920                 m_freem(m);
  921                 return (EINVAL);
  922         }
  923 
  924         /* Check max length */
  925         if (m->m_pkthdr.len >= 0x10000 - 14) {
  926                 priv->stats.xmitTooBig++;
  927                 m_freem(m);
  928                 return (EOVERFLOW);
  929         }
  930 
  931         /* Find next empty slot in transmit queue */
  932         for (i = 0; i < L2TP_MAX_XWIN && seq->xwin[i] != NULL; i++);
  933         if (i == L2TP_MAX_XWIN) {
  934                 priv->stats.xmitDrops++;
  935                 m_freem(m);
  936                 return (ENOBUFS);
  937         }
  938         seq->xwin[i] = m;
  939 
  940         /* Sanity check receive ack timer state */
  941         KASSERT((i == 0) ^ seq->rack_timer_running,
  942             ("%s: xwin %d full but rack timer %srunning",
  943             __FUNCTION__, i, seq->rack_timer_running ? "" : "not "));
  944 
  945         /* If peer's receive window is already full, nothing else to do */
  946         if (i >= seq->cwnd)
  947                 return (0);
  948 
  949         /* Start retransmit timer if not already running */
  950         if (!seq->rack_timer_running) {
  951                 callout_reset(&seq->rack_timer,
  952                     hz, ng_l2tp_seq_rack_timeout, node);
  953                 seq->rack_timer_running = 1;
  954                 NG_NODE_REF(node);
  955         }
  956 
  957         /* Copy packet */
  958         if ((m = L2TP_COPY_MBUF(seq->xwin[i], M_DONTWAIT)) == NULL) {
  959                 priv->stats.memoryFailures++;
  960                 return (ENOBUFS);
  961         }
  962 
  963         /* Send packet and increment xmit sequence number */
  964         return (ng_l2tp_xmit_ctrl(priv, m, seq->ns++));
  965 }
  966 
  967 /*
  968  * Handle an outgoing data frame.
  969  */
  970 static int
  971 ng_l2tp_recv_data(node_p node, item_p item, hookpriv_p hpriv)
  972 {
  973         const priv_p priv = NG_NODE_PRIVATE(node);
  974         struct mbuf *m;
  975         u_int16_t hdr;
  976         int error;
  977         int i = 1;
  978 
  979         /* Get mbuf */
  980         NGI_GET_M(item, m);
  981 
  982         /* Check max length */
  983         if (m->m_pkthdr.len >= 0x10000 - 12) {
  984                 priv->stats.xmitDataTooBig++;
  985                 NG_FREE_ITEM(item);
  986                 NG_FREE_M(m);
  987                 return (EOVERFLOW);
  988         }
  989 
  990         /* Prepend L2TP header */
  991         M_PREPEND(m, 6
  992             + (2 * (hpriv->conf.include_length != 0))
  993             + (4 * (hpriv->conf.enable_dseq != 0)),
  994             M_DONTWAIT);
  995         if (m == NULL) {
  996                 priv->stats.memoryFailures++;
  997                 NG_FREE_ITEM(item);
  998                 return (ENOBUFS);
  999         }
 1000         hdr = L2TP_DATA_HDR;
 1001         if (hpriv->conf.include_length) {
 1002                 hdr |= L2TP_HDR_LEN;
 1003                 mtod(m, u_int16_t *)[i++] = htons(m->m_pkthdr.len);
 1004         }
 1005         mtod(m, u_int16_t *)[i++] = priv->conf.peer_id;
 1006         mtod(m, u_int16_t *)[i++] = hpriv->conf.peer_id;
 1007         if (hpriv->conf.enable_dseq) {
 1008                 hdr |= L2TP_HDR_SEQ;
 1009                 mtod(m, u_int16_t *)[i++] = htons(hpriv->ns);
 1010                 mtod(m, u_int16_t *)[i++] = htons(hpriv->nr);
 1011                 hpriv->ns++;
 1012         }
 1013         mtod(m, u_int16_t *)[0] = htons(hdr);
 1014 
 1015         /* Send packet */
 1016         NG_FWD_NEW_DATA(error, item, priv->lower, m);
 1017         return (error);
 1018 }
 1019 
 1020 /*
 1021  * Send a message to our controlling node that we've failed.
 1022  */
 1023 static void
 1024 ng_l2tp_seq_failure(priv_p priv)
 1025 {
 1026         struct ng_mesg *msg;
 1027         int error;
 1028 
 1029         NG_MKMESSAGE(msg, NGM_L2TP_COOKIE, NGM_L2TP_ACK_FAILURE, 0, M_NOWAIT);
 1030         if (msg == NULL)
 1031                 return;
 1032         NG_SEND_MSG_ID(error, priv->node, msg, priv->ftarget, 0);
 1033 }
 1034 
 1035 /************************************************************************
 1036                         SEQUENCE NUMBER HANDLING
 1037 ************************************************************************/
 1038 
 1039 /*
 1040  * Initialize sequence number state.
 1041  */
 1042 static void
 1043 ng_l2tp_seq_init(priv_p priv)
 1044 {
 1045         struct l2tp_seq *const seq = &priv->seq;
 1046 
 1047         KASSERT(priv->conf.peer_win >= 1,
 1048             ("%s: peer_win is zero", __FUNCTION__));
 1049         memset(seq, 0, sizeof(*seq));
 1050         seq->cwnd = 1;
 1051         seq->wmax = priv->conf.peer_win;
 1052         if (seq->wmax > L2TP_MAX_XWIN)
 1053                 seq->wmax = L2TP_MAX_XWIN;
 1054         seq->ssth = seq->wmax;
 1055         seq->max_rexmits = priv->conf.rexmit_max;
 1056         seq->max_rexmit_to = priv->conf.rexmit_max_to;
 1057         callout_init(&seq->rack_timer, 0);
 1058         callout_init(&seq->xack_timer, 0);
 1059         L2TP_SEQ_CHECK(seq);
 1060 }
 1061 
 1062 /*
 1063  * Adjust sequence number state accordingly after reconfiguration.
 1064  */
 1065 static int
 1066 ng_l2tp_seq_adjust(priv_p priv, const struct ng_l2tp_config *conf)
 1067 {
 1068         struct l2tp_seq *const seq = &priv->seq;
 1069         u_int16_t new_wmax;
 1070 
 1071         /* If disabling node, reset state sequence number */
 1072         if (!conf->enabled) {
 1073                 ng_l2tp_seq_reset(priv);
 1074                 return (0);
 1075         }
 1076 
 1077         /* Adjust peer's max recv window; it can only increase */
 1078         new_wmax = conf->peer_win;
 1079         if (new_wmax > L2TP_MAX_XWIN)
 1080                 new_wmax = L2TP_MAX_XWIN;
 1081         if (new_wmax == 0)
 1082                 return (EINVAL);
 1083         if (new_wmax < seq->wmax)
 1084                 return (EBUSY);
 1085         seq->wmax = new_wmax;
 1086 
 1087         /* Update retransmit parameters */
 1088         seq->max_rexmits = conf->rexmit_max;
 1089         seq->max_rexmit_to = conf->rexmit_max_to;
 1090 
 1091         /* Done */
 1092         return (0);
 1093 }
 1094 
 1095 /*
 1096  * Reset sequence number state.
 1097  */
 1098 static void
 1099 ng_l2tp_seq_reset(priv_p priv)
 1100 {
 1101         struct l2tp_seq *const seq = &priv->seq;
 1102         hook_p hook;
 1103         int i;
 1104 
 1105         /* Sanity check */
 1106         L2TP_SEQ_CHECK(seq);
 1107 
 1108         /* Stop timers */
 1109         if (seq->rack_timer_running && callout_stop(&seq->rack_timer) == 1) {
 1110                 seq->rack_timer_running = 0;
 1111                 NG_NODE_UNREF(priv->node);
 1112         }
 1113         if (seq->xack_timer_running && callout_stop(&seq->xack_timer) == 1) {
 1114                 seq->xack_timer_running = 0;
 1115                 NG_NODE_UNREF(priv->node);
 1116         }
 1117 
 1118         /* Free retransmit queue */
 1119         for (i = 0; i < L2TP_MAX_XWIN; i++) {
 1120                 if (seq->xwin[i] == NULL)
 1121                         break;
 1122                 m_freem(seq->xwin[i]);
 1123         }
 1124 
 1125         /* Reset session hooks' sequence number states */
 1126         NG_NODE_FOREACH_HOOK(priv->node, ng_l2tp_reset_session, NULL, hook);
 1127 
 1128         /* Reset node's sequence number state */
 1129         memset(seq, 0, sizeof(*seq));
 1130         seq->cwnd = 1;
 1131         seq->wmax = L2TP_MAX_XWIN;
 1132         seq->ssth = seq->wmax;
 1133 
 1134         /* Done */
 1135         L2TP_SEQ_CHECK(seq);
 1136 }
 1137 
 1138 /*
 1139  * Handle receipt of an acknowledgement value (Nr) from peer.
 1140  */
 1141 static void
 1142 ng_l2tp_seq_recv_nr(priv_p priv, u_int16_t nr)
 1143 {
 1144         struct l2tp_seq *const seq = &priv->seq;
 1145         struct mbuf *m;
 1146         int nack;
 1147         int i;
 1148 
 1149         /* Verify peer's ACK is in range */
 1150         if ((nack = L2TP_SEQ_DIFF(nr, seq->rack)) <= 0)
 1151                 return;                         /* duplicate ack */
 1152         if (L2TP_SEQ_DIFF(nr, seq->ns) > 0) {
 1153                 priv->stats.recvBadAcks++;      /* ack for packet not sent */
 1154                 return;
 1155         }
 1156         KASSERT(nack <= L2TP_MAX_XWIN,
 1157             ("%s: nack=%d > %d", __FUNCTION__, nack, L2TP_MAX_XWIN));
 1158 
 1159         /* Update receive ack stats */
 1160         seq->rack = nr;
 1161         seq->rexmits = 0;
 1162 
 1163         /* Free acknowledged packets and shift up packets in the xmit queue */
 1164         for (i = 0; i < nack; i++)
 1165                 m_freem(seq->xwin[i]);
 1166         memmove(seq->xwin, seq->xwin + nack,
 1167             (L2TP_MAX_XWIN - nack) * sizeof(*seq->xwin));
 1168         memset(seq->xwin + (L2TP_MAX_XWIN - nack), 0,
 1169             nack * sizeof(*seq->xwin));
 1170 
 1171         /*
 1172          * Do slow-start/congestion avoidance windowing algorithm described
 1173          * in RFC 2661, Appendix A. Here we handle a multiple ACK as if each
 1174          * ACK had arrived separately.
 1175          */
 1176         if (seq->cwnd < seq->wmax) {
 1177 
 1178                 /* Handle slow start phase */
 1179                 if (seq->cwnd < seq->ssth) {
 1180                         seq->cwnd += nack;
 1181                         nack = 0;
 1182                         if (seq->cwnd > seq->ssth) {    /* into cg.av. phase */
 1183                                 nack = seq->cwnd - seq->ssth;
 1184                                 seq->cwnd = seq->ssth;
 1185                         }
 1186                 }
 1187 
 1188                 /* Handle congestion avoidance phase */
 1189                 if (seq->cwnd >= seq->ssth) {
 1190                         seq->acks += nack;
 1191                         while (seq->acks >= seq->cwnd) {
 1192                                 seq->acks -= seq->cwnd;
 1193                                 if (seq->cwnd < seq->wmax)
 1194                                         seq->cwnd++;
 1195                         }
 1196                 }
 1197         }
 1198 
 1199         /* Stop xmit timer */
 1200         if (seq->rack_timer_running && callout_stop(&seq->rack_timer) == 1) {
 1201                 seq->rack_timer_running = 0;
 1202                 NG_NODE_UNREF(priv->node);
 1203         }
 1204 
 1205         /* If transmit queue is empty, we're done for now */
 1206         if (seq->xwin[0] == NULL)
 1207                 return;
 1208 
 1209         /* Start restransmit timer again */
 1210         callout_reset(&seq->rack_timer,
 1211             hz, ng_l2tp_seq_rack_timeout, priv->node);
 1212         seq->rack_timer_running = 1;
 1213         NG_NODE_REF(priv->node);
 1214 
 1215         /*
 1216          * Send more packets, trying to keep peer's receive window full.
 1217          * If there is a memory error, pretend packet was sent, as it
 1218          * will get retransmitted later anyway.
 1219          */
 1220         while ((i = L2TP_SEQ_DIFF(seq->ns, seq->rack)) < seq->cwnd
 1221             && seq->xwin[i] != NULL) {
 1222                 if ((m = L2TP_COPY_MBUF(seq->xwin[i], M_DONTWAIT)) == NULL)
 1223                         priv->stats.memoryFailures++;
 1224                 else
 1225                         ng_l2tp_xmit_ctrl(priv, m, seq->ns);
 1226                 seq->ns++;
 1227         }
 1228 }
 1229 
 1230 /*
 1231  * Handle receipt of a sequence number value (Ns) from peer.
 1232  * We make no attempt to re-order out of order packets.
 1233  *
 1234  * This function should only be called for non-ZLB packets.
 1235  *
 1236  * Returns:
 1237  *       0      Accept packet
 1238  *      -1      Drop packet
 1239  */
 1240 static int
 1241 ng_l2tp_seq_recv_ns(priv_p priv, u_int16_t ns)
 1242 {
 1243         struct l2tp_seq *const seq = &priv->seq;
 1244 
 1245         /* If not what we expect, drop packet and send an immediate ZLB ack */
 1246         if (ns != seq->nr) {
 1247                 if (L2TP_SEQ_DIFF(ns, seq->nr) < 0)
 1248                         priv->stats.recvDuplicates++;
 1249                 else
 1250                         priv->stats.recvOutOfOrder++;
 1251                 ng_l2tp_xmit_ctrl(priv, NULL, seq->ns);
 1252                 return (-1);
 1253         }
 1254 
 1255         /* Update recv sequence number */
 1256         seq->nr++;
 1257 
 1258         /* Start receive ack timer, if not already running */
 1259         if (!seq->xack_timer_running) {
 1260                 callout_reset(&seq->xack_timer,
 1261                     L2TP_DELAYED_ACK, ng_l2tp_seq_xack_timeout, priv->node);
 1262                 seq->xack_timer_running = 1;
 1263                 NG_NODE_REF(priv->node);
 1264         }
 1265 
 1266         /* Accept packet */
 1267         return (0);
 1268 }
 1269 
 1270 /*
 1271  * Handle an ack timeout. We have an outstanding ack that we
 1272  * were hoping to piggy-back, but haven't, so send a ZLB.
 1273  */
 1274 static void
 1275 ng_l2tp_seq_xack_timeout(void *arg)
 1276 {
 1277         const node_p node = arg;
 1278         const priv_p priv = NG_NODE_PRIVATE(node);
 1279         struct l2tp_seq *const seq = &priv->seq;
 1280         int s;
 1281 
 1282         /* Check if node is going away */
 1283         s = splnet();
 1284         if (NG_NODE_NOT_VALID(node)) {
 1285                 seq->xack_timer_running = 0;
 1286                 if (!seq->rack_timer_running) {
 1287                         FREE(priv, M_NETGRAPH_L2TP);
 1288                         NG_NODE_SET_PRIVATE(node, NULL);
 1289                 }
 1290                 NG_NODE_UNREF(node);
 1291                 splx(s);
 1292                 return;
 1293         }
 1294 
 1295         /* Sanity check */
 1296         L2TP_SEQ_CHECK(seq);
 1297 
 1298         /* If ack is still outstanding, send a ZLB */
 1299         if (seq->xack != seq->nr)
 1300                 ng_l2tp_xmit_ctrl(priv, NULL, seq->ns);
 1301 
 1302         /* Done */
 1303         seq->xack_timer_running = 0;
 1304         NG_NODE_UNREF(node);
 1305         L2TP_SEQ_CHECK(seq);
 1306         splx(s);
 1307 }
 1308 
 1309 /* 
 1310  * Handle a transmit timeout. The peer has failed to respond
 1311  * with an ack for our packet, so retransmit it.
 1312  */
 1313 static void
 1314 ng_l2tp_seq_rack_timeout(void *arg)
 1315 {
 1316         const node_p node = arg;
 1317         const priv_p priv = NG_NODE_PRIVATE(node);
 1318         struct l2tp_seq *const seq = &priv->seq;
 1319         struct mbuf *m;
 1320         u_int delay;
 1321         int s;
 1322 
 1323         /* Check if node is going away */
 1324         s = splnet();
 1325         if (NG_NODE_NOT_VALID(node)) {
 1326                 seq->rack_timer_running = 0;
 1327                 if (!seq->xack_timer_running) {
 1328                         FREE(priv, M_NETGRAPH_L2TP);
 1329                         NG_NODE_SET_PRIVATE(node, NULL);
 1330                 }
 1331                 NG_NODE_UNREF(node);
 1332                 splx(s);
 1333                 return;
 1334         }
 1335 
 1336         /* Sanity check */
 1337         L2TP_SEQ_CHECK(seq);
 1338 
 1339         /* Make sure peer's ack is still outstanding before doing anything */
 1340         if (seq->rack == seq->ns) {
 1341                 seq->rack_timer_running = 0;
 1342                 NG_NODE_UNREF(node);
 1343                 goto done;
 1344         }
 1345         priv->stats.xmitRetransmits++;
 1346 
 1347         /* Have we reached the retransmit limit? If so, notify owner. */
 1348         if (seq->rexmits++ >= seq->max_rexmits)
 1349                 ng_l2tp_seq_failure(priv);
 1350 
 1351         /* Restart timer, this time with an increased delay */
 1352         delay = (seq->rexmits > 12) ? (1 << 12) : (1 << seq->rexmits);
 1353         if (delay > seq->max_rexmit_to)
 1354                 delay = seq->max_rexmit_to;
 1355         callout_reset(&seq->rack_timer,
 1356             hz * delay, ng_l2tp_seq_rack_timeout, node);
 1357 
 1358         /* Do slow-start/congestion algorithm windowing algorithm */
 1359         seq->ssth = (seq->cwnd + 1) / 2;
 1360         seq->cwnd = 1;
 1361         seq->acks = 0;
 1362 
 1363         /* Retransmit oldest unack'd packet */
 1364         if ((m = L2TP_COPY_MBUF(seq->xwin[0], M_DONTWAIT)) == NULL)
 1365                 priv->stats.memoryFailures++;
 1366         else
 1367                 ng_l2tp_xmit_ctrl(priv, m, seq->rack);
 1368 
 1369 done:
 1370         /* Done */
 1371         L2TP_SEQ_CHECK(seq);
 1372         splx(s);
 1373 }
 1374 
 1375 /*
 1376  * Transmit a control stream packet, payload optional.
 1377  * The transmit sequence number is not incremented.
 1378  */
 1379 static int
 1380 ng_l2tp_xmit_ctrl(priv_p priv, struct mbuf *m, u_int16_t ns)
 1381 {
 1382         struct l2tp_seq *const seq = &priv->seq;
 1383         u_int16_t session_id = 0;
 1384         meta_p meta = NULL;
 1385         int error;
 1386 
 1387         /* If no mbuf passed, send an empty packet (ZLB) */
 1388         if (m == NULL) {
 1389 
 1390                 /* Create a new mbuf for ZLB packet */
 1391                 MGETHDR(m, M_DONTWAIT, MT_DATA);
 1392                 if (m == NULL) {
 1393                         priv->stats.memoryFailures++;
 1394                         return (ENOBUFS);
 1395                 }
 1396                 m->m_len = m->m_pkthdr.len = 12;
 1397                 m->m_pkthdr.rcvif = NULL;
 1398                 priv->stats.xmitZLBs++;
 1399         } else {
 1400 
 1401                 /* Strip off session ID */
 1402                 if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
 1403                         priv->stats.memoryFailures++;
 1404                         return (ENOBUFS);
 1405                 }
 1406                 memcpy(&session_id, mtod(m, u_int16_t *), 2);
 1407                 m_adj(m, 2);
 1408 
 1409                 /* Make room for L2TP header */
 1410                 M_PREPEND(m, 12, M_DONTWAIT);
 1411                 if (m == NULL) {
 1412                         priv->stats.memoryFailures++;
 1413                         return (ENOBUFS);
 1414                 }
 1415         }
 1416 
 1417         /* Fill in L2TP header */
 1418         mtod(m, u_int16_t *)[0] = htons(L2TP_CTRL_HDR);
 1419         mtod(m, u_int16_t *)[1] = htons(m->m_pkthdr.len);
 1420         mtod(m, u_int16_t *)[2] = priv->conf.peer_id;
 1421         mtod(m, u_int16_t *)[3] = session_id;
 1422         mtod(m, u_int16_t *)[4] = htons(ns);
 1423         mtod(m, u_int16_t *)[5] = htons(seq->nr);
 1424 
 1425         /* Update sequence number info and stats */
 1426         priv->stats.xmitPackets++;
 1427         priv->stats.xmitOctets += m->m_pkthdr.len;
 1428 
 1429         /* Stop ack timer: we're sending an ack with this packet */
 1430         if (seq->xack_timer_running && callout_stop(&seq->xack_timer) == 1) {
 1431                 seq->xack_timer_running = 0;
 1432                 NG_NODE_UNREF(priv->node);
 1433         }
 1434         seq->xack = seq->nr;
 1435 
 1436         /* Send packet */
 1437         NG_SEND_DATA(error, priv->lower, m, meta);
 1438         return (error);
 1439 }
 1440 
 1441 #ifdef INVARIANTS
 1442 /*
 1443  * Sanity check sequence number state.
 1444  */
 1445 static void
 1446 ng_l2tp_seq_check(struct l2tp_seq *seq)
 1447 {
 1448         const int self_unack = L2TP_SEQ_DIFF(seq->nr, seq->xack);
 1449         const int peer_unack = L2TP_SEQ_DIFF(seq->ns, seq->rack);
 1450         int i;
 1451 
 1452 #define CHECK(p)        KASSERT((p), ("%s: not: %s", __FUNCTION__, #p))
 1453 
 1454         CHECK(seq->wmax <= L2TP_MAX_XWIN);
 1455         CHECK(seq->cwnd >= 1);
 1456         CHECK(seq->cwnd <= seq->wmax);
 1457         CHECK(seq->ssth >= 1);
 1458         CHECK(seq->ssth <= seq->wmax);
 1459         if (seq->cwnd < seq->ssth)
 1460                 CHECK(seq->acks == 0);
 1461         else
 1462                 CHECK(seq->acks <= seq->cwnd);
 1463         CHECK(self_unack >= 0);
 1464         CHECK(peer_unack >= 0);
 1465         CHECK(peer_unack <= seq->wmax);
 1466         CHECK((self_unack == 0) ^ seq->xack_timer_running);
 1467         CHECK((peer_unack == 0) ^ seq->rack_timer_running);
 1468         CHECK(seq->rack_timer_running || !callout_pending(&seq->rack_timer));
 1469         CHECK(seq->xack_timer_running || !callout_pending(&seq->xack_timer));
 1470         for (i = 0; i < peer_unack; i++)
 1471                 CHECK(seq->xwin[i] != NULL);
 1472         for ( ; i < seq->cwnd; i++)         /* verify peer's recv window full */
 1473                 CHECK(seq->xwin[i] == NULL);
 1474 
 1475 #undef CHECK
 1476 }
 1477 #endif  /* INVARIANTS */
 1478 
 1479 

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