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dn_nsp_in.c

/*
 * DECnet       An implementation of the DECnet protocol suite for the LINUX
 *              operating system.  DECnet is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              DECnet Network Services Protocol (Input)
 *
 * Author:      Eduardo Marcelo Serrat <emserrat@geocities.com>
 *
 * Changes:
 *
 *    Steve Whitehouse:  Split into dn_nsp_in.c and dn_nsp_out.c from
 *                       original dn_nsp.c.
 *    Steve Whitehouse:  Updated to work with my new routing architecture.
 *    Steve Whitehouse:  Add changes from Eduardo Serrat's patches.
 *    Steve Whitehouse:  Put all ack handling code in a common routine.
 *    Steve Whitehouse:  Put other common bits into dn_nsp_rx()
 *    Steve Whitehouse:  More checks on skb->len to catch bogus packets
 *                       Fixed various race conditions and possible nasties.
 *    Steve Whitehouse:  Now handles returned conninit frames.
 *     David S. Miller:  New socket locking
 *    Steve Whitehouse:  Fixed lockup when socket filtering was enabled.
 *         Paul Koning:  Fix to push CC sockets into RUN when acks are
 *                       received.
 *    Steve Whitehouse:
 *   Patrick Caulfield:  Checking conninits for correctness & sending of error
 *                       responses.
 *    Steve Whitehouse:  Added backlog congestion level return codes.
 *   Patrick Caulfield:
 *    Steve Whitehouse:  Added flow control support (outbound)
 *    Steve Whitehouse:  Prepare for nonlinear skbs
 */

/******************************************************************************
    (c) 1995-1998 E.M. Serrat       emserrat@geocities.com

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
*******************************************************************************/

#include <linux/errno.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/sockios.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/inet.h>
#include <linux/route.h>
#include <net/sock.h>
#include <net/tcp_states.h>
#include <asm/system.h>
#include <linux/fcntl.h>
#include <linux/mm.h>
#include <linux/termios.h>
#include <linux/interrupt.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/netfilter_decnet.h>
#include <net/neighbour.h>
#include <net/dst.h>
#include <net/dn.h>
#include <net/dn_nsp.h>
#include <net/dn_dev.h>
#include <net/dn_route.h>

extern int decnet_log_martians;

static void dn_log_martian(struct sk_buff *skb, const char *msg)
{
      if (decnet_log_martians && net_ratelimit()) {
            char *devname = skb->dev ? skb->dev->name : "???";
            struct dn_skb_cb *cb = DN_SKB_CB(skb);
            printk(KERN_INFO "DECnet: Martian packet (%s) dev=%s src=0x%04hx dst=0x%04hx srcport=0x%04hx dstport=0x%04hx\n", msg, devname, dn_ntohs(cb->src), dn_ntohs(cb->dst), dn_ntohs(cb->src_port), dn_ntohs(cb->dst_port));
      }
}

/*
 * For this function we've flipped the cross-subchannel bit
 * if the message is an otherdata or linkservice message. Thus
 * we can use it to work out what to update.
 */
static void dn_ack(struct sock *sk, struct sk_buff *skb, unsigned short ack)
{
      struct dn_scp *scp = DN_SK(sk);
      unsigned short type = ((ack >> 12) & 0x0003);
      int wakeup = 0;

      switch(type) {
            case 0: /* ACK - Data */
                  if (dn_after(ack, scp->ackrcv_dat)) {
                        scp->ackrcv_dat = ack & 0x0fff;
                        wakeup |= dn_nsp_check_xmit_queue(sk, skb, &scp->data_xmit_queue, ack);
                  }
                  break;
            case 1: /* NAK - Data */
                  break;
            case 2: /* ACK - OtherData */
                  if (dn_after(ack, scp->ackrcv_oth)) {
                        scp->ackrcv_oth = ack & 0x0fff;
                        wakeup |= dn_nsp_check_xmit_queue(sk, skb, &scp->other_xmit_queue, ack);
                  }
                  break;
            case 3: /* NAK - OtherData */
                  break;
      }

      if (wakeup && !sock_flag(sk, SOCK_DEAD))
            sk->sk_state_change(sk);
}

/*
 * This function is a universal ack processor.
 */
static int dn_process_ack(struct sock *sk, struct sk_buff *skb, int oth)
{
      __le16 *ptr = (__le16 *)skb->data;
      int len = 0;
      unsigned short ack;

      if (skb->len < 2)
            return len;

      if ((ack = dn_ntohs(*ptr)) & 0x8000) {
            skb_pull(skb, 2);
            ptr++;
            len += 2;
            if ((ack & 0x4000) == 0) {
                  if (oth)
                        ack ^= 0x2000;
                  dn_ack(sk, skb, ack);
            }
      }

      if (skb->len < 2)
            return len;

      if ((ack = dn_ntohs(*ptr)) & 0x8000) {
            skb_pull(skb, 2);
            len += 2;
            if ((ack & 0x4000) == 0) {
                  if (oth)
                        ack ^= 0x2000;
                  dn_ack(sk, skb, ack);
            }
      }

      return len;
}


/**
 * dn_check_idf - Check an image data field format is correct.
 * @pptr: Pointer to pointer to image data
 * @len: Pointer to length of image data
 * @max: The maximum allowed length of the data in the image data field
 * @follow_on: Check that this many bytes exist beyond the end of the image data
 *
 * Returns: 0 if ok, -1 on error
 */
static inline int dn_check_idf(unsigned char **pptr, int *len, unsigned char max, unsigned char follow_on)
{
      unsigned char *ptr = *pptr;
      unsigned char flen = *ptr++;

      (*len)--;
      if (flen > max)
            return -1;
      if ((flen + follow_on) > *len)
            return -1;

      *len -= flen;
      *pptr = ptr + flen;
      return 0;
}

/*
 * Table of reason codes to pass back to node which sent us a badly
 * formed message, plus text messages for the log. A zero entry in
 * the reason field means "don't reply" otherwise a disc init is sent with
 * the specified reason code.
 */
static struct {
      unsigned short reason;
      const char *text;
} ci_err_table[] = {
 { 0,             "CI: Truncated message" },
 { NSP_REASON_ID, "CI: Destination username error" },
 { NSP_REASON_ID, "CI: Destination username type" },
 { NSP_REASON_US, "CI: Source username error" },
 { 0,             "CI: Truncated at menuver" },
 { 0,             "CI: Truncated before access or user data" },
 { NSP_REASON_IO, "CI: Access data format error" },
 { NSP_REASON_IO, "CI: User data format error" }
};

/*
 * This function uses a slightly different lookup method
 * to find its sockets, since it searches on object name/number
 * rather than port numbers. Various tests are done to ensure that
 * the incoming data is in the correct format before it is queued to
 * a socket.
 */
static struct sock *dn_find_listener(struct sk_buff *skb, unsigned short *reason)
{
      struct dn_skb_cb *cb = DN_SKB_CB(skb);
      struct nsp_conn_init_msg *msg = (struct nsp_conn_init_msg *)skb->data;
      struct sockaddr_dn dstaddr;
      struct sockaddr_dn srcaddr;
      unsigned char type = 0;
      int dstlen;
      int srclen;
      unsigned char *ptr;
      int len;
      int err = 0;
      unsigned char menuver;

      memset(&dstaddr, 0, sizeof(struct sockaddr_dn));
      memset(&srcaddr, 0, sizeof(struct sockaddr_dn));

      /*
       * 1. Decode & remove message header
       */
      cb->src_port = msg->srcaddr;
      cb->dst_port = msg->dstaddr;
      cb->services = msg->services;
      cb->info     = msg->info;
      cb->segsize  = dn_ntohs(msg->segsize);

      if (!pskb_may_pull(skb, sizeof(*msg)))
            goto err_out;

      skb_pull(skb, sizeof(*msg));

      len = skb->len;
      ptr = skb->data;

      /*
       * 2. Check destination end username format
       */
      dstlen = dn_username2sockaddr(ptr, len, &dstaddr, &type);
      err++;
      if (dstlen < 0)
            goto err_out;

      err++;
      if (type > 1)
            goto err_out;

      len -= dstlen;
      ptr += dstlen;

      /*
       * 3. Check source end username format
       */
      srclen = dn_username2sockaddr(ptr, len, &srcaddr, &type);
      err++;
      if (srclen < 0)
            goto err_out;

      len -= srclen;
      ptr += srclen;
      err++;
      if (len < 1)
            goto err_out;

      menuver = *ptr;
      ptr++;
      len--;

      /*
       * 4. Check that optional data actually exists if menuver says it does
       */
      err++;
      if ((menuver & (DN_MENUVER_ACC | DN_MENUVER_USR)) && (len < 1))
            goto err_out;

      /*
       * 5. Check optional access data format
       */
      err++;
      if (menuver & DN_MENUVER_ACC) {
            if (dn_check_idf(&ptr, &len, 39, 1))
                  goto err_out;
            if (dn_check_idf(&ptr, &len, 39, 1))
                  goto err_out;
            if (dn_check_idf(&ptr, &len, 39, (menuver & DN_MENUVER_USR) ? 1 : 0))
                  goto err_out;
      }

      /*
       * 6. Check optional user data format
       */
      err++;
      if (menuver & DN_MENUVER_USR) {
            if (dn_check_idf(&ptr, &len, 16, 0))
                  goto err_out;
      }

      /*
       * 7. Look up socket based on destination end username
       */
      return dn_sklist_find_listener(&dstaddr);
err_out:
      dn_log_martian(skb, ci_err_table[err].text);
      *reason = ci_err_table[err].reason;
      return NULL;
}


static void dn_nsp_conn_init(struct sock *sk, struct sk_buff *skb)
{
      if (sk_acceptq_is_full(sk)) {
            kfree_skb(skb);
            return;
      }

      sk->sk_ack_backlog++;
      skb_queue_tail(&sk->sk_receive_queue, skb);
      sk->sk_state_change(sk);
}

static void dn_nsp_conn_conf(struct sock *sk, struct sk_buff *skb)
{
      struct dn_skb_cb *cb = DN_SKB_CB(skb);
      struct dn_scp *scp = DN_SK(sk);
      unsigned char *ptr;

      if (skb->len < 4)
            goto out;

      ptr = skb->data;
      cb->services = *ptr++;
      cb->info = *ptr++;
      cb->segsize = dn_ntohs(*(__le16 *)ptr);

      if ((scp->state == DN_CI) || (scp->state == DN_CD)) {
            scp->persist = 0;
            scp->addrrem = cb->src_port;
            sk->sk_state = TCP_ESTABLISHED;
            scp->state = DN_RUN;
            scp->services_rem = cb->services;
            scp->info_rem = cb->info;
            scp->segsize_rem = cb->segsize;

            if ((scp->services_rem & NSP_FC_MASK) == NSP_FC_NONE)
                  scp->max_window = decnet_no_fc_max_cwnd;

            if (skb->len > 0) {
                  u16 dlen = *skb->data;
                  if ((dlen <= 16) && (dlen <= skb->len)) {
                        scp->conndata_in.opt_optl = dn_htons(dlen);
                        skb_copy_from_linear_data_offset(skb, 1,
                                    scp->conndata_in.opt_data, dlen);
                  }
            }
            dn_nsp_send_link(sk, DN_NOCHANGE, 0);
            if (!sock_flag(sk, SOCK_DEAD))
                  sk->sk_state_change(sk);
      }

out:
      kfree_skb(skb);
}

static void dn_nsp_conn_ack(struct sock *sk, struct sk_buff *skb)
{
      struct dn_scp *scp = DN_SK(sk);

      if (scp->state == DN_CI) {
            scp->state = DN_CD;
            scp->persist = 0;
      }

      kfree_skb(skb);
}

static void dn_nsp_disc_init(struct sock *sk, struct sk_buff *skb)
{
      struct dn_scp *scp = DN_SK(sk);
      struct dn_skb_cb *cb = DN_SKB_CB(skb);
      unsigned short reason;

      if (skb->len < 2)
            goto out;

      reason = dn_ntohs(*(__le16 *)skb->data);
      skb_pull(skb, 2);

      scp->discdata_in.opt_status = dn_htons(reason);
      scp->discdata_in.opt_optl   = 0;
      memset(scp->discdata_in.opt_data, 0, 16);

      if (skb->len > 0) {
            u16 dlen = *skb->data;
            if ((dlen <= 16) && (dlen <= skb->len)) {
                  scp->discdata_in.opt_optl = dn_htons(dlen);
                  skb_copy_from_linear_data_offset(skb, 1, scp->discdata_in.opt_data, dlen);
            }
      }

      scp->addrrem = cb->src_port;
      sk->sk_state = TCP_CLOSE;

      switch(scp->state) {
            case DN_CI:
            case DN_CD:
                  scp->state = DN_RJ;
                  sk->sk_err = ECONNREFUSED;
                  break;
            case DN_RUN:
                  sk->sk_shutdown |= SHUTDOWN_MASK;
                  scp->state = DN_DN;
                  break;
            case DN_DI:
                  scp->state = DN_DIC;
                  break;
      }

      if (!sock_flag(sk, SOCK_DEAD)) {
            if (sk->sk_socket->state != SS_UNCONNECTED)
                  sk->sk_socket->state = SS_DISCONNECTING;
            sk->sk_state_change(sk);
      }

      /*
       * It appears that its possible for remote machines to send disc
       * init messages with no port identifier if we are in the CI and
       * possibly also the CD state. Obviously we shouldn't reply with
       * a message if we don't know what the end point is.
       */
      if (scp->addrrem) {
            dn_nsp_send_disc(sk, NSP_DISCCONF, NSP_REASON_DC, GFP_ATOMIC);
      }
      scp->persist_fxn = dn_destroy_timer;
      scp->persist = dn_nsp_persist(sk);

out:
      kfree_skb(skb);
}

/*
 * disc_conf messages are also called no_resources or no_link
 * messages depending upon the "reason" field.
 */
static void dn_nsp_disc_conf(struct sock *sk, struct sk_buff *skb)
{
      struct dn_scp *scp = DN_SK(sk);
      unsigned short reason;

      if (skb->len != 2)
            goto out;

      reason = dn_ntohs(*(__le16 *)skb->data);

      sk->sk_state = TCP_CLOSE;

      switch(scp->state) {
            case DN_CI:
                  scp->state = DN_NR;
                  break;
            case DN_DR:
                  if (reason == NSP_REASON_DC)
                        scp->state = DN_DRC;
                  if (reason == NSP_REASON_NL)
                        scp->state = DN_CN;
                  break;
            case DN_DI:
                  scp->state = DN_DIC;
                  break;
            case DN_RUN:
                  sk->sk_shutdown |= SHUTDOWN_MASK;
            case DN_CC:
                  scp->state = DN_CN;
      }

      if (!sock_flag(sk, SOCK_DEAD)) {
            if (sk->sk_socket->state != SS_UNCONNECTED)
                  sk->sk_socket->state = SS_DISCONNECTING;
            sk->sk_state_change(sk);
      }

      scp->persist_fxn = dn_destroy_timer;
      scp->persist = dn_nsp_persist(sk);

out:
      kfree_skb(skb);
}

static void dn_nsp_linkservice(struct sock *sk, struct sk_buff *skb)
{
      struct dn_scp *scp = DN_SK(sk);
      unsigned short segnum;
      unsigned char lsflags;
      signed char fcval;
      int wake_up = 0;
      char *ptr = skb->data;
      unsigned char fctype = scp->services_rem & NSP_FC_MASK;

      if (skb->len != 4)
            goto out;

      segnum = dn_ntohs(*(__le16 *)ptr);
      ptr += 2;
      lsflags = *(unsigned char *)ptr++;
      fcval = *ptr;

      /*
       * Here we ignore erronous packets which should really
       * should cause a connection abort. It is not critical
       * for now though.
       */
      if (lsflags & 0xf8)
            goto out;

      if (seq_next(scp->numoth_rcv, segnum)) {
            seq_add(&scp->numoth_rcv, 1);
            switch(lsflags & 0x04) { /* FCVAL INT */
            case 0x00: /* Normal Request */
                  switch(lsflags & 0x03) { /* FCVAL MOD */
                  case 0x00: /* Request count */
                        if (fcval < 0) {
                              unsigned char p_fcval = -fcval;
                              if ((scp->flowrem_dat > p_fcval) &&
                                  (fctype == NSP_FC_SCMC)) {
                                    scp->flowrem_dat -= p_fcval;
                              }
                        } else if (fcval > 0) {
                              scp->flowrem_dat += fcval;
                              wake_up = 1;
                        }
                        break;
                  case 0x01: /* Stop outgoing data */
                        scp->flowrem_sw = DN_DONTSEND;
                        break;
                  case 0x02: /* Ok to start again */
                        scp->flowrem_sw = DN_SEND;
                        dn_nsp_output(sk);
                        wake_up = 1;
                  }
                  break;
            case 0x04: /* Interrupt Request */
                  if (fcval > 0) {
                        scp->flowrem_oth += fcval;
                        wake_up = 1;
                  }
                  break;
            }
            if (wake_up && !sock_flag(sk, SOCK_DEAD))
                  sk->sk_state_change(sk);
      }

      dn_nsp_send_oth_ack(sk);

out:
      kfree_skb(skb);
}

/*
 * Copy of sock_queue_rcv_skb (from sock.h) without
 * bh_lock_sock() (its already held when this is called) which
 * also allows data and other data to be queued to a socket.
 */
static __inline__ int dn_queue_skb(struct sock *sk, struct sk_buff *skb, int sig, struct sk_buff_head *queue)
{
      int err;

      /* Cast skb->rcvbuf to unsigned... It's pointless, but reduces
         number of warnings when compiling with -W --ANK
       */
      if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
          (unsigned)sk->sk_rcvbuf) {
            err = -ENOMEM;
            goto out;
      }

      err = sk_filter(sk, skb);
      if (err)
            goto out;

      skb_set_owner_r(skb, sk);
      skb_queue_tail(queue, skb);

      /* This code only runs from BH or BH protected context.
       * Therefore the plain read_lock is ok here. -DaveM
       */
      read_lock(&sk->sk_callback_lock);
      if (!sock_flag(sk, SOCK_DEAD)) {
            struct socket *sock = sk->sk_socket;
            wake_up_interruptible(sk->sk_sleep);
            if (sock && sock->fasync_list &&
                !test_bit(SOCK_ASYNC_WAITDATA, &sock->flags))
                  __kill_fasync(sock->fasync_list, sig,
                            (sig == SIGURG) ? POLL_PRI : POLL_IN);
      }
      read_unlock(&sk->sk_callback_lock);
out:
      return err;
}

static void dn_nsp_otherdata(struct sock *sk, struct sk_buff *skb)
{
      struct dn_scp *scp = DN_SK(sk);
      unsigned short segnum;
      struct dn_skb_cb *cb = DN_SKB_CB(skb);
      int queued = 0;

      if (skb->len < 2)
            goto out;

      cb->segnum = segnum = dn_ntohs(*(__le16 *)skb->data);
      skb_pull(skb, 2);

      if (seq_next(scp->numoth_rcv, segnum)) {

            if (dn_queue_skb(sk, skb, SIGURG, &scp->other_receive_queue) == 0) {
                  seq_add(&scp->numoth_rcv, 1);
                  scp->other_report = 0;
                  queued = 1;
            }
      }

      dn_nsp_send_oth_ack(sk);
out:
      if (!queued)
            kfree_skb(skb);
}

static void dn_nsp_data(struct sock *sk, struct sk_buff *skb)
{
      int queued = 0;
      unsigned short segnum;
      struct dn_skb_cb *cb = DN_SKB_CB(skb);
      struct dn_scp *scp = DN_SK(sk);

      if (skb->len < 2)
            goto out;

      cb->segnum = segnum = dn_ntohs(*(__le16 *)skb->data);
      skb_pull(skb, 2);

      if (seq_next(scp->numdat_rcv, segnum)) {
            if (dn_queue_skb(sk, skb, SIGIO, &sk->sk_receive_queue) == 0) {
                  seq_add(&scp->numdat_rcv, 1);
                  queued = 1;
            }

            if ((scp->flowloc_sw == DN_SEND) && dn_congested(sk)) {
                  scp->flowloc_sw = DN_DONTSEND;
                  dn_nsp_send_link(sk, DN_DONTSEND, 0);
            }
      }

      dn_nsp_send_data_ack(sk);
out:
      if (!queued)
            kfree_skb(skb);
}

/*
 * If one of our conninit messages is returned, this function
 * deals with it. It puts the socket into the NO_COMMUNICATION
 * state.
 */
static void dn_returned_conn_init(struct sock *sk, struct sk_buff *skb)
{
      struct dn_scp *scp = DN_SK(sk);

      if (scp->state == DN_CI) {
            scp->state = DN_NC;
            sk->sk_state = TCP_CLOSE;
            if (!sock_flag(sk, SOCK_DEAD))
                  sk->sk_state_change(sk);
      }

      kfree_skb(skb);
}

static int dn_nsp_no_socket(struct sk_buff *skb, unsigned short reason)
{
      struct dn_skb_cb *cb = DN_SKB_CB(skb);
      int ret = NET_RX_DROP;

      /* Must not reply to returned packets */
      if (cb->rt_flags & DN_RT_F_RTS)
            goto out;

      if ((reason != NSP_REASON_OK) && ((cb->nsp_flags & 0x0c) == 0x08)) {
            switch(cb->nsp_flags & 0x70) {
                  case 0x10:
                  case 0x60: /* (Retransmitted) Connect Init */
                        dn_nsp_return_disc(skb, NSP_DISCINIT, reason);
                        ret = NET_RX_SUCCESS;
                        break;
                  case 0x20: /* Connect Confirm */
                        dn_nsp_return_disc(skb, NSP_DISCCONF, reason);
                        ret = NET_RX_SUCCESS;
                        break;
            }
      }

out:
      kfree_skb(skb);
      return ret;
}

static int dn_nsp_rx_packet(struct sk_buff *skb)
{
      struct dn_skb_cb *cb = DN_SKB_CB(skb);
      struct sock *sk = NULL;
      unsigned char *ptr = (unsigned char *)skb->data;
      unsigned short reason = NSP_REASON_NL;

      if (!pskb_may_pull(skb, 2))
            goto free_out;

      skb_reset_transport_header(skb);
      cb->nsp_flags = *ptr++;

      if (decnet_debug_level & 2)
            printk(KERN_DEBUG "dn_nsp_rx: Message type 0x%02x\n", (int)cb->nsp_flags);

      if (cb->nsp_flags & 0x83)
            goto free_out;

      /*
       * Filter out conninits and useless packet types
       */
      if ((cb->nsp_flags & 0x0c) == 0x08) {
            switch(cb->nsp_flags & 0x70) {
                  case 0x00: /* NOP */
                  case 0x70: /* Reserved */
                  case 0x50: /* Reserved, Phase II node init */
                        goto free_out;
                  case 0x10:
                  case 0x60:
                        if (unlikely(cb->rt_flags & DN_RT_F_RTS))
                              goto free_out;
                        sk = dn_find_listener(skb, &reason);
                        goto got_it;
            }
      }

      if (!pskb_may_pull(skb, 3))
            goto free_out;

      /*
       * Grab the destination address.
       */
      cb->dst_port = *(__le16 *)ptr;
      cb->src_port = 0;
      ptr += 2;

      /*
       * If not a connack, grab the source address too.
       */
      if (pskb_may_pull(skb, 5)) {
            cb->src_port = *(__le16 *)ptr;
            ptr += 2;
            skb_pull(skb, 5);
      }

      /*
       * Returned packets...
       * Swap src & dst and look up in the normal way.
       */
      if (unlikely(cb->rt_flags & DN_RT_F_RTS)) {
            __le16 tmp = cb->dst_port;
            cb->dst_port = cb->src_port;
            cb->src_port = tmp;
            tmp = cb->dst;
            cb->dst = cb->src;
            cb->src = tmp;
      }

      /*
       * Find the socket to which this skb is destined.
       */
      sk = dn_find_by_skb(skb);
got_it:
      if (sk != NULL) {
            struct dn_scp *scp = DN_SK(sk);

            /* Reset backoff */
            scp->nsp_rxtshift = 0;

            /*
             * We linearize everything except data segments here.
             */
            if (cb->nsp_flags & ~0x60) {
                  if (unlikely(skb_linearize(skb)))
                        goto free_out;
            }

            return sk_receive_skb(sk, skb, 0);
      }

      return dn_nsp_no_socket(skb, reason);

free_out:
      kfree_skb(skb);
      return NET_RX_DROP;
}

int dn_nsp_rx(struct sk_buff *skb)
{
      return NF_HOOK(PF_DECnet, NF_DN_LOCAL_IN, skb, skb->dev, NULL, dn_nsp_rx_packet);
}

/*
 * This is the main receive routine for sockets. It is called
 * from the above when the socket is not busy, and also from
 * sock_release() when there is a backlog queued up.
 */
int dn_nsp_backlog_rcv(struct sock *sk, struct sk_buff *skb)
{
      struct dn_scp *scp = DN_SK(sk);
      struct dn_skb_cb *cb = DN_SKB_CB(skb);

      if (cb->rt_flags & DN_RT_F_RTS) {
            if (cb->nsp_flags == 0x18 || cb->nsp_flags == 0x68)
                  dn_returned_conn_init(sk, skb);
            else
                  kfree_skb(skb);
            return NET_RX_SUCCESS;
      }

      /*
       * Control packet.
       */
      if ((cb->nsp_flags & 0x0c) == 0x08) {
            switch(cb->nsp_flags & 0x70) {
                  case 0x10:
                  case 0x60:
                        dn_nsp_conn_init(sk, skb);
                        break;
                  case 0x20:
                        dn_nsp_conn_conf(sk, skb);
                        break;
                  case 0x30:
                        dn_nsp_disc_init(sk, skb);
                        break;
                  case 0x40:
                        dn_nsp_disc_conf(sk, skb);
                        break;
            }

      } else if (cb->nsp_flags == 0x24) {
            /*
             * Special for connacks, 'cos they don't have
             * ack data or ack otherdata info.
             */
            dn_nsp_conn_ack(sk, skb);
      } else {
            int other = 1;

            /* both data and ack frames can kick a CC socket into RUN */
            if ((scp->state == DN_CC) && !sock_flag(sk, SOCK_DEAD)) {
                  scp->state = DN_RUN;
                  sk->sk_state = TCP_ESTABLISHED;
                  sk->sk_state_change(sk);
            }

            if ((cb->nsp_flags & 0x1c) == 0)
                  other = 0;
            if (cb->nsp_flags == 0x04)
                  other = 0;

            /*
             * Read out ack data here, this applies equally
             * to data, other data, link serivce and both
             * ack data and ack otherdata.
             */
            dn_process_ack(sk, skb, other);

            /*
             * If we've some sort of data here then call a
             * suitable routine for dealing with it, otherwise
             * the packet is an ack and can be discarded.
             */
            if ((cb->nsp_flags & 0x0c) == 0) {

                  if (scp->state != DN_RUN)
                        goto free_out;

                  switch(cb->nsp_flags) {
                        case 0x10: /* LS */
                              dn_nsp_linkservice(sk, skb);
                              break;
                        case 0x30: /* OD */
                              dn_nsp_otherdata(sk, skb);
                              break;
                        default:
                              dn_nsp_data(sk, skb);
                  }

            } else { /* Ack, chuck it out here */
free_out:
                  kfree_skb(skb);
            }
      }

      return NET_RX_SUCCESS;
}


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