/*
   *  net/dccp/input.c

   *

   *  An implementation of the DCCP protocol
   *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
   *
   *	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 (at your option) any later version.
   */

  #include <linux/dccp.h>
  #include <linux/skbuff.h>

  #include <linux/slab.h>

  
  #include <net/sock.h>

  #include "ackvec.h"

  #include "ccid.h"
  #include "dccp.h"

  /* rate-limit for syncs in reply to sequence-invalid packets; RFC 4340, 7.5.4 */
  int sysctl_dccp_sync_ratelimit	__read_mostly = HZ / 8;

  static void dccp_enqueue_skb(struct sock *sk, struct sk_buff *skb)

  {

  	__skb_pull(skb, dccp_hdr(skb)->dccph_doff * 4);
  	__skb_queue_tail(&sk->sk_receive_queue, skb);
  	skb_set_owner_r(skb, sk);
  	sk->sk_data_ready(sk, 0);
  }

  static void dccp_fin(struct sock *sk, struct sk_buff *skb)
  {
  	/*
  	 * On receiving Close/CloseReq, both RD/WR shutdown are performed.
  	 * RFC 4340, 8.3 says that we MAY send further Data/DataAcks after
  	 * receiving the closing segment, but there is no guarantee that such
  	 * data will be processed at all.
  	 */
  	sk->sk_shutdown = SHUTDOWN_MASK;
  	sock_set_flag(sk, SOCK_DONE);
  	dccp_enqueue_skb(sk, skb);
  }

  static int dccp_rcv_close(struct sock *sk, struct sk_buff *skb)

  {

  	int queued = 0;
  
  	switch (sk->sk_state) {
  	/*
  	 * We ignore Close when received in one of the following states:
  	 *  - CLOSED		(may be a late or duplicate packet)
  	 *  - PASSIVE_CLOSEREQ	(the peer has sent a CloseReq earlier)
  	 *  - RESPOND		(already handled by dccp_check_req)
  	 */
  	case DCCP_CLOSING:
  		/*
  		 * Simultaneous-close: receiving a Close after sending one. This
  		 * can happen if both client and server perform active-close and
  		 * will result in an endless ping-pong of crossing and retrans-
  		 * mitted Close packets, which only terminates when one of the
  		 * nodes times out (min. 64 seconds). Quicker convergence can be
  		 * achieved when one of the nodes acts as tie-breaker.
  		 * This is ok as both ends are done with data transfer and each
  		 * end is just waiting for the other to acknowledge termination.
  		 */
  		if (dccp_sk(sk)->dccps_role != DCCP_ROLE_CLIENT)
  			break;
  		/* fall through */
  	case DCCP_REQUESTING:
  	case DCCP_ACTIVE_CLOSEREQ:
  		dccp_send_reset(sk, DCCP_RESET_CODE_CLOSED);
  		dccp_done(sk);
  		break;
  	case DCCP_OPEN:
  	case DCCP_PARTOPEN:
  		/* Give waiting application a chance to read pending data */
  		queued = 1;
  		dccp_fin(sk, skb);
  		dccp_set_state(sk, DCCP_PASSIVE_CLOSE);
  		/* fall through */
  	case DCCP_PASSIVE_CLOSE:
  		/*
  		 * Retransmitted Close: we have already enqueued the first one.
  		 */
  		sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
  	}
  	return queued;

  }

  static int dccp_rcv_closereq(struct sock *sk, struct sk_buff *skb)

  {

  	int queued = 0;

  	/*
  	 *   Step 7: Check for unexpected packet types
  	 *      If (S.is_server and P.type == CloseReq)
  	 *	  Send Sync packet acknowledging P.seqno
  	 *	  Drop packet and return
  	 */
  	if (dccp_sk(sk)->dccps_role != DCCP_ROLE_CLIENT) {

  		dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq, DCCP_PKT_SYNC);

  		return queued;

  	}

  	/* Step 13: process relevant Client states < CLOSEREQ */
  	switch (sk->sk_state) {
  	case DCCP_REQUESTING:
  		dccp_send_close(sk, 0);

  		dccp_set_state(sk, DCCP_CLOSING);

  		break;
  	case DCCP_OPEN:
  	case DCCP_PARTOPEN:
  		/* Give waiting application a chance to read pending data */
  		queued = 1;
  		dccp_fin(sk, skb);
  		dccp_set_state(sk, DCCP_PASSIVE_CLOSEREQ);
  		/* fall through */
  	case DCCP_PASSIVE_CLOSEREQ:
  		sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
  	}
  	return queued;

  }

  static u16 dccp_reset_code_convert(const u8 code)

  {

  	const u16 error_code[] = {

  	[DCCP_RESET_CODE_CLOSED]	     = 0,	/* normal termination */
  	[DCCP_RESET_CODE_UNSPECIFIED]	     = 0,	/* nothing known */
  	[DCCP_RESET_CODE_ABORTED]	     = ECONNRESET,
  
  	[DCCP_RESET_CODE_NO_CONNECTION]	     = ECONNREFUSED,
  	[DCCP_RESET_CODE_CONNECTION_REFUSED] = ECONNREFUSED,
  	[DCCP_RESET_CODE_TOO_BUSY]	     = EUSERS,
  	[DCCP_RESET_CODE_AGGRESSION_PENALTY] = EDQUOT,
  
  	[DCCP_RESET_CODE_PACKET_ERROR]	     = ENOMSG,
  	[DCCP_RESET_CODE_BAD_INIT_COOKIE]    = EBADR,
  	[DCCP_RESET_CODE_BAD_SERVICE_CODE]   = EBADRQC,
  	[DCCP_RESET_CODE_OPTION_ERROR]	     = EILSEQ,
  	[DCCP_RESET_CODE_MANDATORY_ERROR]    = EOPNOTSUPP,
  	};
  
  	return code >= DCCP_MAX_RESET_CODES ? 0 : error_code[code];
  }
  
  static void dccp_rcv_reset(struct sock *sk, struct sk_buff *skb)
  {

  	u16 err = dccp_reset_code_convert(dccp_hdr_reset(skb)->dccph_reset_code);

  
  	sk->sk_err = err;
  
  	/* Queue the equivalent of TCP fin so that dccp_recvmsg exits the loop */
  	dccp_fin(sk, skb);
  
  	if (err && !sock_flag(sk, SOCK_DEAD))

  		sk_wake_async(sk, SOCK_WAKE_IO, POLL_ERR);

  	dccp_time_wait(sk, DCCP_TIME_WAIT, 0);
  }

  static void dccp_handle_ackvec_processing(struct sock *sk, struct sk_buff *skb)

  {

  	struct dccp_ackvec *av = dccp_sk(sk)->dccps_hc_rx_ackvec;

  	if (av == NULL)
  		return;
  	if (DCCP_SKB_CB(skb)->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
  		dccp_ackvec_clear_state(av, DCCP_SKB_CB(skb)->dccpd_ack_seq);
  	dccp_ackvec_input(av, skb);

  }

  static void dccp_deliver_input_to_ccids(struct sock *sk, struct sk_buff *skb)
  {
  	const struct dccp_sock *dp = dccp_sk(sk);
  
  	/* Don't deliver to RX CCID when node has shut down read end. */
  	if (!(sk->sk_shutdown & RCV_SHUTDOWN))
  		ccid_hc_rx_packet_recv(dp->dccps_hc_rx_ccid, sk, skb);
  	/*
  	 * Until the TX queue has been drained, we can not honour SHUT_WR, since
  	 * we need received feedback as input to adjust congestion control.
  	 */
  	if (sk->sk_write_queue.qlen > 0 || !(sk->sk_shutdown & SEND_SHUTDOWN))
  		ccid_hc_tx_packet_recv(dp->dccps_hc_tx_ccid, sk, skb);
  }

  static int dccp_check_seqno(struct sock *sk, struct sk_buff *skb)
  {
  	const struct dccp_hdr *dh = dccp_hdr(skb);
  	struct dccp_sock *dp = dccp_sk(sk);

  	u64 lswl, lawl, seqno = DCCP_SKB_CB(skb)->dccpd_seq,
  			ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;

  
  	/*
  	 *   Step 5: Prepare sequence numbers for Sync
  	 *     If P.type == Sync or P.type == SyncAck,
  	 *	  If S.AWL <= P.ackno <= S.AWH and P.seqno >= S.SWL,
  	 *	     / * P is valid, so update sequence number variables
  	 *		 accordingly.  After this update, P will pass the tests
  	 *		 in Step 6.  A SyncAck is generated if necessary in
  	 *		 Step 15 * /
  	 *	     Update S.GSR, S.SWL, S.SWH
  	 *	  Otherwise,
  	 *	     Drop packet and return
  	 */

  	if (dh->dccph_type == DCCP_PKT_SYNC ||

  	    dh->dccph_type == DCCP_PKT_SYNCACK) {

  		if (between48(ackno, dp->dccps_awl, dp->dccps_awh) &&
  		    dccp_delta_seqno(dp->dccps_swl, seqno) >= 0)
  			dccp_update_gsr(sk, seqno);

  		else
  			return -1;

  	}

  	/*
  	 *   Step 6: Check sequence numbers
  	 *      Let LSWL = S.SWL and LAWL = S.AWL
  	 *      If P.type == CloseReq or P.type == Close or P.type == Reset,
  	 *	  LSWL := S.GSR + 1, LAWL := S.GAR
  	 *      If LSWL <= P.seqno <= S.SWH
  	 *	     and (P.ackno does not exist or LAWL <= P.ackno <= S.AWH),
  	 *	  Update S.GSR, S.SWL, S.SWH
  	 *	  If P.type != Sync,
  	 *	     Update S.GAR

  	 */

  	lswl = dp->dccps_swl;
  	lawl = dp->dccps_awl;
  
  	if (dh->dccph_type == DCCP_PKT_CLOSEREQ ||

  	    dh->dccph_type == DCCP_PKT_CLOSE ||
  	    dh->dccph_type == DCCP_PKT_RESET) {

  		lswl = ADD48(dp->dccps_gsr, 1);

  		lawl = dp->dccps_gar;
  	}

  	if (between48(seqno, lswl, dp->dccps_swh) &&
  	    (ackno == DCCP_PKT_WITHOUT_ACK_SEQ ||
  	     between48(ackno, lawl, dp->dccps_awh))) {
  		dccp_update_gsr(sk, seqno);

  
  		if (dh->dccph_type != DCCP_PKT_SYNC &&

  		    ackno != DCCP_PKT_WITHOUT_ACK_SEQ &&
  		    after48(ackno, dp->dccps_gar))

  			dp->dccps_gar = ackno;

  	} else {

  		unsigned long now = jiffies;
  		/*
  		 *   Step 6: Check sequence numbers
  		 *      Otherwise,
  		 *         If P.type == Reset,
  		 *            Send Sync packet acknowledging S.GSR
  		 *         Otherwise,
  		 *            Send Sync packet acknowledging P.seqno
  		 *      Drop packet and return
  		 *
  		 *   These Syncs are rate-limited as per RFC 4340, 7.5.4:
  		 *   at most 1 / (dccp_sync_rate_limit * HZ) Syncs per second.
  		 */
  		if (time_before(now, (dp->dccps_rate_last +
  				      sysctl_dccp_sync_ratelimit)))

  			return -1;

  		DCCP_WARN("Step 6 failed for %s packet, "

  			  "(LSWL(%llu) <= P.seqno(%llu) <= S.SWH(%llu)) and "
  			  "(P.ackno %s or LAWL(%llu) <= P.ackno(%llu) <= S.AWH(%llu), "
  			  "sending SYNC...
  ",  dccp_packet_name(dh->dccph_type),

  			  (unsigned long long) lswl, (unsigned long long) seqno,

  			  (unsigned long long) dp->dccps_swh,

  			  (ackno == DCCP_PKT_WITHOUT_ACK_SEQ) ? "doesn't exist"
  							      : "exists",
  			  (unsigned long long) lawl, (unsigned long long) ackno,

  			  (unsigned long long) dp->dccps_awh);

  
  		dp->dccps_rate_last = now;

  		if (dh->dccph_type == DCCP_PKT_RESET)
  			seqno = dp->dccps_gsr;

  		dccp_send_sync(sk, seqno, DCCP_PKT_SYNC);

  		return -1;
  	}
  
  	return 0;
  }

  static int __dccp_rcv_established(struct sock *sk, struct sk_buff *skb,
  				  const struct dccp_hdr *dh, const unsigned len)

  {
  	struct dccp_sock *dp = dccp_sk(sk);

  	switch (dccp_hdr(skb)->dccph_type) {
  	case DCCP_PKT_DATAACK:
  	case DCCP_PKT_DATA:
  		/*

  		 * FIXME: schedule DATA_DROPPED (RFC 4340, 11.7.2) if and when
  		 * - sk_shutdown == RCV_SHUTDOWN, use Code 1, "Not Listening"
  		 * - sk_receive_queue is full, use Code 2, "Receive Buffer"

  		 */

  		dccp_enqueue_skb(sk, skb);

  		return 0;
  	case DCCP_PKT_ACK:
  		goto discard;
  	case DCCP_PKT_RESET:
  		/*
  		 *  Step 9: Process Reset
  		 *	If P.type == Reset,
  		 *		Tear down connection
  		 *		S.state := TIMEWAIT
  		 *		Set TIMEWAIT timer
  		 *		Drop packet and return

  		 */
  		dccp_rcv_reset(sk, skb);

  		return 0;
  	case DCCP_PKT_CLOSEREQ:

  		if (dccp_rcv_closereq(sk, skb))
  			return 0;

  		goto discard;
  	case DCCP_PKT_CLOSE:

  		if (dccp_rcv_close(sk, skb))
  			return 0;
  		goto discard;

  	case DCCP_PKT_REQUEST:

  		/* Step 7
  		 *   or (S.is_server and P.type == Response)

  		 *   or (S.is_client and P.type == Request)
  		 *   or (S.state >= OPEN and P.type == Request
  		 *	and P.seqno >= S.OSR)
  		 *    or (S.state >= OPEN and P.type == Response
  		 *	and P.seqno >= S.OSR)
  		 *    or (S.state == RESPOND and P.type == Data),
  		 *  Send Sync packet acknowledging P.seqno
  		 *  Drop packet and return
  		 */
  		if (dp->dccps_role != DCCP_ROLE_LISTEN)
  			goto send_sync;
  		goto check_seq;
  	case DCCP_PKT_RESPONSE:
  		if (dp->dccps_role != DCCP_ROLE_CLIENT)
  			goto send_sync;
  check_seq:

  		if (dccp_delta_seqno(dp->dccps_osr,
  				     DCCP_SKB_CB(skb)->dccpd_seq) >= 0) {

  send_sync:

  			dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq,
  				       DCCP_PKT_SYNC);

  		}
  		break;

  	case DCCP_PKT_SYNC:
  		dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq,
  			       DCCP_PKT_SYNCACK);
  		/*

  		 * From RFC 4340, sec. 5.7

  		 *
  		 * As with DCCP-Ack packets, DCCP-Sync and DCCP-SyncAck packets
  		 * MAY have non-zero-length application data areas, whose

  		 * contents receivers MUST ignore.

  		 */
  		goto discard;

  	}
  
  	DCCP_INC_STATS_BH(DCCP_MIB_INERRS);
  discard:
  	__kfree_skb(skb);
  	return 0;
  }

  int dccp_rcv_established(struct sock *sk, struct sk_buff *skb,
  			 const struct dccp_hdr *dh, const unsigned len)
  {

  	if (dccp_check_seqno(sk, skb))
  		goto discard;

  	if (dccp_parse_options(sk, NULL, skb))

  		return 1;

  	dccp_handle_ackvec_processing(sk, skb);

  	dccp_deliver_input_to_ccids(sk, skb);

  
  	return __dccp_rcv_established(sk, skb, dh, len);
  discard:
  	__kfree_skb(skb);
  	return 0;
  }

  EXPORT_SYMBOL_GPL(dccp_rcv_established);

  static int dccp_rcv_request_sent_state_process(struct sock *sk,
  					       struct sk_buff *skb,
  					       const struct dccp_hdr *dh,
  					       const unsigned len)
  {

  	/*

  	 *  Step 4: Prepare sequence numbers in REQUEST
  	 *     If S.state == REQUEST,
  	 *	  If (P.type == Response or P.type == Reset)
  	 *		and S.AWL <= P.ackno <= S.AWH,
  	 *	     / * Set sequence number variables corresponding to the
  	 *		other endpoint, so P will pass the tests in Step 6 * /
  	 *	     Set S.GSR, S.ISR, S.SWL, S.SWH
  	 *	     / * Response processing continues in Step 10; Reset
  	 *		processing continues in Step 9 * /
  	*/
  	if (dh->dccph_type == DCCP_PKT_RESPONSE) {
  		const struct inet_connection_sock *icsk = inet_csk(sk);
  		struct dccp_sock *dp = dccp_sk(sk);

  		long tstamp = dccp_timestamp();

  		if (!between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
  			       dp->dccps_awl, dp->dccps_awh)) {
  			dccp_pr_debug("invalid ackno: S.AWL=%llu, "

  				      "P.ackno=%llu, S.AWH=%llu
  ",

  				      (unsigned long long)dp->dccps_awl,
  			   (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq,
  				      (unsigned long long)dp->dccps_awh);

  			goto out_invalid_packet;
  		}

  		/*
  		 * If option processing (Step 8) failed, return 1 here so that
  		 * dccp_v4_do_rcv() sends a Reset. The Reset code depends on
  		 * the option type and is set in dccp_parse_options().
  		 */

  		if (dccp_parse_options(sk, NULL, skb))

  			return 1;

  		/* Obtain usec RTT sample from SYN exchange (used by TFRC). */

  		if (likely(dp->dccps_options_received.dccpor_timestamp_echo))
  			dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * (tstamp -
  			    dp->dccps_options_received.dccpor_timestamp_echo));

  		/* Stop the REQUEST timer */
  		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
  		WARN_ON(sk->sk_send_head == NULL);
  		kfree_skb(sk->sk_send_head);
  		sk->sk_send_head = NULL;

  		/*

  		 * Set ISR, GSR from packet. ISS was set in dccp_v{4,6}_connect
  		 * and GSS in dccp_transmit_skb(). Setting AWL/AWH and SWL/SWH
  		 * is done as part of activating the feature values below, since
  		 * these settings depend on the local/remote Sequence Window
  		 * features, which were undefined or not confirmed until now.

  		 */

  		dp->dccps_gsr = dp->dccps_isr = DCCP_SKB_CB(skb)->dccpd_seq;

  		dccp_sync_mss(sk, icsk->icsk_pmtu_cookie);

  
  		/*
  		 *    Step 10: Process REQUEST state (second part)
  		 *       If S.state == REQUEST,

  		 *	  / * If we get here, P is a valid Response from the
  		 *	      server (see Step 4), and we should move to
  		 *	      PARTOPEN state. PARTOPEN means send an Ack,
  		 *	      don't send Data packets, retransmit Acks
  		 *	      periodically, and always include any Init Cookie
  		 *	      from the Response * /

  		 *	  S.state := PARTOPEN
  		 *	  Set PARTOPEN timer

  		 *	  Continue with S.state == PARTOPEN

  		 *	  / * Step 12 will send the Ack completing the
  		 *	      three-way handshake * /

  		 */
  		dccp_set_state(sk, DCCP_PARTOPEN);

  		/*
  		 * If feature negotiation was successful, activate features now;
  		 * an activation failure means that this host could not activate
  		 * one ore more features (e.g. insufficient memory), which would
  		 * leave at least one feature in an undefined state.
  		 */
  		if (dccp_feat_activate_values(sk, &dp->dccps_featneg))
  			goto unable_to_proceed;

  		/* Make sure socket is routed, for correct metrics. */

  		icsk->icsk_af_ops->rebuild_header(sk);

  
  		if (!sock_flag(sk, SOCK_DEAD)) {
  			sk->sk_state_change(sk);

  			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);

  		}
  
  		if (sk->sk_write_pending || icsk->icsk_ack.pingpong ||
  		    icsk->icsk_accept_queue.rskq_defer_accept) {
  			/* Save one ACK. Data will be ready after
  			 * several ticks, if write_pending is set.
  			 *
  			 * It may be deleted, but with this feature tcpdumps
  			 * look so _wonderfully_ clever, that I was not able
  			 * to stand against the temptation 8)     --ANK
  			 */
  			/*
  			 * OK, in DCCP we can as well do a similar trick, its
  			 * even in the draft, but there is no need for us to
  			 * schedule an ack here, as dccp_sendmsg does this for
  			 * us, also stated in the draft. -acme
  			 */
  			__kfree_skb(skb);
  			return 0;

  		}

  		dccp_send_ack(sk);
  		return -1;
  	}
  
  out_invalid_packet:

  	/* dccp_v4_do_rcv will send a reset */
  	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_PACKET_ERROR;

  	return 1;

  
  unable_to_proceed:
  	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_ABORTED;
  	/*
  	 * We mark this socket as no longer usable, so that the loop in
  	 * dccp_sendmsg() terminates and the application gets notified.
  	 */
  	dccp_set_state(sk, DCCP_CLOSED);
  	sk->sk_err = ECOMM;
  	return 1;

  }
  
  static int dccp_rcv_respond_partopen_state_process(struct sock *sk,
  						   struct sk_buff *skb,
  						   const struct dccp_hdr *dh,
  						   const unsigned len)
  {

  	struct dccp_sock *dp = dccp_sk(sk);
  	u32 sample = dp->dccps_options_received.dccpor_timestamp_echo;

  	int queued = 0;
  
  	switch (dh->dccph_type) {
  	case DCCP_PKT_RESET:
  		inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
  		break;

  	case DCCP_PKT_DATA:
  		if (sk->sk_state == DCCP_RESPOND)
  			break;

  	case DCCP_PKT_DATAACK:
  	case DCCP_PKT_ACK:
  		/*

  		 * FIXME: we should be reseting the PARTOPEN (DELACK) timer
  		 * here but only if we haven't used the DELACK timer for
  		 * something else, like sending a delayed ack for a TIMESTAMP
  		 * echo, etc, for now were not clearing it, sending an extra
  		 * ACK when there is nothing else to do in DELACK is not a big
  		 * deal after all.

  		 */
  
  		/* Stop the PARTOPEN timer */
  		if (sk->sk_state == DCCP_PARTOPEN)
  			inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);

  		/* Obtain usec RTT sample from SYN exchange (used by TFRC). */
  		if (likely(sample)) {
  			long delta = dccp_timestamp() - sample;
  
  			dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * delta);
  		}
  
  		dp->dccps_osr = DCCP_SKB_CB(skb)->dccpd_seq;

  		dccp_set_state(sk, DCCP_OPEN);

  		if (dh->dccph_type == DCCP_PKT_DATAACK ||
  		    dh->dccph_type == DCCP_PKT_DATA) {

  			__dccp_rcv_established(sk, skb, dh, len);

  			queued = 1; /* packet was queued

  				       (by __dccp_rcv_established) */

  		}
  		break;
  	}
  
  	return queued;
  }
  
  int dccp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
  			   struct dccp_hdr *dh, unsigned len)
  {
  	struct dccp_sock *dp = dccp_sk(sk);

  	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);

  	const int old_state = sk->sk_state;
  	int queued = 0;

  	/*
  	 *  Step 3: Process LISTEN state

  	 *
  	 *     If S.state == LISTEN,

  	 *	 If P.type == Request or P contains a valid Init Cookie option,
  	 *	      (* Must scan the packet's options to check for Init
  	 *		 Cookies.  Only Init Cookies are processed here,
  	 *		 however; other options are processed in Step 8.  This
  	 *		 scan need only be performed if the endpoint uses Init
  	 *		 Cookies *)
  	 *	      (* Generate a new socket and switch to that socket *)
  	 *	      Set S := new socket for this port pair
  	 *	      S.state = RESPOND
  	 *	      Choose S.ISS (initial seqno) or set from Init Cookies
  	 *	      Initialize S.GAR := S.ISS
  	 *	      Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init
  	 *	      Cookies Continue with S.state == RESPOND
  	 *	      (* A Response packet will be generated in Step 11 *)
  	 *	 Otherwise,
  	 *	      Generate Reset(No Connection) unless P.type == Reset
  	 *	      Drop packet and return

  	 */
  	if (sk->sk_state == DCCP_LISTEN) {
  		if (dh->dccph_type == DCCP_PKT_REQUEST) {

  			if (inet_csk(sk)->icsk_af_ops->conn_request(sk,
  								    skb) < 0)

  				return 1;

  			goto discard;
  		}
  		if (dh->dccph_type == DCCP_PKT_RESET)
  			goto discard;

  		/* Caller (dccp_v4_do_rcv) will send Reset */
  		dcb->dccpd_reset_code = DCCP_RESET_CODE_NO_CONNECTION;

  		return 1;

  	} else if (sk->sk_state == DCCP_CLOSED) {
  		dcb->dccpd_reset_code = DCCP_RESET_CODE_NO_CONNECTION;
  		return 1;

  	}

  	/* Step 6: Check sequence numbers (omitted in LISTEN/REQUEST state) */
  	if (sk->sk_state != DCCP_REQUESTING && dccp_check_seqno(sk, skb))
  		goto discard;

  	/*
  	 *   Step 7: Check for unexpected packet types
  	 *      If (S.is_server and P.type == Response)
  	 *	    or (S.is_client and P.type == Request)
  	 *	    or (S.state == RESPOND and P.type == Data),
  	 *	  Send Sync packet acknowledging P.seqno
  	 *	  Drop packet and return
  	 */
  	if ((dp->dccps_role != DCCP_ROLE_CLIENT &&
  	     dh->dccph_type == DCCP_PKT_RESPONSE) ||
  	    (dp->dccps_role == DCCP_ROLE_CLIENT &&
  	     dh->dccph_type == DCCP_PKT_REQUEST) ||
  	    (sk->sk_state == DCCP_RESPOND && dh->dccph_type == DCCP_PKT_DATA)) {
  		dccp_send_sync(sk, dcb->dccpd_seq, DCCP_PKT_SYNC);
  		goto discard;

  	}

  	/*  Step 8: Process options */
  	if (dccp_parse_options(sk, NULL, skb))
  		return 1;

  	/*
  	 *  Step 9: Process Reset
  	 *	If P.type == Reset,
  	 *		Tear down connection
  	 *		S.state := TIMEWAIT
  	 *		Set TIMEWAIT timer
  	 *		Drop packet and return

  	 */

  	if (dh->dccph_type == DCCP_PKT_RESET) {

  		dccp_rcv_reset(sk, skb);

  		return 0;

  	} else if (dh->dccph_type == DCCP_PKT_CLOSEREQ) {	/* Step 13 */

  		if (dccp_rcv_closereq(sk, skb))
  			return 0;

  		goto discard;

  	} else if (dh->dccph_type == DCCP_PKT_CLOSE) {		/* Step 14 */

  		if (dccp_rcv_close(sk, skb))
  			return 0;
  		goto discard;

  	}
  
  	switch (sk->sk_state) {

  	case DCCP_REQUESTING:

  		queued = dccp_rcv_request_sent_state_process(sk, skb, dh, len);
  		if (queued >= 0)
  			return queued;
  
  		__kfree_skb(skb);
  		return 0;

  	case DCCP_PARTOPEN:

  		/* Step 8: if using Ack Vectors, mark packet acknowledgeable */
  		dccp_handle_ackvec_processing(sk, skb);
  		dccp_deliver_input_to_ccids(sk, skb);
  		/* fall through */
  	case DCCP_RESPOND:

  		queued = dccp_rcv_respond_partopen_state_process(sk, skb,
  								 dh, len);

  		break;
  	}

  	if (dh->dccph_type == DCCP_PKT_ACK ||
  	    dh->dccph_type == DCCP_PKT_DATAACK) {

  		switch (old_state) {
  		case DCCP_PARTOPEN:
  			sk->sk_state_change(sk);

  			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);

  			break;
  		}

  	} else if (unlikely(dh->dccph_type == DCCP_PKT_SYNC)) {
  		dccp_send_sync(sk, dcb->dccpd_seq, DCCP_PKT_SYNCACK);
  		goto discard;

  	}

  	if (!queued) {

  discard:
  		__kfree_skb(skb);
  	}
  	return 0;
  }

  
  EXPORT_SYMBOL_GPL(dccp_rcv_state_process);

  
  /**

   *  dccp_sample_rtt  -  Validate and finalise computation of RTT sample
   *  @delta:	number of microseconds between packet and acknowledgment
   *  The routine is kept generic to work in different contexts. It should be
   *  called immediately when the ACK used for the RTT sample arrives.

   */

  u32 dccp_sample_rtt(struct sock *sk, long delta)

  {

  	/* dccpor_elapsed_time is either zeroed out or set and > 0 */
  	delta -= dccp_sk(sk)->dccps_options_received.dccpor_elapsed_time * 10;

  	if (unlikely(delta <= 0)) {
  		DCCP_WARN("unusable RTT sample %ld, using min
  ", delta);
  		return DCCP_SANE_RTT_MIN;
  	}
  	if (unlikely(delta > DCCP_SANE_RTT_MAX)) {
  		DCCP_WARN("RTT sample %ld too large, using max
  ", delta);
  		return DCCP_SANE_RTT_MAX;
  	}
  
  	return delta;

  }