// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  net/dccp/input.c
 *
 *  An implementation of the DCCP protocol
 *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 */

#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);
}

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)
{
        static 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...\n",  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 int 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(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 int 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 int 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\n",
                                      (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 || inet_csk_in_pingpong_mode(sk) ||
                    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 int 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;
                /* fall through */
        case DCCP_PKT_DATAACK:
        case DCCP_PKT_ACK:
                /*
                 * FIXME: we should be resetting 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 int len)
{
        struct dccp_sock *dp = dccp_sk(sk);
        struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
        const int old_state = sk->sk_state;
        bool acceptable;
        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) {
                        /* It is possible that we process SYN packets from backlog,
                         * so we need to make sure to disable BH and RCU right there.
                         */
                        rcu_read_lock();
                        local_bh_disable();
                        acceptable = inet_csk(sk)->icsk_af_ops->conn_request(sk, skb) >= 0;
                        local_bh_enable();
                        rcu_read_unlock();
                        if (!acceptable)
                                return 1;
                        consume_skb(skb);
                        return 0;
                }
                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\n", delta);
                return DCCP_SANE_RTT_MIN;
        }
        if (unlikely(delta > DCCP_SANE_RTT_MAX)) {
                DCCP_WARN("RTT sample %ld too large, using max\n", delta);
                return DCCP_SANE_RTT_MAX;
        }

        return delta;
}