input.c

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/*
 *  net/dccp/input.c
 *
 *  An implementation of the DCCP protocol
 *  Arnaldo Carvalho de Melo <[email protected]>
 *
 *  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...\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_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 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 || 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 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;
    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 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;
    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);

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;
}