output.c

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/* SCTP kernel implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 *
 * This file is part of the SCTP kernel implementation
 *
 * These functions handle output processing.
 *
 * This SCTP implementation 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, or (at your option)
 * any later version.
 *
 * This SCTP implementation 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU CC; see the file COPYING.  If not, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <[email protected]>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <[email protected]>
 *    Karl Knutson          <[email protected]>
 *    Jon Grimm             <[email protected]>
 *    Sridhar Samudrala     <[email protected]>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/wait.h>
#include <linux/time.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <net/inet_ecn.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/net_namespace.h>

#include <linux/socket.h> /* for sa_family_t */
#include <net/sock.h>

#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>
#include <net/sctp/checksum.h>

/* Forward declarations for private helpers. */
static sctp_xmit_t __sctp_packet_append_chunk(struct sctp_packet *packet,
                          struct sctp_chunk *chunk);
static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
                       struct sctp_chunk *chunk);
static void sctp_packet_append_data(struct sctp_packet *packet,
                       struct sctp_chunk *chunk);
static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
                    struct sctp_chunk *chunk,
                    u16 chunk_len);

static void sctp_packet_reset(struct sctp_packet *packet)
{
    packet->size = packet->overhead;
    packet->has_cookie_echo = 0;
    packet->has_sack = 0;
    packet->has_data = 0;
    packet->has_auth = 0;
    packet->ipfragok = 0;
    packet->auth = NULL;
}

/* Config a packet.
 * This appears to be a followup set of initializations.
 */
struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
                       __u32 vtag, int ecn_capable)
{
    struct sctp_chunk *chunk = NULL;

    SCTP_DEBUG_PRINTK("%s: packet:%p vtag:0x%x\n", __func__,
              packet, vtag);

    packet->vtag = vtag;

    if (ecn_capable && sctp_packet_empty(packet)) {
        chunk = sctp_get_ecne_prepend(packet->transport->asoc);

        /* If there a is a prepend chunk stick it on the list before
         * any other chunks get appended.
         */
        if (chunk)
            sctp_packet_append_chunk(packet, chunk);
    }

    return packet;
}

/* Initialize the packet structure. */
struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
                     struct sctp_transport *transport,
                     __u16 sport, __u16 dport)
{
    struct sctp_association *asoc = transport->asoc;
    size_t overhead;

    SCTP_DEBUG_PRINTK("%s: packet:%p transport:%p\n", __func__,
              packet, transport);

    packet->transport = transport;
    packet->source_port = sport;
    packet->destination_port = dport;
    INIT_LIST_HEAD(&packet->chunk_list);
    if (asoc) {
        struct sctp_sock *sp = sctp_sk(asoc->base.sk);
        overhead = sp->pf->af->net_header_len;
    } else {
        overhead = sizeof(struct ipv6hdr);
    }
    overhead += sizeof(struct sctphdr);
    packet->overhead = overhead;
    sctp_packet_reset(packet);
    packet->vtag = 0;
    packet->malloced = 0;
    return packet;
}

/* Free a packet.  */
void sctp_packet_free(struct sctp_packet *packet)
{
    struct sctp_chunk *chunk, *tmp;

    SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);

    list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
        list_del_init(&chunk->list);
        sctp_chunk_free(chunk);
    }

    if (packet->malloced)
        kfree(packet);
}

/* This routine tries to append the chunk to the offered packet. If adding
 * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
 * is not present in the packet, it transmits the input packet.
 * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
 * as it can fit in the packet, but any more data that does not fit in this
 * packet can be sent only after receiving the COOKIE_ACK.
 */
sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
                       struct sctp_chunk *chunk,
                       int one_packet)
{
    sctp_xmit_t retval;
    int error = 0;

    SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__,
              packet, chunk);

    switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
    case SCTP_XMIT_PMTU_FULL:
        if (!packet->has_cookie_echo) {
            error = sctp_packet_transmit(packet);
            if (error < 0)
                chunk->skb->sk->sk_err = -error;

            /* If we have an empty packet, then we can NOT ever
             * return PMTU_FULL.
             */
            if (!one_packet)
                retval = sctp_packet_append_chunk(packet,
                                  chunk);
        }
        break;

    case SCTP_XMIT_RWND_FULL:
    case SCTP_XMIT_OK:
    case SCTP_XMIT_NAGLE_DELAY:
        break;
    }

    return retval;
}

/* Try to bundle an auth chunk into the packet. */
static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
                       struct sctp_chunk *chunk)
{
    struct sctp_association *asoc = pkt->transport->asoc;
    struct sctp_chunk *auth;
    sctp_xmit_t retval = SCTP_XMIT_OK;

    /* if we don't have an association, we can't do authentication */
    if (!asoc)
        return retval;

    /* See if this is an auth chunk we are bundling or if
     * auth is already bundled.
     */
    if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->has_auth)
        return retval;

    /* if the peer did not request this chunk to be authenticated,
     * don't do it
     */
    if (!chunk->auth)
        return retval;

    auth = sctp_make_auth(asoc);
    if (!auth)
        return retval;

    retval = __sctp_packet_append_chunk(pkt, auth);

    if (retval != SCTP_XMIT_OK)
        sctp_chunk_free(auth);

    return retval;
}

/* Try to bundle a SACK with the packet. */
static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
                       struct sctp_chunk *chunk)
{
    sctp_xmit_t retval = SCTP_XMIT_OK;

    /* If sending DATA and haven't aleady bundled a SACK, try to
     * bundle one in to the packet.
     */
    if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
        !pkt->has_cookie_echo) {
        struct sctp_association *asoc;
        struct timer_list *timer;
        asoc = pkt->transport->asoc;
        timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];

        /* If the SACK timer is running, we have a pending SACK */
        if (timer_pending(timer)) {
            struct sctp_chunk *sack;

            if (pkt->transport->sack_generation !=
                pkt->transport->asoc->peer.sack_generation)
                return retval;

            asoc->a_rwnd = asoc->rwnd;
            sack = sctp_make_sack(asoc);
            if (sack) {
                retval = __sctp_packet_append_chunk(pkt, sack);
                if (retval != SCTP_XMIT_OK) {
                    sctp_chunk_free(sack);
                    goto out;
                }
                asoc->peer.sack_needed = 0;
                if (del_timer(timer))
                    sctp_association_put(asoc);
            }
        }
    }
out:
    return retval;
}


/* Append a chunk to the offered packet reporting back any inability to do
 * so.
 */
static sctp_xmit_t __sctp_packet_append_chunk(struct sctp_packet *packet,
                          struct sctp_chunk *chunk)
{
    sctp_xmit_t retval = SCTP_XMIT_OK;
    __u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));

    /* Check to see if this chunk will fit into the packet */
    retval = sctp_packet_will_fit(packet, chunk, chunk_len);
    if (retval != SCTP_XMIT_OK)
        goto finish;

    /* We believe that this chunk is OK to add to the packet */
    switch (chunk->chunk_hdr->type) {
        case SCTP_CID_DATA:
        /* Account for the data being in the packet */
        sctp_packet_append_data(packet, chunk);
        /* Disallow SACK bundling after DATA. */
        packet->has_sack = 1;
        /* Disallow AUTH bundling after DATA */
        packet->has_auth = 1;
        /* Let it be knows that packet has DATA in it */
        packet->has_data = 1;
        /* timestamp the chunk for rtx purposes */
        chunk->sent_at = jiffies;
        break;
        case SCTP_CID_COOKIE_ECHO:
        packet->has_cookie_echo = 1;
        break;

        case SCTP_CID_SACK:
        packet->has_sack = 1;
        break;

        case SCTP_CID_AUTH:
        packet->has_auth = 1;
        packet->auth = chunk;
        break;
    }

    /* It is OK to send this chunk.  */
    list_add_tail(&chunk->list, &packet->chunk_list);
    packet->size += chunk_len;
    chunk->transport = packet->transport;
finish:
    return retval;
}

/* Append a chunk to the offered packet reporting back any inability to do
 * so.
 */
sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
                     struct sctp_chunk *chunk)
{
    sctp_xmit_t retval = SCTP_XMIT_OK;

    SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__, packet,
              chunk);

    /* Data chunks are special.  Before seeing what else we can
     * bundle into this packet, check to see if we are allowed to
     * send this DATA.
     */
    if (sctp_chunk_is_data(chunk)) {
        retval = sctp_packet_can_append_data(packet, chunk);
        if (retval != SCTP_XMIT_OK)
            goto finish;
    }

    /* Try to bundle AUTH chunk */
    retval = sctp_packet_bundle_auth(packet, chunk);
    if (retval != SCTP_XMIT_OK)
        goto finish;

    /* Try to bundle SACK chunk */
    retval = sctp_packet_bundle_sack(packet, chunk);
    if (retval != SCTP_XMIT_OK)
        goto finish;

    retval = __sctp_packet_append_chunk(packet, chunk);

finish:
    return retval;
}

static void sctp_packet_release_owner(struct sk_buff *skb)
{
    sk_free(skb->sk);
}

static void sctp_packet_set_owner_w(struct sk_buff *skb, struct sock *sk)
{
    skb_orphan(skb);
    skb->sk = sk;
    skb->destructor = sctp_packet_release_owner;

    /*
     * The data chunks have already been accounted for in sctp_sendmsg(),
     * therefore only reserve a single byte to keep socket around until
     * the packet has been transmitted.
     */
    atomic_inc(&sk->sk_wmem_alloc);
}

/* All packets are sent to the network through this function from
 * sctp_outq_tail().
 *
 * The return value is a normal kernel error return value.
 */
int sctp_packet_transmit(struct sctp_packet *packet)
{
    struct sctp_transport *tp = packet->transport;
    struct sctp_association *asoc = tp->asoc;
    struct sctphdr *sh;
    struct sk_buff *nskb;
    struct sctp_chunk *chunk, *tmp;
    struct sock *sk;
    int err = 0;
    int padding;        /* How much padding do we need?  */
    __u8 has_data = 0;
    struct dst_entry *dst = tp->dst;
    unsigned char *auth = NULL; /* pointer to auth in skb data */
    __u32 cksum_buf_len = sizeof(struct sctphdr);

    SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);

    /* Do NOT generate a chunkless packet. */
    if (list_empty(&packet->chunk_list))
        return err;

    /* Set up convenience variables... */
    chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
    sk = chunk->skb->sk;

    /* Allocate the new skb.  */
    nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
    if (!nskb)
        goto nomem;

    /* Make sure the outbound skb has enough header room reserved. */
    skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);

    /* Set the owning socket so that we know where to get the
     * destination IP address.
     */
    sctp_packet_set_owner_w(nskb, sk);

    if (!sctp_transport_dst_check(tp)) {
        sctp_transport_route(tp, NULL, sctp_sk(sk));
        if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
            sctp_assoc_sync_pmtu(sk, asoc);
        }
    }
    dst = dst_clone(tp->dst);
    skb_dst_set(nskb, dst);
    if (!dst)
        goto no_route;

    /* Build the SCTP header.  */
    sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
    skb_reset_transport_header(nskb);
    sh->source = htons(packet->source_port);
    sh->dest   = htons(packet->destination_port);

    /* From 6.8 Adler-32 Checksum Calculation:
     * After the packet is constructed (containing the SCTP common
     * header and one or more control or DATA chunks), the
     * transmitter shall:
     *
     * 1) Fill in the proper Verification Tag in the SCTP common
     *    header and initialize the checksum field to 0's.
     */
    sh->vtag     = htonl(packet->vtag);
    sh->checksum = 0;

    SCTP_DEBUG_PRINTK("***sctp_transmit_packet***\n");
    list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
        list_del_init(&chunk->list);
        if (sctp_chunk_is_data(chunk)) {
            /* 6.3.1 C4) When data is in flight and when allowed
             * by rule C5, a new RTT measurement MUST be made each
             * round trip.  Furthermore, new RTT measurements
             * SHOULD be made no more than once per round-trip
             * for a given destination transport address.
             */

            if (!tp->rto_pending) {
                chunk->rtt_in_progress = 1;
                tp->rto_pending = 1;
            }
            has_data = 1;
        }

        padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
        if (padding)
            memset(skb_put(chunk->skb, padding), 0, padding);

        /* if this is the auth chunk that we are adding,
         * store pointer where it will be added and put
         * the auth into the packet.
         */
        if (chunk == packet->auth)
            auth = skb_tail_pointer(nskb);

        cksum_buf_len += chunk->skb->len;
        memcpy(skb_put(nskb, chunk->skb->len),
                   chunk->skb->data, chunk->skb->len);

        SCTP_DEBUG_PRINTK("%s %p[%s] %s 0x%x, %s %d, %s %d, %s %d\n",
                  "*** Chunk", chunk,
                  sctp_cname(SCTP_ST_CHUNK(
                      chunk->chunk_hdr->type)),
                  chunk->has_tsn ? "TSN" : "No TSN",
                  chunk->has_tsn ?
                  ntohl(chunk->subh.data_hdr->tsn) : 0,
                  "length", ntohs(chunk->chunk_hdr->length),
                  "chunk->skb->len", chunk->skb->len,
                  "rtt_in_progress", chunk->rtt_in_progress);

        /*
         * If this is a control chunk, this is our last
         * reference. Free data chunks after they've been
         * acknowledged or have failed.
         */
        if (!sctp_chunk_is_data(chunk))
            sctp_chunk_free(chunk);
    }

    /* SCTP-AUTH, Section 6.2
     *    The sender MUST calculate the MAC as described in RFC2104 [2]
     *    using the hash function H as described by the MAC Identifier and
     *    the shared association key K based on the endpoint pair shared key
     *    described by the shared key identifier.  The 'data' used for the
     *    computation of the AUTH-chunk is given by the AUTH chunk with its
     *    HMAC field set to zero (as shown in Figure 6) followed by all
     *    chunks that are placed after the AUTH chunk in the SCTP packet.
     */
    if (auth)
        sctp_auth_calculate_hmac(asoc, nskb,
                    (struct sctp_auth_chunk *)auth,
                    GFP_ATOMIC);

    /* 2) Calculate the Adler-32 checksum of the whole packet,
     *    including the SCTP common header and all the
     *    chunks.
     *
     * Note: Adler-32 is no longer applicable, as has been replaced
     * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
     */
    if (!sctp_checksum_disable) {
        if (!(dst->dev->features & NETIF_F_SCTP_CSUM)) {
            __u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);

            /* 3) Put the resultant value into the checksum field in the
             *    common header, and leave the rest of the bits unchanged.
             */
            sh->checksum = sctp_end_cksum(crc32);
        } else {
            /* no need to seed pseudo checksum for SCTP */
            nskb->ip_summed = CHECKSUM_PARTIAL;
            nskb->csum_start = (skb_transport_header(nskb) -
                                nskb->head);
            nskb->csum_offset = offsetof(struct sctphdr, checksum);
        }
    }

    /* IP layer ECN support
     * From RFC 2481
     *  "The ECN-Capable Transport (ECT) bit would be set by the
     *   data sender to indicate that the end-points of the
     *   transport protocol are ECN-capable."
     *
     * Now setting the ECT bit all the time, as it should not cause
     * any problems protocol-wise even if our peer ignores it.
     *
     * Note: The works for IPv6 layer checks this bit too later
     * in transmission.  See IP6_ECN_flow_xmit().
     */
    (*tp->af_specific->ecn_capable)(nskb->sk);

    /* Set up the IP options.  */
    /* BUG: not implemented
     * For v4 this all lives somewhere in sk->sk_opt...
     */

    /* Dump that on IP!  */
    if (asoc && asoc->peer.last_sent_to != tp) {
        /* Considering the multiple CPU scenario, this is a
         * "correcter" place for last_sent_to.  --xguo
         */
        asoc->peer.last_sent_to = tp;
    }

    if (has_data) {
        struct timer_list *timer;
        unsigned long timeout;

        /* Restart the AUTOCLOSE timer when sending data. */
        if (sctp_state(asoc, ESTABLISHED) && asoc->autoclose) {
            timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
            timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];

            if (!mod_timer(timer, jiffies + timeout))
                sctp_association_hold(asoc);
        }
    }

    SCTP_DEBUG_PRINTK("***sctp_transmit_packet*** skb len %d\n",
              nskb->len);

    nskb->local_df = packet->ipfragok;
    (*tp->af_specific->sctp_xmit)(nskb, tp);

out:
    sctp_packet_reset(packet);
    return err;
no_route:
    kfree_skb(nskb);
    IP_INC_STATS_BH(sock_net(asoc->base.sk), IPSTATS_MIB_OUTNOROUTES);

    /* FIXME: Returning the 'err' will effect all the associations
     * associated with a socket, although only one of the paths of the
     * association is unreachable.
     * The real failure of a transport or association can be passed on
     * to the user via notifications. So setting this error may not be
     * required.
     */
     /* err = -EHOSTUNREACH; */
err:
    /* Control chunks are unreliable so just drop them.  DATA chunks
     * will get resent or dropped later.
     */

    list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
        list_del_init(&chunk->list);
        if (!sctp_chunk_is_data(chunk))
            sctp_chunk_free(chunk);
    }
    goto out;
nomem:
    err = -ENOMEM;
    goto err;
}

/********************************************************************
 * 2nd Level Abstractions
 ********************************************************************/

/* This private function check to see if a chunk can be added */
static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
                       struct sctp_chunk *chunk)
{
    sctp_xmit_t retval = SCTP_XMIT_OK;
    size_t datasize, rwnd, inflight, flight_size;
    struct sctp_transport *transport = packet->transport;
    struct sctp_association *asoc = transport->asoc;
    struct sctp_outq *q = &asoc->outqueue;

    /* RFC 2960 6.1  Transmission of DATA Chunks
     *
     * A) At any given time, the data sender MUST NOT transmit new data to
     * any destination transport address if its peer's rwnd indicates
     * that the peer has no buffer space (i.e. rwnd is 0, see Section
     * 6.2.1).  However, regardless of the value of rwnd (including if it
     * is 0), the data sender can always have one DATA chunk in flight to
     * the receiver if allowed by cwnd (see rule B below).  This rule
     * allows the sender to probe for a change in rwnd that the sender
     * missed due to the SACK having been lost in transit from the data
     * receiver to the data sender.
     */

    rwnd = asoc->peer.rwnd;
    inflight = q->outstanding_bytes;
    flight_size = transport->flight_size;

    datasize = sctp_data_size(chunk);

    if (datasize > rwnd) {
        if (inflight > 0) {
            /* We have (at least) one data chunk in flight,
             * so we can't fall back to rule 6.1 B).
             */
            retval = SCTP_XMIT_RWND_FULL;
            goto finish;
        }
    }

    /* RFC 2960 6.1  Transmission of DATA Chunks
     *
     * B) At any given time, the sender MUST NOT transmit new data
     * to a given transport address if it has cwnd or more bytes
     * of data outstanding to that transport address.
     */
    /* RFC 7.2.4 & the Implementers Guide 2.8.
     *
     * 3) ...
     *    When a Fast Retransmit is being performed the sender SHOULD
     *    ignore the value of cwnd and SHOULD NOT delay retransmission.
     */
    if (chunk->fast_retransmit != SCTP_NEED_FRTX)
        if (flight_size >= transport->cwnd) {
            retval = SCTP_XMIT_RWND_FULL;
            goto finish;
        }

    /* Nagle's algorithm to solve small-packet problem:
     * Inhibit the sending of new chunks when new outgoing data arrives
     * if any previously transmitted data on the connection remains
     * unacknowledged.
     */
    if (!sctp_sk(asoc->base.sk)->nodelay && sctp_packet_empty(packet) &&
        inflight && sctp_state(asoc, ESTABLISHED)) {
        unsigned int max = transport->pathmtu - packet->overhead;
        unsigned int len = chunk->skb->len + q->out_qlen;

        /* Check whether this chunk and all the rest of pending
         * data will fit or delay in hopes of bundling a full
         * sized packet.
         * Don't delay large message writes that may have been
         * fragmeneted into small peices.
         */
        if ((len < max) && chunk->msg->can_delay) {
            retval = SCTP_XMIT_NAGLE_DELAY;
            goto finish;
        }
    }

finish:
    return retval;
}

/* This private function does management things when adding DATA chunk */
static void sctp_packet_append_data(struct sctp_packet *packet,
                struct sctp_chunk *chunk)
{
    struct sctp_transport *transport = packet->transport;
    size_t datasize = sctp_data_size(chunk);
    struct sctp_association *asoc = transport->asoc;
    u32 rwnd = asoc->peer.rwnd;

    /* Keep track of how many bytes are in flight over this transport. */
    transport->flight_size += datasize;

    /* Keep track of how many bytes are in flight to the receiver. */
    asoc->outqueue.outstanding_bytes += datasize;

    /* Update our view of the receiver's rwnd. */
    if (datasize < rwnd)
        rwnd -= datasize;
    else
        rwnd = 0;

    asoc->peer.rwnd = rwnd;
    /* Has been accepted for transmission. */
    if (!asoc->peer.prsctp_capable)
        chunk->msg->can_abandon = 0;
    sctp_chunk_assign_tsn(chunk);
    sctp_chunk_assign_ssn(chunk);
}

static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
                    struct sctp_chunk *chunk,
                    u16 chunk_len)
{
    size_t psize;
    size_t pmtu;
    int too_big;
    sctp_xmit_t retval = SCTP_XMIT_OK;

    psize = packet->size;
    pmtu  = ((packet->transport->asoc) ?
        (packet->transport->asoc->pathmtu) :
        (packet->transport->pathmtu));

    too_big = (psize + chunk_len > pmtu);

    /* Decide if we need to fragment or resubmit later. */
    if (too_big) {
        /* It's OK to fragmet at IP level if any one of the following
         * is true:
         *  1. The packet is empty (meaning this chunk is greater
         *     the MTU)
         *  2. The chunk we are adding is a control chunk
         *  3. The packet doesn't have any data in it yet and data
         *  requires authentication.
         */
        if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
            (!packet->has_data && chunk->auth)) {
            /* We no longer do re-fragmentation.
             * Just fragment at the IP layer, if we
             * actually hit this condition
             */
            packet->ipfragok = 1;
        } else {
            retval = SCTP_XMIT_PMTU_FULL;
        }
    }

    return retval;
}