// SPDX-License-Identifier: GPL-2.0-or-later /* 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. * * Please send any bug reports or fixes you make to the * email address(es): * lksctp developers <linux-sctp@vger.kernel.org> * * Written or modified by: * La Monte H.P. Yarroll <piggy@acm.org> * Karl Knutson <karl@athena.chicago.il.us> * Jon Grimm <jgrimm@austin.ibm.com> * Sridhar Samudrala <sri@us.ibm.com> */ #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 enum sctp_xmit __sctp_packet_append_chunk(struct sctp_packet *packet, struct sctp_chunk *chunk); static enum sctp_xmit 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 enum sctp_xmit sctp_packet_will_fit(struct sctp_packet *packet, struct sctp_chunk *chunk, u16 chunk_len); static void sctp_packet_reset(struct sctp_packet *packet) { /* sctp_packet_transmit() relies on this to reset size to the * current overhead after sending packets. */ 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. */ void sctp_packet_config(struct sctp_packet *packet, __u32 vtag, int ecn_capable) { struct sctp_transport *tp = packet->transport; struct sctp_association *asoc = tp->asoc; struct sctp_sock *sp = NULL; struct sock *sk; pr_debug("%s: packet:%p vtag:0x%x\n", __func__, packet, vtag); packet->vtag = vtag; /* do the following jobs only once for a flush schedule */ if (!sctp_packet_empty(packet)) return; /* set packet max_size with pathmtu, then calculate overhead */ packet->max_size = tp->pathmtu; if (asoc) { sk = asoc->base.sk; sp = sctp_sk(sk); } packet->overhead = sctp_mtu_payload(sp, 0, 0); packet->size = packet->overhead; if (!asoc) return; /* update dst or transport pathmtu if in need */ if (!sctp_transport_dst_check(tp)) { sctp_transport_route(tp, NULL, sp); if (asoc->param_flags & SPP_PMTUD_ENABLE) sctp_assoc_sync_pmtu(asoc); } else if (!sctp_transport_pmtu_check(tp)) { if (asoc->param_flags & SPP_PMTUD_ENABLE) sctp_assoc_sync_pmtu(asoc); } if (asoc->pmtu_pending) { if (asoc->param_flags & SPP_PMTUD_ENABLE) sctp_assoc_sync_pmtu(asoc); asoc->pmtu_pending = 0; } /* If there a is a prepend chunk stick it on the list before * any other chunks get appended. */ if (ecn_capable) { struct sctp_chunk *chunk = sctp_get_ecne_prepend(asoc); if (chunk) sctp_packet_append_chunk(packet, chunk); } if (!tp->dst) return; /* set packet max_size with gso_max_size if gso is enabled*/ rcu_read_lock(); if (__sk_dst_get(sk) != tp->dst) { dst_hold(tp->dst); sk_setup_caps(sk, tp->dst); } packet->max_size = sk_can_gso(sk) ? tp->dst->dev->gso_max_size : asoc->pathmtu; rcu_read_unlock(); } /* Initialize the packet structure. */ void sctp_packet_init(struct sctp_packet *packet, struct sctp_transport *transport, __u16 sport, __u16 dport) { pr_debug("%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); /* The overhead will be calculated by sctp_packet_config() */ packet->overhead = 0; sctp_packet_reset(packet); packet->vtag = 0; } /* Free a packet. */ void sctp_packet_free(struct sctp_packet *packet) { struct sctp_chunk *chunk, *tmp; pr_debug("%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); } } /* 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. */ enum sctp_xmit sctp_packet_transmit_chunk(struct sctp_packet *packet, struct sctp_chunk *chunk, int one_packet, gfp_t gfp) { enum sctp_xmit retval; pr_debug("%s: packet:%p size:%zu chunk:%p size:%d\n", __func__, packet, packet->size, chunk, chunk->skb ? chunk->skb->len : -1); switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) { case SCTP_XMIT_PMTU_FULL: if (!packet->has_cookie_echo) { int error = 0; error = sctp_packet_transmit(packet, gfp); 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_DELAY: break; } return retval; } /* Try to bundle an auth chunk into the packet. */ static enum sctp_xmit sctp_packet_bundle_auth(struct sctp_packet *pkt, struct sctp_chunk *chunk) { struct sctp_association *asoc = pkt->transport->asoc; enum sctp_xmit retval = SCTP_XMIT_OK; struct sctp_chunk *auth; /* 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, chunk->shkey->key_id); if (!auth) return retval; auth->shkey = chunk->shkey; sctp_auth_shkey_hold(auth->shkey); 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 enum sctp_xmit sctp_packet_bundle_sack(struct sctp_packet *pkt, struct sctp_chunk *chunk) { enum sctp_xmit 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; } SCTP_INC_STATS(asoc->base.net, SCTP_MIB_OUTCTRLCHUNKS); asoc->stats.octrlchunks++; 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 enum sctp_xmit __sctp_packet_append_chunk(struct sctp_packet *packet, struct sctp_chunk *chunk) { __u16 chunk_len = SCTP_PAD4(ntohs(chunk->chunk_hdr->length)); enum sctp_xmit retval = SCTP_XMIT_OK; /* 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: case SCTP_CID_I_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; /* Mainly used for prsctp RTX policy */ chunk->sent_count++; break; case SCTP_CID_COOKIE_ECHO: packet->has_cookie_echo = 1; break; case SCTP_CID_SACK: packet->has_sack = 1; if (chunk->asoc) chunk->asoc->stats.osacks++; 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. */ enum sctp_xmit sctp_packet_append_chunk(struct sctp_packet *packet, struct sctp_chunk *chunk) { enum sctp_xmit retval = SCTP_XMIT_OK; pr_debug("%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_gso_append(struct sk_buff *head, struct sk_buff *skb) { if (SCTP_OUTPUT_CB(head)->last == head) skb_shinfo(head)->frag_list = skb; else SCTP_OUTPUT_CB(head)->last->next = skb; SCTP_OUTPUT_CB(head)->last = skb; head->truesize += skb->truesize; head->data_len += skb->len; head->len += skb->len; refcount_add(skb->truesize, &head->sk->sk_wmem_alloc); __skb_header_release(skb); } static int sctp_packet_pack(struct sctp_packet *packet, struct sk_buff *head, int gso, gfp_t gfp) { struct sctp_transport *tp = packet->transport; struct sctp_auth_chunk *auth = NULL; struct sctp_chunk *chunk, *tmp; int pkt_count = 0, pkt_size; struct sock *sk = head->sk; struct sk_buff *nskb; int auth_len = 0; if (gso) { skb_shinfo(head)->gso_type = sk->sk_gso_type; SCTP_OUTPUT_CB(head)->last = head; } else { nskb = head; pkt_size = packet->size; goto merge; } do { /* calculate the pkt_size and alloc nskb */ pkt_size = packet->overhead; list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) { int padded = SCTP_PAD4(chunk->skb->len); if (chunk == packet->auth) auth_len = padded; else if (auth_len + padded + packet->overhead > tp->pathmtu) return 0; else if (pkt_size + padded > tp->pathmtu) break; pkt_size += padded; } nskb = alloc_skb(pkt_size + MAX_HEADER, gfp); if (!nskb) return 0; skb_reserve(nskb, packet->overhead + MAX_HEADER); merge: /* merge chunks into nskb and append nskb into head list */ pkt_size -= packet->overhead; list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) { int padding; list_del_init(&chunk->list); if (sctp_chunk_is_data(chunk)) { if (!sctp_chunk_retransmitted(chunk) && !tp->rto_pending) { chunk->rtt_in_progress = 1; tp->rto_pending = 1; } } padding = SCTP_PAD4(chunk->skb->len) - chunk->skb->len; if (padding) skb_put_zero(chunk->skb, padding); if (chunk == packet->auth) auth = (struct sctp_auth_chunk *) skb_tail_pointer(nskb); skb_put_data(nskb, chunk->skb->data, chunk->skb->len); pr_debug("*** Chunk:%p[%s] %s 0x%x, length:%d, chunk->skb->len:%d, rtt_in_progress:%d\n", 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, ntohs(chunk->chunk_hdr->length), chunk->skb->len, chunk->rtt_in_progress); pkt_size -= SCTP_PAD4(chunk->skb->len); if (!sctp_chunk_is_data(chunk) && chunk != packet->auth) sctp_chunk_free(chunk); if (!pkt_size) break; } if (auth) { sctp_auth_calculate_hmac(tp->asoc, nskb, auth, packet->auth->shkey, gfp); /* free auth if no more chunks, or add it back */ if (list_empty(&packet->chunk_list)) sctp_chunk_free(packet->auth); else list_add(&packet->auth->list, &packet->chunk_list); } if (gso) sctp_packet_gso_append(head, nskb); pkt_count++; } while (!list_empty(&packet->chunk_list)); if (gso) { memset(head->cb, 0, max(sizeof(struct inet_skb_parm), sizeof(struct inet6_skb_parm))); skb_shinfo(head)->gso_segs = pkt_count; skb_shinfo(head)->gso_size = GSO_BY_FRAGS; rcu_read_lock(); if (skb_dst(head) != tp->dst) { dst_hold(tp->dst); sk_setup_caps(sk, tp->dst); } rcu_read_unlock(); goto chksum; } if (sctp_checksum_disable) return 1; if (!(skb_dst(head)->dev->features & NETIF_F_SCTP_CRC) || dst_xfrm(skb_dst(head)) || packet->ipfragok) { struct sctphdr *sh = (struct sctphdr *)skb_transport_header(head); sh->checksum = sctp_compute_cksum(head, 0); } else { chksum: head->ip_summed = CHECKSUM_PARTIAL; head->csum_not_inet = 1; head->csum_start = skb_transport_header(head) - head->head; head->csum_offset = offsetof(struct sctphdr, checksum); } return pkt_count; } /* All packets are sent to the network through this function from * sctp_outq_tail(). * * The return value is always 0 for now. */ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp) { struct sctp_transport *tp = packet->transport; struct sctp_association *asoc = tp->asoc; struct sctp_chunk *chunk, *tmp; int pkt_count, gso = 0; struct dst_entry *dst; struct sk_buff *head; struct sctphdr *sh; struct sock *sk; pr_debug("%s: packet:%p\n", __func__, packet); if (list_empty(&packet->chunk_list)) return 0; chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list); sk = chunk->skb->sk; /* check gso */ if (packet->size > tp->pathmtu && !packet->ipfragok) { if (!sk_can_gso(sk)) { pr_err_once("Trying to GSO but underlying device doesn't support it."); goto out; } gso = 1; } /* alloc head skb */ head = alloc_skb((gso ? packet->overhead : packet->size) + MAX_HEADER, gfp); if (!head) goto out; skb_reserve(head, packet->overhead + MAX_HEADER); skb_set_owner_w(head, sk); /* set sctp header */ sh = skb_push(head, sizeof(struct sctphdr)); skb_reset_transport_header(head); sh->source = htons(packet->source_port); sh->dest = htons(packet->destination_port); sh->vtag = htonl(packet->vtag); sh->checksum = 0; /* drop packet if no dst */ dst = dst_clone(tp->dst); if (!dst) { IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES); kfree_skb(head); goto out; } skb_dst_set(head, dst); /* pack up chunks */ pkt_count = sctp_packet_pack(packet, head, gso, gfp); if (!pkt_count) { kfree_skb(head); goto out; } pr_debug("***sctp_transmit_packet*** skb->len:%d\n", head->len); /* start autoclose timer */ if (packet->has_data && sctp_state(asoc, ESTABLISHED) && asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE]) { struct timer_list *timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE]; unsigned long timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE]; if (!mod_timer(timer, jiffies + timeout)) sctp_association_hold(asoc); } /* sctp xmit */ tp->af_specific->ecn_capable(sk); if (asoc) { asoc->stats.opackets += pkt_count; if (asoc->peer.last_sent_to != tp) asoc->peer.last_sent_to = tp; } head->ignore_df = packet->ipfragok; if (tp->dst_pending_confirm) skb_set_dst_pending_confirm(head, 1); /* neighbour should be confirmed on successful transmission or * positive error */ if (tp->af_specific->sctp_xmit(head, tp) >= 0 && tp->dst_pending_confirm) tp->dst_pending_confirm = 0; out: 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); } sctp_packet_reset(packet); return 0; } /******************************************************************** * 2nd Level Abstractions ********************************************************************/ /* This private function check to see if a chunk can be added */ static enum sctp_xmit sctp_packet_can_append_data(struct sctp_packet *packet, struct sctp_chunk *chunk) { 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 && inflight > 0) /* We have (at least) one data chunk in flight, * so we can't fall back to rule 6.1 B). */ return SCTP_XMIT_RWND_FULL; /* 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 && flight_size >= transport->cwnd) return SCTP_XMIT_RWND_FULL; /* 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 || inflight == 0) && !asoc->force_delay) /* Nothing unacked */ return SCTP_XMIT_OK; if (!sctp_packet_empty(packet)) /* Append to packet */ return SCTP_XMIT_OK; if (!sctp_state(asoc, ESTABLISHED)) return SCTP_XMIT_OK; /* Check whether this chunk and all the rest of pending data will fit * or delay in hopes of bundling a full sized packet. */ if (chunk->skb->len + q->out_qlen > transport->pathmtu - packet->overhead - sctp_datachk_len(&chunk->asoc->stream) - 4) /* Enough data queued to fill a packet */ return SCTP_XMIT_OK; /* Don't delay large message writes that may have been fragmented */ if (!chunk->msg->can_delay) return SCTP_XMIT_OK; /* Defer until all data acked or packet full */ return SCTP_XMIT_DELAY; } /* 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; sctp_chunk_assign_tsn(chunk); asoc->stream.si->assign_number(chunk); } static enum sctp_xmit sctp_packet_will_fit(struct sctp_packet *packet, struct sctp_chunk *chunk, u16 chunk_len) { enum sctp_xmit retval = SCTP_XMIT_OK; size_t psize, pmtu, maxsize; /* Don't bundle in this packet if this chunk's auth key doesn't * match other chunks already enqueued on this packet. Also, * don't bundle the chunk with auth key if other chunks in this * packet don't have auth key. */ if ((packet->auth && chunk->shkey != packet->auth->shkey) || (!packet->auth && chunk->shkey && chunk->chunk_hdr->type != SCTP_CID_AUTH)) return SCTP_XMIT_PMTU_FULL; psize = packet->size; if (packet->transport->asoc) pmtu = packet->transport->asoc->pathmtu; else pmtu = packet->transport->pathmtu; /* Decide if we need to fragment or resubmit later. */ if (psize + chunk_len > pmtu) { /* It's OK to fragment 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 packet doesn't have any data in it yet and data * requires authentication. */ if (sctp_packet_empty(packet) || (!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; goto out; } /* Similarly, if this chunk was built before a PMTU * reduction, we have to fragment it at IP level now. So * if the packet already contains something, we need to * flush. */ maxsize = pmtu - packet->overhead; if (packet->auth) maxsize -= SCTP_PAD4(packet->auth->skb->len); if (chunk_len > maxsize) retval = SCTP_XMIT_PMTU_FULL; /* It is also okay to fragment if the chunk we are * adding is a control chunk, but only if current packet * is not a GSO one otherwise it causes fragmentation of * a large frame. So in this case we allow the * fragmentation by forcing it to be in a new packet. */ if (!sctp_chunk_is_data(chunk) && packet->has_data) retval = SCTP_XMIT_PMTU_FULL; if (psize + chunk_len > packet->max_size) /* Hit GSO/PMTU limit, gotta flush */ retval = SCTP_XMIT_PMTU_FULL; if (!packet->transport->burst_limited && psize + chunk_len > (packet->transport->cwnd >> 1)) /* Do not allow a single GSO packet to use more * than half of cwnd. */ retval = SCTP_XMIT_PMTU_FULL; if (packet->transport->burst_limited && psize + chunk_len > (packet->transport->burst_limited >> 1)) /* Do not allow a single GSO packet to use more * than half of original cwnd. */ retval = SCTP_XMIT_PMTU_FULL; /* Otherwise it will fit in the GSO packet */ } out: return retval; }