Merge tag 'nfs-for-5.2-2' of git://git.linux-nfs.org/projects/anna/linux-nfs
[sfrench/cifs-2.6.git] / net / sctp / output.c
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* SCTP kernel implementation
3  * (C) Copyright IBM Corp. 2001, 2004
4  * Copyright (c) 1999-2000 Cisco, Inc.
5  * Copyright (c) 1999-2001 Motorola, Inc.
6  *
7  * This file is part of the SCTP kernel implementation
8  *
9  * These functions handle output processing.
10  *
11  * Please send any bug reports or fixes you make to the
12  * email address(es):
13  *    lksctp developers <linux-sctp@vger.kernel.org>
14  *
15  * Written or modified by:
16  *    La Monte H.P. Yarroll <piggy@acm.org>
17  *    Karl Knutson          <karl@athena.chicago.il.us>
18  *    Jon Grimm             <jgrimm@austin.ibm.com>
19  *    Sridhar Samudrala     <sri@us.ibm.com>
20  */
21
22 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
23
24 #include <linux/types.h>
25 #include <linux/kernel.h>
26 #include <linux/wait.h>
27 #include <linux/time.h>
28 #include <linux/ip.h>
29 #include <linux/ipv6.h>
30 #include <linux/init.h>
31 #include <linux/slab.h>
32 #include <net/inet_ecn.h>
33 #include <net/ip.h>
34 #include <net/icmp.h>
35 #include <net/net_namespace.h>
36
37 #include <linux/socket.h> /* for sa_family_t */
38 #include <net/sock.h>
39
40 #include <net/sctp/sctp.h>
41 #include <net/sctp/sm.h>
42 #include <net/sctp/checksum.h>
43
44 /* Forward declarations for private helpers. */
45 static enum sctp_xmit __sctp_packet_append_chunk(struct sctp_packet *packet,
46                                                  struct sctp_chunk *chunk);
47 static enum sctp_xmit sctp_packet_can_append_data(struct sctp_packet *packet,
48                                                   struct sctp_chunk *chunk);
49 static void sctp_packet_append_data(struct sctp_packet *packet,
50                                     struct sctp_chunk *chunk);
51 static enum sctp_xmit sctp_packet_will_fit(struct sctp_packet *packet,
52                                            struct sctp_chunk *chunk,
53                                            u16 chunk_len);
54
55 static void sctp_packet_reset(struct sctp_packet *packet)
56 {
57         /* sctp_packet_transmit() relies on this to reset size to the
58          * current overhead after sending packets.
59          */
60         packet->size = packet->overhead;
61
62         packet->has_cookie_echo = 0;
63         packet->has_sack = 0;
64         packet->has_data = 0;
65         packet->has_auth = 0;
66         packet->ipfragok = 0;
67         packet->auth = NULL;
68 }
69
70 /* Config a packet.
71  * This appears to be a followup set of initializations.
72  */
73 void sctp_packet_config(struct sctp_packet *packet, __u32 vtag,
74                         int ecn_capable)
75 {
76         struct sctp_transport *tp = packet->transport;
77         struct sctp_association *asoc = tp->asoc;
78         struct sctp_sock *sp = NULL;
79         struct sock *sk;
80
81         pr_debug("%s: packet:%p vtag:0x%x\n", __func__, packet, vtag);
82         packet->vtag = vtag;
83
84         /* do the following jobs only once for a flush schedule */
85         if (!sctp_packet_empty(packet))
86                 return;
87
88         /* set packet max_size with pathmtu, then calculate overhead */
89         packet->max_size = tp->pathmtu;
90
91         if (asoc) {
92                 sk = asoc->base.sk;
93                 sp = sctp_sk(sk);
94         }
95         packet->overhead = sctp_mtu_payload(sp, 0, 0);
96         packet->size = packet->overhead;
97
98         if (!asoc)
99                 return;
100
101         /* update dst or transport pathmtu if in need */
102         if (!sctp_transport_dst_check(tp)) {
103                 sctp_transport_route(tp, NULL, sp);
104                 if (asoc->param_flags & SPP_PMTUD_ENABLE)
105                         sctp_assoc_sync_pmtu(asoc);
106         } else if (!sctp_transport_pmtu_check(tp)) {
107                 if (asoc->param_flags & SPP_PMTUD_ENABLE)
108                         sctp_assoc_sync_pmtu(asoc);
109         }
110
111         if (asoc->pmtu_pending) {
112                 if (asoc->param_flags & SPP_PMTUD_ENABLE)
113                         sctp_assoc_sync_pmtu(asoc);
114                 asoc->pmtu_pending = 0;
115         }
116
117         /* If there a is a prepend chunk stick it on the list before
118          * any other chunks get appended.
119          */
120         if (ecn_capable) {
121                 struct sctp_chunk *chunk = sctp_get_ecne_prepend(asoc);
122
123                 if (chunk)
124                         sctp_packet_append_chunk(packet, chunk);
125         }
126
127         if (!tp->dst)
128                 return;
129
130         /* set packet max_size with gso_max_size if gso is enabled*/
131         rcu_read_lock();
132         if (__sk_dst_get(sk) != tp->dst) {
133                 dst_hold(tp->dst);
134                 sk_setup_caps(sk, tp->dst);
135         }
136         packet->max_size = sk_can_gso(sk) ? tp->dst->dev->gso_max_size
137                                           : asoc->pathmtu;
138         rcu_read_unlock();
139 }
140
141 /* Initialize the packet structure. */
142 void sctp_packet_init(struct sctp_packet *packet,
143                       struct sctp_transport *transport,
144                       __u16 sport, __u16 dport)
145 {
146         pr_debug("%s: packet:%p transport:%p\n", __func__, packet, transport);
147
148         packet->transport = transport;
149         packet->source_port = sport;
150         packet->destination_port = dport;
151         INIT_LIST_HEAD(&packet->chunk_list);
152         /* The overhead will be calculated by sctp_packet_config() */
153         packet->overhead = 0;
154         sctp_packet_reset(packet);
155         packet->vtag = 0;
156 }
157
158 /* Free a packet.  */
159 void sctp_packet_free(struct sctp_packet *packet)
160 {
161         struct sctp_chunk *chunk, *tmp;
162
163         pr_debug("%s: packet:%p\n", __func__, packet);
164
165         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
166                 list_del_init(&chunk->list);
167                 sctp_chunk_free(chunk);
168         }
169 }
170
171 /* This routine tries to append the chunk to the offered packet. If adding
172  * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
173  * is not present in the packet, it transmits the input packet.
174  * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
175  * as it can fit in the packet, but any more data that does not fit in this
176  * packet can be sent only after receiving the COOKIE_ACK.
177  */
178 enum sctp_xmit sctp_packet_transmit_chunk(struct sctp_packet *packet,
179                                           struct sctp_chunk *chunk,
180                                           int one_packet, gfp_t gfp)
181 {
182         enum sctp_xmit retval;
183
184         pr_debug("%s: packet:%p size:%zu chunk:%p size:%d\n", __func__,
185                  packet, packet->size, chunk, chunk->skb ? chunk->skb->len : -1);
186
187         switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
188         case SCTP_XMIT_PMTU_FULL:
189                 if (!packet->has_cookie_echo) {
190                         int error = 0;
191
192                         error = sctp_packet_transmit(packet, gfp);
193                         if (error < 0)
194                                 chunk->skb->sk->sk_err = -error;
195
196                         /* If we have an empty packet, then we can NOT ever
197                          * return PMTU_FULL.
198                          */
199                         if (!one_packet)
200                                 retval = sctp_packet_append_chunk(packet,
201                                                                   chunk);
202                 }
203                 break;
204
205         case SCTP_XMIT_RWND_FULL:
206         case SCTP_XMIT_OK:
207         case SCTP_XMIT_DELAY:
208                 break;
209         }
210
211         return retval;
212 }
213
214 /* Try to bundle an auth chunk into the packet. */
215 static enum sctp_xmit sctp_packet_bundle_auth(struct sctp_packet *pkt,
216                                               struct sctp_chunk *chunk)
217 {
218         struct sctp_association *asoc = pkt->transport->asoc;
219         enum sctp_xmit retval = SCTP_XMIT_OK;
220         struct sctp_chunk *auth;
221
222         /* if we don't have an association, we can't do authentication */
223         if (!asoc)
224                 return retval;
225
226         /* See if this is an auth chunk we are bundling or if
227          * auth is already bundled.
228          */
229         if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->has_auth)
230                 return retval;
231
232         /* if the peer did not request this chunk to be authenticated,
233          * don't do it
234          */
235         if (!chunk->auth)
236                 return retval;
237
238         auth = sctp_make_auth(asoc, chunk->shkey->key_id);
239         if (!auth)
240                 return retval;
241
242         auth->shkey = chunk->shkey;
243         sctp_auth_shkey_hold(auth->shkey);
244
245         retval = __sctp_packet_append_chunk(pkt, auth);
246
247         if (retval != SCTP_XMIT_OK)
248                 sctp_chunk_free(auth);
249
250         return retval;
251 }
252
253 /* Try to bundle a SACK with the packet. */
254 static enum sctp_xmit sctp_packet_bundle_sack(struct sctp_packet *pkt,
255                                               struct sctp_chunk *chunk)
256 {
257         enum sctp_xmit retval = SCTP_XMIT_OK;
258
259         /* If sending DATA and haven't aleady bundled a SACK, try to
260          * bundle one in to the packet.
261          */
262         if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
263             !pkt->has_cookie_echo) {
264                 struct sctp_association *asoc;
265                 struct timer_list *timer;
266                 asoc = pkt->transport->asoc;
267                 timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
268
269                 /* If the SACK timer is running, we have a pending SACK */
270                 if (timer_pending(timer)) {
271                         struct sctp_chunk *sack;
272
273                         if (pkt->transport->sack_generation !=
274                             pkt->transport->asoc->peer.sack_generation)
275                                 return retval;
276
277                         asoc->a_rwnd = asoc->rwnd;
278                         sack = sctp_make_sack(asoc);
279                         if (sack) {
280                                 retval = __sctp_packet_append_chunk(pkt, sack);
281                                 if (retval != SCTP_XMIT_OK) {
282                                         sctp_chunk_free(sack);
283                                         goto out;
284                                 }
285                                 asoc->peer.sack_needed = 0;
286                                 if (del_timer(timer))
287                                         sctp_association_put(asoc);
288                         }
289                 }
290         }
291 out:
292         return retval;
293 }
294
295
296 /* Append a chunk to the offered packet reporting back any inability to do
297  * so.
298  */
299 static enum sctp_xmit __sctp_packet_append_chunk(struct sctp_packet *packet,
300                                                  struct sctp_chunk *chunk)
301 {
302         __u16 chunk_len = SCTP_PAD4(ntohs(chunk->chunk_hdr->length));
303         enum sctp_xmit retval = SCTP_XMIT_OK;
304
305         /* Check to see if this chunk will fit into the packet */
306         retval = sctp_packet_will_fit(packet, chunk, chunk_len);
307         if (retval != SCTP_XMIT_OK)
308                 goto finish;
309
310         /* We believe that this chunk is OK to add to the packet */
311         switch (chunk->chunk_hdr->type) {
312         case SCTP_CID_DATA:
313         case SCTP_CID_I_DATA:
314                 /* Account for the data being in the packet */
315                 sctp_packet_append_data(packet, chunk);
316                 /* Disallow SACK bundling after DATA. */
317                 packet->has_sack = 1;
318                 /* Disallow AUTH bundling after DATA */
319                 packet->has_auth = 1;
320                 /* Let it be knows that packet has DATA in it */
321                 packet->has_data = 1;
322                 /* timestamp the chunk for rtx purposes */
323                 chunk->sent_at = jiffies;
324                 /* Mainly used for prsctp RTX policy */
325                 chunk->sent_count++;
326                 break;
327         case SCTP_CID_COOKIE_ECHO:
328                 packet->has_cookie_echo = 1;
329                 break;
330
331         case SCTP_CID_SACK:
332                 packet->has_sack = 1;
333                 if (chunk->asoc)
334                         chunk->asoc->stats.osacks++;
335                 break;
336
337         case SCTP_CID_AUTH:
338                 packet->has_auth = 1;
339                 packet->auth = chunk;
340                 break;
341         }
342
343         /* It is OK to send this chunk.  */
344         list_add_tail(&chunk->list, &packet->chunk_list);
345         packet->size += chunk_len;
346         chunk->transport = packet->transport;
347 finish:
348         return retval;
349 }
350
351 /* Append a chunk to the offered packet reporting back any inability to do
352  * so.
353  */
354 enum sctp_xmit sctp_packet_append_chunk(struct sctp_packet *packet,
355                                         struct sctp_chunk *chunk)
356 {
357         enum sctp_xmit retval = SCTP_XMIT_OK;
358
359         pr_debug("%s: packet:%p chunk:%p\n", __func__, packet, chunk);
360
361         /* Data chunks are special.  Before seeing what else we can
362          * bundle into this packet, check to see if we are allowed to
363          * send this DATA.
364          */
365         if (sctp_chunk_is_data(chunk)) {
366                 retval = sctp_packet_can_append_data(packet, chunk);
367                 if (retval != SCTP_XMIT_OK)
368                         goto finish;
369         }
370
371         /* Try to bundle AUTH chunk */
372         retval = sctp_packet_bundle_auth(packet, chunk);
373         if (retval != SCTP_XMIT_OK)
374                 goto finish;
375
376         /* Try to bundle SACK chunk */
377         retval = sctp_packet_bundle_sack(packet, chunk);
378         if (retval != SCTP_XMIT_OK)
379                 goto finish;
380
381         retval = __sctp_packet_append_chunk(packet, chunk);
382
383 finish:
384         return retval;
385 }
386
387 static void sctp_packet_gso_append(struct sk_buff *head, struct sk_buff *skb)
388 {
389         if (SCTP_OUTPUT_CB(head)->last == head)
390                 skb_shinfo(head)->frag_list = skb;
391         else
392                 SCTP_OUTPUT_CB(head)->last->next = skb;
393         SCTP_OUTPUT_CB(head)->last = skb;
394
395         head->truesize += skb->truesize;
396         head->data_len += skb->len;
397         head->len += skb->len;
398         refcount_add(skb->truesize, &head->sk->sk_wmem_alloc);
399
400         __skb_header_release(skb);
401 }
402
403 static int sctp_packet_pack(struct sctp_packet *packet,
404                             struct sk_buff *head, int gso, gfp_t gfp)
405 {
406         struct sctp_transport *tp = packet->transport;
407         struct sctp_auth_chunk *auth = NULL;
408         struct sctp_chunk *chunk, *tmp;
409         int pkt_count = 0, pkt_size;
410         struct sock *sk = head->sk;
411         struct sk_buff *nskb;
412         int auth_len = 0;
413
414         if (gso) {
415                 skb_shinfo(head)->gso_type = sk->sk_gso_type;
416                 SCTP_OUTPUT_CB(head)->last = head;
417         } else {
418                 nskb = head;
419                 pkt_size = packet->size;
420                 goto merge;
421         }
422
423         do {
424                 /* calculate the pkt_size and alloc nskb */
425                 pkt_size = packet->overhead;
426                 list_for_each_entry_safe(chunk, tmp, &packet->chunk_list,
427                                          list) {
428                         int padded = SCTP_PAD4(chunk->skb->len);
429
430                         if (chunk == packet->auth)
431                                 auth_len = padded;
432                         else if (auth_len + padded + packet->overhead >
433                                  tp->pathmtu)
434                                 return 0;
435                         else if (pkt_size + padded > tp->pathmtu)
436                                 break;
437                         pkt_size += padded;
438                 }
439                 nskb = alloc_skb(pkt_size + MAX_HEADER, gfp);
440                 if (!nskb)
441                         return 0;
442                 skb_reserve(nskb, packet->overhead + MAX_HEADER);
443
444 merge:
445                 /* merge chunks into nskb and append nskb into head list */
446                 pkt_size -= packet->overhead;
447                 list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
448                         int padding;
449
450                         list_del_init(&chunk->list);
451                         if (sctp_chunk_is_data(chunk)) {
452                                 if (!sctp_chunk_retransmitted(chunk) &&
453                                     !tp->rto_pending) {
454                                         chunk->rtt_in_progress = 1;
455                                         tp->rto_pending = 1;
456                                 }
457                         }
458
459                         padding = SCTP_PAD4(chunk->skb->len) - chunk->skb->len;
460                         if (padding)
461                                 skb_put_zero(chunk->skb, padding);
462
463                         if (chunk == packet->auth)
464                                 auth = (struct sctp_auth_chunk *)
465                                                         skb_tail_pointer(nskb);
466
467                         skb_put_data(nskb, chunk->skb->data, chunk->skb->len);
468
469                         pr_debug("*** Chunk:%p[%s] %s 0x%x, length:%d, chunk->skb->len:%d, rtt_in_progress:%d\n",
470                                  chunk,
471                                  sctp_cname(SCTP_ST_CHUNK(chunk->chunk_hdr->type)),
472                                  chunk->has_tsn ? "TSN" : "No TSN",
473                                  chunk->has_tsn ? ntohl(chunk->subh.data_hdr->tsn) : 0,
474                                  ntohs(chunk->chunk_hdr->length), chunk->skb->len,
475                                  chunk->rtt_in_progress);
476
477                         pkt_size -= SCTP_PAD4(chunk->skb->len);
478
479                         if (!sctp_chunk_is_data(chunk) && chunk != packet->auth)
480                                 sctp_chunk_free(chunk);
481
482                         if (!pkt_size)
483                                 break;
484                 }
485
486                 if (auth) {
487                         sctp_auth_calculate_hmac(tp->asoc, nskb, auth,
488                                                  packet->auth->shkey, gfp);
489                         /* free auth if no more chunks, or add it back */
490                         if (list_empty(&packet->chunk_list))
491                                 sctp_chunk_free(packet->auth);
492                         else
493                                 list_add(&packet->auth->list,
494                                          &packet->chunk_list);
495                 }
496
497                 if (gso)
498                         sctp_packet_gso_append(head, nskb);
499
500                 pkt_count++;
501         } while (!list_empty(&packet->chunk_list));
502
503         if (gso) {
504                 memset(head->cb, 0, max(sizeof(struct inet_skb_parm),
505                                         sizeof(struct inet6_skb_parm)));
506                 skb_shinfo(head)->gso_segs = pkt_count;
507                 skb_shinfo(head)->gso_size = GSO_BY_FRAGS;
508                 rcu_read_lock();
509                 if (skb_dst(head) != tp->dst) {
510                         dst_hold(tp->dst);
511                         sk_setup_caps(sk, tp->dst);
512                 }
513                 rcu_read_unlock();
514                 goto chksum;
515         }
516
517         if (sctp_checksum_disable)
518                 return 1;
519
520         if (!(skb_dst(head)->dev->features & NETIF_F_SCTP_CRC) ||
521             dst_xfrm(skb_dst(head)) || packet->ipfragok) {
522                 struct sctphdr *sh =
523                         (struct sctphdr *)skb_transport_header(head);
524
525                 sh->checksum = sctp_compute_cksum(head, 0);
526         } else {
527 chksum:
528                 head->ip_summed = CHECKSUM_PARTIAL;
529                 head->csum_not_inet = 1;
530                 head->csum_start = skb_transport_header(head) - head->head;
531                 head->csum_offset = offsetof(struct sctphdr, checksum);
532         }
533
534         return pkt_count;
535 }
536
537 /* All packets are sent to the network through this function from
538  * sctp_outq_tail().
539  *
540  * The return value is always 0 for now.
541  */
542 int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
543 {
544         struct sctp_transport *tp = packet->transport;
545         struct sctp_association *asoc = tp->asoc;
546         struct sctp_chunk *chunk, *tmp;
547         int pkt_count, gso = 0;
548         struct dst_entry *dst;
549         struct sk_buff *head;
550         struct sctphdr *sh;
551         struct sock *sk;
552
553         pr_debug("%s: packet:%p\n", __func__, packet);
554         if (list_empty(&packet->chunk_list))
555                 return 0;
556         chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
557         sk = chunk->skb->sk;
558
559         /* check gso */
560         if (packet->size > tp->pathmtu && !packet->ipfragok) {
561                 if (!sk_can_gso(sk)) {
562                         pr_err_once("Trying to GSO but underlying device doesn't support it.");
563                         goto out;
564                 }
565                 gso = 1;
566         }
567
568         /* alloc head skb */
569         head = alloc_skb((gso ? packet->overhead : packet->size) +
570                          MAX_HEADER, gfp);
571         if (!head)
572                 goto out;
573         skb_reserve(head, packet->overhead + MAX_HEADER);
574         skb_set_owner_w(head, sk);
575
576         /* set sctp header */
577         sh = skb_push(head, sizeof(struct sctphdr));
578         skb_reset_transport_header(head);
579         sh->source = htons(packet->source_port);
580         sh->dest = htons(packet->destination_port);
581         sh->vtag = htonl(packet->vtag);
582         sh->checksum = 0;
583
584         /* drop packet if no dst */
585         dst = dst_clone(tp->dst);
586         if (!dst) {
587                 IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);
588                 kfree_skb(head);
589                 goto out;
590         }
591         skb_dst_set(head, dst);
592
593         /* pack up chunks */
594         pkt_count = sctp_packet_pack(packet, head, gso, gfp);
595         if (!pkt_count) {
596                 kfree_skb(head);
597                 goto out;
598         }
599         pr_debug("***sctp_transmit_packet*** skb->len:%d\n", head->len);
600
601         /* start autoclose timer */
602         if (packet->has_data && sctp_state(asoc, ESTABLISHED) &&
603             asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE]) {
604                 struct timer_list *timer =
605                         &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
606                 unsigned long timeout =
607                         asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
608
609                 if (!mod_timer(timer, jiffies + timeout))
610                         sctp_association_hold(asoc);
611         }
612
613         /* sctp xmit */
614         tp->af_specific->ecn_capable(sk);
615         if (asoc) {
616                 asoc->stats.opackets += pkt_count;
617                 if (asoc->peer.last_sent_to != tp)
618                         asoc->peer.last_sent_to = tp;
619         }
620         head->ignore_df = packet->ipfragok;
621         if (tp->dst_pending_confirm)
622                 skb_set_dst_pending_confirm(head, 1);
623         /* neighbour should be confirmed on successful transmission or
624          * positive error
625          */
626         if (tp->af_specific->sctp_xmit(head, tp) >= 0 &&
627             tp->dst_pending_confirm)
628                 tp->dst_pending_confirm = 0;
629
630 out:
631         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
632                 list_del_init(&chunk->list);
633                 if (!sctp_chunk_is_data(chunk))
634                         sctp_chunk_free(chunk);
635         }
636         sctp_packet_reset(packet);
637         return 0;
638 }
639
640 /********************************************************************
641  * 2nd Level Abstractions
642  ********************************************************************/
643
644 /* This private function check to see if a chunk can be added */
645 static enum sctp_xmit sctp_packet_can_append_data(struct sctp_packet *packet,
646                                                   struct sctp_chunk *chunk)
647 {
648         size_t datasize, rwnd, inflight, flight_size;
649         struct sctp_transport *transport = packet->transport;
650         struct sctp_association *asoc = transport->asoc;
651         struct sctp_outq *q = &asoc->outqueue;
652
653         /* RFC 2960 6.1  Transmission of DATA Chunks
654          *
655          * A) At any given time, the data sender MUST NOT transmit new data to
656          * any destination transport address if its peer's rwnd indicates
657          * that the peer has no buffer space (i.e. rwnd is 0, see Section
658          * 6.2.1).  However, regardless of the value of rwnd (including if it
659          * is 0), the data sender can always have one DATA chunk in flight to
660          * the receiver if allowed by cwnd (see rule B below).  This rule
661          * allows the sender to probe for a change in rwnd that the sender
662          * missed due to the SACK having been lost in transit from the data
663          * receiver to the data sender.
664          */
665
666         rwnd = asoc->peer.rwnd;
667         inflight = q->outstanding_bytes;
668         flight_size = transport->flight_size;
669
670         datasize = sctp_data_size(chunk);
671
672         if (datasize > rwnd && inflight > 0)
673                 /* We have (at least) one data chunk in flight,
674                  * so we can't fall back to rule 6.1 B).
675                  */
676                 return SCTP_XMIT_RWND_FULL;
677
678         /* RFC 2960 6.1  Transmission of DATA Chunks
679          *
680          * B) At any given time, the sender MUST NOT transmit new data
681          * to a given transport address if it has cwnd or more bytes
682          * of data outstanding to that transport address.
683          */
684         /* RFC 7.2.4 & the Implementers Guide 2.8.
685          *
686          * 3) ...
687          *    When a Fast Retransmit is being performed the sender SHOULD
688          *    ignore the value of cwnd and SHOULD NOT delay retransmission.
689          */
690         if (chunk->fast_retransmit != SCTP_NEED_FRTX &&
691             flight_size >= transport->cwnd)
692                 return SCTP_XMIT_RWND_FULL;
693
694         /* Nagle's algorithm to solve small-packet problem:
695          * Inhibit the sending of new chunks when new outgoing data arrives
696          * if any previously transmitted data on the connection remains
697          * unacknowledged.
698          */
699
700         if ((sctp_sk(asoc->base.sk)->nodelay || inflight == 0) &&
701             !asoc->force_delay)
702                 /* Nothing unacked */
703                 return SCTP_XMIT_OK;
704
705         if (!sctp_packet_empty(packet))
706                 /* Append to packet */
707                 return SCTP_XMIT_OK;
708
709         if (!sctp_state(asoc, ESTABLISHED))
710                 return SCTP_XMIT_OK;
711
712         /* Check whether this chunk and all the rest of pending data will fit
713          * or delay in hopes of bundling a full sized packet.
714          */
715         if (chunk->skb->len + q->out_qlen > transport->pathmtu -
716             packet->overhead - sctp_datachk_len(&chunk->asoc->stream) - 4)
717                 /* Enough data queued to fill a packet */
718                 return SCTP_XMIT_OK;
719
720         /* Don't delay large message writes that may have been fragmented */
721         if (!chunk->msg->can_delay)
722                 return SCTP_XMIT_OK;
723
724         /* Defer until all data acked or packet full */
725         return SCTP_XMIT_DELAY;
726 }
727
728 /* This private function does management things when adding DATA chunk */
729 static void sctp_packet_append_data(struct sctp_packet *packet,
730                                 struct sctp_chunk *chunk)
731 {
732         struct sctp_transport *transport = packet->transport;
733         size_t datasize = sctp_data_size(chunk);
734         struct sctp_association *asoc = transport->asoc;
735         u32 rwnd = asoc->peer.rwnd;
736
737         /* Keep track of how many bytes are in flight over this transport. */
738         transport->flight_size += datasize;
739
740         /* Keep track of how many bytes are in flight to the receiver. */
741         asoc->outqueue.outstanding_bytes += datasize;
742
743         /* Update our view of the receiver's rwnd. */
744         if (datasize < rwnd)
745                 rwnd -= datasize;
746         else
747                 rwnd = 0;
748
749         asoc->peer.rwnd = rwnd;
750         sctp_chunk_assign_tsn(chunk);
751         asoc->stream.si->assign_number(chunk);
752 }
753
754 static enum sctp_xmit sctp_packet_will_fit(struct sctp_packet *packet,
755                                            struct sctp_chunk *chunk,
756                                            u16 chunk_len)
757 {
758         enum sctp_xmit retval = SCTP_XMIT_OK;
759         size_t psize, pmtu, maxsize;
760
761         /* Don't bundle in this packet if this chunk's auth key doesn't
762          * match other chunks already enqueued on this packet. Also,
763          * don't bundle the chunk with auth key if other chunks in this
764          * packet don't have auth key.
765          */
766         if ((packet->auth && chunk->shkey != packet->auth->shkey) ||
767             (!packet->auth && chunk->shkey &&
768              chunk->chunk_hdr->type != SCTP_CID_AUTH))
769                 return SCTP_XMIT_PMTU_FULL;
770
771         psize = packet->size;
772         if (packet->transport->asoc)
773                 pmtu = packet->transport->asoc->pathmtu;
774         else
775                 pmtu = packet->transport->pathmtu;
776
777         /* Decide if we need to fragment or resubmit later. */
778         if (psize + chunk_len > pmtu) {
779                 /* It's OK to fragment at IP level if any one of the following
780                  * is true:
781                  *      1. The packet is empty (meaning this chunk is greater
782                  *         the MTU)
783                  *      2. The packet doesn't have any data in it yet and data
784                  *         requires authentication.
785                  */
786                 if (sctp_packet_empty(packet) ||
787                     (!packet->has_data && chunk->auth)) {
788                         /* We no longer do re-fragmentation.
789                          * Just fragment at the IP layer, if we
790                          * actually hit this condition
791                          */
792                         packet->ipfragok = 1;
793                         goto out;
794                 }
795
796                 /* Similarly, if this chunk was built before a PMTU
797                  * reduction, we have to fragment it at IP level now. So
798                  * if the packet already contains something, we need to
799                  * flush.
800                  */
801                 maxsize = pmtu - packet->overhead;
802                 if (packet->auth)
803                         maxsize -= SCTP_PAD4(packet->auth->skb->len);
804                 if (chunk_len > maxsize)
805                         retval = SCTP_XMIT_PMTU_FULL;
806
807                 /* It is also okay to fragment if the chunk we are
808                  * adding is a control chunk, but only if current packet
809                  * is not a GSO one otherwise it causes fragmentation of
810                  * a large frame. So in this case we allow the
811                  * fragmentation by forcing it to be in a new packet.
812                  */
813                 if (!sctp_chunk_is_data(chunk) && packet->has_data)
814                         retval = SCTP_XMIT_PMTU_FULL;
815
816                 if (psize + chunk_len > packet->max_size)
817                         /* Hit GSO/PMTU limit, gotta flush */
818                         retval = SCTP_XMIT_PMTU_FULL;
819
820                 if (!packet->transport->burst_limited &&
821                     psize + chunk_len > (packet->transport->cwnd >> 1))
822                         /* Do not allow a single GSO packet to use more
823                          * than half of cwnd.
824                          */
825                         retval = SCTP_XMIT_PMTU_FULL;
826
827                 if (packet->transport->burst_limited &&
828                     psize + chunk_len > (packet->transport->burst_limited >> 1))
829                         /* Do not allow a single GSO packet to use more
830                          * than half of original cwnd.
831                          */
832                         retval = SCTP_XMIT_PMTU_FULL;
833                 /* Otherwise it will fit in the GSO packet */
834         }
835
836 out:
837         return retval;
838 }