xref: /openbmc/linux/net/sctp/output.c (revision 9d56dd3b083a3bec56e9da35ce07baca81030b03)
1 /* SCTP kernel implementation
2  * (C) Copyright IBM Corp. 2001, 2004
3  * Copyright (c) 1999-2000 Cisco, Inc.
4  * Copyright (c) 1999-2001 Motorola, Inc.
5  *
6  * This file is part of the SCTP kernel implementation
7  *
8  * These functions handle output processing.
9  *
10  * This SCTP implementation is free software;
11  * you can redistribute it and/or modify it under the terms of
12  * the GNU General Public License as published by
13  * the Free Software Foundation; either version 2, or (at your option)
14  * any later version.
15  *
16  * This SCTP implementation is distributed in the hope that it
17  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
18  *                 ************************
19  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
20  * See the GNU General Public License for more details.
21  *
22  * You should have received a copy of the GNU General Public License
23  * along with GNU CC; see the file COPYING.  If not, write to
24  * the Free Software Foundation, 59 Temple Place - Suite 330,
25  * Boston, MA 02111-1307, USA.
26  *
27  * Please send any bug reports or fixes you make to the
28  * email address(es):
29  *    lksctp developers <lksctp-developers@lists.sourceforge.net>
30  *
31  * Or submit a bug report through the following website:
32  *    http://www.sf.net/projects/lksctp
33  *
34  * Written or modified by:
35  *    La Monte H.P. Yarroll <piggy@acm.org>
36  *    Karl Knutson          <karl@athena.chicago.il.us>
37  *    Jon Grimm             <jgrimm@austin.ibm.com>
38  *    Sridhar Samudrala     <sri@us.ibm.com>
39  *
40  * Any bugs reported given to us we will try to fix... any fixes shared will
41  * be incorporated into the next SCTP release.
42  */
43 
44 #include <linux/types.h>
45 #include <linux/kernel.h>
46 #include <linux/wait.h>
47 #include <linux/time.h>
48 #include <linux/ip.h>
49 #include <linux/ipv6.h>
50 #include <linux/init.h>
51 #include <net/inet_ecn.h>
52 #include <net/ip.h>
53 #include <net/icmp.h>
54 #include <net/net_namespace.h>
55 
56 #include <linux/socket.h> /* for sa_family_t */
57 #include <net/sock.h>
58 
59 #include <net/sctp/sctp.h>
60 #include <net/sctp/sm.h>
61 #include <net/sctp/checksum.h>
62 
63 /* Forward declarations for private helpers. */
64 static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
65 					   struct sctp_chunk *chunk);
66 static void sctp_packet_append_data(struct sctp_packet *packet,
67 					   struct sctp_chunk *chunk);
68 static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
69 					struct sctp_chunk *chunk,
70 					u16 chunk_len);
71 
72 static void sctp_packet_reset(struct sctp_packet *packet)
73 {
74 	packet->size = packet->overhead;
75 	packet->has_cookie_echo = 0;
76 	packet->has_sack = 0;
77 	packet->has_data = 0;
78 	packet->has_auth = 0;
79 	packet->ipfragok = 0;
80 	packet->auth = NULL;
81 }
82 
83 /* Config a packet.
84  * This appears to be a followup set of initializations.
85  */
86 struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
87 				       __u32 vtag, int ecn_capable)
88 {
89 	struct sctp_chunk *chunk = NULL;
90 
91 	SCTP_DEBUG_PRINTK("%s: packet:%p vtag:0x%x\n", __func__,
92 			  packet, vtag);
93 
94 	sctp_packet_reset(packet);
95 	packet->vtag = vtag;
96 
97 	if (ecn_capable && sctp_packet_empty(packet)) {
98 		chunk = sctp_get_ecne_prepend(packet->transport->asoc);
99 
100 		/* If there a is a prepend chunk stick it on the list before
101 		 * any other chunks get appended.
102 		 */
103 		if (chunk)
104 			sctp_packet_append_chunk(packet, chunk);
105 	}
106 
107 	return packet;
108 }
109 
110 /* Initialize the packet structure. */
111 struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
112 				     struct sctp_transport *transport,
113 				     __u16 sport, __u16 dport)
114 {
115 	struct sctp_association *asoc = transport->asoc;
116 	size_t overhead;
117 
118 	SCTP_DEBUG_PRINTK("%s: packet:%p transport:%p\n", __func__,
119 			  packet, transport);
120 
121 	packet->transport = transport;
122 	packet->source_port = sport;
123 	packet->destination_port = dport;
124 	INIT_LIST_HEAD(&packet->chunk_list);
125 	if (asoc) {
126 		struct sctp_sock *sp = sctp_sk(asoc->base.sk);
127 		overhead = sp->pf->af->net_header_len;
128 	} else {
129 		overhead = sizeof(struct ipv6hdr);
130 	}
131 	overhead += sizeof(struct sctphdr);
132 	packet->overhead = overhead;
133 	sctp_packet_reset(packet);
134 	packet->vtag = 0;
135 	packet->malloced = 0;
136 	return packet;
137 }
138 
139 /* Free a packet.  */
140 void sctp_packet_free(struct sctp_packet *packet)
141 {
142 	struct sctp_chunk *chunk, *tmp;
143 
144 	SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
145 
146 	list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
147 		list_del_init(&chunk->list);
148 		sctp_chunk_free(chunk);
149 	}
150 
151 	if (packet->malloced)
152 		kfree(packet);
153 }
154 
155 /* This routine tries to append the chunk to the offered packet. If adding
156  * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
157  * is not present in the packet, it transmits the input packet.
158  * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
159  * as it can fit in the packet, but any more data that does not fit in this
160  * packet can be sent only after receiving the COOKIE_ACK.
161  */
162 sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
163 				       struct sctp_chunk *chunk,
164 				       int one_packet)
165 {
166 	sctp_xmit_t retval;
167 	int error = 0;
168 
169 	SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__,
170 			  packet, chunk);
171 
172 	switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
173 	case SCTP_XMIT_PMTU_FULL:
174 		if (!packet->has_cookie_echo) {
175 			error = sctp_packet_transmit(packet);
176 			if (error < 0)
177 				chunk->skb->sk->sk_err = -error;
178 
179 			/* If we have an empty packet, then we can NOT ever
180 			 * return PMTU_FULL.
181 			 */
182 			if (!one_packet)
183 				retval = sctp_packet_append_chunk(packet,
184 								  chunk);
185 		}
186 		break;
187 
188 	case SCTP_XMIT_RWND_FULL:
189 	case SCTP_XMIT_OK:
190 	case SCTP_XMIT_NAGLE_DELAY:
191 		break;
192 	}
193 
194 	return retval;
195 }
196 
197 /* Try to bundle an auth chunk into the packet. */
198 static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
199 					   struct sctp_chunk *chunk)
200 {
201 	struct sctp_association *asoc = pkt->transport->asoc;
202 	struct sctp_chunk *auth;
203 	sctp_xmit_t retval = SCTP_XMIT_OK;
204 
205 	/* if we don't have an association, we can't do authentication */
206 	if (!asoc)
207 		return retval;
208 
209 	/* See if this is an auth chunk we are bundling or if
210 	 * auth is already bundled.
211 	 */
212 	if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->has_auth)
213 		return retval;
214 
215 	/* if the peer did not request this chunk to be authenticated,
216 	 * don't do it
217 	 */
218 	if (!chunk->auth)
219 		return retval;
220 
221 	auth = sctp_make_auth(asoc);
222 	if (!auth)
223 		return retval;
224 
225 	retval = sctp_packet_append_chunk(pkt, auth);
226 
227 	return retval;
228 }
229 
230 /* Try to bundle a SACK with the packet. */
231 static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
232 					   struct sctp_chunk *chunk)
233 {
234 	sctp_xmit_t retval = SCTP_XMIT_OK;
235 
236 	/* If sending DATA and haven't aleady bundled a SACK, try to
237 	 * bundle one in to the packet.
238 	 */
239 	if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
240 	    !pkt->has_cookie_echo) {
241 		struct sctp_association *asoc;
242 		struct timer_list *timer;
243 		asoc = pkt->transport->asoc;
244 		timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
245 
246 		/* If the SACK timer is running, we have a pending SACK */
247 		if (timer_pending(timer)) {
248 			struct sctp_chunk *sack;
249 			asoc->a_rwnd = asoc->rwnd;
250 			sack = sctp_make_sack(asoc);
251 			if (sack) {
252 				retval = sctp_packet_append_chunk(pkt, sack);
253 				asoc->peer.sack_needed = 0;
254 				if (del_timer(timer))
255 					sctp_association_put(asoc);
256 			}
257 		}
258 	}
259 	return retval;
260 }
261 
262 /* Append a chunk to the offered packet reporting back any inability to do
263  * so.
264  */
265 sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
266 				     struct sctp_chunk *chunk)
267 {
268 	sctp_xmit_t retval = SCTP_XMIT_OK;
269 	__u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
270 
271 	SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__, packet,
272 			  chunk);
273 
274 	/* Data chunks are special.  Before seeing what else we can
275 	 * bundle into this packet, check to see if we are allowed to
276 	 * send this DATA.
277 	 */
278 	if (sctp_chunk_is_data(chunk)) {
279 		retval = sctp_packet_can_append_data(packet, chunk);
280 		if (retval != SCTP_XMIT_OK)
281 			goto finish;
282 	}
283 
284 	/* Try to bundle AUTH chunk */
285 	retval = sctp_packet_bundle_auth(packet, chunk);
286 	if (retval != SCTP_XMIT_OK)
287 		goto finish;
288 
289 	/* Try to bundle SACK chunk */
290 	retval = sctp_packet_bundle_sack(packet, chunk);
291 	if (retval != SCTP_XMIT_OK)
292 		goto finish;
293 
294 	/* Check to see if this chunk will fit into the packet */
295 	retval = sctp_packet_will_fit(packet, chunk, chunk_len);
296 	if (retval != SCTP_XMIT_OK)
297 		goto finish;
298 
299 	/* We believe that this chunk is OK to add to the packet */
300 	switch (chunk->chunk_hdr->type) {
301 	    case SCTP_CID_DATA:
302 		/* Account for the data being in the packet */
303 		sctp_packet_append_data(packet, chunk);
304 		/* Disallow SACK bundling after DATA. */
305 		packet->has_sack = 1;
306 		/* Disallow AUTH bundling after DATA */
307 		packet->has_auth = 1;
308 		/* Let it be knows that packet has DATA in it */
309 		packet->has_data = 1;
310 		/* timestamp the chunk for rtx purposes */
311 		chunk->sent_at = jiffies;
312 		break;
313 	    case SCTP_CID_COOKIE_ECHO:
314 		packet->has_cookie_echo = 1;
315 		break;
316 
317 	    case SCTP_CID_SACK:
318 		packet->has_sack = 1;
319 		break;
320 
321 	    case SCTP_CID_AUTH:
322 		packet->has_auth = 1;
323 		packet->auth = chunk;
324 		break;
325 	}
326 
327 	/* It is OK to send this chunk.  */
328 	list_add_tail(&chunk->list, &packet->chunk_list);
329 	packet->size += chunk_len;
330 	chunk->transport = packet->transport;
331 finish:
332 	return retval;
333 }
334 
335 /* All packets are sent to the network through this function from
336  * sctp_outq_tail().
337  *
338  * The return value is a normal kernel error return value.
339  */
340 int sctp_packet_transmit(struct sctp_packet *packet)
341 {
342 	struct sctp_transport *tp = packet->transport;
343 	struct sctp_association *asoc = tp->asoc;
344 	struct sctphdr *sh;
345 	struct sk_buff *nskb;
346 	struct sctp_chunk *chunk, *tmp;
347 	struct sock *sk;
348 	int err = 0;
349 	int padding;		/* How much padding do we need?  */
350 	__u8 has_data = 0;
351 	struct dst_entry *dst = tp->dst;
352 	unsigned char *auth = NULL;	/* pointer to auth in skb data */
353 	__u32 cksum_buf_len = sizeof(struct sctphdr);
354 
355 	SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
356 
357 	/* Do NOT generate a chunkless packet. */
358 	if (list_empty(&packet->chunk_list))
359 		return err;
360 
361 	/* Set up convenience variables... */
362 	chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
363 	sk = chunk->skb->sk;
364 
365 	/* Allocate the new skb.  */
366 	nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
367 	if (!nskb)
368 		goto nomem;
369 
370 	/* Make sure the outbound skb has enough header room reserved. */
371 	skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);
372 
373 	/* Set the owning socket so that we know where to get the
374 	 * destination IP address.
375 	 */
376 	skb_set_owner_w(nskb, sk);
377 
378 	/* The 'obsolete' field of dst is set to 2 when a dst is freed. */
379 	if (!dst || (dst->obsolete > 1)) {
380 		dst_release(dst);
381 		sctp_transport_route(tp, NULL, sctp_sk(sk));
382 		if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
383 			sctp_assoc_sync_pmtu(asoc);
384 		}
385 	}
386 	dst = dst_clone(tp->dst);
387 	skb_dst_set(nskb, dst);
388 	if (!dst)
389 		goto no_route;
390 
391 	/* Build the SCTP header.  */
392 	sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
393 	skb_reset_transport_header(nskb);
394 	sh->source = htons(packet->source_port);
395 	sh->dest   = htons(packet->destination_port);
396 
397 	/* From 6.8 Adler-32 Checksum Calculation:
398 	 * After the packet is constructed (containing the SCTP common
399 	 * header and one or more control or DATA chunks), the
400 	 * transmitter shall:
401 	 *
402 	 * 1) Fill in the proper Verification Tag in the SCTP common
403 	 *    header and initialize the checksum field to 0's.
404 	 */
405 	sh->vtag     = htonl(packet->vtag);
406 	sh->checksum = 0;
407 
408 	/**
409 	 * 6.10 Bundling
410 	 *
411 	 *    An endpoint bundles chunks by simply including multiple
412 	 *    chunks in one outbound SCTP packet.  ...
413 	 */
414 
415 	/**
416 	 * 3.2  Chunk Field Descriptions
417 	 *
418 	 * The total length of a chunk (including Type, Length and
419 	 * Value fields) MUST be a multiple of 4 bytes.  If the length
420 	 * of the chunk is not a multiple of 4 bytes, the sender MUST
421 	 * pad the chunk with all zero bytes and this padding is not
422 	 * included in the chunk length field.  The sender should
423 	 * never pad with more than 3 bytes.
424 	 *
425 	 * [This whole comment explains WORD_ROUND() below.]
426 	 */
427 	SCTP_DEBUG_PRINTK("***sctp_transmit_packet***\n");
428 	list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
429 		list_del_init(&chunk->list);
430 		if (sctp_chunk_is_data(chunk)) {
431 
432 			if (!chunk->resent) {
433 
434 				/* 6.3.1 C4) When data is in flight and when allowed
435 				 * by rule C5, a new RTT measurement MUST be made each
436 				 * round trip.  Furthermore, new RTT measurements
437 				 * SHOULD be made no more than once per round-trip
438 				 * for a given destination transport address.
439 				 */
440 
441 				if (!tp->rto_pending) {
442 					chunk->rtt_in_progress = 1;
443 					tp->rto_pending = 1;
444 				}
445 			}
446 
447 			chunk->resent = 1;
448 
449 			has_data = 1;
450 		}
451 
452 		padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
453 		if (padding)
454 			memset(skb_put(chunk->skb, padding), 0, padding);
455 
456 		/* if this is the auth chunk that we are adding,
457 		 * store pointer where it will be added and put
458 		 * the auth into the packet.
459 		 */
460 		if (chunk == packet->auth)
461 			auth = skb_tail_pointer(nskb);
462 
463 		cksum_buf_len += chunk->skb->len;
464 		memcpy(skb_put(nskb, chunk->skb->len),
465 			       chunk->skb->data, chunk->skb->len);
466 
467 		SCTP_DEBUG_PRINTK("%s %p[%s] %s 0x%x, %s %d, %s %d, %s %d\n",
468 				  "*** Chunk", chunk,
469 				  sctp_cname(SCTP_ST_CHUNK(
470 					  chunk->chunk_hdr->type)),
471 				  chunk->has_tsn ? "TSN" : "No TSN",
472 				  chunk->has_tsn ?
473 				  ntohl(chunk->subh.data_hdr->tsn) : 0,
474 				  "length", ntohs(chunk->chunk_hdr->length),
475 				  "chunk->skb->len", chunk->skb->len,
476 				  "rtt_in_progress", chunk->rtt_in_progress);
477 
478 		/*
479 		 * If this is a control chunk, this is our last
480 		 * reference. Free data chunks after they've been
481 		 * acknowledged or have failed.
482 		 */
483 		if (!sctp_chunk_is_data(chunk))
484 			sctp_chunk_free(chunk);
485 	}
486 
487 	/* SCTP-AUTH, Section 6.2
488 	 *    The sender MUST calculate the MAC as described in RFC2104 [2]
489 	 *    using the hash function H as described by the MAC Identifier and
490 	 *    the shared association key K based on the endpoint pair shared key
491 	 *    described by the shared key identifier.  The 'data' used for the
492 	 *    computation of the AUTH-chunk is given by the AUTH chunk with its
493 	 *    HMAC field set to zero (as shown in Figure 6) followed by all
494 	 *    chunks that are placed after the AUTH chunk in the SCTP packet.
495 	 */
496 	if (auth)
497 		sctp_auth_calculate_hmac(asoc, nskb,
498 					(struct sctp_auth_chunk *)auth,
499 					GFP_ATOMIC);
500 
501 	/* 2) Calculate the Adler-32 checksum of the whole packet,
502 	 *    including the SCTP common header and all the
503 	 *    chunks.
504 	 *
505 	 * Note: Adler-32 is no longer applicable, as has been replaced
506 	 * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
507 	 */
508 	if (!sctp_checksum_disable &&
509 	    !(dst->dev->features & (NETIF_F_NO_CSUM | NETIF_F_SCTP_CSUM))) {
510 		__u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
511 
512 		/* 3) Put the resultant value into the checksum field in the
513 		 *    common header, and leave the rest of the bits unchanged.
514 		 */
515 		sh->checksum = sctp_end_cksum(crc32);
516 	} else {
517 		if (dst->dev->features & NETIF_F_SCTP_CSUM) {
518 			/* no need to seed psuedo checksum for SCTP */
519 			nskb->ip_summed = CHECKSUM_PARTIAL;
520 			nskb->csum_start = (skb_transport_header(nskb) -
521 			                    nskb->head);
522 			nskb->csum_offset = offsetof(struct sctphdr, checksum);
523 		} else {
524 			nskb->ip_summed = CHECKSUM_UNNECESSARY;
525 		}
526 	}
527 
528 	/* IP layer ECN support
529 	 * From RFC 2481
530 	 *  "The ECN-Capable Transport (ECT) bit would be set by the
531 	 *   data sender to indicate that the end-points of the
532 	 *   transport protocol are ECN-capable."
533 	 *
534 	 * Now setting the ECT bit all the time, as it should not cause
535 	 * any problems protocol-wise even if our peer ignores it.
536 	 *
537 	 * Note: The works for IPv6 layer checks this bit too later
538 	 * in transmission.  See IP6_ECN_flow_xmit().
539 	 */
540 	(*tp->af_specific->ecn_capable)(nskb->sk);
541 
542 	/* Set up the IP options.  */
543 	/* BUG: not implemented
544 	 * For v4 this all lives somewhere in sk->sk_opt...
545 	 */
546 
547 	/* Dump that on IP!  */
548 	if (asoc && asoc->peer.last_sent_to != tp) {
549 		/* Considering the multiple CPU scenario, this is a
550 		 * "correcter" place for last_sent_to.  --xguo
551 		 */
552 		asoc->peer.last_sent_to = tp;
553 	}
554 
555 	if (has_data) {
556 		struct timer_list *timer;
557 		unsigned long timeout;
558 
559 		/* Restart the AUTOCLOSE timer when sending data. */
560 		if (sctp_state(asoc, ESTABLISHED) && asoc->autoclose) {
561 			timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
562 			timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
563 
564 			if (!mod_timer(timer, jiffies + timeout))
565 				sctp_association_hold(asoc);
566 		}
567 	}
568 
569 	SCTP_DEBUG_PRINTK("***sctp_transmit_packet*** skb len %d\n",
570 			  nskb->len);
571 
572 	nskb->local_df = packet->ipfragok;
573 	(*tp->af_specific->sctp_xmit)(nskb, tp);
574 
575 out:
576 	sctp_packet_reset(packet);
577 	return err;
578 no_route:
579 	kfree_skb(nskb);
580 	IP_INC_STATS_BH(&init_net, IPSTATS_MIB_OUTNOROUTES);
581 
582 	/* FIXME: Returning the 'err' will effect all the associations
583 	 * associated with a socket, although only one of the paths of the
584 	 * association is unreachable.
585 	 * The real failure of a transport or association can be passed on
586 	 * to the user via notifications. So setting this error may not be
587 	 * required.
588 	 */
589 	 /* err = -EHOSTUNREACH; */
590 err:
591 	/* Control chunks are unreliable so just drop them.  DATA chunks
592 	 * will get resent or dropped later.
593 	 */
594 
595 	list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
596 		list_del_init(&chunk->list);
597 		if (!sctp_chunk_is_data(chunk))
598 			sctp_chunk_free(chunk);
599 	}
600 	goto out;
601 nomem:
602 	err = -ENOMEM;
603 	goto err;
604 }
605 
606 /********************************************************************
607  * 2nd Level Abstractions
608  ********************************************************************/
609 
610 /* This private function check to see if a chunk can be added */
611 static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
612 					   struct sctp_chunk *chunk)
613 {
614 	sctp_xmit_t retval = SCTP_XMIT_OK;
615 	size_t datasize, rwnd, inflight, flight_size;
616 	struct sctp_transport *transport = packet->transport;
617 	struct sctp_association *asoc = transport->asoc;
618 	struct sctp_outq *q = &asoc->outqueue;
619 
620 	/* RFC 2960 6.1  Transmission of DATA Chunks
621 	 *
622 	 * A) At any given time, the data sender MUST NOT transmit new data to
623 	 * any destination transport address if its peer's rwnd indicates
624 	 * that the peer has no buffer space (i.e. rwnd is 0, see Section
625 	 * 6.2.1).  However, regardless of the value of rwnd (including if it
626 	 * is 0), the data sender can always have one DATA chunk in flight to
627 	 * the receiver if allowed by cwnd (see rule B below).  This rule
628 	 * allows the sender to probe for a change in rwnd that the sender
629 	 * missed due to the SACK having been lost in transit from the data
630 	 * receiver to the data sender.
631 	 */
632 
633 	rwnd = asoc->peer.rwnd;
634 	inflight = q->outstanding_bytes;
635 	flight_size = transport->flight_size;
636 
637 	datasize = sctp_data_size(chunk);
638 
639 	if (datasize > rwnd) {
640 		if (inflight > 0) {
641 			/* We have (at least) one data chunk in flight,
642 			 * so we can't fall back to rule 6.1 B).
643 			 */
644 			retval = SCTP_XMIT_RWND_FULL;
645 			goto finish;
646 		}
647 	}
648 
649 	/* RFC 2960 6.1  Transmission of DATA Chunks
650 	 *
651 	 * B) At any given time, the sender MUST NOT transmit new data
652 	 * to a given transport address if it has cwnd or more bytes
653 	 * of data outstanding to that transport address.
654 	 */
655 	/* RFC 7.2.4 & the Implementers Guide 2.8.
656 	 *
657 	 * 3) ...
658 	 *    When a Fast Retransmit is being performed the sender SHOULD
659 	 *    ignore the value of cwnd and SHOULD NOT delay retransmission.
660 	 */
661 	if (chunk->fast_retransmit != SCTP_NEED_FRTX)
662 		if (flight_size >= transport->cwnd) {
663 			retval = SCTP_XMIT_RWND_FULL;
664 			goto finish;
665 		}
666 
667 	/* Nagle's algorithm to solve small-packet problem:
668 	 * Inhibit the sending of new chunks when new outgoing data arrives
669 	 * if any previously transmitted data on the connection remains
670 	 * unacknowledged.
671 	 */
672 	if (!sctp_sk(asoc->base.sk)->nodelay && sctp_packet_empty(packet) &&
673 	    inflight && sctp_state(asoc, ESTABLISHED)) {
674 		unsigned max = transport->pathmtu - packet->overhead;
675 		unsigned len = chunk->skb->len + q->out_qlen;
676 
677 		/* Check whether this chunk and all the rest of pending
678 		 * data will fit or delay in hopes of bundling a full
679 		 * sized packet.
680 		 * Don't delay large message writes that may have been
681 		 * fragmeneted into small peices.
682 		 */
683 		if ((len < max) && (chunk->msg->msg_size < max)) {
684 			retval = SCTP_XMIT_NAGLE_DELAY;
685 			goto finish;
686 		}
687 	}
688 
689 finish:
690 	return retval;
691 }
692 
693 /* This private function does management things when adding DATA chunk */
694 static void sctp_packet_append_data(struct sctp_packet *packet,
695 				struct sctp_chunk *chunk)
696 {
697 	struct sctp_transport *transport = packet->transport;
698 	size_t datasize = sctp_data_size(chunk);
699 	struct sctp_association *asoc = transport->asoc;
700 	u32 rwnd = asoc->peer.rwnd;
701 
702 	/* Keep track of how many bytes are in flight over this transport. */
703 	transport->flight_size += datasize;
704 
705 	/* Keep track of how many bytes are in flight to the receiver. */
706 	asoc->outqueue.outstanding_bytes += datasize;
707 
708 	/* Update our view of the receiver's rwnd. Include sk_buff overhead
709 	 * while updating peer.rwnd so that it reduces the chances of a
710 	 * receiver running out of receive buffer space even when receive
711 	 * window is still open. This can happen when a sender is sending
712 	 * sending small messages.
713 	 */
714 	datasize += sizeof(struct sk_buff);
715 	if (datasize < rwnd)
716 		rwnd -= datasize;
717 	else
718 		rwnd = 0;
719 
720 	asoc->peer.rwnd = rwnd;
721 	/* Has been accepted for transmission. */
722 	if (!asoc->peer.prsctp_capable)
723 		chunk->msg->can_abandon = 0;
724 	sctp_chunk_assign_tsn(chunk);
725 	sctp_chunk_assign_ssn(chunk);
726 }
727 
728 static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
729 					struct sctp_chunk *chunk,
730 					u16 chunk_len)
731 {
732 	size_t psize;
733 	size_t pmtu;
734 	int too_big;
735 	sctp_xmit_t retval = SCTP_XMIT_OK;
736 
737 	psize = packet->size;
738 	pmtu  = ((packet->transport->asoc) ?
739 		(packet->transport->asoc->pathmtu) :
740 		(packet->transport->pathmtu));
741 
742 	too_big = (psize + chunk_len > pmtu);
743 
744 	/* Decide if we need to fragment or resubmit later. */
745 	if (too_big) {
746 		/* It's OK to fragmet at IP level if any one of the following
747 		 * is true:
748 		 * 	1. The packet is empty (meaning this chunk is greater
749 		 * 	   the MTU)
750 		 * 	2. The chunk we are adding is a control chunk
751 		 * 	3. The packet doesn't have any data in it yet and data
752 		 * 	requires authentication.
753 		 */
754 		if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
755 		    (!packet->has_data && chunk->auth)) {
756 			/* We no longer do re-fragmentation.
757 			 * Just fragment at the IP layer, if we
758 			 * actually hit this condition
759 			 */
760 			packet->ipfragok = 1;
761 		} else {
762 			retval = SCTP_XMIT_PMTU_FULL;
763 		}
764 	}
765 
766 	return retval;
767 }
768