1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 *  net/dccp/ackvec.c
4 *
5 *  An implementation of Ack Vectors for the DCCP protocol
6 *  Copyright (c) 2007 University of Aberdeen, Scotland, UK
7 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
8 */
9#include "dccp.h"
10#include <linux/kernel.h>
11#include <linux/slab.h>
12#include <linux/export.h>
13
14static struct kmem_cache *dccp_ackvec_slab;
15static struct kmem_cache *dccp_ackvec_record_slab;
16
17struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
18{
19	struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);
20
21	if (av != NULL) {
22		av->av_buf_head	= av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
23		INIT_LIST_HEAD(&av->av_records);
24	}
25	return av;
26}
27
28static void dccp_ackvec_purge_records(struct dccp_ackvec *av)
29{
30	struct dccp_ackvec_record *cur, *next;
31
32	list_for_each_entry_safe(cur, next, &av->av_records, avr_node)
33		kmem_cache_free(dccp_ackvec_record_slab, cur);
34	INIT_LIST_HEAD(&av->av_records);
35}
36
37void dccp_ackvec_free(struct dccp_ackvec *av)
38{
39	if (likely(av != NULL)) {
40		dccp_ackvec_purge_records(av);
41		kmem_cache_free(dccp_ackvec_slab, av);
42	}
43}
44
45/**
46 * dccp_ackvec_update_records  -  Record information about sent Ack Vectors
47 * @av:		Ack Vector records to update
48 * @seqno:	Sequence number of the packet carrying the Ack Vector just sent
49 * @nonce_sum:	The sum of all buffer nonces contained in the Ack Vector
50 */
51int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
52{
53	struct dccp_ackvec_record *avr;
54
55	avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);
56	if (avr == NULL)
57		return -ENOBUFS;
58
59	avr->avr_ack_seqno  = seqno;
60	avr->avr_ack_ptr    = av->av_buf_head;
61	avr->avr_ack_ackno  = av->av_buf_ackno;
62	avr->avr_ack_nonce  = nonce_sum;
63	avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
64	/*
65	 * When the buffer overflows, we keep no more than one record. This is
66	 * the simplest way of disambiguating sender-Acks dating from before the
67	 * overflow from sender-Acks which refer to after the overflow; a simple
68	 * solution is preferable here since we are handling an exception.
69	 */
70	if (av->av_overflow)
71		dccp_ackvec_purge_records(av);
72	/*
73	 * Since GSS is incremented for each packet, the list is automatically
74	 * arranged in descending order of @ack_seqno.
75	 */
76	list_add(&avr->avr_node, &av->av_records);
77
78	dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)\n",
79		      (unsigned long long)avr->avr_ack_seqno,
80		      (unsigned long long)avr->avr_ack_ackno,
81		      avr->avr_ack_runlen);
82	return 0;
83}
84
85static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list,
86						     const u64 ackno)
87{
88	struct dccp_ackvec_record *avr;
89	/*
90	 * Exploit that records are inserted in descending order of sequence
91	 * number, start with the oldest record first. If @ackno is `before'
92	 * the earliest ack_ackno, the packet is too old to be considered.
93	 */
94	list_for_each_entry_reverse(avr, av_list, avr_node) {
95		if (avr->avr_ack_seqno == ackno)
96			return avr;
97		if (before48(ackno, avr->avr_ack_seqno))
98			break;
99	}
100	return NULL;
101}
102
103/*
104 * Buffer index and length computation using modulo-buffersize arithmetic.
105 * Note that, as pointers move from right to left, head is `before' tail.
106 */
107static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
108{
109	return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
110}
111
112static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
113{
114	return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
115}
116
117u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
118{
119	if (unlikely(av->av_overflow))
120		return DCCPAV_MAX_ACKVEC_LEN;
121	return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
122}
123
124/**
125 * dccp_ackvec_update_old  -  Update previous state as per RFC 4340, 11.4.1
126 * @av:		non-empty buffer to update
127 * @distance:   negative or zero distance of @seqno from buf_ackno downward
128 * @seqno:	the (old) sequence number whose record is to be updated
129 * @state:	state in which packet carrying @seqno was received
130 */
131static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
132				   u64 seqno, enum dccp_ackvec_states state)
133{
134	u16 ptr = av->av_buf_head;
135
136	BUG_ON(distance > 0);
137	if (unlikely(dccp_ackvec_is_empty(av)))
138		return;
139
140	do {
141		u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);
142
143		if (distance + runlen >= 0) {
144			/*
145			 * Only update the state if packet has not been received
146			 * yet. This is OK as per the second table in RFC 4340,
147			 * 11.4.1; i.e. here we are using the following table:
148			 *                     RECEIVED
149			 *                      0   1   3
150			 *              S     +---+---+---+
151			 *              T   0 | 0 | 0 | 0 |
152			 *              O     +---+---+---+
153			 *              R   1 | 1 | 1 | 1 |
154			 *              E     +---+---+---+
155			 *              D   3 | 0 | 1 | 3 |
156			 *                    +---+---+---+
157			 * The "Not Received" state was set by reserve_seats().
158			 */
159			if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
160				av->av_buf[ptr] = state;
161			else
162				dccp_pr_debug("Not changing %llu state to %u\n",
163					      (unsigned long long)seqno, state);
164			break;
165		}
166
167		distance += runlen + 1;
168		ptr	  = __ackvec_idx_add(ptr, 1);
169
170	} while (ptr != av->av_buf_tail);
171}
172
173/* Mark @num entries after buf_head as "Not yet received". */
174static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
175{
176	u16 start = __ackvec_idx_add(av->av_buf_head, 1),
177	    len	  = DCCPAV_MAX_ACKVEC_LEN - start;
178
179	/* check for buffer wrap-around */
180	if (num > len) {
181		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
182		start = 0;
183		num  -= len;
184	}
185	if (num)
186		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
187}
188
189/**
190 * dccp_ackvec_add_new  -  Record one or more new entries in Ack Vector buffer
191 * @av:		 container of buffer to update (can be empty or non-empty)
192 * @num_packets: number of packets to register (must be >= 1)
193 * @seqno:	 sequence number of the first packet in @num_packets
194 * @state:	 state in which packet carrying @seqno was received
195 */
196static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets,
197				u64 seqno, enum dccp_ackvec_states state)
198{
199	u32 num_cells = num_packets;
200
201	if (num_packets > DCCPAV_BURST_THRESH) {
202		u32 lost_packets = num_packets - 1;
203
204		DCCP_WARN("Warning: large burst loss (%u)\n", lost_packets);
205		/*
206		 * We received 1 packet and have a loss of size "num_packets-1"
207		 * which we squeeze into num_cells-1 rather than reserving an
208		 * entire byte for each lost packet.
209		 * The reason is that the vector grows in O(burst_length); when
210		 * it grows too large there will no room left for the payload.
211		 * This is a trade-off: if a few packets out of the burst show
212		 * up later, their state will not be changed; it is simply too
213		 * costly to reshuffle/reallocate/copy the buffer each time.
214		 * Should such problems persist, we will need to switch to a
215		 * different underlying data structure.
216		 */
217		for (num_packets = num_cells = 1; lost_packets; ++num_cells) {
218			u8 len = min_t(u32, lost_packets, DCCPAV_MAX_RUNLEN);
219
220			av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1);
221			av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len;
222
223			lost_packets -= len;
224		}
225	}
226
227	if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) {
228		DCCP_CRIT("Ack Vector buffer overflow: dropping old entries");
229		av->av_overflow = true;
230	}
231
232	av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets);
233	if (av->av_overflow)
234		av->av_buf_tail = av->av_buf_head;
235
236	av->av_buf[av->av_buf_head] = state;
237	av->av_buf_ackno	    = seqno;
238
239	if (num_packets > 1)
240		dccp_ackvec_reserve_seats(av, num_packets - 1);
241}
242
243/**
244 * dccp_ackvec_input  -  Register incoming packet in the buffer
245 * @av: Ack Vector to register packet to
246 * @skb: Packet to register
247 */
248void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb)
249{
250	u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq;
251	enum dccp_ackvec_states state = DCCPAV_RECEIVED;
252
253	if (dccp_ackvec_is_empty(av)) {
254		dccp_ackvec_add_new(av, 1, seqno, state);
255		av->av_tail_ackno = seqno;
256
257	} else {
258		s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
259		u8 *current_head = av->av_buf + av->av_buf_head;
260
261		if (num_packets == 1 &&
262		    dccp_ackvec_state(current_head) == state &&
263		    dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {
264
265			*current_head   += 1;
266			av->av_buf_ackno = seqno;
267
268		} else if (num_packets > 0) {
269			dccp_ackvec_add_new(av, num_packets, seqno, state);
270		} else {
271			dccp_ackvec_update_old(av, num_packets, seqno, state);
272		}
273	}
274}
275
276/**
277 * dccp_ackvec_clear_state  -  Perform house-keeping / garbage-collection
278 * @av: Ack Vector record to clean
279 * @ackno: last Ack Vector which has been acknowledged
280 *
281 * This routine is called when the peer acknowledges the receipt of Ack Vectors
282 * up to and including @ackno. While based on section A.3 of RFC 4340, here
283 * are additional precautions to prevent corrupted buffer state. In particular,
284 * we use tail_ackno to identify outdated records; it always marks the earliest
285 * packet of group (2) in 11.4.2.
286 */
287void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno)
288{
289	struct dccp_ackvec_record *avr, *next;
290	u8 runlen_now, eff_runlen;
291	s64 delta;
292
293	avr = dccp_ackvec_lookup(&av->av_records, ackno);
294	if (avr == NULL)
295		return;
296	/*
297	 * Deal with outdated acknowledgments: this arises when e.g. there are
298	 * several old records and the acks from the peer come in slowly. In
299	 * that case we may still have records that pre-date tail_ackno.
300	 */
301	delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno);
302	if (delta < 0)
303		goto free_records;
304	/*
305	 * Deal with overlapping Ack Vectors: don't subtract more than the
306	 * number of packets between tail_ackno and ack_ackno.
307	 */
308	eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen;
309
310	runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr);
311	/*
312	 * The run length of Ack Vector cells does not decrease over time. If
313	 * the run length is the same as at the time the Ack Vector was sent, we
314	 * free the ack_ptr cell. That cell can however not be freed if the run
315	 * length has increased: in this case we need to move the tail pointer
316	 * backwards (towards higher indices), to its next-oldest neighbour.
317	 */
318	if (runlen_now > eff_runlen) {
319
320		av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1;
321		av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1);
322
323		/* This move may not have cleared the overflow flag. */
324		if (av->av_overflow)
325			av->av_overflow = (av->av_buf_head == av->av_buf_tail);
326	} else {
327		av->av_buf_tail	= avr->avr_ack_ptr;
328		/*
329		 * We have made sure that avr points to a valid cell within the
330		 * buffer. This cell is either older than head, or equals head
331		 * (empty buffer): in both cases we no longer have any overflow.
332		 */
333		av->av_overflow	= 0;
334	}
335
336	/*
337	 * The peer has acknowledged up to and including ack_ackno. Hence the
338	 * first packet in group (2) of 11.4.2 is the successor of ack_ackno.
339	 */
340	av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1);
341
342free_records:
343	list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
344		list_del(&avr->avr_node);
345		kmem_cache_free(dccp_ackvec_record_slab, avr);
346	}
347}
348
349/*
350 *	Routines to keep track of Ack Vectors received in an skb
351 */
352int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce)
353{
354	struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC);
355
356	if (new == NULL)
357		return -ENOBUFS;
358	new->vec   = vec;
359	new->len   = len;
360	new->nonce = nonce;
361
362	list_add_tail(&new->node, head);
363	return 0;
364}
365EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);
366
367void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks)
368{
369	struct dccp_ackvec_parsed *cur, *next;
370
371	list_for_each_entry_safe(cur, next, parsed_chunks, node)
372		kfree(cur);
373	INIT_LIST_HEAD(parsed_chunks);
374}
375EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);
376
377int __init dccp_ackvec_init(void)
378{
379	dccp_ackvec_slab = KMEM_CACHE(dccp_ackvec, SLAB_HWCACHE_ALIGN);
380	if (dccp_ackvec_slab == NULL)
381		goto out_err;
382
383	dccp_ackvec_record_slab = KMEM_CACHE(dccp_ackvec_record, SLAB_HWCACHE_ALIGN);
384	if (dccp_ackvec_record_slab == NULL)
385		goto out_destroy_slab;
386
387	return 0;
388
389out_destroy_slab:
390	kmem_cache_destroy(dccp_ackvec_slab);
391	dccp_ackvec_slab = NULL;
392out_err:
393	DCCP_CRIT("Unable to create Ack Vector slab cache");
394	return -ENOBUFS;
395}
396
397void dccp_ackvec_exit(void)
398{
399	kmem_cache_destroy(dccp_ackvec_slab);
400	dccp_ackvec_slab = NULL;
401	kmem_cache_destroy(dccp_ackvec_record_slab);
402	dccp_ackvec_record_slab = NULL;
403}
404