xref: /linux/net/dccp/ackvec.c (revision 79790b6818e96c58fe2bffee1b418c16e64e7b80)
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 
14 static struct kmem_cache *dccp_ackvec_slab;
15 static struct kmem_cache *dccp_ackvec_record_slab;
16 
dccp_ackvec_alloc(const gfp_t priority)17 struct 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 
dccp_ackvec_purge_records(struct dccp_ackvec * av)28 static 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 
dccp_ackvec_free(struct dccp_ackvec * av)37 void 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  */
dccp_ackvec_update_records(struct dccp_ackvec * av,u64 seqno,u8 nonce_sum)51 int 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 
dccp_ackvec_lookup(struct list_head * av_list,const u64 ackno)85 static 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  */
__ackvec_idx_add(const u16 a,const u16 b)107 static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
108 {
109 	return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
110 }
111 
__ackvec_idx_sub(const u16 a,const u16 b)112 static 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 
dccp_ackvec_buflen(const struct dccp_ackvec * av)117 u16 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  */
dccp_ackvec_update_old(struct dccp_ackvec * av,s64 distance,u64 seqno,enum dccp_ackvec_states state)131 static 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". */
dccp_ackvec_reserve_seats(struct dccp_ackvec * av,u16 num)174 static 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  */
dccp_ackvec_add_new(struct dccp_ackvec * av,u32 num_packets,u64 seqno,enum dccp_ackvec_states state)196 static 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  */
dccp_ackvec_input(struct dccp_ackvec * av,struct sk_buff * skb)248 void 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  */
dccp_ackvec_clear_state(struct dccp_ackvec * av,const u64 ackno)287 void 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 
342 free_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  */
dccp_ackvec_parsed_add(struct list_head * head,u8 * vec,u8 len,u8 nonce)352 int 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 }
365 EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);
366 
dccp_ackvec_parsed_cleanup(struct list_head * parsed_chunks)367 void 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 }
375 EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);
376 
dccp_ackvec_init(void)377 int __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 
389 out_destroy_slab:
390 	kmem_cache_destroy(dccp_ackvec_slab);
391 	dccp_ackvec_slab = NULL;
392 out_err:
393 	DCCP_CRIT("Unable to create Ack Vector slab cache");
394 	return -ENOBUFS;
395 }
396 
dccp_ackvec_exit(void)397 void 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