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 | |
17 | struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority) |
18 | { |
19 | struct dccp_ackvec *av = kmem_cache_zalloc(k: dccp_ackvec_slab, flags: priority); |
20 | |
21 | if (av != NULL) { |
22 | av->av_buf_head = av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1; |
23 | INIT_LIST_HEAD(list: &av->av_records); |
24 | } |
25 | return av; |
26 | } |
27 | |
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(s: dccp_ackvec_record_slab, objp: cur); |
34 | INIT_LIST_HEAD(list: &av->av_records); |
35 | } |
36 | |
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(s: dccp_ackvec_slab, objp: 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 | */ |
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(cachep: 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(cell: 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(new: &avr->avr_node, head: &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 | |
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(seq1: ackno, seq2: 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 | */ |
107 | static inline u16 __ackvec_idx_add(const u16 a, const u16 b) |
108 | { |
109 | return (a + b) % DCCPAV_MAX_ACKVEC_LEN; |
110 | } |
111 | |
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 | |
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(a: av->av_buf_tail, b: 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 | */ |
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(cell: 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(a: ptr, b: 1); |
169 | |
170 | } while (ptr != av->av_buf_tail); |
171 | } |
172 | |
173 | /* Mark @num entries after buf_head as "Not yet received". */ |
174 | static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num) |
175 | { |
176 | u16 start = __ackvec_idx_add(a: av->av_buf_head, b: 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 | */ |
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(a: av->av_buf_head, b: 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(a: av->av_buf_head, b: 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: 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 | */ |
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, num_packets: 1, seqno, state); |
255 | av->av_tail_ackno = seqno; |
256 | |
257 | } else { |
258 | s64 num_packets = dccp_delta_seqno(seqno1: av->av_buf_ackno, seqno2: seqno); |
259 | u8 *current_head = av->av_buf + av->av_buf_head; |
260 | |
261 | if (num_packets == 1 && |
262 | dccp_ackvec_state(cell: current_head) == state && |
263 | dccp_ackvec_runlen(cell: 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, distance: 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 | */ |
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_list: &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(seqno1: av->av_tail_ackno, seqno2: 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(cell: 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(a: avr->avr_ack_ptr, b: 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(entry: &avr->avr_node); |
345 | kmem_cache_free(s: dccp_ackvec_record_slab, objp: avr); |
346 | } |
347 | } |
348 | |
349 | /* |
350 | * Routines to keep track of Ack Vectors received in an skb |
351 | */ |
352 | int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce) |
353 | { |
354 | struct dccp_ackvec_parsed *new = kmalloc(size: 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: &new->node, head); |
363 | return 0; |
364 | } |
365 | EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add); |
366 | |
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(objp: cur); |
373 | INIT_LIST_HEAD(list: parsed_chunks); |
374 | } |
375 | EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup); |
376 | |
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(s: 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 | |
397 | void dccp_ackvec_exit(void) |
398 | { |
399 | kmem_cache_destroy(s: dccp_ackvec_slab); |
400 | dccp_ackvec_slab = NULL; |
401 | kmem_cache_destroy(s: dccp_ackvec_record_slab); |
402 | dccp_ackvec_record_slab = NULL; |
403 | } |
404 | |