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(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 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 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 */ 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 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 */ 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(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 */ 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". */ 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 */ 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 */ 246 void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb) 247 { 248 u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq; 249 enum dccp_ackvec_states state = DCCPAV_RECEIVED; 250 251 if (dccp_ackvec_is_empty(av)) { 252 dccp_ackvec_add_new(av, 1, seqno, state); 253 av->av_tail_ackno = seqno; 254 255 } else { 256 s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno); 257 u8 *current_head = av->av_buf + av->av_buf_head; 258 259 if (num_packets == 1 && 260 dccp_ackvec_state(current_head) == state && 261 dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) { 262 263 *current_head += 1; 264 av->av_buf_ackno = seqno; 265 266 } else if (num_packets > 0) { 267 dccp_ackvec_add_new(av, num_packets, seqno, state); 268 } else { 269 dccp_ackvec_update_old(av, num_packets, seqno, state); 270 } 271 } 272 } 273 274 /** 275 * dccp_ackvec_clear_state - Perform house-keeping / garbage-collection 276 * This routine is called when the peer acknowledges the receipt of Ack Vectors 277 * up to and including @ackno. While based on section A.3 of RFC 4340, here 278 * are additional precautions to prevent corrupted buffer state. In particular, 279 * we use tail_ackno to identify outdated records; it always marks the earliest 280 * packet of group (2) in 11.4.2. 281 */ 282 void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno) 283 { 284 struct dccp_ackvec_record *avr, *next; 285 u8 runlen_now, eff_runlen; 286 s64 delta; 287 288 avr = dccp_ackvec_lookup(&av->av_records, ackno); 289 if (avr == NULL) 290 return; 291 /* 292 * Deal with outdated acknowledgments: this arises when e.g. there are 293 * several old records and the acks from the peer come in slowly. In 294 * that case we may still have records that pre-date tail_ackno. 295 */ 296 delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno); 297 if (delta < 0) 298 goto free_records; 299 /* 300 * Deal with overlapping Ack Vectors: don't subtract more than the 301 * number of packets between tail_ackno and ack_ackno. 302 */ 303 eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen; 304 305 runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr); 306 /* 307 * The run length of Ack Vector cells does not decrease over time. If 308 * the run length is the same as at the time the Ack Vector was sent, we 309 * free the ack_ptr cell. That cell can however not be freed if the run 310 * length has increased: in this case we need to move the tail pointer 311 * backwards (towards higher indices), to its next-oldest neighbour. 312 */ 313 if (runlen_now > eff_runlen) { 314 315 av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1; 316 av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1); 317 318 /* This move may not have cleared the overflow flag. */ 319 if (av->av_overflow) 320 av->av_overflow = (av->av_buf_head == av->av_buf_tail); 321 } else { 322 av->av_buf_tail = avr->avr_ack_ptr; 323 /* 324 * We have made sure that avr points to a valid cell within the 325 * buffer. This cell is either older than head, or equals head 326 * (empty buffer): in both cases we no longer have any overflow. 327 */ 328 av->av_overflow = 0; 329 } 330 331 /* 332 * The peer has acknowledged up to and including ack_ackno. Hence the 333 * first packet in group (2) of 11.4.2 is the successor of ack_ackno. 334 */ 335 av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1); 336 337 free_records: 338 list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) { 339 list_del(&avr->avr_node); 340 kmem_cache_free(dccp_ackvec_record_slab, avr); 341 } 342 } 343 344 /* 345 * Routines to keep track of Ack Vectors received in an skb 346 */ 347 int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce) 348 { 349 struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC); 350 351 if (new == NULL) 352 return -ENOBUFS; 353 new->vec = vec; 354 new->len = len; 355 new->nonce = nonce; 356 357 list_add_tail(&new->node, head); 358 return 0; 359 } 360 EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add); 361 362 void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks) 363 { 364 struct dccp_ackvec_parsed *cur, *next; 365 366 list_for_each_entry_safe(cur, next, parsed_chunks, node) 367 kfree(cur); 368 INIT_LIST_HEAD(parsed_chunks); 369 } 370 EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup); 371 372 int __init dccp_ackvec_init(void) 373 { 374 dccp_ackvec_slab = kmem_cache_create("dccp_ackvec", 375 sizeof(struct dccp_ackvec), 0, 376 SLAB_HWCACHE_ALIGN, NULL); 377 if (dccp_ackvec_slab == NULL) 378 goto out_err; 379 380 dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record", 381 sizeof(struct dccp_ackvec_record), 382 0, SLAB_HWCACHE_ALIGN, NULL); 383 if (dccp_ackvec_record_slab == NULL) 384 goto out_destroy_slab; 385 386 return 0; 387 388 out_destroy_slab: 389 kmem_cache_destroy(dccp_ackvec_slab); 390 dccp_ackvec_slab = NULL; 391 out_err: 392 DCCP_CRIT("Unable to create Ack Vector slab cache"); 393 return -ENOBUFS; 394 } 395 396 void dccp_ackvec_exit(void) 397 { 398 kmem_cache_destroy(dccp_ackvec_slab); 399 dccp_ackvec_slab = NULL; 400 kmem_cache_destroy(dccp_ackvec_record_slab); 401 dccp_ackvec_record_slab = NULL; 402 } 403