linux/net/dccp/ackvec.c
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   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_create("dccp_ackvec",
 380                                             sizeof(struct dccp_ackvec), 0,
 381                                             SLAB_HWCACHE_ALIGN, NULL);
 382        if (dccp_ackvec_slab == NULL)
 383                goto out_err;
 384
 385        dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
 386                                             sizeof(struct dccp_ackvec_record),
 387                                             0, SLAB_HWCACHE_ALIGN, NULL);
 388        if (dccp_ackvec_record_slab == NULL)
 389                goto out_destroy_slab;
 390
 391        return 0;
 392
 393out_destroy_slab:
 394        kmem_cache_destroy(dccp_ackvec_slab);
 395        dccp_ackvec_slab = NULL;
 396out_err:
 397        DCCP_CRIT("Unable to create Ack Vector slab cache");
 398        return -ENOBUFS;
 399}
 400
 401void dccp_ackvec_exit(void)
 402{
 403        kmem_cache_destroy(dccp_ackvec_slab);
 404        dccp_ackvec_slab = NULL;
 405        kmem_cache_destroy(dccp_ackvec_record_slab);
 406        dccp_ackvec_record_slab = NULL;
 407}
 408