linux/net/batman-adv/fragmentation.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/* Copyright (C) 2013-2020  B.A.T.M.A.N. contributors:
   3 *
   4 * Martin Hundebøll <martin@hundeboll.net>
   5 */
   6
   7#include "fragmentation.h"
   8#include "main.h"
   9
  10#include <linux/atomic.h>
  11#include <linux/byteorder/generic.h>
  12#include <linux/errno.h>
  13#include <linux/etherdevice.h>
  14#include <linux/gfp.h>
  15#include <linux/if_ether.h>
  16#include <linux/jiffies.h>
  17#include <linux/lockdep.h>
  18#include <linux/minmax.h>
  19#include <linux/netdevice.h>
  20#include <linux/skbuff.h>
  21#include <linux/slab.h>
  22#include <linux/spinlock.h>
  23#include <linux/string.h>
  24#include <uapi/linux/batadv_packet.h>
  25
  26#include "hard-interface.h"
  27#include "originator.h"
  28#include "routing.h"
  29#include "send.h"
  30
  31/**
  32 * batadv_frag_clear_chain() - delete entries in the fragment buffer chain
  33 * @head: head of chain with entries.
  34 * @dropped: whether the chain is cleared because all fragments are dropped
  35 *
  36 * Free fragments in the passed hlist. Should be called with appropriate lock.
  37 */
  38static void batadv_frag_clear_chain(struct hlist_head *head, bool dropped)
  39{
  40        struct batadv_frag_list_entry *entry;
  41        struct hlist_node *node;
  42
  43        hlist_for_each_entry_safe(entry, node, head, list) {
  44                hlist_del(&entry->list);
  45
  46                if (dropped)
  47                        kfree_skb(entry->skb);
  48                else
  49                        consume_skb(entry->skb);
  50
  51                kfree(entry);
  52        }
  53}
  54
  55/**
  56 * batadv_frag_purge_orig() - free fragments associated to an orig
  57 * @orig_node: originator to free fragments from
  58 * @check_cb: optional function to tell if an entry should be purged
  59 */
  60void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
  61                            bool (*check_cb)(struct batadv_frag_table_entry *))
  62{
  63        struct batadv_frag_table_entry *chain;
  64        u8 i;
  65
  66        for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
  67                chain = &orig_node->fragments[i];
  68                spin_lock_bh(&chain->lock);
  69
  70                if (!check_cb || check_cb(chain)) {
  71                        batadv_frag_clear_chain(&chain->fragment_list, true);
  72                        chain->size = 0;
  73                }
  74
  75                spin_unlock_bh(&chain->lock);
  76        }
  77}
  78
  79/**
  80 * batadv_frag_size_limit() - maximum possible size of packet to be fragmented
  81 *
  82 * Return: the maximum size of payload that can be fragmented.
  83 */
  84static int batadv_frag_size_limit(void)
  85{
  86        int limit = BATADV_FRAG_MAX_FRAG_SIZE;
  87
  88        limit -= sizeof(struct batadv_frag_packet);
  89        limit *= BATADV_FRAG_MAX_FRAGMENTS;
  90
  91        return limit;
  92}
  93
  94/**
  95 * batadv_frag_init_chain() - check and prepare fragment chain for new fragment
  96 * @chain: chain in fragments table to init
  97 * @seqno: sequence number of the received fragment
  98 *
  99 * Make chain ready for a fragment with sequence number "seqno". Delete existing
 100 * entries if they have an "old" sequence number.
 101 *
 102 * Caller must hold chain->lock.
 103 *
 104 * Return: true if chain is empty and the caller can just insert the new
 105 * fragment without searching for the right position.
 106 */
 107static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,
 108                                   u16 seqno)
 109{
 110        lockdep_assert_held(&chain->lock);
 111
 112        if (chain->seqno == seqno)
 113                return false;
 114
 115        if (!hlist_empty(&chain->fragment_list))
 116                batadv_frag_clear_chain(&chain->fragment_list, true);
 117
 118        chain->size = 0;
 119        chain->seqno = seqno;
 120
 121        return true;
 122}
 123
 124/**
 125 * batadv_frag_insert_packet() - insert a fragment into a fragment chain
 126 * @orig_node: originator that the fragment was received from
 127 * @skb: skb to insert
 128 * @chain_out: list head to attach complete chains of fragments to
 129 *
 130 * Insert a new fragment into the reverse ordered chain in the right table
 131 * entry. The hash table entry is cleared if "old" fragments exist in it.
 132 *
 133 * Return: true if skb is buffered, false on error. If the chain has all the
 134 * fragments needed to merge the packet, the chain is moved to the passed head
 135 * to avoid locking the chain in the table.
 136 */
 137static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
 138                                      struct sk_buff *skb,
 139                                      struct hlist_head *chain_out)
 140{
 141        struct batadv_frag_table_entry *chain;
 142        struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;
 143        struct batadv_frag_list_entry *frag_entry_last = NULL;
 144        struct batadv_frag_packet *frag_packet;
 145        u8 bucket;
 146        u16 seqno, hdr_size = sizeof(struct batadv_frag_packet);
 147        bool ret = false;
 148
 149        /* Linearize packet to avoid linearizing 16 packets in a row when doing
 150         * the later merge. Non-linear merge should be added to remove this
 151         * linearization.
 152         */
 153        if (skb_linearize(skb) < 0)
 154                goto err;
 155
 156        frag_packet = (struct batadv_frag_packet *)skb->data;
 157        seqno = ntohs(frag_packet->seqno);
 158        bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
 159
 160        frag_entry_new = kmalloc(sizeof(*frag_entry_new), GFP_ATOMIC);
 161        if (!frag_entry_new)
 162                goto err;
 163
 164        frag_entry_new->skb = skb;
 165        frag_entry_new->no = frag_packet->no;
 166
 167        /* Select entry in the "chain table" and delete any prior fragments
 168         * with another sequence number. batadv_frag_init_chain() returns true,
 169         * if the list is empty at return.
 170         */
 171        chain = &orig_node->fragments[bucket];
 172        spin_lock_bh(&chain->lock);
 173        if (batadv_frag_init_chain(chain, seqno)) {
 174                hlist_add_head(&frag_entry_new->list, &chain->fragment_list);
 175                chain->size = skb->len - hdr_size;
 176                chain->timestamp = jiffies;
 177                chain->total_size = ntohs(frag_packet->total_size);
 178                ret = true;
 179                goto out;
 180        }
 181
 182        /* Find the position for the new fragment. */
 183        hlist_for_each_entry(frag_entry_curr, &chain->fragment_list, list) {
 184                /* Drop packet if fragment already exists. */
 185                if (frag_entry_curr->no == frag_entry_new->no)
 186                        goto err_unlock;
 187
 188                /* Order fragments from highest to lowest. */
 189                if (frag_entry_curr->no < frag_entry_new->no) {
 190                        hlist_add_before(&frag_entry_new->list,
 191                                         &frag_entry_curr->list);
 192                        chain->size += skb->len - hdr_size;
 193                        chain->timestamp = jiffies;
 194                        ret = true;
 195                        goto out;
 196                }
 197
 198                /* store current entry because it could be the last in list */
 199                frag_entry_last = frag_entry_curr;
 200        }
 201
 202        /* Reached the end of the list, so insert after 'frag_entry_last'. */
 203        if (likely(frag_entry_last)) {
 204                hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
 205                chain->size += skb->len - hdr_size;
 206                chain->timestamp = jiffies;
 207                ret = true;
 208        }
 209
 210out:
 211        if (chain->size > batadv_frag_size_limit() ||
 212            chain->total_size != ntohs(frag_packet->total_size) ||
 213            chain->total_size > batadv_frag_size_limit()) {
 214                /* Clear chain if total size of either the list or the packet
 215                 * exceeds the maximum size of one merged packet. Don't allow
 216                 * packets to have different total_size.
 217                 */
 218                batadv_frag_clear_chain(&chain->fragment_list, true);
 219                chain->size = 0;
 220        } else if (ntohs(frag_packet->total_size) == chain->size) {
 221                /* All fragments received. Hand over chain to caller. */
 222                hlist_move_list(&chain->fragment_list, chain_out);
 223                chain->size = 0;
 224        }
 225
 226err_unlock:
 227        spin_unlock_bh(&chain->lock);
 228
 229err:
 230        if (!ret) {
 231                kfree(frag_entry_new);
 232                kfree_skb(skb);
 233        }
 234
 235        return ret;
 236}
 237
 238/**
 239 * batadv_frag_merge_packets() - merge a chain of fragments
 240 * @chain: head of chain with fragments
 241 *
 242 * Expand the first skb in the chain and copy the content of the remaining
 243 * skb's into the expanded one. After doing so, clear the chain.
 244 *
 245 * Return: the merged skb or NULL on error.
 246 */
 247static struct sk_buff *
 248batadv_frag_merge_packets(struct hlist_head *chain)
 249{
 250        struct batadv_frag_packet *packet;
 251        struct batadv_frag_list_entry *entry;
 252        struct sk_buff *skb_out;
 253        int size, hdr_size = sizeof(struct batadv_frag_packet);
 254        bool dropped = false;
 255
 256        /* Remove first entry, as this is the destination for the rest of the
 257         * fragments.
 258         */
 259        entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
 260        hlist_del(&entry->list);
 261        skb_out = entry->skb;
 262        kfree(entry);
 263
 264        packet = (struct batadv_frag_packet *)skb_out->data;
 265        size = ntohs(packet->total_size) + hdr_size;
 266
 267        /* Make room for the rest of the fragments. */
 268        if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
 269                kfree_skb(skb_out);
 270                skb_out = NULL;
 271                dropped = true;
 272                goto free;
 273        }
 274
 275        /* Move the existing MAC header to just before the payload. (Override
 276         * the fragment header.)
 277         */
 278        skb_pull(skb_out, hdr_size);
 279        skb_out->ip_summed = CHECKSUM_NONE;
 280        memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
 281        skb_set_mac_header(skb_out, -ETH_HLEN);
 282        skb_reset_network_header(skb_out);
 283        skb_reset_transport_header(skb_out);
 284
 285        /* Copy the payload of the each fragment into the last skb */
 286        hlist_for_each_entry(entry, chain, list) {
 287                size = entry->skb->len - hdr_size;
 288                skb_put_data(skb_out, entry->skb->data + hdr_size, size);
 289        }
 290
 291free:
 292        /* Locking is not needed, because 'chain' is not part of any orig. */
 293        batadv_frag_clear_chain(chain, dropped);
 294        return skb_out;
 295}
 296
 297/**
 298 * batadv_frag_skb_buffer() - buffer fragment for later merge
 299 * @skb: skb to buffer
 300 * @orig_node_src: originator that the skb is received from
 301 *
 302 * Add fragment to buffer and merge fragments if possible.
 303 *
 304 * There are three possible outcomes: 1) Packet is merged: Return true and
 305 * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
 306 * to NULL; 3) Error: Return false and free skb.
 307 *
 308 * Return: true when the packet is merged or buffered, false when skb is not
 309 * used.
 310 */
 311bool batadv_frag_skb_buffer(struct sk_buff **skb,
 312                            struct batadv_orig_node *orig_node_src)
 313{
 314        struct sk_buff *skb_out = NULL;
 315        struct hlist_head head = HLIST_HEAD_INIT;
 316        bool ret = false;
 317
 318        /* Add packet to buffer and table entry if merge is possible. */
 319        if (!batadv_frag_insert_packet(orig_node_src, *skb, &head))
 320                goto out_err;
 321
 322        /* Leave if more fragments are needed to merge. */
 323        if (hlist_empty(&head))
 324                goto out;
 325
 326        skb_out = batadv_frag_merge_packets(&head);
 327        if (!skb_out)
 328                goto out_err;
 329
 330out:
 331        ret = true;
 332out_err:
 333        *skb = skb_out;
 334        return ret;
 335}
 336
 337/**
 338 * batadv_frag_skb_fwd() - forward fragments that would exceed MTU when merged
 339 * @skb: skb to forward
 340 * @recv_if: interface that the skb is received on
 341 * @orig_node_src: originator that the skb is received from
 342 *
 343 * Look up the next-hop of the fragments payload and check if the merged packet
 344 * will exceed the MTU towards the next-hop. If so, the fragment is forwarded
 345 * without merging it.
 346 *
 347 * Return: true if the fragment is consumed/forwarded, false otherwise.
 348 */
 349bool batadv_frag_skb_fwd(struct sk_buff *skb,
 350                         struct batadv_hard_iface *recv_if,
 351                         struct batadv_orig_node *orig_node_src)
 352{
 353        struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
 354        struct batadv_orig_node *orig_node_dst;
 355        struct batadv_neigh_node *neigh_node = NULL;
 356        struct batadv_frag_packet *packet;
 357        u16 total_size;
 358        bool ret = false;
 359
 360        packet = (struct batadv_frag_packet *)skb->data;
 361        orig_node_dst = batadv_orig_hash_find(bat_priv, packet->dest);
 362        if (!orig_node_dst)
 363                goto out;
 364
 365        neigh_node = batadv_find_router(bat_priv, orig_node_dst, recv_if);
 366        if (!neigh_node)
 367                goto out;
 368
 369        /* Forward the fragment, if the merged packet would be too big to
 370         * be assembled.
 371         */
 372        total_size = ntohs(packet->total_size);
 373        if (total_size > neigh_node->if_incoming->net_dev->mtu) {
 374                batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
 375                batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
 376                                   skb->len + ETH_HLEN);
 377
 378                packet->ttl--;
 379                batadv_send_unicast_skb(skb, neigh_node);
 380                ret = true;
 381        }
 382
 383out:
 384        if (orig_node_dst)
 385                batadv_orig_node_put(orig_node_dst);
 386        if (neigh_node)
 387                batadv_neigh_node_put(neigh_node);
 388        return ret;
 389}
 390
 391/**
 392 * batadv_frag_create() - create a fragment from skb
 393 * @net_dev: outgoing device for fragment
 394 * @skb: skb to create fragment from
 395 * @frag_head: header to use in new fragment
 396 * @fragment_size: size of new fragment
 397 *
 398 * Split the passed skb into two fragments: A new one with size matching the
 399 * passed mtu and the old one with the rest. The new skb contains data from the
 400 * tail of the old skb.
 401 *
 402 * Return: the new fragment, NULL on error.
 403 */
 404static struct sk_buff *batadv_frag_create(struct net_device *net_dev,
 405                                          struct sk_buff *skb,
 406                                          struct batadv_frag_packet *frag_head,
 407                                          unsigned int fragment_size)
 408{
 409        unsigned int ll_reserved = LL_RESERVED_SPACE(net_dev);
 410        unsigned int tailroom = net_dev->needed_tailroom;
 411        struct sk_buff *skb_fragment;
 412        unsigned int header_size = sizeof(*frag_head);
 413        unsigned int mtu = fragment_size + header_size;
 414
 415        skb_fragment = dev_alloc_skb(ll_reserved + mtu + tailroom);
 416        if (!skb_fragment)
 417                goto err;
 418
 419        skb_fragment->priority = skb->priority;
 420
 421        /* Eat the last mtu-bytes of the skb */
 422        skb_reserve(skb_fragment, ll_reserved + header_size);
 423        skb_split(skb, skb_fragment, skb->len - fragment_size);
 424
 425        /* Add the header */
 426        skb_push(skb_fragment, header_size);
 427        memcpy(skb_fragment->data, frag_head, header_size);
 428
 429err:
 430        return skb_fragment;
 431}
 432
 433/**
 434 * batadv_frag_send_packet() - create up to 16 fragments from the passed skb
 435 * @skb: skb to create fragments from
 436 * @orig_node: final destination of the created fragments
 437 * @neigh_node: next-hop of the created fragments
 438 *
 439 * Return: the netdev tx status or a negative errno code on a failure
 440 */
 441int batadv_frag_send_packet(struct sk_buff *skb,
 442                            struct batadv_orig_node *orig_node,
 443                            struct batadv_neigh_node *neigh_node)
 444{
 445        struct net_device *net_dev = neigh_node->if_incoming->net_dev;
 446        struct batadv_priv *bat_priv;
 447        struct batadv_hard_iface *primary_if = NULL;
 448        struct batadv_frag_packet frag_header;
 449        struct sk_buff *skb_fragment;
 450        unsigned int mtu = net_dev->mtu;
 451        unsigned int header_size = sizeof(frag_header);
 452        unsigned int max_fragment_size, num_fragments;
 453        int ret;
 454
 455        /* To avoid merge and refragmentation at next-hops we never send
 456         * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
 457         */
 458        mtu = min_t(unsigned int, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
 459        max_fragment_size = mtu - header_size;
 460
 461        if (skb->len == 0 || max_fragment_size == 0)
 462                return -EINVAL;
 463
 464        num_fragments = (skb->len - 1) / max_fragment_size + 1;
 465        max_fragment_size = (skb->len - 1) / num_fragments + 1;
 466
 467        /* Don't even try to fragment, if we need more than 16 fragments */
 468        if (num_fragments > BATADV_FRAG_MAX_FRAGMENTS) {
 469                ret = -EAGAIN;
 470                goto free_skb;
 471        }
 472
 473        bat_priv = orig_node->bat_priv;
 474        primary_if = batadv_primary_if_get_selected(bat_priv);
 475        if (!primary_if) {
 476                ret = -EINVAL;
 477                goto free_skb;
 478        }
 479
 480        /* Create one header to be copied to all fragments */
 481        frag_header.packet_type = BATADV_UNICAST_FRAG;
 482        frag_header.version = BATADV_COMPAT_VERSION;
 483        frag_header.ttl = BATADV_TTL;
 484        frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
 485        frag_header.reserved = 0;
 486        frag_header.no = 0;
 487        frag_header.total_size = htons(skb->len);
 488
 489        /* skb->priority values from 256->263 are magic values to
 490         * directly indicate a specific 802.1d priority.  This is used
 491         * to allow 802.1d priority to be passed directly in from VLAN
 492         * tags, etc.
 493         */
 494        if (skb->priority >= 256 && skb->priority <= 263)
 495                frag_header.priority = skb->priority - 256;
 496        else
 497                frag_header.priority = 0;
 498
 499        ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
 500        ether_addr_copy(frag_header.dest, orig_node->orig);
 501
 502        /* Eat and send fragments from the tail of skb */
 503        while (skb->len > max_fragment_size) {
 504                /* The initial check in this function should cover this case */
 505                if (unlikely(frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)) {
 506                        ret = -EINVAL;
 507                        goto put_primary_if;
 508                }
 509
 510                skb_fragment = batadv_frag_create(net_dev, skb, &frag_header,
 511                                                  max_fragment_size);
 512                if (!skb_fragment) {
 513                        ret = -ENOMEM;
 514                        goto put_primary_if;
 515                }
 516
 517                batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
 518                batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
 519                                   skb_fragment->len + ETH_HLEN);
 520                ret = batadv_send_unicast_skb(skb_fragment, neigh_node);
 521                if (ret != NET_XMIT_SUCCESS) {
 522                        ret = NET_XMIT_DROP;
 523                        goto put_primary_if;
 524                }
 525
 526                frag_header.no++;
 527        }
 528
 529        /* make sure that there is at least enough head for the fragmentation
 530         * and ethernet headers
 531         */
 532        ret = skb_cow_head(skb, ETH_HLEN + header_size);
 533        if (ret < 0)
 534                goto put_primary_if;
 535
 536        skb_push(skb, header_size);
 537        memcpy(skb->data, &frag_header, header_size);
 538
 539        /* Send the last fragment */
 540        batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
 541        batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
 542                           skb->len + ETH_HLEN);
 543        ret = batadv_send_unicast_skb(skb, neigh_node);
 544        /* skb was consumed */
 545        skb = NULL;
 546
 547put_primary_if:
 548        batadv_hardif_put(primary_if);
 549free_skb:
 550        kfree_skb(skb);
 551
 552        return ret;
 553}
 554