root/net/batman-adv/fragmentation.c

DEFINITIONS

1. batadv_frag_clear_chain
2. batadv_frag_purge_orig
3. batadv_frag_size_limit
4. batadv_frag_init_chain
5. batadv_frag_insert_packet
6. batadv_frag_merge_packets
7. batadv_frag_skb_buffer
8. batadv_frag_skb_fwd
9. batadv_frag_create
10. batadv_frag_send_packet

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* Copyright (C) 2013-2019  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/kernel.h>
  18 #include <linux/lockdep.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 #include "soft-interface.h"
  31 
  32 /**
  33  * batadv_frag_clear_chain() - delete entries in the fragment buffer chain
  34  * @head: head of chain with entries.
  35  * @dropped: whether the chain is cleared because all fragments are dropped
  36  *
  37  * Free fragments in the passed hlist. Should be called with appropriate lock.
  38  */
  39 static void batadv_frag_clear_chain(struct hlist_head *head, bool dropped)
  40 {
  41         struct batadv_frag_list_entry *entry;
  42         struct hlist_node *node;
  43 
  44         hlist_for_each_entry_safe(entry, node, head, list) {
  45                 hlist_del(&entry->list);
  46 
  47                 if (dropped)
  48                         kfree_skb(entry->skb);
  49                 else
  50                         consume_skb(entry->skb);
  51 
  52                 kfree(entry);
  53         }
  54 }
  55 
  56 /**
  57  * batadv_frag_purge_orig() - free fragments associated to an orig
  58  * @orig_node: originator to free fragments from
  59  * @check_cb: optional function to tell if an entry should be purged
  60  */
  61 void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
  62                             bool (*check_cb)(struct batadv_frag_table_entry *))
  63 {
  64         struct batadv_frag_table_entry *chain;
  65         u8 i;
  66 
  67         for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
  68                 chain = &orig_node->fragments[i];
  69                 spin_lock_bh(&chain->lock);
  70 
  71                 if (!check_cb || check_cb(chain)) {
  72                         batadv_frag_clear_chain(&chain->fragment_list, true);
  73                         chain->size = 0;
  74                 }
  75 
  76                 spin_unlock_bh(&chain->lock);
  77         }
  78 }
  79 
  80 /**
  81  * batadv_frag_size_limit() - maximum possible size of packet to be fragmented
  82  *
  83  * Return: the maximum size of payload that can be fragmented.
  84  */
  85 static int batadv_frag_size_limit(void)
  86 {
  87         int limit = BATADV_FRAG_MAX_FRAG_SIZE;
  88 
  89         limit -= sizeof(struct batadv_frag_packet);
  90         limit *= BATADV_FRAG_MAX_FRAGMENTS;
  91 
  92         return limit;
  93 }
  94 
  95 /**
  96  * batadv_frag_init_chain() - check and prepare fragment chain for new fragment
  97  * @chain: chain in fragments table to init
  98  * @seqno: sequence number of the received fragment
  99  *
 100  * Make chain ready for a fragment with sequence number "seqno". Delete existing
 101  * entries if they have an "old" sequence number.
 102  *
 103  * Caller must hold chain->lock.
 104  *
 105  * Return: true if chain is empty and caller can just insert the new fragment
 106  * without searching for the right position.
 107  */
 108 static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,
 109                                    u16 seqno)
 110 {
 111         lockdep_assert_held(&chain->lock);
 112 
 113         if (chain->seqno == seqno)
 114                 return false;
 115 
 116         if (!hlist_empty(&chain->fragment_list))
 117                 batadv_frag_clear_chain(&chain->fragment_list, true);
 118 
 119         chain->size = 0;
 120         chain->seqno = seqno;
 121 
 122         return true;
 123 }
 124 
 125 /**
 126  * batadv_frag_insert_packet() - insert a fragment into a fragment chain
 127  * @orig_node: originator that the fragment was received from
 128  * @skb: skb to insert
 129  * @chain_out: list head to attach complete chains of fragments to
 130  *
 131  * Insert a new fragment into the reverse ordered chain in the right table
 132  * entry. The hash table entry is cleared if "old" fragments exist in it.
 133  *
 134  * Return: true if skb is buffered, false on error. If the chain has all the
 135  * fragments needed to merge the packet, the chain is moved to the passed head
 136  * to avoid locking the chain in the table.
 137  */
 138 static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
 139                                       struct sk_buff *skb,
 140                                       struct hlist_head *chain_out)
 141 {
 142         struct batadv_frag_table_entry *chain;
 143         struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;
 144         struct batadv_frag_list_entry *frag_entry_last = NULL;
 145         struct batadv_frag_packet *frag_packet;
 146         u8 bucket;
 147         u16 seqno, hdr_size = sizeof(struct batadv_frag_packet);
 148         bool ret = false;
 149 
 150         /* Linearize packet to avoid linearizing 16 packets in a row when doing
 151          * the later merge. Non-linear merge should be added to remove this
 152          * linearization.
 153          */
 154         if (skb_linearize(skb) < 0)
 155                 goto err;
 156 
 157         frag_packet = (struct batadv_frag_packet *)skb->data;
 158         seqno = ntohs(frag_packet->seqno);
 159         bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
 160 
 161         frag_entry_new = kmalloc(sizeof(*frag_entry_new), GFP_ATOMIC);
 162         if (!frag_entry_new)
 163                 goto err;
 164 
 165         frag_entry_new->skb = skb;
 166         frag_entry_new->no = frag_packet->no;
 167 
 168         /* Select entry in the "chain table" and delete any prior fragments
 169          * with another sequence number. batadv_frag_init_chain() returns true,
 170          * if the list is empty at return.
 171          */
 172         chain = &orig_node->fragments[bucket];
 173         spin_lock_bh(&chain->lock);
 174         if (batadv_frag_init_chain(chain, seqno)) {
 175                 hlist_add_head(&frag_entry_new->list, &chain->fragment_list);
 176                 chain->size = skb->len - hdr_size;
 177                 chain->timestamp = jiffies;
 178                 chain->total_size = ntohs(frag_packet->total_size);
 179                 ret = true;
 180                 goto out;
 181         }
 182 
 183         /* Find the position for the new fragment. */
 184         hlist_for_each_entry(frag_entry_curr, &chain->fragment_list, list) {
 185                 /* Drop packet if fragment already exists. */
 186                 if (frag_entry_curr->no == frag_entry_new->no)
 187                         goto err_unlock;
 188 
 189                 /* Order fragments from highest to lowest. */
 190                 if (frag_entry_curr->no < frag_entry_new->no) {
 191                         hlist_add_before(&frag_entry_new->list,
 192                                          &frag_entry_curr->list);
 193                         chain->size += skb->len - hdr_size;
 194                         chain->timestamp = jiffies;
 195                         ret = true;
 196                         goto out;
 197                 }
 198 
 199                 /* store current entry because it could be the last in list */
 200                 frag_entry_last = frag_entry_curr;
 201         }
 202 
 203         /* Reached the end of the list, so insert after 'frag_entry_last'. */
 204         if (likely(frag_entry_last)) {
 205                 hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
 206                 chain->size += skb->len - hdr_size;
 207                 chain->timestamp = jiffies;
 208                 ret = true;
 209         }
 210 
 211 out:
 212         if (chain->size > batadv_frag_size_limit() ||
 213             chain->total_size != ntohs(frag_packet->total_size) ||
 214             chain->total_size > batadv_frag_size_limit()) {
 215                 /* Clear chain if total size of either the list or the packet
 216                  * exceeds the maximum size of one merged packet. Don't allow
 217                  * packets to have different total_size.
 218                  */
 219                 batadv_frag_clear_chain(&chain->fragment_list, true);
 220                 chain->size = 0;
 221         } else if (ntohs(frag_packet->total_size) == chain->size) {
 222                 /* All fragments received. Hand over chain to caller. */
 223                 hlist_move_list(&chain->fragment_list, chain_out);
 224                 chain->size = 0;
 225         }
 226 
 227 err_unlock:
 228         spin_unlock_bh(&chain->lock);
 229 
 230 err:
 231         if (!ret) {
 232                 kfree(frag_entry_new);
 233                 kfree_skb(skb);
 234         }
 235 
 236         return ret;
 237 }
 238 
 239 /**
 240  * batadv_frag_merge_packets() - merge a chain of fragments
 241  * @chain: head of chain with fragments
 242  *
 243  * Expand the first skb in the chain and copy the content of the remaining
 244  * skb's into the expanded one. After doing so, clear the chain.
 245  *
 246  * Return: the merged skb or NULL on error.
 247  */
 248 static struct sk_buff *
 249 batadv_frag_merge_packets(struct hlist_head *chain)
 250 {
 251         struct batadv_frag_packet *packet;
 252         struct batadv_frag_list_entry *entry;
 253         struct sk_buff *skb_out;
 254         int size, hdr_size = sizeof(struct batadv_frag_packet);
 255         bool dropped = false;
 256 
 257         /* Remove first entry, as this is the destination for the rest of the
 258          * fragments.
 259          */
 260         entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
 261         hlist_del(&entry->list);
 262         skb_out = entry->skb;
 263         kfree(entry);
 264 
 265         packet = (struct batadv_frag_packet *)skb_out->data;
 266         size = ntohs(packet->total_size) + hdr_size;
 267 
 268         /* Make room for the rest of the fragments. */
 269         if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
 270                 kfree_skb(skb_out);
 271                 skb_out = NULL;
 272                 dropped = true;
 273                 goto free;
 274         }
 275 
 276         /* Move the existing MAC header to just before the payload. (Override
 277          * the fragment header.)
 278          */
 279         skb_pull(skb_out, hdr_size);
 280         skb_out->ip_summed = CHECKSUM_NONE;
 281         memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
 282         skb_set_mac_header(skb_out, -ETH_HLEN);
 283         skb_reset_network_header(skb_out);
 284         skb_reset_transport_header(skb_out);
 285 
 286         /* Copy the payload of the each fragment into the last skb */
 287         hlist_for_each_entry(entry, chain, list) {
 288                 size = entry->skb->len - hdr_size;
 289                 skb_put_data(skb_out, entry->skb->data + hdr_size, size);
 290         }
 291 
 292 free:
 293         /* Locking is not needed, because 'chain' is not part of any orig. */
 294         batadv_frag_clear_chain(chain, dropped);
 295         return skb_out;
 296 }
 297 
 298 /**
 299  * batadv_frag_skb_buffer() - buffer fragment for later merge
 300  * @skb: skb to buffer
 301  * @orig_node_src: originator that the skb is received from
 302  *
 303  * Add fragment to buffer and merge fragments if possible.
 304  *
 305  * There are three possible outcomes: 1) Packet is merged: Return true and
 306  * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
 307  * to NULL; 3) Error: Return false and free skb.
 308  *
 309  * Return: true when packet is merged or buffered, false when skb is not not
 310  * used.
 311  */
 312 bool batadv_frag_skb_buffer(struct sk_buff **skb,
 313                             struct batadv_orig_node *orig_node_src)
 314 {
 315         struct sk_buff *skb_out = NULL;
 316         struct hlist_head head = HLIST_HEAD_INIT;
 317         bool ret = false;
 318 
 319         /* Add packet to buffer and table entry if merge is possible. */
 320         if (!batadv_frag_insert_packet(orig_node_src, *skb, &head))
 321                 goto out_err;
 322 
 323         /* Leave if more fragments are needed to merge. */
 324         if (hlist_empty(&head))
 325                 goto out;
 326 
 327         skb_out = batadv_frag_merge_packets(&head);
 328         if (!skb_out)
 329                 goto out_err;
 330 
 331 out:
 332         ret = true;
 333 out_err:
 334         *skb = skb_out;
 335         return ret;
 336 }
 337 
 338 /**
 339  * batadv_frag_skb_fwd() - forward fragments that would exceed MTU when merged
 340  * @skb: skb to forward
 341  * @recv_if: interface that the skb is received on
 342  * @orig_node_src: originator that the skb is received from
 343  *
 344  * Look up the next-hop of the fragments payload and check if the merged packet
 345  * will exceed the MTU towards the next-hop. If so, the fragment is forwarded
 346  * without merging it.
 347  *
 348  * Return: true if the fragment is consumed/forwarded, false otherwise.
 349  */
 350 bool batadv_frag_skb_fwd(struct sk_buff *skb,
 351                          struct batadv_hard_iface *recv_if,
 352                          struct batadv_orig_node *orig_node_src)
 353 {
 354         struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
 355         struct batadv_orig_node *orig_node_dst;
 356         struct batadv_neigh_node *neigh_node = NULL;
 357         struct batadv_frag_packet *packet;
 358         u16 total_size;
 359         bool ret = false;
 360 
 361         packet = (struct batadv_frag_packet *)skb->data;
 362         orig_node_dst = batadv_orig_hash_find(bat_priv, packet->dest);
 363         if (!orig_node_dst)
 364                 goto out;
 365 
 366         neigh_node = batadv_find_router(bat_priv, orig_node_dst, recv_if);
 367         if (!neigh_node)
 368                 goto out;
 369 
 370         /* Forward the fragment, if the merged packet would be too big to
 371          * be assembled.
 372          */
 373         total_size = ntohs(packet->total_size);
 374         if (total_size > neigh_node->if_incoming->net_dev->mtu) {
 375                 batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
 376                 batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
 377                                    skb->len + ETH_HLEN);
 378 
 379                 packet->ttl--;
 380                 batadv_send_unicast_skb(skb, neigh_node);
 381                 ret = true;
 382         }
 383 
 384 out:
 385         if (orig_node_dst)
 386                 batadv_orig_node_put(orig_node_dst);
 387         if (neigh_node)
 388                 batadv_neigh_node_put(neigh_node);
 389         return ret;
 390 }
 391 
 392 /**
 393  * batadv_frag_create() - create a fragment from skb
 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  */
 404 static struct sk_buff *batadv_frag_create(struct sk_buff *skb,
 405                                           struct batadv_frag_packet *frag_head,
 406                                           unsigned int fragment_size)
 407 {
 408         struct sk_buff *skb_fragment;
 409         unsigned int header_size = sizeof(*frag_head);
 410         unsigned int mtu = fragment_size + header_size;
 411 
 412         skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN);
 413         if (!skb_fragment)
 414                 goto err;
 415 
 416         skb_fragment->priority = skb->priority;
 417 
 418         /* Eat the last mtu-bytes of the skb */
 419         skb_reserve(skb_fragment, header_size + ETH_HLEN);
 420         skb_split(skb, skb_fragment, skb->len - fragment_size);
 421 
 422         /* Add the header */
 423         skb_push(skb_fragment, header_size);
 424         memcpy(skb_fragment->data, frag_head, header_size);
 425 
 426 err:
 427         return skb_fragment;
 428 }
 429 
 430 /**
 431  * batadv_frag_send_packet() - create up to 16 fragments from the passed skb
 432  * @skb: skb to create fragments from
 433  * @orig_node: final destination of the created fragments
 434  * @neigh_node: next-hop of the created fragments
 435  *
 436  * Return: the netdev tx status or a negative errno code on a failure
 437  */
 438 int batadv_frag_send_packet(struct sk_buff *skb,
 439                             struct batadv_orig_node *orig_node,
 440                             struct batadv_neigh_node *neigh_node)
 441 {
 442         struct batadv_priv *bat_priv;
 443         struct batadv_hard_iface *primary_if = NULL;
 444         struct batadv_frag_packet frag_header;
 445         struct sk_buff *skb_fragment;
 446         unsigned int mtu = neigh_node->if_incoming->net_dev->mtu;
 447         unsigned int header_size = sizeof(frag_header);
 448         unsigned int max_fragment_size, num_fragments;
 449         int ret;
 450 
 451         /* To avoid merge and refragmentation at next-hops we never send
 452          * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
 453          */
 454         mtu = min_t(unsigned int, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
 455         max_fragment_size = mtu - header_size;
 456 
 457         if (skb->len == 0 || max_fragment_size == 0)
 458                 return -EINVAL;
 459 
 460         num_fragments = (skb->len - 1) / max_fragment_size + 1;
 461         max_fragment_size = (skb->len - 1) / num_fragments + 1;
 462 
 463         /* Don't even try to fragment, if we need more than 16 fragments */
 464         if (num_fragments > BATADV_FRAG_MAX_FRAGMENTS) {
 465                 ret = -EAGAIN;
 466                 goto free_skb;
 467         }
 468 
 469         bat_priv = orig_node->bat_priv;
 470         primary_if = batadv_primary_if_get_selected(bat_priv);
 471         if (!primary_if) {
 472                 ret = -EINVAL;
 473                 goto free_skb;
 474         }
 475 
 476         /* Create one header to be copied to all fragments */
 477         frag_header.packet_type = BATADV_UNICAST_FRAG;
 478         frag_header.version = BATADV_COMPAT_VERSION;
 479         frag_header.ttl = BATADV_TTL;
 480         frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
 481         frag_header.reserved = 0;
 482         frag_header.no = 0;
 483         frag_header.total_size = htons(skb->len);
 484 
 485         /* skb->priority values from 256->263 are magic values to
 486          * directly indicate a specific 802.1d priority.  This is used
 487          * to allow 802.1d priority to be passed directly in from VLAN
 488          * tags, etc.
 489          */
 490         if (skb->priority >= 256 && skb->priority <= 263)
 491                 frag_header.priority = skb->priority - 256;
 492         else
 493                 frag_header.priority = 0;
 494 
 495         ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
 496         ether_addr_copy(frag_header.dest, orig_node->orig);
 497 
 498         /* Eat and send fragments from the tail of skb */
 499         while (skb->len > max_fragment_size) {
 500                 /* The initial check in this function should cover this case */
 501                 if (unlikely(frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)) {
 502                         ret = -EINVAL;
 503                         goto put_primary_if;
 504                 }
 505 
 506                 skb_fragment = batadv_frag_create(skb, &frag_header,
 507                                                   max_fragment_size);
 508                 if (!skb_fragment) {
 509                         ret = -ENOMEM;
 510                         goto put_primary_if;
 511                 }
 512 
 513                 batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
 514                 batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
 515                                    skb_fragment->len + ETH_HLEN);
 516                 ret = batadv_send_unicast_skb(skb_fragment, neigh_node);
 517                 if (ret != NET_XMIT_SUCCESS) {
 518                         ret = NET_XMIT_DROP;
 519                         goto put_primary_if;
 520                 }
 521 
 522                 frag_header.no++;
 523         }
 524 
 525         /* Make room for the fragment header. */
 526         if (batadv_skb_head_push(skb, header_size) < 0 ||
 527             pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0) {
 528                 ret = -ENOMEM;
 529                 goto put_primary_if;
 530         }
 531 
 532         memcpy(skb->data, &frag_header, header_size);
 533 
 534         /* Send the last fragment */
 535         batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
 536         batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
 537                            skb->len + ETH_HLEN);
 538         ret = batadv_send_unicast_skb(skb, neigh_node);
 539         /* skb was consumed */
 540         skb = NULL;
 541 
 542 put_primary_if:
 543         batadv_hardif_put(primary_if);
 544 free_skb:
 545         kfree_skb(skb);
 546 
 547         return ret;
 548 }