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TOMOYO Linux Cross Reference
Linux/net/batman-adv/fragmentation.c

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  1 /* Copyright (C) 2013-2015 B.A.T.M.A.N. contributors:
  2  *
  3  * Martin Hundebøll <martin@hundeboll.net>
  4  *
  5  * This program is free software; you can redistribute it and/or
  6  * modify it under the terms of version 2 of the GNU General Public
  7  * License as published by the Free Software Foundation.
  8  *
  9  * This program is distributed in the hope that it will be useful, but
 10  * WITHOUT ANY WARRANTY; without even the implied warranty of
 11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 12  * General Public License for more details.
 13  *
 14  * You should have received a copy of the GNU General Public License
 15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
 16  */
 17 
 18 #include "fragmentation.h"
 19 #include "main.h"
 20 
 21 #include <linux/atomic.h>
 22 #include <linux/byteorder/generic.h>
 23 #include <linux/etherdevice.h>
 24 #include <linux/fs.h>
 25 #include <linux/if_ether.h>
 26 #include <linux/jiffies.h>
 27 #include <linux/kernel.h>
 28 #include <linux/lockdep.h>
 29 #include <linux/netdevice.h>
 30 #include <linux/pkt_sched.h>
 31 #include <linux/skbuff.h>
 32 #include <linux/slab.h>
 33 #include <linux/spinlock.h>
 34 #include <linux/string.h>
 35 
 36 #include "hard-interface.h"
 37 #include "originator.h"
 38 #include "packet.h"
 39 #include "routing.h"
 40 #include "send.h"
 41 #include "soft-interface.h"
 42 
 43 /**
 44  * batadv_frag_clear_chain - delete entries in the fragment buffer chain
 45  * @head: head of chain with entries.
 46  *
 47  * Free fragments in the passed hlist. Should be called with appropriate lock.
 48  */
 49 static void batadv_frag_clear_chain(struct hlist_head *head)
 50 {
 51         struct batadv_frag_list_entry *entry;
 52         struct hlist_node *node;
 53 
 54         hlist_for_each_entry_safe(entry, node, head, list) {
 55                 hlist_del(&entry->list);
 56                 kfree_skb(entry->skb);
 57                 kfree(entry);
 58         }
 59 }
 60 
 61 /**
 62  * batadv_frag_purge_orig - free fragments associated to an orig
 63  * @orig_node: originator to free fragments from
 64  * @check_cb: optional function to tell if an entry should be purged
 65  */
 66 void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
 67                             bool (*check_cb)(struct batadv_frag_table_entry *))
 68 {
 69         struct batadv_frag_table_entry *chain;
 70         u8 i;
 71 
 72         for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
 73                 chain = &orig_node->fragments[i];
 74                 spin_lock_bh(&orig_node->fragments[i].lock);
 75 
 76                 if (!check_cb || check_cb(chain)) {
 77                         batadv_frag_clear_chain(&orig_node->fragments[i].head);
 78                         orig_node->fragments[i].size = 0;
 79                 }
 80 
 81                 spin_unlock_bh(&orig_node->fragments[i].lock);
 82         }
 83 }
 84 
 85 /**
 86  * batadv_frag_size_limit - maximum possible size of packet to be fragmented
 87  *
 88  * Returns the maximum size of payload that can be fragmented.
 89  */
 90 static int batadv_frag_size_limit(void)
 91 {
 92         int limit = BATADV_FRAG_MAX_FRAG_SIZE;
 93 
 94         limit -= sizeof(struct batadv_frag_packet);
 95         limit *= BATADV_FRAG_MAX_FRAGMENTS;
 96 
 97         return limit;
 98 }
 99 
100 /**
101  * batadv_frag_init_chain - check and prepare fragment chain for new fragment
102  * @chain: chain in fragments table to init
103  * @seqno: sequence number of the received fragment
104  *
105  * Make chain ready for a fragment with sequence number "seqno". Delete existing
106  * entries if they have an "old" sequence number.
107  *
108  * Caller must hold chain->lock.
109  *
110  * Returns true if chain is empty and caller can just insert the new fragment
111  * without searching for the right position.
112  */
113 static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,
114                                    u16 seqno)
115 {
116         lockdep_assert_held(&chain->lock);
117 
118         if (chain->seqno == seqno)
119                 return false;
120 
121         if (!hlist_empty(&chain->head))
122                 batadv_frag_clear_chain(&chain->head);
123 
124         chain->size = 0;
125         chain->seqno = seqno;
126 
127         return true;
128 }
129 
130 /**
131  * batadv_frag_insert_packet - insert a fragment into a fragment chain
132  * @orig_node: originator that the fragment was received from
133  * @skb: skb to insert
134  * @chain_out: list head to attach complete chains of fragments to
135  *
136  * Insert a new fragment into the reverse ordered chain in the right table
137  * entry. The hash table entry is cleared if "old" fragments exist in it.
138  *
139  * Returns true if skb is buffered, false on error. If the chain has all the
140  * fragments needed to merge the packet, the chain is moved to the passed head
141  * to avoid locking the chain in the table.
142  */
143 static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
144                                       struct sk_buff *skb,
145                                       struct hlist_head *chain_out)
146 {
147         struct batadv_frag_table_entry *chain;
148         struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;
149         struct batadv_frag_list_entry *frag_entry_last = NULL;
150         struct batadv_frag_packet *frag_packet;
151         u8 bucket;
152         u16 seqno, hdr_size = sizeof(struct batadv_frag_packet);
153         bool ret = false;
154 
155         /* Linearize packet to avoid linearizing 16 packets in a row when doing
156          * the later merge. Non-linear merge should be added to remove this
157          * linearization.
158          */
159         if (skb_linearize(skb) < 0)
160                 goto err;
161 
162         frag_packet = (struct batadv_frag_packet *)skb->data;
163         seqno = ntohs(frag_packet->seqno);
164         bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
165 
166         frag_entry_new = kmalloc(sizeof(*frag_entry_new), GFP_ATOMIC);
167         if (!frag_entry_new)
168                 goto err;
169 
170         frag_entry_new->skb = skb;
171         frag_entry_new->no = frag_packet->no;
172 
173         /* Select entry in the "chain table" and delete any prior fragments
174          * with another sequence number. batadv_frag_init_chain() returns true,
175          * if the list is empty at return.
176          */
177         chain = &orig_node->fragments[bucket];
178         spin_lock_bh(&chain->lock);
179         if (batadv_frag_init_chain(chain, seqno)) {
180                 hlist_add_head(&frag_entry_new->list, &chain->head);
181                 chain->size = skb->len - hdr_size;
182                 chain->timestamp = jiffies;
183                 chain->total_size = ntohs(frag_packet->total_size);
184                 ret = true;
185                 goto out;
186         }
187 
188         /* Find the position for the new fragment. */
189         hlist_for_each_entry(frag_entry_curr, &chain->head, list) {
190                 /* Drop packet if fragment already exists. */
191                 if (frag_entry_curr->no == frag_entry_new->no)
192                         goto err_unlock;
193 
194                 /* Order fragments from highest to lowest. */
195                 if (frag_entry_curr->no < frag_entry_new->no) {
196                         hlist_add_before(&frag_entry_new->list,
197                                          &frag_entry_curr->list);
198                         chain->size += skb->len - hdr_size;
199                         chain->timestamp = jiffies;
200                         ret = true;
201                         goto out;
202                 }
203 
204                 /* store current entry because it could be the last in list */
205                 frag_entry_last = frag_entry_curr;
206         }
207 
208         /* Reached the end of the list, so insert after 'frag_entry_last'. */
209         if (likely(frag_entry_last)) {
210                 hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
211                 chain->size += skb->len - hdr_size;
212                 chain->timestamp = jiffies;
213                 ret = true;
214         }
215 
216 out:
217         if (chain->size > batadv_frag_size_limit() ||
218             chain->total_size != ntohs(frag_packet->total_size) ||
219             chain->total_size > batadv_frag_size_limit()) {
220                 /* Clear chain if total size of either the list or the packet
221                  * exceeds the maximum size of one merged packet. Don't allow
222                  * packets to have different total_size.
223                  */
224                 batadv_frag_clear_chain(&chain->head);
225                 chain->size = 0;
226         } else if (ntohs(frag_packet->total_size) == chain->size) {
227                 /* All fragments received. Hand over chain to caller. */
228                 hlist_move_list(&chain->head, chain_out);
229                 chain->size = 0;
230         }
231 
232 err_unlock:
233         spin_unlock_bh(&chain->lock);
234 
235 err:
236         if (!ret)
237                 kfree(frag_entry_new);
238 
239         return ret;
240 }
241 
242 /**
243  * batadv_frag_merge_packets - merge a chain of fragments
244  * @chain: head of chain with fragments
245  * @skb: packet with total size of skb after merging
246  *
247  * Expand the first skb in the chain and copy the content of the remaining
248  * skb's into the expanded one. After doing so, clear the chain.
249  *
250  * Returns the merged skb or NULL on error.
251  */
252 static struct sk_buff *
253 batadv_frag_merge_packets(struct hlist_head *chain)
254 {
255         struct batadv_frag_packet *packet;
256         struct batadv_frag_list_entry *entry;
257         struct sk_buff *skb_out = NULL;
258         int size, hdr_size = sizeof(struct batadv_frag_packet);
259 
260         /* Remove first entry, as this is the destination for the rest of the
261          * fragments.
262          */
263         entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
264         hlist_del(&entry->list);
265         skb_out = entry->skb;
266         kfree(entry);
267 
268         packet = (struct batadv_frag_packet *)skb_out->data;
269         size = ntohs(packet->total_size);
270 
271         /* Make room for the rest of the fragments. */
272         if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
273                 kfree_skb(skb_out);
274                 skb_out = NULL;
275                 goto free;
276         }
277 
278         /* Move the existing MAC header to just before the payload. (Override
279          * the fragment header.)
280          */
281         skb_pull_rcsum(skb_out, hdr_size);
282         memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
283         skb_set_mac_header(skb_out, -ETH_HLEN);
284         skb_reset_network_header(skb_out);
285         skb_reset_transport_header(skb_out);
286 
287         /* Copy the payload of the each fragment into the last skb */
288         hlist_for_each_entry(entry, chain, list) {
289                 size = entry->skb->len - hdr_size;
290                 memcpy(skb_put(skb_out, size), entry->skb->data + hdr_size,
291                        size);
292         }
293 
294 free:
295         /* Locking is not needed, because 'chain' is not part of any orig. */
296         batadv_frag_clear_chain(chain);
297         return skb_out;
298 }
299 
300 /**
301  * batadv_frag_skb_buffer - buffer fragment for later merge
302  * @skb: skb to buffer
303  * @orig_node_src: originator that the skb is received from
304  *
305  * Add fragment to buffer and merge fragments if possible.
306  *
307  * There are three possible outcomes: 1) Packet is merged: Return true and
308  * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
309  * to NULL; 3) Error: Return false and leave skb as is.
310  */
311 bool 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 
330 out:
331         *skb = skb_out;
332         ret = true;
333 out_err:
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  * Returns true if the fragment is consumed/forwarded, false otherwise.
348  */
349 bool 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 = NULL;
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_skb_packet(skb, neigh_node->if_incoming,
380                                        neigh_node->addr);
381                 ret = true;
382         }
383 
384 out:
385         if (orig_node_dst)
386                 batadv_orig_node_free_ref(orig_node_dst);
387         if (neigh_node)
388                 batadv_neigh_node_free_ref(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  * @mtu: 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  * Returns 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 mtu)
407 {
408         struct sk_buff *skb_fragment;
409         unsigned header_size = sizeof(*frag_head);
410         unsigned fragment_size = mtu - header_size;
411 
412         skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN);
413         if (!skb_fragment)
414                 goto err;
415 
416         skb->priority = TC_PRIO_CONTROL;
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  * Returns true on success, false otherwise.
437  */
438 bool 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 mtu = neigh_node->if_incoming->net_dev->mtu;
447         unsigned header_size = sizeof(frag_header);
448         unsigned max_fragment_size, max_packet_size;
449         bool ret = false;
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, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
455         max_fragment_size = mtu - header_size;
456         max_packet_size = max_fragment_size * BATADV_FRAG_MAX_FRAGMENTS;
457 
458         /* Don't even try to fragment, if we need more than 16 fragments */
459         if (skb->len > max_packet_size)
460                 goto out_err;
461 
462         bat_priv = orig_node->bat_priv;
463         primary_if = batadv_primary_if_get_selected(bat_priv);
464         if (!primary_if)
465                 goto out_err;
466 
467         /* Create one header to be copied to all fragments */
468         frag_header.packet_type = BATADV_UNICAST_FRAG;
469         frag_header.version = BATADV_COMPAT_VERSION;
470         frag_header.ttl = BATADV_TTL;
471         frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
472         frag_header.reserved = 0;
473         frag_header.no = 0;
474         frag_header.total_size = htons(skb->len);
475         ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
476         ether_addr_copy(frag_header.dest, orig_node->orig);
477 
478         /* Eat and send fragments from the tail of skb */
479         while (skb->len > max_fragment_size) {
480                 skb_fragment = batadv_frag_create(skb, &frag_header, mtu);
481                 if (!skb_fragment)
482                         goto out_err;
483 
484                 batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
485                 batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
486                                    skb_fragment->len + ETH_HLEN);
487                 batadv_send_skb_packet(skb_fragment, neigh_node->if_incoming,
488                                        neigh_node->addr);
489                 frag_header.no++;
490 
491                 /* The initial check in this function should cover this case */
492                 if (frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)
493                         goto out_err;
494         }
495 
496         /* Make room for the fragment header. */
497         if (batadv_skb_head_push(skb, header_size) < 0 ||
498             pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0)
499                 goto out_err;
500 
501         memcpy(skb->data, &frag_header, header_size);
502 
503         /* Send the last fragment */
504         batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
505         batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
506                            skb->len + ETH_HLEN);
507         batadv_send_skb_packet(skb, neigh_node->if_incoming, neigh_node->addr);
508 
509         ret = true;
510 
511 out_err:
512         if (primary_if)
513                 batadv_hardif_free_ref(primary_if);
514 
515         return ret;
516 }
517 

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