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

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  1 /* Copyright (C) 2013-2017  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/errno.h>
 24 #include <linux/etherdevice.h>
 25 #include <linux/fs.h>
 26 #include <linux/if_ether.h>
 27 #include <linux/jiffies.h>
 28 #include <linux/kernel.h>
 29 #include <linux/lockdep.h>
 30 #include <linux/netdevice.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  * @dropped: whether the chain is cleared because all fragments are dropped
 47  *
 48  * Free fragments in the passed hlist. Should be called with appropriate lock.
 49  */
 50 static void batadv_frag_clear_chain(struct hlist_head *head, bool dropped)
 51 {
 52         struct batadv_frag_list_entry *entry;
 53         struct hlist_node *node;
 54 
 55         hlist_for_each_entry_safe(entry, node, head, list) {
 56                 hlist_del(&entry->list);
 57 
 58                 if (dropped)
 59                         kfree_skb(entry->skb);
 60                 else
 61                         consume_skb(entry->skb);
 62 
 63                 kfree(entry);
 64         }
 65 }
 66 
 67 /**
 68  * batadv_frag_purge_orig - free fragments associated to an orig
 69  * @orig_node: originator to free fragments from
 70  * @check_cb: optional function to tell if an entry should be purged
 71  */
 72 void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
 73                             bool (*check_cb)(struct batadv_frag_table_entry *))
 74 {
 75         struct batadv_frag_table_entry *chain;
 76         u8 i;
 77 
 78         for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
 79                 chain = &orig_node->fragments[i];
 80                 spin_lock_bh(&chain->lock);
 81 
 82                 if (!check_cb || check_cb(chain)) {
 83                         batadv_frag_clear_chain(&chain->fragment_list, true);
 84                         chain->size = 0;
 85                 }
 86 
 87                 spin_unlock_bh(&chain->lock);
 88         }
 89 }
 90 
 91 /**
 92  * batadv_frag_size_limit - maximum possible size of packet to be fragmented
 93  *
 94  * Return: the maximum size of payload that can be fragmented.
 95  */
 96 static int batadv_frag_size_limit(void)
 97 {
 98         int limit = BATADV_FRAG_MAX_FRAG_SIZE;
 99 
100         limit -= sizeof(struct batadv_frag_packet);
101         limit *= BATADV_FRAG_MAX_FRAGMENTS;
102 
103         return limit;
104 }
105 
106 /**
107  * batadv_frag_init_chain - check and prepare fragment chain for new fragment
108  * @chain: chain in fragments table to init
109  * @seqno: sequence number of the received fragment
110  *
111  * Make chain ready for a fragment with sequence number "seqno". Delete existing
112  * entries if they have an "old" sequence number.
113  *
114  * Caller must hold chain->lock.
115  *
116  * Return: true if chain is empty and caller can just insert the new fragment
117  * without searching for the right position.
118  */
119 static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,
120                                    u16 seqno)
121 {
122         lockdep_assert_held(&chain->lock);
123 
124         if (chain->seqno == seqno)
125                 return false;
126 
127         if (!hlist_empty(&chain->fragment_list))
128                 batadv_frag_clear_chain(&chain->fragment_list, true);
129 
130         chain->size = 0;
131         chain->seqno = seqno;
132 
133         return true;
134 }
135 
136 /**
137  * batadv_frag_insert_packet - insert a fragment into a fragment chain
138  * @orig_node: originator that the fragment was received from
139  * @skb: skb to insert
140  * @chain_out: list head to attach complete chains of fragments to
141  *
142  * Insert a new fragment into the reverse ordered chain in the right table
143  * entry. The hash table entry is cleared if "old" fragments exist in it.
144  *
145  * Return: true if skb is buffered, false on error. If the chain has all the
146  * fragments needed to merge the packet, the chain is moved to the passed head
147  * to avoid locking the chain in the table.
148  */
149 static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
150                                       struct sk_buff *skb,
151                                       struct hlist_head *chain_out)
152 {
153         struct batadv_frag_table_entry *chain;
154         struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;
155         struct batadv_frag_list_entry *frag_entry_last = NULL;
156         struct batadv_frag_packet *frag_packet;
157         u8 bucket;
158         u16 seqno, hdr_size = sizeof(struct batadv_frag_packet);
159         bool ret = false;
160 
161         /* Linearize packet to avoid linearizing 16 packets in a row when doing
162          * the later merge. Non-linear merge should be added to remove this
163          * linearization.
164          */
165         if (skb_linearize(skb) < 0)
166                 goto err;
167 
168         frag_packet = (struct batadv_frag_packet *)skb->data;
169         seqno = ntohs(frag_packet->seqno);
170         bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
171 
172         frag_entry_new = kmalloc(sizeof(*frag_entry_new), GFP_ATOMIC);
173         if (!frag_entry_new)
174                 goto err;
175 
176         frag_entry_new->skb = skb;
177         frag_entry_new->no = frag_packet->no;
178 
179         /* Select entry in the "chain table" and delete any prior fragments
180          * with another sequence number. batadv_frag_init_chain() returns true,
181          * if the list is empty at return.
182          */
183         chain = &orig_node->fragments[bucket];
184         spin_lock_bh(&chain->lock);
185         if (batadv_frag_init_chain(chain, seqno)) {
186                 hlist_add_head(&frag_entry_new->list, &chain->fragment_list);
187                 chain->size = skb->len - hdr_size;
188                 chain->timestamp = jiffies;
189                 chain->total_size = ntohs(frag_packet->total_size);
190                 ret = true;
191                 goto out;
192         }
193 
194         /* Find the position for the new fragment. */
195         hlist_for_each_entry(frag_entry_curr, &chain->fragment_list, list) {
196                 /* Drop packet if fragment already exists. */
197                 if (frag_entry_curr->no == frag_entry_new->no)
198                         goto err_unlock;
199 
200                 /* Order fragments from highest to lowest. */
201                 if (frag_entry_curr->no < frag_entry_new->no) {
202                         hlist_add_before(&frag_entry_new->list,
203                                          &frag_entry_curr->list);
204                         chain->size += skb->len - hdr_size;
205                         chain->timestamp = jiffies;
206                         ret = true;
207                         goto out;
208                 }
209 
210                 /* store current entry because it could be the last in list */
211                 frag_entry_last = frag_entry_curr;
212         }
213 
214         /* Reached the end of the list, so insert after 'frag_entry_last'. */
215         if (likely(frag_entry_last)) {
216                 hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
217                 chain->size += skb->len - hdr_size;
218                 chain->timestamp = jiffies;
219                 ret = true;
220         }
221 
222 out:
223         if (chain->size > batadv_frag_size_limit() ||
224             chain->total_size != ntohs(frag_packet->total_size) ||
225             chain->total_size > batadv_frag_size_limit()) {
226                 /* Clear chain if total size of either the list or the packet
227                  * exceeds the maximum size of one merged packet. Don't allow
228                  * packets to have different total_size.
229                  */
230                 batadv_frag_clear_chain(&chain->fragment_list, true);
231                 chain->size = 0;
232         } else if (ntohs(frag_packet->total_size) == chain->size) {
233                 /* All fragments received. Hand over chain to caller. */
234                 hlist_move_list(&chain->fragment_list, chain_out);
235                 chain->size = 0;
236         }
237 
238 err_unlock:
239         spin_unlock_bh(&chain->lock);
240 
241 err:
242         if (!ret) {
243                 kfree(frag_entry_new);
244                 kfree_skb(skb);
245         }
246 
247         return ret;
248 }
249 
250 /**
251  * batadv_frag_merge_packets - merge a chain of fragments
252  * @chain: head of chain with fragments
253  *
254  * Expand the first skb in the chain and copy the content of the remaining
255  * skb's into the expanded one. After doing so, clear the chain.
256  *
257  * Return: the merged skb or NULL on error.
258  */
259 static struct sk_buff *
260 batadv_frag_merge_packets(struct hlist_head *chain)
261 {
262         struct batadv_frag_packet *packet;
263         struct batadv_frag_list_entry *entry;
264         struct sk_buff *skb_out;
265         int size, hdr_size = sizeof(struct batadv_frag_packet);
266         bool dropped = false;
267 
268         /* Remove first entry, as this is the destination for the rest of the
269          * fragments.
270          */
271         entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
272         hlist_del(&entry->list);
273         skb_out = entry->skb;
274         kfree(entry);
275 
276         packet = (struct batadv_frag_packet *)skb_out->data;
277         size = ntohs(packet->total_size);
278 
279         /* Make room for the rest of the fragments. */
280         if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
281                 kfree_skb(skb_out);
282                 skb_out = NULL;
283                 dropped = true;
284                 goto free;
285         }
286 
287         /* Move the existing MAC header to just before the payload. (Override
288          * the fragment header.)
289          */
290         skb_pull_rcsum(skb_out, hdr_size);
291         memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
292         skb_set_mac_header(skb_out, -ETH_HLEN);
293         skb_reset_network_header(skb_out);
294         skb_reset_transport_header(skb_out);
295 
296         /* Copy the payload of the each fragment into the last skb */
297         hlist_for_each_entry(entry, chain, list) {
298                 size = entry->skb->len - hdr_size;
299                 skb_put_data(skb_out, entry->skb->data + hdr_size, size);
300         }
301 
302 free:
303         /* Locking is not needed, because 'chain' is not part of any orig. */
304         batadv_frag_clear_chain(chain, dropped);
305         return skb_out;
306 }
307 
308 /**
309  * batadv_frag_skb_buffer - buffer fragment for later merge
310  * @skb: skb to buffer
311  * @orig_node_src: originator that the skb is received from
312  *
313  * Add fragment to buffer and merge fragments if possible.
314  *
315  * There are three possible outcomes: 1) Packet is merged: Return true and
316  * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
317  * to NULL; 3) Error: Return false and free skb.
318  *
319  * Return: true when packet is merged or buffered, false when skb is not not
320  * used.
321  */
322 bool batadv_frag_skb_buffer(struct sk_buff **skb,
323                             struct batadv_orig_node *orig_node_src)
324 {
325         struct sk_buff *skb_out = NULL;
326         struct hlist_head head = HLIST_HEAD_INIT;
327         bool ret = false;
328 
329         /* Add packet to buffer and table entry if merge is possible. */
330         if (!batadv_frag_insert_packet(orig_node_src, *skb, &head))
331                 goto out_err;
332 
333         /* Leave if more fragments are needed to merge. */
334         if (hlist_empty(&head))
335                 goto out;
336 
337         skb_out = batadv_frag_merge_packets(&head);
338         if (!skb_out)
339                 goto out_err;
340 
341 out:
342         ret = true;
343 out_err:
344         *skb = skb_out;
345         return ret;
346 }
347 
348 /**
349  * batadv_frag_skb_fwd - forward fragments that would exceed MTU when merged
350  * @skb: skb to forward
351  * @recv_if: interface that the skb is received on
352  * @orig_node_src: originator that the skb is received from
353  *
354  * Look up the next-hop of the fragments payload and check if the merged packet
355  * will exceed the MTU towards the next-hop. If so, the fragment is forwarded
356  * without merging it.
357  *
358  * Return: true if the fragment is consumed/forwarded, false otherwise.
359  */
360 bool batadv_frag_skb_fwd(struct sk_buff *skb,
361                          struct batadv_hard_iface *recv_if,
362                          struct batadv_orig_node *orig_node_src)
363 {
364         struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
365         struct batadv_orig_node *orig_node_dst;
366         struct batadv_neigh_node *neigh_node = NULL;
367         struct batadv_frag_packet *packet;
368         u16 total_size;
369         bool ret = false;
370 
371         packet = (struct batadv_frag_packet *)skb->data;
372         orig_node_dst = batadv_orig_hash_find(bat_priv, packet->dest);
373         if (!orig_node_dst)
374                 goto out;
375 
376         neigh_node = batadv_find_router(bat_priv, orig_node_dst, recv_if);
377         if (!neigh_node)
378                 goto out;
379 
380         /* Forward the fragment, if the merged packet would be too big to
381          * be assembled.
382          */
383         total_size = ntohs(packet->total_size);
384         if (total_size > neigh_node->if_incoming->net_dev->mtu) {
385                 batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
386                 batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
387                                    skb->len + ETH_HLEN);
388 
389                 packet->ttl--;
390                 batadv_send_unicast_skb(skb, neigh_node);
391                 ret = true;
392         }
393 
394 out:
395         if (orig_node_dst)
396                 batadv_orig_node_put(orig_node_dst);
397         if (neigh_node)
398                 batadv_neigh_node_put(neigh_node);
399         return ret;
400 }
401 
402 /**
403  * batadv_frag_create - create a fragment from skb
404  * @skb: skb to create fragment from
405  * @frag_head: header to use in new fragment
406  * @fragment_size: size of new fragment
407  *
408  * Split the passed skb into two fragments: A new one with size matching the
409  * passed mtu and the old one with the rest. The new skb contains data from the
410  * tail of the old skb.
411  *
412  * Return: the new fragment, NULL on error.
413  */
414 static struct sk_buff *batadv_frag_create(struct sk_buff *skb,
415                                           struct batadv_frag_packet *frag_head,
416                                           unsigned int fragment_size)
417 {
418         struct sk_buff *skb_fragment;
419         unsigned int header_size = sizeof(*frag_head);
420         unsigned int mtu = fragment_size + header_size;
421 
422         skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN);
423         if (!skb_fragment)
424                 goto err;
425 
426         skb_fragment->priority = skb->priority;
427 
428         /* Eat the last mtu-bytes of the skb */
429         skb_reserve(skb_fragment, header_size + ETH_HLEN);
430         skb_split(skb, skb_fragment, skb->len - fragment_size);
431 
432         /* Add the header */
433         skb_push(skb_fragment, header_size);
434         memcpy(skb_fragment->data, frag_head, header_size);
435 
436 err:
437         return skb_fragment;
438 }
439 
440 /**
441  * batadv_frag_send_packet - create up to 16 fragments from the passed skb
442  * @skb: skb to create fragments from
443  * @orig_node: final destination of the created fragments
444  * @neigh_node: next-hop of the created fragments
445  *
446  * Return: the netdev tx status or a negative errno code on a failure
447  */
448 int batadv_frag_send_packet(struct sk_buff *skb,
449                             struct batadv_orig_node *orig_node,
450                             struct batadv_neigh_node *neigh_node)
451 {
452         struct batadv_priv *bat_priv;
453         struct batadv_hard_iface *primary_if = NULL;
454         struct batadv_frag_packet frag_header;
455         struct sk_buff *skb_fragment;
456         unsigned int mtu = neigh_node->if_incoming->net_dev->mtu;
457         unsigned int header_size = sizeof(frag_header);
458         unsigned int max_fragment_size, num_fragments;
459         int ret;
460 
461         /* To avoid merge and refragmentation at next-hops we never send
462          * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
463          */
464         mtu = min_t(unsigned int, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
465         max_fragment_size = mtu - header_size;
466 
467         if (skb->len == 0 || max_fragment_size == 0)
468                 return -EINVAL;
469 
470         num_fragments = (skb->len - 1) / max_fragment_size + 1;
471         max_fragment_size = (skb->len - 1) / num_fragments + 1;
472 
473         /* Don't even try to fragment, if we need more than 16 fragments */
474         if (num_fragments > BATADV_FRAG_MAX_FRAGMENTS) {
475                 ret = -EAGAIN;
476                 goto free_skb;
477         }
478 
479         bat_priv = orig_node->bat_priv;
480         primary_if = batadv_primary_if_get_selected(bat_priv);
481         if (!primary_if) {
482                 ret = -EINVAL;
483                 goto free_skb;
484         }
485 
486         /* Create one header to be copied to all fragments */
487         frag_header.packet_type = BATADV_UNICAST_FRAG;
488         frag_header.version = BATADV_COMPAT_VERSION;
489         frag_header.ttl = BATADV_TTL;
490         frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
491         frag_header.reserved = 0;
492         frag_header.no = 0;
493         frag_header.total_size = htons(skb->len);
494 
495         /* skb->priority values from 256->263 are magic values to
496          * directly indicate a specific 802.1d priority.  This is used
497          * to allow 802.1d priority to be passed directly in from VLAN
498          * tags, etc.
499          */
500         if (skb->priority >= 256 && skb->priority <= 263)
501                 frag_header.priority = skb->priority - 256;
502 
503         ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
504         ether_addr_copy(frag_header.dest, orig_node->orig);
505 
506         /* Eat and send fragments from the tail of skb */
507         while (skb->len > max_fragment_size) {
508                 /* The initial check in this function should cover this case */
509                 if (unlikely(frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)) {
510                         ret = -EINVAL;
511                         goto put_primary_if;
512                 }
513 
514                 skb_fragment = batadv_frag_create(skb, &frag_header,
515                                                   max_fragment_size);
516                 if (!skb_fragment) {
517                         ret = -ENOMEM;
518                         goto put_primary_if;
519                 }
520 
521                 batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
522                 batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
523                                    skb_fragment->len + ETH_HLEN);
524                 ret = batadv_send_unicast_skb(skb_fragment, neigh_node);
525                 if (ret != NET_XMIT_SUCCESS) {
526                         ret = NET_XMIT_DROP;
527                         goto put_primary_if;
528                 }
529 
530                 frag_header.no++;
531         }
532 
533         /* Make room for the fragment header. */
534         if (batadv_skb_head_push(skb, header_size) < 0 ||
535             pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0) {
536                 ret = -ENOMEM;
537                 goto put_primary_if;
538         }
539 
540         memcpy(skb->data, &frag_header, header_size);
541 
542         /* Send the last fragment */
543         batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
544         batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
545                            skb->len + ETH_HLEN);
546         ret = batadv_send_unicast_skb(skb, neigh_node);
547         /* skb was consumed */
548         skb = NULL;
549 
550 put_primary_if:
551         batadv_hardif_put(primary_if);
552 free_skb:
553         kfree_skb(skb);
554 
555         return ret;
556 }
557 

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