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TOMOYO Linux Cross Reference
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/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 the caller can just insert the new
106  * fragment 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 the 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  * @net_dev: outgoing device for fragment
395  * @skb: skb to create fragment from
396  * @frag_head: header to use in new fragment
397  * @fragment_size: size of new fragment
398  *
399  * Split the passed skb into two fragments: A new one with size matching the
400  * passed mtu and the old one with the rest. The new skb contains data from the
401  * tail of the old skb.
402  *
403  * Return: the new fragment, NULL on error.
404  */
405 static struct sk_buff *batadv_frag_create(struct net_device *net_dev,
406                                           struct sk_buff *skb,
407                                           struct batadv_frag_packet *frag_head,
408                                           unsigned int fragment_size)
409 {
410         unsigned int ll_reserved = LL_RESERVED_SPACE(net_dev);
411         unsigned int tailroom = net_dev->needed_tailroom;
412         struct sk_buff *skb_fragment;
413         unsigned int header_size = sizeof(*frag_head);
414         unsigned int mtu = fragment_size + header_size;
415 
416         skb_fragment = dev_alloc_skb(ll_reserved + mtu + tailroom);
417         if (!skb_fragment)
418                 goto err;
419 
420         skb_fragment->priority = skb->priority;
421 
422         /* Eat the last mtu-bytes of the skb */
423         skb_reserve(skb_fragment, ll_reserved + header_size);
424         skb_split(skb, skb_fragment, skb->len - fragment_size);
425 
426         /* Add the header */
427         skb_push(skb_fragment, header_size);
428         memcpy(skb_fragment->data, frag_head, header_size);
429 
430 err:
431         return skb_fragment;
432 }
433 
434 /**
435  * batadv_frag_send_packet() - create up to 16 fragments from the passed skb
436  * @skb: skb to create fragments from
437  * @orig_node: final destination of the created fragments
438  * @neigh_node: next-hop of the created fragments
439  *
440  * Return: the netdev tx status or a negative errno code on a failure
441  */
442 int batadv_frag_send_packet(struct sk_buff *skb,
443                             struct batadv_orig_node *orig_node,
444                             struct batadv_neigh_node *neigh_node)
445 {
446         struct net_device *net_dev = neigh_node->if_incoming->net_dev;
447         struct batadv_priv *bat_priv;
448         struct batadv_hard_iface *primary_if = NULL;
449         struct batadv_frag_packet frag_header;
450         struct sk_buff *skb_fragment;
451         unsigned int mtu = net_dev->mtu;
452         unsigned int header_size = sizeof(frag_header);
453         unsigned int max_fragment_size, num_fragments;
454         int ret;
455 
456         /* To avoid merge and refragmentation at next-hops we never send
457          * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
458          */
459         mtu = min_t(unsigned int, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
460         max_fragment_size = mtu - header_size;
461 
462         if (skb->len == 0 || max_fragment_size == 0)
463                 return -EINVAL;
464 
465         num_fragments = (skb->len - 1) / max_fragment_size + 1;
466         max_fragment_size = (skb->len - 1) / num_fragments + 1;
467 
468         /* Don't even try to fragment, if we need more than 16 fragments */
469         if (num_fragments > BATADV_FRAG_MAX_FRAGMENTS) {
470                 ret = -EAGAIN;
471                 goto free_skb;
472         }
473 
474         bat_priv = orig_node->bat_priv;
475         primary_if = batadv_primary_if_get_selected(bat_priv);
476         if (!primary_if) {
477                 ret = -EINVAL;
478                 goto free_skb;
479         }
480 
481         /* Create one header to be copied to all fragments */
482         frag_header.packet_type = BATADV_UNICAST_FRAG;
483         frag_header.version = BATADV_COMPAT_VERSION;
484         frag_header.ttl = BATADV_TTL;
485         frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
486         frag_header.reserved = 0;
487         frag_header.no = 0;
488         frag_header.total_size = htons(skb->len);
489 
490         /* skb->priority values from 256->263 are magic values to
491          * directly indicate a specific 802.1d priority.  This is used
492          * to allow 802.1d priority to be passed directly in from VLAN
493          * tags, etc.
494          */
495         if (skb->priority >= 256 && skb->priority <= 263)
496                 frag_header.priority = skb->priority - 256;
497         else
498                 frag_header.priority = 0;
499 
500         ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
501         ether_addr_copy(frag_header.dest, orig_node->orig);
502 
503         /* Eat and send fragments from the tail of skb */
504         while (skb->len > max_fragment_size) {
505                 /* The initial check in this function should cover this case */
506                 if (unlikely(frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)) {
507                         ret = -EINVAL;
508                         goto put_primary_if;
509                 }
510 
511                 skb_fragment = batadv_frag_create(net_dev, skb, &frag_header,
512                                                   max_fragment_size);
513                 if (!skb_fragment) {
514                         ret = -ENOMEM;
515                         goto put_primary_if;
516                 }
517 
518                 batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
519                 batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
520                                    skb_fragment->len + ETH_HLEN);
521                 ret = batadv_send_unicast_skb(skb_fragment, neigh_node);
522                 if (ret != NET_XMIT_SUCCESS) {
523                         ret = NET_XMIT_DROP;
524                         goto put_primary_if;
525                 }
526 
527                 frag_header.no++;
528         }
529 
530         /* make sure that there is at least enough head for the fragmentation
531          * and ethernet headers
532          */
533         ret = skb_cow_head(skb, ETH_HLEN + header_size);
534         if (ret < 0)
535                 goto put_primary_if;
536 
537         skb_push(skb, header_size);
538         memcpy(skb->data, &frag_header, header_size);
539 
540         /* Send the last fragment */
541         batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
542         batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
543                            skb->len + ETH_HLEN);
544         ret = batadv_send_unicast_skb(skb, neigh_node);
545         /* skb was consumed */
546         skb = NULL;
547 
548 put_primary_if:
549         batadv_hardif_put(primary_if);
550 free_skb:
551         kfree_skb(skb);
552 
553         return ret;
554 }
555 

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