1 /* Copyright (C) 2013-2014 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 "main.h"
19 #include "fragmentation.h"
20 #include "send.h"
21 #include "originator.h"
22 #include "routing.h"
23 #include "hard-interface.h"
24 #include "soft-interface.h"
25 
26 
27 /**
28  * batadv_frag_clear_chain - delete entries in the fragment buffer chain
29  * @head: head of chain with entries.
30  *
31  * Free fragments in the passed hlist. Should be called with appropriate lock.
32  */
33 static void batadv_frag_clear_chain(struct hlist_head *head)
34 {
35 	struct batadv_frag_list_entry *entry;
36 	struct hlist_node *node;
37 
38 	hlist_for_each_entry_safe(entry, node, head, list) {
39 		hlist_del(&entry->list);
40 		kfree_skb(entry->skb);
41 		kfree(entry);
42 	}
43 }
44 
45 /**
46  * batadv_frag_purge_orig - free fragments associated to an orig
47  * @orig_node: originator to free fragments from
48  * @check_cb: optional function to tell if an entry should be purged
49  */
50 void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
51 			    bool (*check_cb)(struct batadv_frag_table_entry *))
52 {
53 	struct batadv_frag_table_entry *chain;
54 	uint8_t i;
55 
56 	for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
57 		chain = &orig_node->fragments[i];
58 		spin_lock_bh(&orig_node->fragments[i].lock);
59 
60 		if (!check_cb || check_cb(chain)) {
61 			batadv_frag_clear_chain(&orig_node->fragments[i].head);
62 			orig_node->fragments[i].size = 0;
63 		}
64 
65 		spin_unlock_bh(&orig_node->fragments[i].lock);
66 	}
67 }
68 
69 /**
70  * batadv_frag_size_limit - maximum possible size of packet to be fragmented
71  *
72  * Returns the maximum size of payload that can be fragmented.
73  */
74 static int batadv_frag_size_limit(void)
75 {
76 	int limit = BATADV_FRAG_MAX_FRAG_SIZE;
77 
78 	limit -= sizeof(struct batadv_frag_packet);
79 	limit *= BATADV_FRAG_MAX_FRAGMENTS;
80 
81 	return limit;
82 }
83 
84 /**
85  * batadv_frag_init_chain - check and prepare fragment chain for new fragment
86  * @chain: chain in fragments table to init
87  * @seqno: sequence number of the received fragment
88  *
89  * Make chain ready for a fragment with sequence number "seqno". Delete existing
90  * entries if they have an "old" sequence number.
91  *
92  * Caller must hold chain->lock.
93  *
94  * Returns true if chain is empty and caller can just insert the new fragment
95  * without searching for the right position.
96  */
97 static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,
98 				   uint16_t seqno)
99 {
100 	if (chain->seqno == seqno)
101 		return false;
102 
103 	if (!hlist_empty(&chain->head))
104 		batadv_frag_clear_chain(&chain->head);
105 
106 	chain->size = 0;
107 	chain->seqno = seqno;
108 
109 	return true;
110 }
111 
112 /**
113  * batadv_frag_insert_packet - insert a fragment into a fragment chain
114  * @orig_node: originator that the fragment was received from
115  * @skb: skb to insert
116  * @chain_out: list head to attach complete chains of fragments to
117  *
118  * Insert a new fragment into the reverse ordered chain in the right table
119  * entry. The hash table entry is cleared if "old" fragments exist in it.
120  *
121  * Returns true if skb is buffered, false on error. If the chain has all the
122  * fragments needed to merge the packet, the chain is moved to the passed head
123  * to avoid locking the chain in the table.
124  */
125 static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
126 				      struct sk_buff *skb,
127 				      struct hlist_head *chain_out)
128 {
129 	struct batadv_frag_table_entry *chain;
130 	struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;
131 	struct batadv_frag_list_entry *frag_entry_last = NULL;
132 	struct batadv_frag_packet *frag_packet;
133 	uint8_t bucket;
134 	uint16_t seqno, hdr_size = sizeof(struct batadv_frag_packet);
135 	bool ret = false;
136 
137 	/* Linearize packet to avoid linearizing 16 packets in a row when doing
138 	 * the later merge. Non-linear merge should be added to remove this
139 	 * linearization.
140 	 */
141 	if (skb_linearize(skb) < 0)
142 		goto err;
143 
144 	frag_packet = (struct batadv_frag_packet *)skb->data;
145 	seqno = ntohs(frag_packet->seqno);
146 	bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
147 
148 	frag_entry_new = kmalloc(sizeof(*frag_entry_new), GFP_ATOMIC);
149 	if (!frag_entry_new)
150 		goto err;
151 
152 	frag_entry_new->skb = skb;
153 	frag_entry_new->no = frag_packet->no;
154 
155 	/* Select entry in the "chain table" and delete any prior fragments
156 	 * with another sequence number. batadv_frag_init_chain() returns true,
157 	 * if the list is empty at return.
158 	 */
159 	chain = &orig_node->fragments[bucket];
160 	spin_lock_bh(&chain->lock);
161 	if (batadv_frag_init_chain(chain, seqno)) {
162 		hlist_add_head(&frag_entry_new->list, &chain->head);
163 		chain->size = skb->len - hdr_size;
164 		chain->timestamp = jiffies;
165 		ret = true;
166 		goto out;
167 	}
168 
169 	/* Find the position for the new fragment. */
170 	hlist_for_each_entry(frag_entry_curr, &chain->head, list) {
171 		/* Drop packet if fragment already exists. */
172 		if (frag_entry_curr->no == frag_entry_new->no)
173 			goto err_unlock;
174 
175 		/* Order fragments from highest to lowest. */
176 		if (frag_entry_curr->no < frag_entry_new->no) {
177 			hlist_add_before(&frag_entry_new->list,
178 					 &frag_entry_curr->list);
179 			chain->size += skb->len - hdr_size;
180 			chain->timestamp = jiffies;
181 			ret = true;
182 			goto out;
183 		}
184 
185 		/* store current entry because it could be the last in list */
186 		frag_entry_last = frag_entry_curr;
187 	}
188 
189 	/* Reached the end of the list, so insert after 'frag_entry_last'. */
190 	if (likely(frag_entry_last)) {
191 		hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
192 		chain->size += skb->len - hdr_size;
193 		chain->timestamp = jiffies;
194 		ret = true;
195 	}
196 
197 out:
198 	if (chain->size > batadv_frag_size_limit() ||
199 	    ntohs(frag_packet->total_size) > batadv_frag_size_limit()) {
200 		/* Clear chain if total size of either the list or the packet
201 		 * exceeds the maximum size of one merged packet.
202 		 */
203 		batadv_frag_clear_chain(&chain->head);
204 		chain->size = 0;
205 	} else if (ntohs(frag_packet->total_size) == chain->size) {
206 		/* All fragments received. Hand over chain to caller. */
207 		hlist_move_list(&chain->head, chain_out);
208 		chain->size = 0;
209 	}
210 
211 err_unlock:
212 	spin_unlock_bh(&chain->lock);
213 
214 err:
215 	if (!ret)
216 		kfree(frag_entry_new);
217 
218 	return ret;
219 }
220 
221 /**
222  * batadv_frag_merge_packets - merge a chain of fragments
223  * @chain: head of chain with fragments
224  * @skb: packet with total size of skb after merging
225  *
226  * Expand the first skb in the chain and copy the content of the remaining
227  * skb's into the expanded one. After doing so, clear the chain.
228  *
229  * Returns the merged skb or NULL on error.
230  */
231 static struct sk_buff *
232 batadv_frag_merge_packets(struct hlist_head *chain, struct sk_buff *skb)
233 {
234 	struct batadv_frag_packet *packet;
235 	struct batadv_frag_list_entry *entry;
236 	struct sk_buff *skb_out = NULL;
237 	int size, hdr_size = sizeof(struct batadv_frag_packet);
238 
239 	/* Make sure incoming skb has non-bogus data. */
240 	packet = (struct batadv_frag_packet *)skb->data;
241 	size = ntohs(packet->total_size);
242 	if (size > batadv_frag_size_limit())
243 		goto free;
244 
245 	/* Remove first entry, as this is the destination for the rest of the
246 	 * fragments.
247 	 */
248 	entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
249 	hlist_del(&entry->list);
250 	skb_out = entry->skb;
251 	kfree(entry);
252 
253 	/* Make room for the rest of the fragments. */
254 	if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
255 		kfree_skb(skb_out);
256 		skb_out = NULL;
257 		goto free;
258 	}
259 
260 	/* Move the existing MAC header to just before the payload. (Override
261 	 * the fragment header.)
262 	 */
263 	skb_pull_rcsum(skb_out, hdr_size);
264 	memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
265 	skb_set_mac_header(skb_out, -ETH_HLEN);
266 	skb_reset_network_header(skb_out);
267 	skb_reset_transport_header(skb_out);
268 
269 	/* Copy the payload of the each fragment into the last skb */
270 	hlist_for_each_entry(entry, chain, list) {
271 		size = entry->skb->len - hdr_size;
272 		memcpy(skb_put(skb_out, size), entry->skb->data + hdr_size,
273 		       size);
274 	}
275 
276 free:
277 	/* Locking is not needed, because 'chain' is not part of any orig. */
278 	batadv_frag_clear_chain(chain);
279 	return skb_out;
280 }
281 
282 /**
283  * batadv_frag_skb_buffer - buffer fragment for later merge
284  * @skb: skb to buffer
285  * @orig_node_src: originator that the skb is received from
286  *
287  * Add fragment to buffer and merge fragments if possible.
288  *
289  * There are three possible outcomes: 1) Packet is merged: Return true and
290  * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
291  * to NULL; 3) Error: Return false and leave skb as is.
292  */
293 bool batadv_frag_skb_buffer(struct sk_buff **skb,
294 			    struct batadv_orig_node *orig_node_src)
295 {
296 	struct sk_buff *skb_out = NULL;
297 	struct hlist_head head = HLIST_HEAD_INIT;
298 	bool ret = false;
299 
300 	/* Add packet to buffer and table entry if merge is possible. */
301 	if (!batadv_frag_insert_packet(orig_node_src, *skb, &head))
302 		goto out_err;
303 
304 	/* Leave if more fragments are needed to merge. */
305 	if (hlist_empty(&head))
306 		goto out;
307 
308 	skb_out = batadv_frag_merge_packets(&head, *skb);
309 	if (!skb_out)
310 		goto out_err;
311 
312 out:
313 	*skb = skb_out;
314 	ret = true;
315 out_err:
316 	return ret;
317 }
318 
319 /**
320  * batadv_frag_skb_fwd - forward fragments that would exceed MTU when merged
321  * @skb: skb to forward
322  * @recv_if: interface that the skb is received on
323  * @orig_node_src: originator that the skb is received from
324  *
325  * Look up the next-hop of the fragments payload and check if the merged packet
326  * will exceed the MTU towards the next-hop. If so, the fragment is forwarded
327  * without merging it.
328  *
329  * Returns true if the fragment is consumed/forwarded, false otherwise.
330  */
331 bool batadv_frag_skb_fwd(struct sk_buff *skb,
332 			 struct batadv_hard_iface *recv_if,
333 			 struct batadv_orig_node *orig_node_src)
334 {
335 	struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
336 	struct batadv_orig_node *orig_node_dst = NULL;
337 	struct batadv_neigh_node *neigh_node = NULL;
338 	struct batadv_frag_packet *packet;
339 	uint16_t total_size;
340 	bool ret = false;
341 
342 	packet = (struct batadv_frag_packet *)skb->data;
343 	orig_node_dst = batadv_orig_hash_find(bat_priv, packet->dest);
344 	if (!orig_node_dst)
345 		goto out;
346 
347 	neigh_node = batadv_find_router(bat_priv, orig_node_dst, recv_if);
348 	if (!neigh_node)
349 		goto out;
350 
351 	/* Forward the fragment, if the merged packet would be too big to
352 	 * be assembled.
353 	 */
354 	total_size = ntohs(packet->total_size);
355 	if (total_size > neigh_node->if_incoming->net_dev->mtu) {
356 		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
357 		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
358 				   skb->len + ETH_HLEN);
359 
360 		packet->ttl--;
361 		batadv_send_skb_packet(skb, neigh_node->if_incoming,
362 				       neigh_node->addr);
363 		ret = true;
364 	}
365 
366 out:
367 	if (orig_node_dst)
368 		batadv_orig_node_free_ref(orig_node_dst);
369 	if (neigh_node)
370 		batadv_neigh_node_free_ref(neigh_node);
371 	return ret;
372 }
373 
374 /**
375  * batadv_frag_create - create a fragment from skb
376  * @skb: skb to create fragment from
377  * @frag_head: header to use in new fragment
378  * @mtu: size of new fragment
379  *
380  * Split the passed skb into two fragments: A new one with size matching the
381  * passed mtu and the old one with the rest. The new skb contains data from the
382  * tail of the old skb.
383  *
384  * Returns the new fragment, NULL on error.
385  */
386 static struct sk_buff *batadv_frag_create(struct sk_buff *skb,
387 					  struct batadv_frag_packet *frag_head,
388 					  unsigned int mtu)
389 {
390 	struct sk_buff *skb_fragment;
391 	unsigned header_size = sizeof(*frag_head);
392 	unsigned fragment_size = mtu - header_size;
393 
394 	skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN);
395 	if (!skb_fragment)
396 		goto err;
397 
398 	skb->priority = TC_PRIO_CONTROL;
399 
400 	/* Eat the last mtu-bytes of the skb */
401 	skb_reserve(skb_fragment, header_size + ETH_HLEN);
402 	skb_split(skb, skb_fragment, skb->len - fragment_size);
403 
404 	/* Add the header */
405 	skb_push(skb_fragment, header_size);
406 	memcpy(skb_fragment->data, frag_head, header_size);
407 
408 err:
409 	return skb_fragment;
410 }
411 
412 /**
413  * batadv_frag_send_packet - create up to 16 fragments from the passed skb
414  * @skb: skb to create fragments from
415  * @orig_node: final destination of the created fragments
416  * @neigh_node: next-hop of the created fragments
417  *
418  * Returns true on success, false otherwise.
419  */
420 bool batadv_frag_send_packet(struct sk_buff *skb,
421 			     struct batadv_orig_node *orig_node,
422 			     struct batadv_neigh_node *neigh_node)
423 {
424 	struct batadv_priv *bat_priv;
425 	struct batadv_hard_iface *primary_if = NULL;
426 	struct batadv_frag_packet frag_header;
427 	struct sk_buff *skb_fragment;
428 	unsigned mtu = neigh_node->if_incoming->net_dev->mtu;
429 	unsigned header_size = sizeof(frag_header);
430 	unsigned max_fragment_size, max_packet_size;
431 	bool ret = false;
432 
433 	/* To avoid merge and refragmentation at next-hops we never send
434 	 * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
435 	 */
436 	mtu = min_t(unsigned, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
437 	max_fragment_size = mtu - header_size;
438 	max_packet_size = max_fragment_size * BATADV_FRAG_MAX_FRAGMENTS;
439 
440 	/* Don't even try to fragment, if we need more than 16 fragments */
441 	if (skb->len > max_packet_size)
442 		goto out_err;
443 
444 	bat_priv = orig_node->bat_priv;
445 	primary_if = batadv_primary_if_get_selected(bat_priv);
446 	if (!primary_if)
447 		goto out_err;
448 
449 	/* Create one header to be copied to all fragments */
450 	frag_header.packet_type = BATADV_UNICAST_FRAG;
451 	frag_header.version = BATADV_COMPAT_VERSION;
452 	frag_header.ttl = BATADV_TTL;
453 	frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
454 	frag_header.reserved = 0;
455 	frag_header.no = 0;
456 	frag_header.total_size = htons(skb->len);
457 	ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
458 	ether_addr_copy(frag_header.dest, orig_node->orig);
459 
460 	/* Eat and send fragments from the tail of skb */
461 	while (skb->len > max_fragment_size) {
462 		skb_fragment = batadv_frag_create(skb, &frag_header, mtu);
463 		if (!skb_fragment)
464 			goto out_err;
465 
466 		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
467 		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
468 				   skb_fragment->len + ETH_HLEN);
469 		batadv_send_skb_packet(skb_fragment, neigh_node->if_incoming,
470 				       neigh_node->addr);
471 		frag_header.no++;
472 
473 		/* The initial check in this function should cover this case */
474 		if (frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)
475 			goto out_err;
476 	}
477 
478 	/* Make room for the fragment header. */
479 	if (batadv_skb_head_push(skb, header_size) < 0 ||
480 	    pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0)
481 		goto out_err;
482 
483 	memcpy(skb->data, &frag_header, header_size);
484 
485 	/* Send the last fragment */
486 	batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
487 	batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
488 			   skb->len + ETH_HLEN);
489 	batadv_send_skb_packet(skb, neigh_node->if_incoming, neigh_node->addr);
490 
491 	ret = true;
492 
493 out_err:
494 	if (primary_if)
495 		batadv_hardif_free_ref(primary_if);
496 
497 	return ret;
498 }
499