1 // SPDX-License-Identifier: GPL-2.0
2 /* Copyright (C) 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/lockdep.h>
18 #include <linux/minmax.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 
31 /**
32  * batadv_frag_clear_chain() - delete entries in the fragment buffer chain
33  * @head: head of chain with entries.
34  * @dropped: whether the chain is cleared because all fragments are dropped
35  *
36  * Free fragments in the passed hlist. Should be called with appropriate lock.
37  */
38 static void batadv_frag_clear_chain(struct hlist_head *head, bool dropped)
39 {
40 	struct batadv_frag_list_entry *entry;
41 	struct hlist_node *node;
42 
43 	hlist_for_each_entry_safe(entry, node, head, list) {
44 		hlist_del(&entry->list);
45 
46 		if (dropped)
47 			kfree_skb(entry->skb);
48 		else
49 			consume_skb(entry->skb);
50 
51 		kfree(entry);
52 	}
53 }
54 
55 /**
56  * batadv_frag_purge_orig() - free fragments associated to an orig
57  * @orig_node: originator to free fragments from
58  * @check_cb: optional function to tell if an entry should be purged
59  */
60 void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
61 			    bool (*check_cb)(struct batadv_frag_table_entry *))
62 {
63 	struct batadv_frag_table_entry *chain;
64 	u8 i;
65 
66 	for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
67 		chain = &orig_node->fragments[i];
68 		spin_lock_bh(&chain->lock);
69 
70 		if (!check_cb || check_cb(chain)) {
71 			batadv_frag_clear_chain(&chain->fragment_list, true);
72 			chain->size = 0;
73 		}
74 
75 		spin_unlock_bh(&chain->lock);
76 	}
77 }
78 
79 /**
80  * batadv_frag_size_limit() - maximum possible size of packet to be fragmented
81  *
82  * Return: the maximum size of payload that can be fragmented.
83  */
84 static int batadv_frag_size_limit(void)
85 {
86 	int limit = BATADV_FRAG_MAX_FRAG_SIZE;
87 
88 	limit -= sizeof(struct batadv_frag_packet);
89 	limit *= BATADV_FRAG_MAX_FRAGMENTS;
90 
91 	return limit;
92 }
93 
94 /**
95  * batadv_frag_init_chain() - check and prepare fragment chain for new fragment
96  * @chain: chain in fragments table to init
97  * @seqno: sequence number of the received fragment
98  *
99  * Make chain ready for a fragment with sequence number "seqno". Delete existing
100  * entries if they have an "old" sequence number.
101  *
102  * Caller must hold chain->lock.
103  *
104  * Return: true if chain is empty and the caller can just insert the new
105  * fragment without searching for the right position.
106  */
107 static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,
108 				   u16 seqno)
109 {
110 	lockdep_assert_held(&chain->lock);
111 
112 	if (chain->seqno == seqno)
113 		return false;
114 
115 	if (!hlist_empty(&chain->fragment_list))
116 		batadv_frag_clear_chain(&chain->fragment_list, true);
117 
118 	chain->size = 0;
119 	chain->seqno = seqno;
120 
121 	return true;
122 }
123 
124 /**
125  * batadv_frag_insert_packet() - insert a fragment into a fragment chain
126  * @orig_node: originator that the fragment was received from
127  * @skb: skb to insert
128  * @chain_out: list head to attach complete chains of fragments to
129  *
130  * Insert a new fragment into the reverse ordered chain in the right table
131  * entry. The hash table entry is cleared if "old" fragments exist in it.
132  *
133  * Return: true if skb is buffered, false on error. If the chain has all the
134  * fragments needed to merge the packet, the chain is moved to the passed head
135  * to avoid locking the chain in the table.
136  */
137 static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
138 				      struct sk_buff *skb,
139 				      struct hlist_head *chain_out)
140 {
141 	struct batadv_frag_table_entry *chain;
142 	struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;
143 	struct batadv_frag_list_entry *frag_entry_last = NULL;
144 	struct batadv_frag_packet *frag_packet;
145 	u8 bucket;
146 	u16 seqno, hdr_size = sizeof(struct batadv_frag_packet);
147 	bool ret = false;
148 
149 	/* Linearize packet to avoid linearizing 16 packets in a row when doing
150 	 * the later merge. Non-linear merge should be added to remove this
151 	 * linearization.
152 	 */
153 	if (skb_linearize(skb) < 0)
154 		goto err;
155 
156 	frag_packet = (struct batadv_frag_packet *)skb->data;
157 	seqno = ntohs(frag_packet->seqno);
158 	bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
159 
160 	frag_entry_new = kmalloc(sizeof(*frag_entry_new), GFP_ATOMIC);
161 	if (!frag_entry_new)
162 		goto err;
163 
164 	frag_entry_new->skb = skb;
165 	frag_entry_new->no = frag_packet->no;
166 
167 	/* Select entry in the "chain table" and delete any prior fragments
168 	 * with another sequence number. batadv_frag_init_chain() returns true,
169 	 * if the list is empty at return.
170 	 */
171 	chain = &orig_node->fragments[bucket];
172 	spin_lock_bh(&chain->lock);
173 	if (batadv_frag_init_chain(chain, seqno)) {
174 		hlist_add_head(&frag_entry_new->list, &chain->fragment_list);
175 		chain->size = skb->len - hdr_size;
176 		chain->timestamp = jiffies;
177 		chain->total_size = ntohs(frag_packet->total_size);
178 		ret = true;
179 		goto out;
180 	}
181 
182 	/* Find the position for the new fragment. */
183 	hlist_for_each_entry(frag_entry_curr, &chain->fragment_list, list) {
184 		/* Drop packet if fragment already exists. */
185 		if (frag_entry_curr->no == frag_entry_new->no)
186 			goto err_unlock;
187 
188 		/* Order fragments from highest to lowest. */
189 		if (frag_entry_curr->no < frag_entry_new->no) {
190 			hlist_add_before(&frag_entry_new->list,
191 					 &frag_entry_curr->list);
192 			chain->size += skb->len - hdr_size;
193 			chain->timestamp = jiffies;
194 			ret = true;
195 			goto out;
196 		}
197 
198 		/* store current entry because it could be the last in list */
199 		frag_entry_last = frag_entry_curr;
200 	}
201 
202 	/* Reached the end of the list, so insert after 'frag_entry_last'. */
203 	if (likely(frag_entry_last)) {
204 		hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
205 		chain->size += skb->len - hdr_size;
206 		chain->timestamp = jiffies;
207 		ret = true;
208 	}
209 
210 out:
211 	if (chain->size > batadv_frag_size_limit() ||
212 	    chain->total_size != ntohs(frag_packet->total_size) ||
213 	    chain->total_size > batadv_frag_size_limit()) {
214 		/* Clear chain if total size of either the list or the packet
215 		 * exceeds the maximum size of one merged packet. Don't allow
216 		 * packets to have different total_size.
217 		 */
218 		batadv_frag_clear_chain(&chain->fragment_list, true);
219 		chain->size = 0;
220 	} else if (ntohs(frag_packet->total_size) == chain->size) {
221 		/* All fragments received. Hand over chain to caller. */
222 		hlist_move_list(&chain->fragment_list, chain_out);
223 		chain->size = 0;
224 	}
225 
226 err_unlock:
227 	spin_unlock_bh(&chain->lock);
228 
229 err:
230 	if (!ret) {
231 		kfree(frag_entry_new);
232 		kfree_skb(skb);
233 	}
234 
235 	return ret;
236 }
237 
238 /**
239  * batadv_frag_merge_packets() - merge a chain of fragments
240  * @chain: head of chain with fragments
241  *
242  * Expand the first skb in the chain and copy the content of the remaining
243  * skb's into the expanded one. After doing so, clear the chain.
244  *
245  * Return: the merged skb or NULL on error.
246  */
247 static struct sk_buff *
248 batadv_frag_merge_packets(struct hlist_head *chain)
249 {
250 	struct batadv_frag_packet *packet;
251 	struct batadv_frag_list_entry *entry;
252 	struct sk_buff *skb_out;
253 	int size, hdr_size = sizeof(struct batadv_frag_packet);
254 	bool dropped = false;
255 
256 	/* Remove first entry, as this is the destination for the rest of the
257 	 * fragments.
258 	 */
259 	entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
260 	hlist_del(&entry->list);
261 	skb_out = entry->skb;
262 	kfree(entry);
263 
264 	packet = (struct batadv_frag_packet *)skb_out->data;
265 	size = ntohs(packet->total_size) + hdr_size;
266 
267 	/* Make room for the rest of the fragments. */
268 	if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
269 		kfree_skb(skb_out);
270 		skb_out = NULL;
271 		dropped = true;
272 		goto free;
273 	}
274 
275 	/* Move the existing MAC header to just before the payload. (Override
276 	 * the fragment header.)
277 	 */
278 	skb_pull(skb_out, hdr_size);
279 	skb_out->ip_summed = CHECKSUM_NONE;
280 	memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
281 	skb_set_mac_header(skb_out, -ETH_HLEN);
282 	skb_reset_network_header(skb_out);
283 	skb_reset_transport_header(skb_out);
284 
285 	/* Copy the payload of the each fragment into the last skb */
286 	hlist_for_each_entry(entry, chain, list) {
287 		size = entry->skb->len - hdr_size;
288 		skb_put_data(skb_out, entry->skb->data + hdr_size, size);
289 	}
290 
291 free:
292 	/* Locking is not needed, because 'chain' is not part of any orig. */
293 	batadv_frag_clear_chain(chain, dropped);
294 	return skb_out;
295 }
296 
297 /**
298  * batadv_frag_skb_buffer() - buffer fragment for later merge
299  * @skb: skb to buffer
300  * @orig_node_src: originator that the skb is received from
301  *
302  * Add fragment to buffer and merge fragments if possible.
303  *
304  * There are three possible outcomes: 1) Packet is merged: Return true and
305  * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
306  * to NULL; 3) Error: Return false and free skb.
307  *
308  * Return: true when the packet is merged or buffered, false when skb is not
309  * used.
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 	ret = true;
332 out_err:
333 	*skb = skb_out;
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  * Return: 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;
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_unicast_skb(skb, neigh_node);
380 		ret = true;
381 	}
382 
383 out:
384 	batadv_orig_node_put(orig_node_dst);
385 	batadv_neigh_node_put(neigh_node);
386 	return ret;
387 }
388 
389 /**
390  * batadv_frag_create() - create a fragment from skb
391  * @net_dev: outgoing device for fragment
392  * @skb: skb to create fragment from
393  * @frag_head: header to use in new fragment
394  * @fragment_size: size of new fragment
395  *
396  * Split the passed skb into two fragments: A new one with size matching the
397  * passed mtu and the old one with the rest. The new skb contains data from the
398  * tail of the old skb.
399  *
400  * Return: the new fragment, NULL on error.
401  */
402 static struct sk_buff *batadv_frag_create(struct net_device *net_dev,
403 					  struct sk_buff *skb,
404 					  struct batadv_frag_packet *frag_head,
405 					  unsigned int fragment_size)
406 {
407 	unsigned int ll_reserved = LL_RESERVED_SPACE(net_dev);
408 	unsigned int tailroom = net_dev->needed_tailroom;
409 	struct sk_buff *skb_fragment;
410 	unsigned int header_size = sizeof(*frag_head);
411 	unsigned int mtu = fragment_size + header_size;
412 
413 	skb_fragment = dev_alloc_skb(ll_reserved + mtu + tailroom);
414 	if (!skb_fragment)
415 		goto err;
416 
417 	skb_fragment->priority = skb->priority;
418 
419 	/* Eat the last mtu-bytes of the skb */
420 	skb_reserve(skb_fragment, ll_reserved + header_size);
421 	skb_split(skb, skb_fragment, skb->len - fragment_size);
422 
423 	/* Add the header */
424 	skb_push(skb_fragment, header_size);
425 	memcpy(skb_fragment->data, frag_head, header_size);
426 
427 err:
428 	return skb_fragment;
429 }
430 
431 /**
432  * batadv_frag_send_packet() - create up to 16 fragments from the passed skb
433  * @skb: skb to create fragments from
434  * @orig_node: final destination of the created fragments
435  * @neigh_node: next-hop of the created fragments
436  *
437  * Return: the netdev tx status or a negative errno code on a failure
438  */
439 int batadv_frag_send_packet(struct sk_buff *skb,
440 			    struct batadv_orig_node *orig_node,
441 			    struct batadv_neigh_node *neigh_node)
442 {
443 	struct net_device *net_dev = neigh_node->if_incoming->net_dev;
444 	struct batadv_priv *bat_priv;
445 	struct batadv_hard_iface *primary_if = NULL;
446 	struct batadv_frag_packet frag_header;
447 	struct sk_buff *skb_fragment;
448 	unsigned int mtu = net_dev->mtu;
449 	unsigned int header_size = sizeof(frag_header);
450 	unsigned int max_fragment_size, num_fragments;
451 	int ret;
452 
453 	/* To avoid merge and refragmentation at next-hops we never send
454 	 * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
455 	 */
456 	mtu = min_t(unsigned int, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
457 	max_fragment_size = mtu - header_size;
458 
459 	if (skb->len == 0 || max_fragment_size == 0)
460 		return -EINVAL;
461 
462 	num_fragments = (skb->len - 1) / max_fragment_size + 1;
463 	max_fragment_size = (skb->len - 1) / num_fragments + 1;
464 
465 	/* Don't even try to fragment, if we need more than 16 fragments */
466 	if (num_fragments > BATADV_FRAG_MAX_FRAGMENTS) {
467 		ret = -EAGAIN;
468 		goto free_skb;
469 	}
470 
471 	bat_priv = orig_node->bat_priv;
472 	primary_if = batadv_primary_if_get_selected(bat_priv);
473 	if (!primary_if) {
474 		ret = -EINVAL;
475 		goto free_skb;
476 	}
477 
478 	/* GRO might have added fragments to the fragment list instead of
479 	 * frags[]. But this is not handled by skb_split and must be
480 	 * linearized to avoid incorrect length information after all
481 	 * batman-adv fragments were created and submitted to the
482 	 * hard-interface
483 	 */
484 	if (skb_has_frag_list(skb) && __skb_linearize(skb)) {
485 		ret = -ENOMEM;
486 		goto free_skb;
487 	}
488 
489 	/* Create one header to be copied to all fragments */
490 	frag_header.packet_type = BATADV_UNICAST_FRAG;
491 	frag_header.version = BATADV_COMPAT_VERSION;
492 	frag_header.ttl = BATADV_TTL;
493 	frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
494 	frag_header.reserved = 0;
495 	frag_header.no = 0;
496 	frag_header.total_size = htons(skb->len);
497 
498 	/* skb->priority values from 256->263 are magic values to
499 	 * directly indicate a specific 802.1d priority.  This is used
500 	 * to allow 802.1d priority to be passed directly in from VLAN
501 	 * tags, etc.
502 	 */
503 	if (skb->priority >= 256 && skb->priority <= 263)
504 		frag_header.priority = skb->priority - 256;
505 	else
506 		frag_header.priority = 0;
507 
508 	ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
509 	ether_addr_copy(frag_header.dest, orig_node->orig);
510 
511 	/* Eat and send fragments from the tail of skb */
512 	while (skb->len > max_fragment_size) {
513 		/* The initial check in this function should cover this case */
514 		if (unlikely(frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)) {
515 			ret = -EINVAL;
516 			goto put_primary_if;
517 		}
518 
519 		skb_fragment = batadv_frag_create(net_dev, skb, &frag_header,
520 						  max_fragment_size);
521 		if (!skb_fragment) {
522 			ret = -ENOMEM;
523 			goto put_primary_if;
524 		}
525 
526 		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
527 		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
528 				   skb_fragment->len + ETH_HLEN);
529 		ret = batadv_send_unicast_skb(skb_fragment, neigh_node);
530 		if (ret != NET_XMIT_SUCCESS) {
531 			ret = NET_XMIT_DROP;
532 			goto put_primary_if;
533 		}
534 
535 		frag_header.no++;
536 	}
537 
538 	/* make sure that there is at least enough head for the fragmentation
539 	 * and ethernet headers
540 	 */
541 	ret = skb_cow_head(skb, ETH_HLEN + header_size);
542 	if (ret < 0)
543 		goto put_primary_if;
544 
545 	skb_push(skb, header_size);
546 	memcpy(skb->data, &frag_header, header_size);
547 
548 	/* Send the last fragment */
549 	batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
550 	batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
551 			   skb->len + ETH_HLEN);
552 	ret = batadv_send_unicast_skb(skb, neigh_node);
553 	/* skb was consumed */
554 	skb = NULL;
555 
556 put_primary_if:
557 	batadv_hardif_put(primary_if);
558 free_skb:
559 	kfree_skb(skb);
560 
561 	return ret;
562 }
563