xref: /openbmc/linux/net/ipv4/inet_fragment.c (revision e8254a8e)
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * inet fragments management
4  *
5  * 		Authors:	Pavel Emelyanov <xemul@openvz.org>
6  *				Started as consolidation of ipv4/ip_fragment.c,
7  *				ipv6/reassembly. and ipv6 nf conntrack reassembly
8  */
9 
10 #include <linux/list.h>
11 #include <linux/spinlock.h>
12 #include <linux/module.h>
13 #include <linux/timer.h>
14 #include <linux/mm.h>
15 #include <linux/random.h>
16 #include <linux/skbuff.h>
17 #include <linux/rtnetlink.h>
18 #include <linux/slab.h>
19 #include <linux/rhashtable.h>
20 
21 #include <net/sock.h>
22 #include <net/inet_frag.h>
23 #include <net/inet_ecn.h>
24 #include <net/ip.h>
25 #include <net/ipv6.h>
26 
27 /* Use skb->cb to track consecutive/adjacent fragments coming at
28  * the end of the queue. Nodes in the rb-tree queue will
29  * contain "runs" of one or more adjacent fragments.
30  *
31  * Invariants:
32  * - next_frag is NULL at the tail of a "run";
33  * - the head of a "run" has the sum of all fragment lengths in frag_run_len.
34  */
35 struct ipfrag_skb_cb {
36 	union {
37 		struct inet_skb_parm	h4;
38 		struct inet6_skb_parm	h6;
39 	};
40 	struct sk_buff		*next_frag;
41 	int			frag_run_len;
42 };
43 
44 #define FRAG_CB(skb)		((struct ipfrag_skb_cb *)((skb)->cb))
45 
46 static void fragcb_clear(struct sk_buff *skb)
47 {
48 	RB_CLEAR_NODE(&skb->rbnode);
49 	FRAG_CB(skb)->next_frag = NULL;
50 	FRAG_CB(skb)->frag_run_len = skb->len;
51 }
52 
53 /* Append skb to the last "run". */
54 static void fragrun_append_to_last(struct inet_frag_queue *q,
55 				   struct sk_buff *skb)
56 {
57 	fragcb_clear(skb);
58 
59 	FRAG_CB(q->last_run_head)->frag_run_len += skb->len;
60 	FRAG_CB(q->fragments_tail)->next_frag = skb;
61 	q->fragments_tail = skb;
62 }
63 
64 /* Create a new "run" with the skb. */
65 static void fragrun_create(struct inet_frag_queue *q, struct sk_buff *skb)
66 {
67 	BUILD_BUG_ON(sizeof(struct ipfrag_skb_cb) > sizeof(skb->cb));
68 	fragcb_clear(skb);
69 
70 	if (q->last_run_head)
71 		rb_link_node(&skb->rbnode, &q->last_run_head->rbnode,
72 			     &q->last_run_head->rbnode.rb_right);
73 	else
74 		rb_link_node(&skb->rbnode, NULL, &q->rb_fragments.rb_node);
75 	rb_insert_color(&skb->rbnode, &q->rb_fragments);
76 
77 	q->fragments_tail = skb;
78 	q->last_run_head = skb;
79 }
80 
81 /* Given the OR values of all fragments, apply RFC 3168 5.3 requirements
82  * Value : 0xff if frame should be dropped.
83  *         0 or INET_ECN_CE value, to be ORed in to final iph->tos field
84  */
85 const u8 ip_frag_ecn_table[16] = {
86 	/* at least one fragment had CE, and others ECT_0 or ECT_1 */
87 	[IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0]			= INET_ECN_CE,
88 	[IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1]			= INET_ECN_CE,
89 	[IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1]	= INET_ECN_CE,
90 
91 	/* invalid combinations : drop frame */
92 	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE] = 0xff,
93 	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0] = 0xff,
94 	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_1] = 0xff,
95 	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
96 	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = 0xff,
97 	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = 0xff,
98 	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
99 };
100 EXPORT_SYMBOL(ip_frag_ecn_table);
101 
102 int inet_frags_init(struct inet_frags *f)
103 {
104 	f->frags_cachep = kmem_cache_create(f->frags_cache_name, f->qsize, 0, 0,
105 					    NULL);
106 	if (!f->frags_cachep)
107 		return -ENOMEM;
108 
109 	refcount_set(&f->refcnt, 1);
110 	init_completion(&f->completion);
111 	return 0;
112 }
113 EXPORT_SYMBOL(inet_frags_init);
114 
115 void inet_frags_fini(struct inet_frags *f)
116 {
117 	if (refcount_dec_and_test(&f->refcnt))
118 		complete(&f->completion);
119 
120 	wait_for_completion(&f->completion);
121 
122 	kmem_cache_destroy(f->frags_cachep);
123 	f->frags_cachep = NULL;
124 }
125 EXPORT_SYMBOL(inet_frags_fini);
126 
127 /* called from rhashtable_free_and_destroy() at netns_frags dismantle */
128 static void inet_frags_free_cb(void *ptr, void *arg)
129 {
130 	struct inet_frag_queue *fq = ptr;
131 	int count;
132 
133 	count = del_timer_sync(&fq->timer) ? 1 : 0;
134 
135 	spin_lock_bh(&fq->lock);
136 	fq->flags |= INET_FRAG_DROP;
137 	if (!(fq->flags & INET_FRAG_COMPLETE)) {
138 		fq->flags |= INET_FRAG_COMPLETE;
139 		count++;
140 	} else if (fq->flags & INET_FRAG_HASH_DEAD) {
141 		count++;
142 	}
143 	spin_unlock_bh(&fq->lock);
144 
145 	if (refcount_sub_and_test(count, &fq->refcnt))
146 		inet_frag_destroy(fq);
147 }
148 
149 static LLIST_HEAD(fqdir_free_list);
150 
151 static void fqdir_free_fn(struct work_struct *work)
152 {
153 	struct llist_node *kill_list;
154 	struct fqdir *fqdir, *tmp;
155 	struct inet_frags *f;
156 
157 	/* Atomically snapshot the list of fqdirs to free */
158 	kill_list = llist_del_all(&fqdir_free_list);
159 
160 	/* We need to make sure all ongoing call_rcu(..., inet_frag_destroy_rcu)
161 	 * have completed, since they need to dereference fqdir.
162 	 * Would it not be nice to have kfree_rcu_barrier() ? :)
163 	 */
164 	rcu_barrier();
165 
166 	llist_for_each_entry_safe(fqdir, tmp, kill_list, free_list) {
167 		f = fqdir->f;
168 		if (refcount_dec_and_test(&f->refcnt))
169 			complete(&f->completion);
170 
171 		kfree(fqdir);
172 	}
173 }
174 
175 static DECLARE_WORK(fqdir_free_work, fqdir_free_fn);
176 
177 static void fqdir_work_fn(struct work_struct *work)
178 {
179 	struct fqdir *fqdir = container_of(work, struct fqdir, destroy_work);
180 
181 	rhashtable_free_and_destroy(&fqdir->rhashtable, inet_frags_free_cb, NULL);
182 
183 	if (llist_add(&fqdir->free_list, &fqdir_free_list))
184 		queue_work(system_wq, &fqdir_free_work);
185 }
186 
187 int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net)
188 {
189 	struct fqdir *fqdir = kzalloc(sizeof(*fqdir), GFP_KERNEL);
190 	int res;
191 
192 	if (!fqdir)
193 		return -ENOMEM;
194 	fqdir->f = f;
195 	fqdir->net = net;
196 	res = rhashtable_init(&fqdir->rhashtable, &fqdir->f->rhash_params);
197 	if (res < 0) {
198 		kfree(fqdir);
199 		return res;
200 	}
201 	refcount_inc(&f->refcnt);
202 	*fqdirp = fqdir;
203 	return 0;
204 }
205 EXPORT_SYMBOL(fqdir_init);
206 
207 static struct workqueue_struct *inet_frag_wq;
208 
209 static int __init inet_frag_wq_init(void)
210 {
211 	inet_frag_wq = create_workqueue("inet_frag_wq");
212 	if (!inet_frag_wq)
213 		panic("Could not create inet frag workq");
214 	return 0;
215 }
216 
217 pure_initcall(inet_frag_wq_init);
218 
219 void fqdir_exit(struct fqdir *fqdir)
220 {
221 	INIT_WORK(&fqdir->destroy_work, fqdir_work_fn);
222 	queue_work(inet_frag_wq, &fqdir->destroy_work);
223 }
224 EXPORT_SYMBOL(fqdir_exit);
225 
226 void inet_frag_kill(struct inet_frag_queue *fq)
227 {
228 	if (del_timer(&fq->timer))
229 		refcount_dec(&fq->refcnt);
230 
231 	if (!(fq->flags & INET_FRAG_COMPLETE)) {
232 		struct fqdir *fqdir = fq->fqdir;
233 
234 		fq->flags |= INET_FRAG_COMPLETE;
235 		rcu_read_lock();
236 		/* The RCU read lock provides a memory barrier
237 		 * guaranteeing that if fqdir->dead is false then
238 		 * the hash table destruction will not start until
239 		 * after we unlock.  Paired with fqdir_pre_exit().
240 		 */
241 		if (!READ_ONCE(fqdir->dead)) {
242 			rhashtable_remove_fast(&fqdir->rhashtable, &fq->node,
243 					       fqdir->f->rhash_params);
244 			refcount_dec(&fq->refcnt);
245 		} else {
246 			fq->flags |= INET_FRAG_HASH_DEAD;
247 		}
248 		rcu_read_unlock();
249 	}
250 }
251 EXPORT_SYMBOL(inet_frag_kill);
252 
253 static void inet_frag_destroy_rcu(struct rcu_head *head)
254 {
255 	struct inet_frag_queue *q = container_of(head, struct inet_frag_queue,
256 						 rcu);
257 	struct inet_frags *f = q->fqdir->f;
258 
259 	if (f->destructor)
260 		f->destructor(q);
261 	kmem_cache_free(f->frags_cachep, q);
262 }
263 
264 unsigned int inet_frag_rbtree_purge(struct rb_root *root,
265 				    enum skb_drop_reason reason)
266 {
267 	struct rb_node *p = rb_first(root);
268 	unsigned int sum = 0;
269 
270 	while (p) {
271 		struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);
272 
273 		p = rb_next(p);
274 		rb_erase(&skb->rbnode, root);
275 		while (skb) {
276 			struct sk_buff *next = FRAG_CB(skb)->next_frag;
277 
278 			sum += skb->truesize;
279 			kfree_skb_reason(skb, reason);
280 			skb = next;
281 		}
282 	}
283 	return sum;
284 }
285 EXPORT_SYMBOL(inet_frag_rbtree_purge);
286 
287 void inet_frag_destroy(struct inet_frag_queue *q)
288 {
289 	unsigned int sum, sum_truesize = 0;
290 	enum skb_drop_reason reason;
291 	struct inet_frags *f;
292 	struct fqdir *fqdir;
293 
294 	WARN_ON(!(q->flags & INET_FRAG_COMPLETE));
295 	reason = (q->flags & INET_FRAG_DROP) ?
296 			SKB_DROP_REASON_FRAG_REASM_TIMEOUT :
297 			SKB_CONSUMED;
298 	WARN_ON(del_timer(&q->timer) != 0);
299 
300 	/* Release all fragment data. */
301 	fqdir = q->fqdir;
302 	f = fqdir->f;
303 	sum_truesize = inet_frag_rbtree_purge(&q->rb_fragments, reason);
304 	sum = sum_truesize + f->qsize;
305 
306 	call_rcu(&q->rcu, inet_frag_destroy_rcu);
307 
308 	sub_frag_mem_limit(fqdir, sum);
309 }
310 EXPORT_SYMBOL(inet_frag_destroy);
311 
312 static struct inet_frag_queue *inet_frag_alloc(struct fqdir *fqdir,
313 					       struct inet_frags *f,
314 					       void *arg)
315 {
316 	struct inet_frag_queue *q;
317 
318 	q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);
319 	if (!q)
320 		return NULL;
321 
322 	q->fqdir = fqdir;
323 	f->constructor(q, arg);
324 	add_frag_mem_limit(fqdir, f->qsize);
325 
326 	timer_setup(&q->timer, f->frag_expire, 0);
327 	spin_lock_init(&q->lock);
328 	refcount_set(&q->refcnt, 3);
329 
330 	return q;
331 }
332 
333 static struct inet_frag_queue *inet_frag_create(struct fqdir *fqdir,
334 						void *arg,
335 						struct inet_frag_queue **prev)
336 {
337 	struct inet_frags *f = fqdir->f;
338 	struct inet_frag_queue *q;
339 
340 	q = inet_frag_alloc(fqdir, f, arg);
341 	if (!q) {
342 		*prev = ERR_PTR(-ENOMEM);
343 		return NULL;
344 	}
345 	mod_timer(&q->timer, jiffies + fqdir->timeout);
346 
347 	*prev = rhashtable_lookup_get_insert_key(&fqdir->rhashtable, &q->key,
348 						 &q->node, f->rhash_params);
349 	if (*prev) {
350 		q->flags |= INET_FRAG_COMPLETE;
351 		inet_frag_kill(q);
352 		inet_frag_destroy(q);
353 		return NULL;
354 	}
355 	return q;
356 }
357 
358 /* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
359 struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key)
360 {
361 	/* This pairs with WRITE_ONCE() in fqdir_pre_exit(). */
362 	long high_thresh = READ_ONCE(fqdir->high_thresh);
363 	struct inet_frag_queue *fq = NULL, *prev;
364 
365 	if (!high_thresh || frag_mem_limit(fqdir) > high_thresh)
366 		return NULL;
367 
368 	rcu_read_lock();
369 
370 	prev = rhashtable_lookup(&fqdir->rhashtable, key, fqdir->f->rhash_params);
371 	if (!prev)
372 		fq = inet_frag_create(fqdir, key, &prev);
373 	if (!IS_ERR_OR_NULL(prev)) {
374 		fq = prev;
375 		if (!refcount_inc_not_zero(&fq->refcnt))
376 			fq = NULL;
377 	}
378 	rcu_read_unlock();
379 	return fq;
380 }
381 EXPORT_SYMBOL(inet_frag_find);
382 
383 int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
384 			   int offset, int end)
385 {
386 	struct sk_buff *last = q->fragments_tail;
387 
388 	/* RFC5722, Section 4, amended by Errata ID : 3089
389 	 *                          When reassembling an IPv6 datagram, if
390 	 *   one or more its constituent fragments is determined to be an
391 	 *   overlapping fragment, the entire datagram (and any constituent
392 	 *   fragments) MUST be silently discarded.
393 	 *
394 	 * Duplicates, however, should be ignored (i.e. skb dropped, but the
395 	 * queue/fragments kept for later reassembly).
396 	 */
397 	if (!last)
398 		fragrun_create(q, skb);  /* First fragment. */
399 	else if (last->ip_defrag_offset + last->len < end) {
400 		/* This is the common case: skb goes to the end. */
401 		/* Detect and discard overlaps. */
402 		if (offset < last->ip_defrag_offset + last->len)
403 			return IPFRAG_OVERLAP;
404 		if (offset == last->ip_defrag_offset + last->len)
405 			fragrun_append_to_last(q, skb);
406 		else
407 			fragrun_create(q, skb);
408 	} else {
409 		/* Binary search. Note that skb can become the first fragment,
410 		 * but not the last (covered above).
411 		 */
412 		struct rb_node **rbn, *parent;
413 
414 		rbn = &q->rb_fragments.rb_node;
415 		do {
416 			struct sk_buff *curr;
417 			int curr_run_end;
418 
419 			parent = *rbn;
420 			curr = rb_to_skb(parent);
421 			curr_run_end = curr->ip_defrag_offset +
422 					FRAG_CB(curr)->frag_run_len;
423 			if (end <= curr->ip_defrag_offset)
424 				rbn = &parent->rb_left;
425 			else if (offset >= curr_run_end)
426 				rbn = &parent->rb_right;
427 			else if (offset >= curr->ip_defrag_offset &&
428 				 end <= curr_run_end)
429 				return IPFRAG_DUP;
430 			else
431 				return IPFRAG_OVERLAP;
432 		} while (*rbn);
433 		/* Here we have parent properly set, and rbn pointing to
434 		 * one of its NULL left/right children. Insert skb.
435 		 */
436 		fragcb_clear(skb);
437 		rb_link_node(&skb->rbnode, parent, rbn);
438 		rb_insert_color(&skb->rbnode, &q->rb_fragments);
439 	}
440 
441 	skb->ip_defrag_offset = offset;
442 
443 	return IPFRAG_OK;
444 }
445 EXPORT_SYMBOL(inet_frag_queue_insert);
446 
447 void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
448 			      struct sk_buff *parent)
449 {
450 	struct sk_buff *fp, *head = skb_rb_first(&q->rb_fragments);
451 	struct sk_buff **nextp;
452 	int delta;
453 
454 	if (head != skb) {
455 		fp = skb_clone(skb, GFP_ATOMIC);
456 		if (!fp)
457 			return NULL;
458 		FRAG_CB(fp)->next_frag = FRAG_CB(skb)->next_frag;
459 		if (RB_EMPTY_NODE(&skb->rbnode))
460 			FRAG_CB(parent)->next_frag = fp;
461 		else
462 			rb_replace_node(&skb->rbnode, &fp->rbnode,
463 					&q->rb_fragments);
464 		if (q->fragments_tail == skb)
465 			q->fragments_tail = fp;
466 		skb_morph(skb, head);
467 		FRAG_CB(skb)->next_frag = FRAG_CB(head)->next_frag;
468 		rb_replace_node(&head->rbnode, &skb->rbnode,
469 				&q->rb_fragments);
470 		consume_skb(head);
471 		head = skb;
472 	}
473 	WARN_ON(head->ip_defrag_offset != 0);
474 
475 	delta = -head->truesize;
476 
477 	/* Head of list must not be cloned. */
478 	if (skb_unclone(head, GFP_ATOMIC))
479 		return NULL;
480 
481 	delta += head->truesize;
482 	if (delta)
483 		add_frag_mem_limit(q->fqdir, delta);
484 
485 	/* If the first fragment is fragmented itself, we split
486 	 * it to two chunks: the first with data and paged part
487 	 * and the second, holding only fragments.
488 	 */
489 	if (skb_has_frag_list(head)) {
490 		struct sk_buff *clone;
491 		int i, plen = 0;
492 
493 		clone = alloc_skb(0, GFP_ATOMIC);
494 		if (!clone)
495 			return NULL;
496 		skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
497 		skb_frag_list_init(head);
498 		for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
499 			plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
500 		clone->data_len = head->data_len - plen;
501 		clone->len = clone->data_len;
502 		head->truesize += clone->truesize;
503 		clone->csum = 0;
504 		clone->ip_summed = head->ip_summed;
505 		add_frag_mem_limit(q->fqdir, clone->truesize);
506 		skb_shinfo(head)->frag_list = clone;
507 		nextp = &clone->next;
508 	} else {
509 		nextp = &skb_shinfo(head)->frag_list;
510 	}
511 
512 	return nextp;
513 }
514 EXPORT_SYMBOL(inet_frag_reasm_prepare);
515 
516 void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
517 			    void *reasm_data, bool try_coalesce)
518 {
519 	struct sk_buff **nextp = reasm_data;
520 	struct rb_node *rbn;
521 	struct sk_buff *fp;
522 	int sum_truesize;
523 
524 	skb_push(head, head->data - skb_network_header(head));
525 
526 	/* Traverse the tree in order, to build frag_list. */
527 	fp = FRAG_CB(head)->next_frag;
528 	rbn = rb_next(&head->rbnode);
529 	rb_erase(&head->rbnode, &q->rb_fragments);
530 
531 	sum_truesize = head->truesize;
532 	while (rbn || fp) {
533 		/* fp points to the next sk_buff in the current run;
534 		 * rbn points to the next run.
535 		 */
536 		/* Go through the current run. */
537 		while (fp) {
538 			struct sk_buff *next_frag = FRAG_CB(fp)->next_frag;
539 			bool stolen;
540 			int delta;
541 
542 			sum_truesize += fp->truesize;
543 			if (head->ip_summed != fp->ip_summed)
544 				head->ip_summed = CHECKSUM_NONE;
545 			else if (head->ip_summed == CHECKSUM_COMPLETE)
546 				head->csum = csum_add(head->csum, fp->csum);
547 
548 			if (try_coalesce && skb_try_coalesce(head, fp, &stolen,
549 							     &delta)) {
550 				kfree_skb_partial(fp, stolen);
551 			} else {
552 				fp->prev = NULL;
553 				memset(&fp->rbnode, 0, sizeof(fp->rbnode));
554 				fp->sk = NULL;
555 
556 				head->data_len += fp->len;
557 				head->len += fp->len;
558 				head->truesize += fp->truesize;
559 
560 				*nextp = fp;
561 				nextp = &fp->next;
562 			}
563 
564 			fp = next_frag;
565 		}
566 		/* Move to the next run. */
567 		if (rbn) {
568 			struct rb_node *rbnext = rb_next(rbn);
569 
570 			fp = rb_to_skb(rbn);
571 			rb_erase(rbn, &q->rb_fragments);
572 			rbn = rbnext;
573 		}
574 	}
575 	sub_frag_mem_limit(q->fqdir, sum_truesize);
576 
577 	*nextp = NULL;
578 	skb_mark_not_on_list(head);
579 	head->prev = NULL;
580 	head->tstamp = q->stamp;
581 	head->mono_delivery_time = q->mono_delivery_time;
582 }
583 EXPORT_SYMBOL(inet_frag_reasm_finish);
584 
585 struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q)
586 {
587 	struct sk_buff *head, *skb;
588 
589 	head = skb_rb_first(&q->rb_fragments);
590 	if (!head)
591 		return NULL;
592 	skb = FRAG_CB(head)->next_frag;
593 	if (skb)
594 		rb_replace_node(&head->rbnode, &skb->rbnode,
595 				&q->rb_fragments);
596 	else
597 		rb_erase(&head->rbnode, &q->rb_fragments);
598 	memset(&head->rbnode, 0, sizeof(head->rbnode));
599 	barrier();
600 
601 	if (head == q->fragments_tail)
602 		q->fragments_tail = NULL;
603 
604 	sub_frag_mem_limit(q->fqdir, head->truesize);
605 
606 	return head;
607 }
608 EXPORT_SYMBOL(inet_frag_pull_head);
609