1 // SPDX-License-Identifier: GPL-2.0
2 /* Copyright (c) 2019 Facebook  */
3 #include <linux/rculist.h>
4 #include <linux/list.h>
5 #include <linux/hash.h>
6 #include <linux/types.h>
7 #include <linux/spinlock.h>
8 #include <linux/bpf.h>
9 #include <linux/btf_ids.h>
10 #include <linux/bpf_local_storage.h>
11 #include <net/sock.h>
12 #include <uapi/linux/sock_diag.h>
13 #include <uapi/linux/btf.h>
14 #include <linux/rcupdate.h>
15 #include <linux/rcupdate_trace.h>
16 #include <linux/rcupdate_wait.h>
17 
18 #define BPF_LOCAL_STORAGE_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_CLONE)
19 
20 static struct bpf_local_storage_map_bucket *
21 select_bucket(struct bpf_local_storage_map *smap,
22 	      struct bpf_local_storage_elem *selem)
23 {
24 	return &smap->buckets[hash_ptr(selem, smap->bucket_log)];
25 }
26 
27 static int mem_charge(struct bpf_local_storage_map *smap, void *owner, u32 size)
28 {
29 	struct bpf_map *map = &smap->map;
30 
31 	if (!map->ops->map_local_storage_charge)
32 		return 0;
33 
34 	return map->ops->map_local_storage_charge(smap, owner, size);
35 }
36 
37 static void mem_uncharge(struct bpf_local_storage_map *smap, void *owner,
38 			 u32 size)
39 {
40 	struct bpf_map *map = &smap->map;
41 
42 	if (map->ops->map_local_storage_uncharge)
43 		map->ops->map_local_storage_uncharge(smap, owner, size);
44 }
45 
46 static struct bpf_local_storage __rcu **
47 owner_storage(struct bpf_local_storage_map *smap, void *owner)
48 {
49 	struct bpf_map *map = &smap->map;
50 
51 	return map->ops->map_owner_storage_ptr(owner);
52 }
53 
54 static bool selem_linked_to_storage(const struct bpf_local_storage_elem *selem)
55 {
56 	return !hlist_unhashed(&selem->snode);
57 }
58 
59 static bool selem_linked_to_map(const struct bpf_local_storage_elem *selem)
60 {
61 	return !hlist_unhashed(&selem->map_node);
62 }
63 
64 struct bpf_local_storage_elem *
65 bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
66 		void *value, bool charge_mem, gfp_t gfp_flags)
67 {
68 	struct bpf_local_storage_elem *selem;
69 
70 	if (charge_mem && mem_charge(smap, owner, smap->elem_size))
71 		return NULL;
72 
73 	selem = bpf_map_kzalloc(&smap->map, smap->elem_size,
74 				gfp_flags | __GFP_NOWARN);
75 	if (selem) {
76 		if (value)
77 			copy_map_value(&smap->map, SDATA(selem)->data, value);
78 		return selem;
79 	}
80 
81 	if (charge_mem)
82 		mem_uncharge(smap, owner, smap->elem_size);
83 
84 	return NULL;
85 }
86 
87 void bpf_local_storage_free_rcu(struct rcu_head *rcu)
88 {
89 	struct bpf_local_storage *local_storage;
90 
91 	/* If RCU Tasks Trace grace period implies RCU grace period, do
92 	 * kfree(), else do kfree_rcu().
93 	 */
94 	local_storage = container_of(rcu, struct bpf_local_storage, rcu);
95 	if (rcu_trace_implies_rcu_gp())
96 		kfree(local_storage);
97 	else
98 		kfree_rcu(local_storage, rcu);
99 }
100 
101 static void bpf_selem_free_rcu(struct rcu_head *rcu)
102 {
103 	struct bpf_local_storage_elem *selem;
104 
105 	selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
106 	if (rcu_trace_implies_rcu_gp())
107 		kfree(selem);
108 	else
109 		kfree_rcu(selem, rcu);
110 }
111 
112 /* local_storage->lock must be held and selem->local_storage == local_storage.
113  * The caller must ensure selem->smap is still valid to be
114  * dereferenced for its smap->elem_size and smap->cache_idx.
115  */
116 static bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
117 					    struct bpf_local_storage_elem *selem,
118 					    bool uncharge_mem, bool use_trace_rcu)
119 {
120 	struct bpf_local_storage_map *smap;
121 	bool free_local_storage;
122 	void *owner;
123 
124 	smap = rcu_dereference_check(SDATA(selem)->smap, bpf_rcu_lock_held());
125 	owner = local_storage->owner;
126 
127 	/* All uncharging on the owner must be done first.
128 	 * The owner may be freed once the last selem is unlinked
129 	 * from local_storage.
130 	 */
131 	if (uncharge_mem)
132 		mem_uncharge(smap, owner, smap->elem_size);
133 
134 	free_local_storage = hlist_is_singular_node(&selem->snode,
135 						    &local_storage->list);
136 	if (free_local_storage) {
137 		mem_uncharge(smap, owner, sizeof(struct bpf_local_storage));
138 		local_storage->owner = NULL;
139 
140 		/* After this RCU_INIT, owner may be freed and cannot be used */
141 		RCU_INIT_POINTER(*owner_storage(smap, owner), NULL);
142 
143 		/* local_storage is not freed now.  local_storage->lock is
144 		 * still held and raw_spin_unlock_bh(&local_storage->lock)
145 		 * will be done by the caller.
146 		 *
147 		 * Although the unlock will be done under
148 		 * rcu_read_lock(),  it is more intuitive to
149 		 * read if the freeing of the storage is done
150 		 * after the raw_spin_unlock_bh(&local_storage->lock).
151 		 *
152 		 * Hence, a "bool free_local_storage" is returned
153 		 * to the caller which then calls then frees the storage after
154 		 * all the RCU grace periods have expired.
155 		 */
156 	}
157 	hlist_del_init_rcu(&selem->snode);
158 	if (rcu_access_pointer(local_storage->cache[smap->cache_idx]) ==
159 	    SDATA(selem))
160 		RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);
161 
162 	if (use_trace_rcu)
163 		call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_rcu);
164 	else
165 		kfree_rcu(selem, rcu);
166 
167 	return free_local_storage;
168 }
169 
170 static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem,
171 				       bool use_trace_rcu)
172 {
173 	struct bpf_local_storage *local_storage;
174 	bool free_local_storage = false;
175 	unsigned long flags;
176 
177 	if (unlikely(!selem_linked_to_storage(selem)))
178 		/* selem has already been unlinked from sk */
179 		return;
180 
181 	local_storage = rcu_dereference_check(selem->local_storage,
182 					      bpf_rcu_lock_held());
183 	raw_spin_lock_irqsave(&local_storage->lock, flags);
184 	if (likely(selem_linked_to_storage(selem)))
185 		free_local_storage = bpf_selem_unlink_storage_nolock(
186 			local_storage, selem, true, use_trace_rcu);
187 	raw_spin_unlock_irqrestore(&local_storage->lock, flags);
188 
189 	if (free_local_storage) {
190 		if (use_trace_rcu)
191 			call_rcu_tasks_trace(&local_storage->rcu,
192 				     bpf_local_storage_free_rcu);
193 		else
194 			kfree_rcu(local_storage, rcu);
195 	}
196 }
197 
198 void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
199 				   struct bpf_local_storage_elem *selem)
200 {
201 	RCU_INIT_POINTER(selem->local_storage, local_storage);
202 	hlist_add_head_rcu(&selem->snode, &local_storage->list);
203 }
204 
205 void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
206 {
207 	struct bpf_local_storage_map *smap;
208 	struct bpf_local_storage_map_bucket *b;
209 	unsigned long flags;
210 
211 	if (unlikely(!selem_linked_to_map(selem)))
212 		/* selem has already be unlinked from smap */
213 		return;
214 
215 	smap = rcu_dereference_check(SDATA(selem)->smap, bpf_rcu_lock_held());
216 	b = select_bucket(smap, selem);
217 	raw_spin_lock_irqsave(&b->lock, flags);
218 	if (likely(selem_linked_to_map(selem)))
219 		hlist_del_init_rcu(&selem->map_node);
220 	raw_spin_unlock_irqrestore(&b->lock, flags);
221 }
222 
223 void bpf_selem_link_map(struct bpf_local_storage_map *smap,
224 			struct bpf_local_storage_elem *selem)
225 {
226 	struct bpf_local_storage_map_bucket *b = select_bucket(smap, selem);
227 	unsigned long flags;
228 
229 	raw_spin_lock_irqsave(&b->lock, flags);
230 	RCU_INIT_POINTER(SDATA(selem)->smap, smap);
231 	hlist_add_head_rcu(&selem->map_node, &b->list);
232 	raw_spin_unlock_irqrestore(&b->lock, flags);
233 }
234 
235 void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool use_trace_rcu)
236 {
237 	/* Always unlink from map before unlinking from local_storage
238 	 * because selem will be freed after successfully unlinked from
239 	 * the local_storage.
240 	 */
241 	bpf_selem_unlink_map(selem);
242 	__bpf_selem_unlink_storage(selem, use_trace_rcu);
243 }
244 
245 /* If cacheit_lockit is false, this lookup function is lockless */
246 struct bpf_local_storage_data *
247 bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
248 			 struct bpf_local_storage_map *smap,
249 			 bool cacheit_lockit)
250 {
251 	struct bpf_local_storage_data *sdata;
252 	struct bpf_local_storage_elem *selem;
253 
254 	/* Fast path (cache hit) */
255 	sdata = rcu_dereference_check(local_storage->cache[smap->cache_idx],
256 				      bpf_rcu_lock_held());
257 	if (sdata && rcu_access_pointer(sdata->smap) == smap)
258 		return sdata;
259 
260 	/* Slow path (cache miss) */
261 	hlist_for_each_entry_rcu(selem, &local_storage->list, snode,
262 				  rcu_read_lock_trace_held())
263 		if (rcu_access_pointer(SDATA(selem)->smap) == smap)
264 			break;
265 
266 	if (!selem)
267 		return NULL;
268 
269 	sdata = SDATA(selem);
270 	if (cacheit_lockit) {
271 		unsigned long flags;
272 
273 		/* spinlock is needed to avoid racing with the
274 		 * parallel delete.  Otherwise, publishing an already
275 		 * deleted sdata to the cache will become a use-after-free
276 		 * problem in the next bpf_local_storage_lookup().
277 		 */
278 		raw_spin_lock_irqsave(&local_storage->lock, flags);
279 		if (selem_linked_to_storage(selem))
280 			rcu_assign_pointer(local_storage->cache[smap->cache_idx],
281 					   sdata);
282 		raw_spin_unlock_irqrestore(&local_storage->lock, flags);
283 	}
284 
285 	return sdata;
286 }
287 
288 static int check_flags(const struct bpf_local_storage_data *old_sdata,
289 		       u64 map_flags)
290 {
291 	if (old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
292 		/* elem already exists */
293 		return -EEXIST;
294 
295 	if (!old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
296 		/* elem doesn't exist, cannot update it */
297 		return -ENOENT;
298 
299 	return 0;
300 }
301 
302 int bpf_local_storage_alloc(void *owner,
303 			    struct bpf_local_storage_map *smap,
304 			    struct bpf_local_storage_elem *first_selem,
305 			    gfp_t gfp_flags)
306 {
307 	struct bpf_local_storage *prev_storage, *storage;
308 	struct bpf_local_storage **owner_storage_ptr;
309 	int err;
310 
311 	err = mem_charge(smap, owner, sizeof(*storage));
312 	if (err)
313 		return err;
314 
315 	storage = bpf_map_kzalloc(&smap->map, sizeof(*storage),
316 				  gfp_flags | __GFP_NOWARN);
317 	if (!storage) {
318 		err = -ENOMEM;
319 		goto uncharge;
320 	}
321 
322 	INIT_HLIST_HEAD(&storage->list);
323 	raw_spin_lock_init(&storage->lock);
324 	storage->owner = owner;
325 
326 	bpf_selem_link_storage_nolock(storage, first_selem);
327 	bpf_selem_link_map(smap, first_selem);
328 
329 	owner_storage_ptr =
330 		(struct bpf_local_storage **)owner_storage(smap, owner);
331 	/* Publish storage to the owner.
332 	 * Instead of using any lock of the kernel object (i.e. owner),
333 	 * cmpxchg will work with any kernel object regardless what
334 	 * the running context is, bh, irq...etc.
335 	 *
336 	 * From now on, the owner->storage pointer (e.g. sk->sk_bpf_storage)
337 	 * is protected by the storage->lock.  Hence, when freeing
338 	 * the owner->storage, the storage->lock must be held before
339 	 * setting owner->storage ptr to NULL.
340 	 */
341 	prev_storage = cmpxchg(owner_storage_ptr, NULL, storage);
342 	if (unlikely(prev_storage)) {
343 		bpf_selem_unlink_map(first_selem);
344 		err = -EAGAIN;
345 		goto uncharge;
346 
347 		/* Note that even first_selem was linked to smap's
348 		 * bucket->list, first_selem can be freed immediately
349 		 * (instead of kfree_rcu) because
350 		 * bpf_local_storage_map_free() does a
351 		 * synchronize_rcu_mult (waiting for both sleepable and
352 		 * normal programs) before walking the bucket->list.
353 		 * Hence, no one is accessing selem from the
354 		 * bucket->list under rcu_read_lock().
355 		 */
356 	}
357 
358 	return 0;
359 
360 uncharge:
361 	kfree(storage);
362 	mem_uncharge(smap, owner, sizeof(*storage));
363 	return err;
364 }
365 
366 /* sk cannot be going away because it is linking new elem
367  * to sk->sk_bpf_storage. (i.e. sk->sk_refcnt cannot be 0).
368  * Otherwise, it will become a leak (and other memory issues
369  * during map destruction).
370  */
371 struct bpf_local_storage_data *
372 bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
373 			 void *value, u64 map_flags, gfp_t gfp_flags)
374 {
375 	struct bpf_local_storage_data *old_sdata = NULL;
376 	struct bpf_local_storage_elem *selem = NULL;
377 	struct bpf_local_storage *local_storage;
378 	unsigned long flags;
379 	int err;
380 
381 	/* BPF_EXIST and BPF_NOEXIST cannot be both set */
382 	if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
383 	    /* BPF_F_LOCK can only be used in a value with spin_lock */
384 	    unlikely((map_flags & BPF_F_LOCK) &&
385 		     !btf_record_has_field(smap->map.record, BPF_SPIN_LOCK)))
386 		return ERR_PTR(-EINVAL);
387 
388 	if (gfp_flags == GFP_KERNEL && (map_flags & ~BPF_F_LOCK) != BPF_NOEXIST)
389 		return ERR_PTR(-EINVAL);
390 
391 	local_storage = rcu_dereference_check(*owner_storage(smap, owner),
392 					      bpf_rcu_lock_held());
393 	if (!local_storage || hlist_empty(&local_storage->list)) {
394 		/* Very first elem for the owner */
395 		err = check_flags(NULL, map_flags);
396 		if (err)
397 			return ERR_PTR(err);
398 
399 		selem = bpf_selem_alloc(smap, owner, value, true, gfp_flags);
400 		if (!selem)
401 			return ERR_PTR(-ENOMEM);
402 
403 		err = bpf_local_storage_alloc(owner, smap, selem, gfp_flags);
404 		if (err) {
405 			kfree(selem);
406 			mem_uncharge(smap, owner, smap->elem_size);
407 			return ERR_PTR(err);
408 		}
409 
410 		return SDATA(selem);
411 	}
412 
413 	if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
414 		/* Hoping to find an old_sdata to do inline update
415 		 * such that it can avoid taking the local_storage->lock
416 		 * and changing the lists.
417 		 */
418 		old_sdata =
419 			bpf_local_storage_lookup(local_storage, smap, false);
420 		err = check_flags(old_sdata, map_flags);
421 		if (err)
422 			return ERR_PTR(err);
423 		if (old_sdata && selem_linked_to_storage(SELEM(old_sdata))) {
424 			copy_map_value_locked(&smap->map, old_sdata->data,
425 					      value, false);
426 			return old_sdata;
427 		}
428 	}
429 
430 	if (gfp_flags == GFP_KERNEL) {
431 		selem = bpf_selem_alloc(smap, owner, value, true, gfp_flags);
432 		if (!selem)
433 			return ERR_PTR(-ENOMEM);
434 	}
435 
436 	raw_spin_lock_irqsave(&local_storage->lock, flags);
437 
438 	/* Recheck local_storage->list under local_storage->lock */
439 	if (unlikely(hlist_empty(&local_storage->list))) {
440 		/* A parallel del is happening and local_storage is going
441 		 * away.  It has just been checked before, so very
442 		 * unlikely.  Return instead of retry to keep things
443 		 * simple.
444 		 */
445 		err = -EAGAIN;
446 		goto unlock_err;
447 	}
448 
449 	old_sdata = bpf_local_storage_lookup(local_storage, smap, false);
450 	err = check_flags(old_sdata, map_flags);
451 	if (err)
452 		goto unlock_err;
453 
454 	if (old_sdata && (map_flags & BPF_F_LOCK)) {
455 		copy_map_value_locked(&smap->map, old_sdata->data, value,
456 				      false);
457 		selem = SELEM(old_sdata);
458 		goto unlock;
459 	}
460 
461 	if (gfp_flags != GFP_KERNEL) {
462 		/* local_storage->lock is held.  Hence, we are sure
463 		 * we can unlink and uncharge the old_sdata successfully
464 		 * later.  Hence, instead of charging the new selem now
465 		 * and then uncharge the old selem later (which may cause
466 		 * a potential but unnecessary charge failure),  avoid taking
467 		 * a charge at all here (the "!old_sdata" check) and the
468 		 * old_sdata will not be uncharged later during
469 		 * bpf_selem_unlink_storage_nolock().
470 		 */
471 		selem = bpf_selem_alloc(smap, owner, value, !old_sdata, gfp_flags);
472 		if (!selem) {
473 			err = -ENOMEM;
474 			goto unlock_err;
475 		}
476 	}
477 
478 	/* First, link the new selem to the map */
479 	bpf_selem_link_map(smap, selem);
480 
481 	/* Second, link (and publish) the new selem to local_storage */
482 	bpf_selem_link_storage_nolock(local_storage, selem);
483 
484 	/* Third, remove old selem, SELEM(old_sdata) */
485 	if (old_sdata) {
486 		bpf_selem_unlink_map(SELEM(old_sdata));
487 		bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
488 						false, true);
489 	}
490 
491 unlock:
492 	raw_spin_unlock_irqrestore(&local_storage->lock, flags);
493 	return SDATA(selem);
494 
495 unlock_err:
496 	raw_spin_unlock_irqrestore(&local_storage->lock, flags);
497 	if (selem) {
498 		mem_uncharge(smap, owner, smap->elem_size);
499 		kfree(selem);
500 	}
501 	return ERR_PTR(err);
502 }
503 
504 static u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
505 {
506 	u64 min_usage = U64_MAX;
507 	u16 i, res = 0;
508 
509 	spin_lock(&cache->idx_lock);
510 
511 	for (i = 0; i < BPF_LOCAL_STORAGE_CACHE_SIZE; i++) {
512 		if (cache->idx_usage_counts[i] < min_usage) {
513 			min_usage = cache->idx_usage_counts[i];
514 			res = i;
515 
516 			/* Found a free cache_idx */
517 			if (!min_usage)
518 				break;
519 		}
520 	}
521 	cache->idx_usage_counts[res]++;
522 
523 	spin_unlock(&cache->idx_lock);
524 
525 	return res;
526 }
527 
528 static void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
529 					     u16 idx)
530 {
531 	spin_lock(&cache->idx_lock);
532 	cache->idx_usage_counts[idx]--;
533 	spin_unlock(&cache->idx_lock);
534 }
535 
536 int bpf_local_storage_map_alloc_check(union bpf_attr *attr)
537 {
538 	if (attr->map_flags & ~BPF_LOCAL_STORAGE_CREATE_FLAG_MASK ||
539 	    !(attr->map_flags & BPF_F_NO_PREALLOC) ||
540 	    attr->max_entries ||
541 	    attr->key_size != sizeof(int) || !attr->value_size ||
542 	    /* Enforce BTF for userspace sk dumping */
543 	    !attr->btf_key_type_id || !attr->btf_value_type_id)
544 		return -EINVAL;
545 
546 	if (!bpf_capable())
547 		return -EPERM;
548 
549 	if (attr->value_size > BPF_LOCAL_STORAGE_MAX_VALUE_SIZE)
550 		return -E2BIG;
551 
552 	return 0;
553 }
554 
555 static struct bpf_local_storage_map *__bpf_local_storage_map_alloc(union bpf_attr *attr)
556 {
557 	struct bpf_local_storage_map *smap;
558 	unsigned int i;
559 	u32 nbuckets;
560 
561 	smap = bpf_map_area_alloc(sizeof(*smap), NUMA_NO_NODE);
562 	if (!smap)
563 		return ERR_PTR(-ENOMEM);
564 	bpf_map_init_from_attr(&smap->map, attr);
565 
566 	nbuckets = roundup_pow_of_two(num_possible_cpus());
567 	/* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */
568 	nbuckets = max_t(u32, 2, nbuckets);
569 	smap->bucket_log = ilog2(nbuckets);
570 
571 	smap->buckets = bpf_map_kvcalloc(&smap->map, sizeof(*smap->buckets),
572 					 nbuckets, GFP_USER | __GFP_NOWARN);
573 	if (!smap->buckets) {
574 		bpf_map_area_free(smap);
575 		return ERR_PTR(-ENOMEM);
576 	}
577 
578 	for (i = 0; i < nbuckets; i++) {
579 		INIT_HLIST_HEAD(&smap->buckets[i].list);
580 		raw_spin_lock_init(&smap->buckets[i].lock);
581 	}
582 
583 	smap->elem_size = offsetof(struct bpf_local_storage_elem,
584 				   sdata.data[attr->value_size]);
585 
586 	return smap;
587 }
588 
589 int bpf_local_storage_map_check_btf(const struct bpf_map *map,
590 				    const struct btf *btf,
591 				    const struct btf_type *key_type,
592 				    const struct btf_type *value_type)
593 {
594 	u32 int_data;
595 
596 	if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
597 		return -EINVAL;
598 
599 	int_data = *(u32 *)(key_type + 1);
600 	if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
601 		return -EINVAL;
602 
603 	return 0;
604 }
605 
606 bool bpf_local_storage_unlink_nolock(struct bpf_local_storage *local_storage)
607 {
608 	struct bpf_local_storage_elem *selem;
609 	bool free_storage = false;
610 	struct hlist_node *n;
611 
612 	/* Neither the bpf_prog nor the bpf_map's syscall
613 	 * could be modifying the local_storage->list now.
614 	 * Thus, no elem can be added to or deleted from the
615 	 * local_storage->list by the bpf_prog or by the bpf_map's syscall.
616 	 *
617 	 * It is racing with bpf_local_storage_map_free() alone
618 	 * when unlinking elem from the local_storage->list and
619 	 * the map's bucket->list.
620 	 */
621 	hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) {
622 		/* Always unlink from map before unlinking from
623 		 * local_storage.
624 		 */
625 		bpf_selem_unlink_map(selem);
626 		/* If local_storage list has only one element, the
627 		 * bpf_selem_unlink_storage_nolock() will return true.
628 		 * Otherwise, it will return false. The current loop iteration
629 		 * intends to remove all local storage. So the last iteration
630 		 * of the loop will set the free_cgroup_storage to true.
631 		 */
632 		free_storage = bpf_selem_unlink_storage_nolock(
633 			local_storage, selem, false, false);
634 	}
635 
636 	return free_storage;
637 }
638 
639 struct bpf_map *
640 bpf_local_storage_map_alloc(union bpf_attr *attr,
641 			    struct bpf_local_storage_cache *cache)
642 {
643 	struct bpf_local_storage_map *smap;
644 
645 	smap = __bpf_local_storage_map_alloc(attr);
646 	if (IS_ERR(smap))
647 		return ERR_CAST(smap);
648 
649 	smap->cache_idx = bpf_local_storage_cache_idx_get(cache);
650 	return &smap->map;
651 }
652 
653 void bpf_local_storage_map_free(struct bpf_map *map,
654 				struct bpf_local_storage_cache *cache,
655 				int __percpu *busy_counter)
656 {
657 	struct bpf_local_storage_map_bucket *b;
658 	struct bpf_local_storage_elem *selem;
659 	struct bpf_local_storage_map *smap;
660 	unsigned int i;
661 
662 	smap = (struct bpf_local_storage_map *)map;
663 	bpf_local_storage_cache_idx_free(cache, smap->cache_idx);
664 
665 	/* Note that this map might be concurrently cloned from
666 	 * bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
667 	 * RCU read section to finish before proceeding. New RCU
668 	 * read sections should be prevented via bpf_map_inc_not_zero.
669 	 */
670 	synchronize_rcu();
671 
672 	/* bpf prog and the userspace can no longer access this map
673 	 * now.  No new selem (of this map) can be added
674 	 * to the owner->storage or to the map bucket's list.
675 	 *
676 	 * The elem of this map can be cleaned up here
677 	 * or when the storage is freed e.g.
678 	 * by bpf_sk_storage_free() during __sk_destruct().
679 	 */
680 	for (i = 0; i < (1U << smap->bucket_log); i++) {
681 		b = &smap->buckets[i];
682 
683 		rcu_read_lock();
684 		/* No one is adding to b->list now */
685 		while ((selem = hlist_entry_safe(
686 				rcu_dereference_raw(hlist_first_rcu(&b->list)),
687 				struct bpf_local_storage_elem, map_node))) {
688 			if (busy_counter) {
689 				migrate_disable();
690 				this_cpu_inc(*busy_counter);
691 			}
692 			bpf_selem_unlink(selem, false);
693 			if (busy_counter) {
694 				this_cpu_dec(*busy_counter);
695 				migrate_enable();
696 			}
697 			cond_resched_rcu();
698 		}
699 		rcu_read_unlock();
700 	}
701 
702 	/* While freeing the storage we may still need to access the map.
703 	 *
704 	 * e.g. when bpf_sk_storage_free() has unlinked selem from the map
705 	 * which then made the above while((selem = ...)) loop
706 	 * exit immediately.
707 	 *
708 	 * However, while freeing the storage one still needs to access the
709 	 * smap->elem_size to do the uncharging in
710 	 * bpf_selem_unlink_storage_nolock().
711 	 *
712 	 * Hence, wait another rcu grace period for the storage to be freed.
713 	 */
714 	synchronize_rcu();
715 
716 	kvfree(smap->buckets);
717 	bpf_map_area_free(smap);
718 }
719