linux/kernel/bpf/bpf_local_storage.c
Song Liu bc235cdb42 bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete]
BPF helpers bpf_task_storage_[get|delete] could hold two locks:
bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling
these helpers from fentry/fexit programs on functions in bpf_*_storage.c
may cause deadlock on either locks.

Prevent such deadlock with a per cpu counter, bpf_task_storage_busy. We
need this counter to be global, because the two locks here belong to two
different objects: bpf_local_storage_map and bpf_local_storage. If we
pick one of them as the owner of the counter, it is still possible to
trigger deadlock on the other lock. For example, if bpf_local_storage_map
owns the counters, it cannot prevent deadlock on bpf_local_storage->lock
when two maps are used.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210225234319.336131-3-songliubraving@fb.com
2021-02-26 11:51:48 -08:00

608 lines
17 KiB
C

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019 Facebook */
#include <linux/rculist.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/types.h>
#include <linux/spinlock.h>
#include <linux/bpf.h>
#include <linux/btf_ids.h>
#include <linux/bpf_local_storage.h>
#include <net/sock.h>
#include <uapi/linux/sock_diag.h>
#include <uapi/linux/btf.h>
#define BPF_LOCAL_STORAGE_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_CLONE)
static struct bpf_local_storage_map_bucket *
select_bucket(struct bpf_local_storage_map *smap,
struct bpf_local_storage_elem *selem)
{
return &smap->buckets[hash_ptr(selem, smap->bucket_log)];
}
static int mem_charge(struct bpf_local_storage_map *smap, void *owner, u32 size)
{
struct bpf_map *map = &smap->map;
if (!map->ops->map_local_storage_charge)
return 0;
return map->ops->map_local_storage_charge(smap, owner, size);
}
static void mem_uncharge(struct bpf_local_storage_map *smap, void *owner,
u32 size)
{
struct bpf_map *map = &smap->map;
if (map->ops->map_local_storage_uncharge)
map->ops->map_local_storage_uncharge(smap, owner, size);
}
static struct bpf_local_storage __rcu **
owner_storage(struct bpf_local_storage_map *smap, void *owner)
{
struct bpf_map *map = &smap->map;
return map->ops->map_owner_storage_ptr(owner);
}
static bool selem_linked_to_storage(const struct bpf_local_storage_elem *selem)
{
return !hlist_unhashed(&selem->snode);
}
static bool selem_linked_to_map(const struct bpf_local_storage_elem *selem)
{
return !hlist_unhashed(&selem->map_node);
}
struct bpf_local_storage_elem *
bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
void *value, bool charge_mem)
{
struct bpf_local_storage_elem *selem;
if (charge_mem && mem_charge(smap, owner, smap->elem_size))
return NULL;
selem = bpf_map_kzalloc(&smap->map, smap->elem_size,
GFP_ATOMIC | __GFP_NOWARN);
if (selem) {
if (value)
memcpy(SDATA(selem)->data, value, smap->map.value_size);
return selem;
}
if (charge_mem)
mem_uncharge(smap, owner, smap->elem_size);
return NULL;
}
/* local_storage->lock must be held and selem->local_storage == local_storage.
* The caller must ensure selem->smap is still valid to be
* dereferenced for its smap->elem_size and smap->cache_idx.
*/
bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
struct bpf_local_storage_elem *selem,
bool uncharge_mem)
{
struct bpf_local_storage_map *smap;
bool free_local_storage;
void *owner;
smap = rcu_dereference(SDATA(selem)->smap);
owner = local_storage->owner;
/* All uncharging on the owner must be done first.
* The owner may be freed once the last selem is unlinked
* from local_storage.
*/
if (uncharge_mem)
mem_uncharge(smap, owner, smap->elem_size);
free_local_storage = hlist_is_singular_node(&selem->snode,
&local_storage->list);
if (free_local_storage) {
mem_uncharge(smap, owner, sizeof(struct bpf_local_storage));
local_storage->owner = NULL;
/* After this RCU_INIT, owner may be freed and cannot be used */
RCU_INIT_POINTER(*owner_storage(smap, owner), NULL);
/* local_storage is not freed now. local_storage->lock is
* still held and raw_spin_unlock_bh(&local_storage->lock)
* will be done by the caller.
*
* Although the unlock will be done under
* rcu_read_lock(), it is more intutivie to
* read if kfree_rcu(local_storage, rcu) is done
* after the raw_spin_unlock_bh(&local_storage->lock).
*
* Hence, a "bool free_local_storage" is returned
* to the caller which then calls the kfree_rcu()
* after unlock.
*/
}
hlist_del_init_rcu(&selem->snode);
if (rcu_access_pointer(local_storage->cache[smap->cache_idx]) ==
SDATA(selem))
RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);
kfree_rcu(selem, rcu);
return free_local_storage;
}
static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
{
struct bpf_local_storage *local_storage;
bool free_local_storage = false;
unsigned long flags;
if (unlikely(!selem_linked_to_storage(selem)))
/* selem has already been unlinked from sk */
return;
local_storage = rcu_dereference(selem->local_storage);
raw_spin_lock_irqsave(&local_storage->lock, flags);
if (likely(selem_linked_to_storage(selem)))
free_local_storage = bpf_selem_unlink_storage_nolock(
local_storage, selem, true);
raw_spin_unlock_irqrestore(&local_storage->lock, flags);
if (free_local_storage)
kfree_rcu(local_storage, rcu);
}
void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
struct bpf_local_storage_elem *selem)
{
RCU_INIT_POINTER(selem->local_storage, local_storage);
hlist_add_head_rcu(&selem->snode, &local_storage->list);
}
void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
{
struct bpf_local_storage_map *smap;
struct bpf_local_storage_map_bucket *b;
unsigned long flags;
if (unlikely(!selem_linked_to_map(selem)))
/* selem has already be unlinked from smap */
return;
smap = rcu_dereference(SDATA(selem)->smap);
b = select_bucket(smap, selem);
raw_spin_lock_irqsave(&b->lock, flags);
if (likely(selem_linked_to_map(selem)))
hlist_del_init_rcu(&selem->map_node);
raw_spin_unlock_irqrestore(&b->lock, flags);
}
void bpf_selem_link_map(struct bpf_local_storage_map *smap,
struct bpf_local_storage_elem *selem)
{
struct bpf_local_storage_map_bucket *b = select_bucket(smap, selem);
unsigned long flags;
raw_spin_lock_irqsave(&b->lock, flags);
RCU_INIT_POINTER(SDATA(selem)->smap, smap);
hlist_add_head_rcu(&selem->map_node, &b->list);
raw_spin_unlock_irqrestore(&b->lock, flags);
}
void bpf_selem_unlink(struct bpf_local_storage_elem *selem)
{
/* Always unlink from map before unlinking from local_storage
* because selem will be freed after successfully unlinked from
* the local_storage.
*/
bpf_selem_unlink_map(selem);
__bpf_selem_unlink_storage(selem);
}
struct bpf_local_storage_data *
bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
struct bpf_local_storage_map *smap,
bool cacheit_lockit)
{
struct bpf_local_storage_data *sdata;
struct bpf_local_storage_elem *selem;
/* Fast path (cache hit) */
sdata = rcu_dereference(local_storage->cache[smap->cache_idx]);
if (sdata && rcu_access_pointer(sdata->smap) == smap)
return sdata;
/* Slow path (cache miss) */
hlist_for_each_entry_rcu(selem, &local_storage->list, snode)
if (rcu_access_pointer(SDATA(selem)->smap) == smap)
break;
if (!selem)
return NULL;
sdata = SDATA(selem);
if (cacheit_lockit) {
unsigned long flags;
/* spinlock is needed to avoid racing with the
* parallel delete. Otherwise, publishing an already
* deleted sdata to the cache will become a use-after-free
* problem in the next bpf_local_storage_lookup().
*/
raw_spin_lock_irqsave(&local_storage->lock, flags);
if (selem_linked_to_storage(selem))
rcu_assign_pointer(local_storage->cache[smap->cache_idx],
sdata);
raw_spin_unlock_irqrestore(&local_storage->lock, flags);
}
return sdata;
}
static int check_flags(const struct bpf_local_storage_data *old_sdata,
u64 map_flags)
{
if (old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
/* elem already exists */
return -EEXIST;
if (!old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
/* elem doesn't exist, cannot update it */
return -ENOENT;
return 0;
}
int bpf_local_storage_alloc(void *owner,
struct bpf_local_storage_map *smap,
struct bpf_local_storage_elem *first_selem)
{
struct bpf_local_storage *prev_storage, *storage;
struct bpf_local_storage **owner_storage_ptr;
int err;
err = mem_charge(smap, owner, sizeof(*storage));
if (err)
return err;
storage = bpf_map_kzalloc(&smap->map, sizeof(*storage),
GFP_ATOMIC | __GFP_NOWARN);
if (!storage) {
err = -ENOMEM;
goto uncharge;
}
INIT_HLIST_HEAD(&storage->list);
raw_spin_lock_init(&storage->lock);
storage->owner = owner;
bpf_selem_link_storage_nolock(storage, first_selem);
bpf_selem_link_map(smap, first_selem);
owner_storage_ptr =
(struct bpf_local_storage **)owner_storage(smap, owner);
/* Publish storage to the owner.
* Instead of using any lock of the kernel object (i.e. owner),
* cmpxchg will work with any kernel object regardless what
* the running context is, bh, irq...etc.
*
* From now on, the owner->storage pointer (e.g. sk->sk_bpf_storage)
* is protected by the storage->lock. Hence, when freeing
* the owner->storage, the storage->lock must be held before
* setting owner->storage ptr to NULL.
*/
prev_storage = cmpxchg(owner_storage_ptr, NULL, storage);
if (unlikely(prev_storage)) {
bpf_selem_unlink_map(first_selem);
err = -EAGAIN;
goto uncharge;
/* Note that even first_selem was linked to smap's
* bucket->list, first_selem can be freed immediately
* (instead of kfree_rcu) because
* bpf_local_storage_map_free() does a
* synchronize_rcu() before walking the bucket->list.
* Hence, no one is accessing selem from the
* bucket->list under rcu_read_lock().
*/
}
return 0;
uncharge:
kfree(storage);
mem_uncharge(smap, owner, sizeof(*storage));
return err;
}
/* sk cannot be going away because it is linking new elem
* to sk->sk_bpf_storage. (i.e. sk->sk_refcnt cannot be 0).
* Otherwise, it will become a leak (and other memory issues
* during map destruction).
*/
struct bpf_local_storage_data *
bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
void *value, u64 map_flags)
{
struct bpf_local_storage_data *old_sdata = NULL;
struct bpf_local_storage_elem *selem;
struct bpf_local_storage *local_storage;
unsigned long flags;
int err;
/* BPF_EXIST and BPF_NOEXIST cannot be both set */
if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
/* BPF_F_LOCK can only be used in a value with spin_lock */
unlikely((map_flags & BPF_F_LOCK) &&
!map_value_has_spin_lock(&smap->map)))
return ERR_PTR(-EINVAL);
local_storage = rcu_dereference(*owner_storage(smap, owner));
if (!local_storage || hlist_empty(&local_storage->list)) {
/* Very first elem for the owner */
err = check_flags(NULL, map_flags);
if (err)
return ERR_PTR(err);
selem = bpf_selem_alloc(smap, owner, value, true);
if (!selem)
return ERR_PTR(-ENOMEM);
err = bpf_local_storage_alloc(owner, smap, selem);
if (err) {
kfree(selem);
mem_uncharge(smap, owner, smap->elem_size);
return ERR_PTR(err);
}
return SDATA(selem);
}
if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
/* Hoping to find an old_sdata to do inline update
* such that it can avoid taking the local_storage->lock
* and changing the lists.
*/
old_sdata =
bpf_local_storage_lookup(local_storage, smap, false);
err = check_flags(old_sdata, map_flags);
if (err)
return ERR_PTR(err);
if (old_sdata && selem_linked_to_storage(SELEM(old_sdata))) {
copy_map_value_locked(&smap->map, old_sdata->data,
value, false);
return old_sdata;
}
}
raw_spin_lock_irqsave(&local_storage->lock, flags);
/* Recheck local_storage->list under local_storage->lock */
if (unlikely(hlist_empty(&local_storage->list))) {
/* A parallel del is happening and local_storage is going
* away. It has just been checked before, so very
* unlikely. Return instead of retry to keep things
* simple.
*/
err = -EAGAIN;
goto unlock_err;
}
old_sdata = bpf_local_storage_lookup(local_storage, smap, false);
err = check_flags(old_sdata, map_flags);
if (err)
goto unlock_err;
if (old_sdata && (map_flags & BPF_F_LOCK)) {
copy_map_value_locked(&smap->map, old_sdata->data, value,
false);
selem = SELEM(old_sdata);
goto unlock;
}
/* local_storage->lock is held. Hence, we are sure
* we can unlink and uncharge the old_sdata successfully
* later. Hence, instead of charging the new selem now
* and then uncharge the old selem later (which may cause
* a potential but unnecessary charge failure), avoid taking
* a charge at all here (the "!old_sdata" check) and the
* old_sdata will not be uncharged later during
* bpf_selem_unlink_storage_nolock().
*/
selem = bpf_selem_alloc(smap, owner, value, !old_sdata);
if (!selem) {
err = -ENOMEM;
goto unlock_err;
}
/* First, link the new selem to the map */
bpf_selem_link_map(smap, selem);
/* Second, link (and publish) the new selem to local_storage */
bpf_selem_link_storage_nolock(local_storage, selem);
/* Third, remove old selem, SELEM(old_sdata) */
if (old_sdata) {
bpf_selem_unlink_map(SELEM(old_sdata));
bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
false);
}
unlock:
raw_spin_unlock_irqrestore(&local_storage->lock, flags);
return SDATA(selem);
unlock_err:
raw_spin_unlock_irqrestore(&local_storage->lock, flags);
return ERR_PTR(err);
}
u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
{
u64 min_usage = U64_MAX;
u16 i, res = 0;
spin_lock(&cache->idx_lock);
for (i = 0; i < BPF_LOCAL_STORAGE_CACHE_SIZE; i++) {
if (cache->idx_usage_counts[i] < min_usage) {
min_usage = cache->idx_usage_counts[i];
res = i;
/* Found a free cache_idx */
if (!min_usage)
break;
}
}
cache->idx_usage_counts[res]++;
spin_unlock(&cache->idx_lock);
return res;
}
void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
u16 idx)
{
spin_lock(&cache->idx_lock);
cache->idx_usage_counts[idx]--;
spin_unlock(&cache->idx_lock);
}
void bpf_local_storage_map_free(struct bpf_local_storage_map *smap,
int __percpu *busy_counter)
{
struct bpf_local_storage_elem *selem;
struct bpf_local_storage_map_bucket *b;
unsigned int i;
/* Note that this map might be concurrently cloned from
* bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
* RCU read section to finish before proceeding. New RCU
* read sections should be prevented via bpf_map_inc_not_zero.
*/
synchronize_rcu();
/* bpf prog and the userspace can no longer access this map
* now. No new selem (of this map) can be added
* to the owner->storage or to the map bucket's list.
*
* The elem of this map can be cleaned up here
* or when the storage is freed e.g.
* by bpf_sk_storage_free() during __sk_destruct().
*/
for (i = 0; i < (1U << smap->bucket_log); i++) {
b = &smap->buckets[i];
rcu_read_lock();
/* No one is adding to b->list now */
while ((selem = hlist_entry_safe(
rcu_dereference_raw(hlist_first_rcu(&b->list)),
struct bpf_local_storage_elem, map_node))) {
if (busy_counter) {
migrate_disable();
__this_cpu_inc(*busy_counter);
}
bpf_selem_unlink(selem);
if (busy_counter) {
__this_cpu_dec(*busy_counter);
migrate_enable();
}
cond_resched_rcu();
}
rcu_read_unlock();
}
/* While freeing the storage we may still need to access the map.
*
* e.g. when bpf_sk_storage_free() has unlinked selem from the map
* which then made the above while((selem = ...)) loop
* exit immediately.
*
* However, while freeing the storage one still needs to access the
* smap->elem_size to do the uncharging in
* bpf_selem_unlink_storage_nolock().
*
* Hence, wait another rcu grace period for the storage to be freed.
*/
synchronize_rcu();
kvfree(smap->buckets);
kfree(smap);
}
int bpf_local_storage_map_alloc_check(union bpf_attr *attr)
{
if (attr->map_flags & ~BPF_LOCAL_STORAGE_CREATE_FLAG_MASK ||
!(attr->map_flags & BPF_F_NO_PREALLOC) ||
attr->max_entries ||
attr->key_size != sizeof(int) || !attr->value_size ||
/* Enforce BTF for userspace sk dumping */
!attr->btf_key_type_id || !attr->btf_value_type_id)
return -EINVAL;
if (!bpf_capable())
return -EPERM;
if (attr->value_size > BPF_LOCAL_STORAGE_MAX_VALUE_SIZE)
return -E2BIG;
return 0;
}
struct bpf_local_storage_map *bpf_local_storage_map_alloc(union bpf_attr *attr)
{
struct bpf_local_storage_map *smap;
unsigned int i;
u32 nbuckets;
smap = kzalloc(sizeof(*smap), GFP_USER | __GFP_NOWARN | __GFP_ACCOUNT);
if (!smap)
return ERR_PTR(-ENOMEM);
bpf_map_init_from_attr(&smap->map, attr);
nbuckets = roundup_pow_of_two(num_possible_cpus());
/* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */
nbuckets = max_t(u32, 2, nbuckets);
smap->bucket_log = ilog2(nbuckets);
smap->buckets = kvcalloc(sizeof(*smap->buckets), nbuckets,
GFP_USER | __GFP_NOWARN | __GFP_ACCOUNT);
if (!smap->buckets) {
kfree(smap);
return ERR_PTR(-ENOMEM);
}
for (i = 0; i < nbuckets; i++) {
INIT_HLIST_HEAD(&smap->buckets[i].list);
raw_spin_lock_init(&smap->buckets[i].lock);
}
smap->elem_size =
sizeof(struct bpf_local_storage_elem) + attr->value_size;
return smap;
}
int bpf_local_storage_map_check_btf(const struct bpf_map *map,
const struct btf *btf,
const struct btf_type *key_type,
const struct btf_type *value_type)
{
u32 int_data;
if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
return -EINVAL;
int_data = *(u32 *)(key_type + 1);
if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
return -EINVAL;
return 0;
}