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bpf: fix a memory leak in the LRU and LRU_PERCPU hash maps

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The LRU and LRU_PERCPU maps allocate a new element on update before locking the
target hash table bucket. Right after that the maps try to lock the bucket.
If this fails, then maps return -EBUSY to the caller without releasing the
allocated element. This makes the element untracked: it doesn't belong to
either of free lists, and it doesn't belong to the hash table, so can't be
re-used; this eventually leads to the permanent -ENOMEM on LRU map updates,
which is unexpected. Fix this by returning the element to the local free list
if bucket locking fails.

Fixes: 20b6cc34ea ("bpf: Avoid hashtab deadlock with map_locked")
Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
Link: https://lore.kernel.org/r/20230522154558.2166815-1-aspsk@isovalent.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
This commit is contained in:
Anton Protopopov 2023-05-22 15:45:58 +00:00 committed by Martin KaFai Lau
parent 0613d8ca9a
commit b34ffb0c6d
1 changed files with 4 additions and 2 deletions
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6
kernel/bpf/hashtab.c
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@ -1215,7 +1215,7 @@ static long htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value
ret = htab_lock_bucket(htab, b, hash, &flags);
if (ret)
return ret;
goto err_lock_bucket;
l_old = lookup_elem_raw(head, hash, key, key_size);
@ -1236,6 +1236,7 @@ static long htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value
err:
htab_unlock_bucket(htab, b, hash, flags);
err_lock_bucket:
if (ret)
htab_lru_push_free(htab, l_new);
else if (l_old)
@ -1338,7 +1339,7 @@ static long __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
ret = htab_lock_bucket(htab, b, hash, &flags);
if (ret)
return ret;
goto err_lock_bucket;
l_old = lookup_elem_raw(head, hash, key, key_size);
@ -1361,6 +1362,7 @@ static long __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
ret = 0;
err:
htab_unlock_bucket(htab, b, hash, flags);
err_lock_bucket:
if (l_new)
bpf_lru_push_free(&htab->lru, &l_new->lru_node);
return ret;