From: Eric Biggers ebiggers@google.com
commit 5c7cb94452901a93e90c2230632e2c12a681bc92 upstream.
If blk_crypto_evict_key() sees that the key is still in-use (due to a bug) or that ->keyslot_evict failed, it currently just returns while leaving the key linked into the keyslot management structures.
However, blk_crypto_evict_key() is only called in contexts such as inode eviction where failure is not an option. So actually the caller proceeds with freeing the blk_crypto_key regardless of the return value of blk_crypto_evict_key().
These two assumptions don't match, and the result is that there can be a use-after-free in blk_crypto_reprogram_all_keys() after one of these errors occurs. (Note, these errors *shouldn't* happen; we're just talking about what happens if they do anyway.)
Fix this by making blk_crypto_evict_key() unlink the key from the keyslot management structures even on failure.
Also improve some comments.
Fixes: 1b2628397058 ("block: Keyslot Manager for Inline Encryption") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers ebiggers@google.com Reviewed-by: Christoph Hellwig hch@lst.de Link: https://lore.kernel.org/r/20230315183907.53675-2-ebiggers@kernel.org Signed-off-by: Jens Axboe axboe@kernel.dk --- block/blk-crypto.c | 29 +++++++++++++++++++-------- block/keyslot-manager.c | 43 ++++++++++++++++++++--------------------- 2 files changed, 42 insertions(+), 30 deletions(-)
diff --git a/block/blk-crypto.c b/block/blk-crypto.c index d8c48ee44ba69..87ec55d4354f5 100644 --- a/block/blk-crypto.c +++ b/block/blk-crypto.c @@ -385,15 +385,20 @@ int blk_crypto_start_using_key(const struct blk_crypto_key *key, }
/** - * blk_crypto_evict_key() - Evict a key from any inline encryption hardware - * it may have been programmed into - * @q: The request queue who's associated inline encryption hardware this key - * might have been programmed into - * @key: The key to evict + * blk_crypto_evict_key() - Evict a blk_crypto_key from a request_queue + * @q: a request_queue on which I/O using the key may have been done + * @key: the key to evict * - * Upper layers (filesystems) must call this function to ensure that a key is - * evicted from any hardware that it might have been programmed into. The key - * must not be in use by any in-flight IO when this function is called. + * For a given request_queue, this function removes the given blk_crypto_key + * from the keyslot management structures and evicts it from any underlying + * hardware keyslot(s) or blk-crypto-fallback keyslot it may have been + * programmed into. + * + * Upper layers must call this before freeing the blk_crypto_key. It must be + * called for every request_queue the key may have been used on. The key must + * no longer be in use by any I/O when this function is called. + * + * Context: May sleep. */ void blk_crypto_evict_key(struct request_queue *q, const struct blk_crypto_key *key) @@ -404,6 +409,14 @@ void blk_crypto_evict_key(struct request_queue *q, err = blk_ksm_evict_key(q->ksm, key); else err = blk_crypto_fallback_evict_key(key); + /* + * An error can only occur here if the key failed to be evicted from a + * keyslot (due to a hardware or driver issue) or is allegedly still in + * use by I/O (due to a kernel bug). Even in these cases, the key is + * still unlinked from the keyslot management structures, and the caller + * is allowed and expected to free it right away. There's nothing + * callers can do to handle errors, so just log them and return void. + */ if (err) pr_warn_ratelimited("error %d evicting key\n", err); } diff --git a/block/keyslot-manager.c b/block/keyslot-manager.c index 86f8195d8039e..17a1f1ba44efc 100644 --- a/block/keyslot-manager.c +++ b/block/keyslot-manager.c @@ -305,44 +305,43 @@ bool blk_ksm_crypto_cfg_supported(struct blk_keyslot_manager *ksm, return true; }
-/** - * blk_ksm_evict_key() - Evict a key from the lower layer device. - * @ksm: The keyslot manager to evict from - * @key: The key to evict - * - * Find the keyslot that the specified key was programmed into, and evict that - * slot from the lower layer device. The slot must not be in use by any - * in-flight IO when this function is called. - * - * Context: Process context. Takes and releases ksm->lock. - * Return: 0 on success or if there's no keyslot with the specified key, -EBUSY - * if the keyslot is still in use, or another -errno value on other - * error. +/* + * This is an internal function that evicts a key from an inline encryption + * device that can be either a real device or the blk-crypto-fallback "device". + * It is used only by blk_crypto_evict_key(); see that function for details. */ int blk_ksm_evict_key(struct blk_keyslot_manager *ksm, const struct blk_crypto_key *key) { struct blk_ksm_keyslot *slot; - int err = 0; + int err;
blk_ksm_hw_enter(ksm); slot = blk_ksm_find_keyslot(ksm, key); - if (!slot) - goto out_unlock; + if (!slot) { + /* + * Not an error, since a key not in use by I/O is not guaranteed + * to be in a keyslot. There can be more keys than keyslots. + */ + err = 0; + goto out; + }
if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { + /* BUG: key is still in use by I/O */ err = -EBUSY; - goto out_unlock; + goto out_remove; } err = ksm->ksm_ll_ops.keyslot_evict(ksm, key, blk_ksm_get_slot_idx(slot)); - if (err) - goto out_unlock; - +out_remove: + /* + * Callers free the key even on error, so unlink the key from the hash + * table and clear slot->key even on error. + */ hlist_del(&slot->hash_node); slot->key = NULL; - err = 0; -out_unlock: +out: blk_ksm_hw_exit(ksm); return err; }