From: Eric Biggers ebiggers@google.com

commit 9cd1e566676bbcb8a126acd921e4e194e6339603 upstream.

Once all I/O using a blk_crypto_key has completed, filesystems can call blk_crypto_evict_key(). However, the block layer currently doesn't call blk_crypto_put_keyslot() until the request is being freed, which happens after upper layers have been told (via bio_endio()) the I/O has completed. This causes a race condition where blk_crypto_evict_key() can see 'slot_refs != 0' without there being an actual bug.

This makes __blk_crypto_evict_key() hit the 'WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)' and return without doing anything, eventually causing a use-after-free in blk_crypto_reprogram_all_keys(). (This is a very rare bug and has only been seen when per-file keys are being used with fscrypt.)

There are two options to fix this: either release the keyslot before bio_endio() is called on the request's last bio, or make __blk_crypto_evict_key() ignore slot_refs. Let's go with the first solution, since it preserves the ability to report bugs (via WARN_ON_ONCE) where a key is evicted while still in-use.

Fixes: a892c8d52c02 ("block: Inline encryption support for blk-mq") Cc: stable@vger.kernel.org Reviewed-by: Nathan Huckleberry nhuck@google.com Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Eric Biggers ebiggers@google.com Link: https://lore.kernel.org/r/20230315183907.53675-2-ebiggers@kernel.org Signed-off-by: Jens Axboe axboe@kernel.dk --- block/blk-core.c | 7 +++++++ block/blk-crypto-internal.h | 25 +++++++++++++++++++++---- block/blk-crypto.c | 24 ++++++++++++------------ block/blk-merge.c | 2 ++ block/blk-mq.c | 2 +- 5 files changed, 43 insertions(+), 17 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c index ed6271dcc1b16..0c4a4e42ad870 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1421,6 +1421,13 @@ bool blk_update_request(struct request *req, blk_status_t error, req->q->integrity.profile->complete_fn(req, nr_bytes); #endif

+ /* + * Upper layers may call blk_crypto_evict_key() anytime after the last + * bio_endio(). Therefore, the keyslot must be released before that. + */ + if (blk_crypto_rq_has_keyslot(req) && nr_bytes >= blk_rq_bytes(req)) + __blk_crypto_rq_put_keyslot(req); + if (unlikely(error && !blk_rq_is_passthrough(req) && !(req->rq_flags & RQF_QUIET))) print_req_error(req, error, __func__); diff --git a/block/blk-crypto-internal.h b/block/blk-crypto-internal.h index 0d36aae538d7b..8e08345576203 100644 --- a/block/blk-crypto-internal.h +++ b/block/blk-crypto-internal.h @@ -60,6 +60,11 @@ static inline bool blk_crypto_rq_is_encrypted(struct request *rq) return rq->crypt_ctx; }

+static inline bool blk_crypto_rq_has_keyslot(struct request *rq) +{ + return rq->crypt_keyslot; +} + #else /* CONFIG_BLK_INLINE_ENCRYPTION */

static inline bool bio_crypt_rq_ctx_compatible(struct request *rq, @@ -93,6 +98,11 @@ static inline bool blk_crypto_rq_is_encrypted(struct request *rq) return false; }

+static inline bool blk_crypto_rq_has_keyslot(struct request *rq) +{ + return false; +} + #endif /* CONFIG_BLK_INLINE_ENCRYPTION */

void __bio_crypt_advance(struct bio *bio, unsigned int bytes); @@ -127,14 +137,21 @@ static inline bool blk_crypto_bio_prep(struct bio **bio_ptr) return true; }

-blk_status_t __blk_crypto_init_request(struct request *rq); -static inline blk_status_t blk_crypto_init_request(struct request *rq) +blk_status_t __blk_crypto_rq_get_keyslot(struct request *rq); +static inline blk_status_t blk_crypto_rq_get_keyslot(struct request *rq) { if (blk_crypto_rq_is_encrypted(rq)) - return __blk_crypto_init_request(rq); + return __blk_crypto_rq_get_keyslot(rq); return BLK_STS_OK; }

+void __blk_crypto_rq_put_keyslot(struct request *rq); +static inline void blk_crypto_rq_put_keyslot(struct request *rq) +{ + if (blk_crypto_rq_has_keyslot(rq)) + __blk_crypto_rq_put_keyslot(rq); +} + void __blk_crypto_free_request(struct request *rq); static inline void blk_crypto_free_request(struct request *rq) { @@ -173,7 +190,7 @@ static inline blk_status_t blk_crypto_insert_cloned_request(struct request *rq) {

if (blk_crypto_rq_is_encrypted(rq)) - return blk_crypto_init_request(rq); + return blk_crypto_rq_get_keyslot(rq); return BLK_STS_OK; }

diff --git a/block/blk-crypto.c b/block/blk-crypto.c index 103c2e2d50d67..183d7439cf416 100644 --- a/block/blk-crypto.c +++ b/block/blk-crypto.c @@ -216,26 +216,26 @@ static bool bio_crypt_check_alignment(struct bio *bio) return true; }

-blk_status_t __blk_crypto_init_request(struct request *rq) +blk_status_t __blk_crypto_rq_get_keyslot(struct request *rq) { return blk_ksm_get_slot_for_key(rq->q->ksm, rq->crypt_ctx->bc_key, &rq->crypt_keyslot); }

-/** - * __blk_crypto_free_request - Uninitialize the crypto fields of a request. - * - * @rq: The request whose crypto fields to uninitialize. - * - * Completely uninitializes the crypto fields of a request. If a keyslot has - * been programmed into some inline encryption hardware, that keyslot is - * released. The rq->crypt_ctx is also freed. - */ -void __blk_crypto_free_request(struct request *rq) +void __blk_crypto_rq_put_keyslot(struct request *rq) { blk_ksm_put_slot(rq->crypt_keyslot); + rq->crypt_keyslot = NULL; +} + +void __blk_crypto_free_request(struct request *rq) +{ + /* The keyslot, if one was needed, should have been released earlier. */ + if (WARN_ON_ONCE(rq->crypt_keyslot)) + __blk_crypto_rq_put_keyslot(rq); + mempool_free(rq->crypt_ctx, bio_crypt_ctx_pool); - blk_crypto_rq_set_defaults(rq); + rq->crypt_ctx = NULL; }

/** diff --git a/block/blk-merge.c b/block/blk-merge.c index d1435b6572977..1affc5fd35f0c 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -818,6 +818,8 @@ static struct request *attempt_merge(struct request_queue *q, if (!blk_discard_mergable(req)) elv_merge_requests(q, req, next);

+ blk_crypto_rq_put_keyslot(next); + /* * 'next' is going away, so update stats accordingly */ diff --git a/block/blk-mq.c b/block/blk-mq.c index 01e281801453d..bbbbcd2c19418 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2228,7 +2228,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)

blk_mq_bio_to_request(rq, bio, nr_segs);

- ret = blk_crypto_init_request(rq); + ret = blk_crypto_rq_get_keyslot(rq); if (ret != BLK_STS_OK) { bio->bi_status = ret; bio_endio(bio);

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 686c657f91917..5029a50807d5d 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 2c4a55bea6ca1..2a7a36551cfae 100644 --- a/block/keyslot-manager.c +++ b/block/keyslot-manager.c @@ -343,25 +343,16 @@ 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;

if (blk_ksm_is_passthrough(ksm)) { if (ksm->ksm_ll_ops.keyslot_evict) { @@ -375,22 +366,30 @@ int blk_ksm_evict_key(struct blk_keyslot_manager *ksm,

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; }