From: Eric Biggers ebiggers@google.com

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 --- block/blk-crypto-internal.h | 25 +++++++++++++++++++++---- block/blk-crypto.c | 24 ++++++++++++------------ block/blk-merge.c | 2 ++ block/blk-mq.c | 15 ++++++++++++++- 4 files changed, 49 insertions(+), 17 deletions(-)

diff --git a/block/blk-crypto-internal.h b/block/blk-crypto-internal.h index a8cdaf26851e1..4f1de2495f0c3 100644 --- a/block/blk-crypto-internal.h +++ b/block/blk-crypto-internal.h @@ -65,6 +65,11 @@ 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; +} + blk_status_t blk_crypto_get_keyslot(struct blk_crypto_profile *profile, const struct blk_crypto_key *key, struct blk_crypto_keyslot **slot_ptr); @@ -119,6 +124,11 @@ 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); @@ -153,14 +163,21 @@ 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) { @@ -199,7 +216,7 @@ 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 45378586151f7..d0c7feb447e96 100644 --- a/block/blk-crypto.c +++ b/block/blk-crypto.c @@ -224,27 +224,27 @@ 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_crypto_get_keyslot(rq->q->crypto_profile, 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_crypto_put_keyslot(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 6460abdb24267..65e75efa9bd36 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -867,6 +867,8 @@ 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 d0cb2ef18fe21..49825538d932d 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -840,6 +840,12 @@ static void blk_complete_request(struct request *req) req->q->integrity.profile->complete_fn(req, total_bytes); #endif

+ /* + * Upper layers may call blk_crypto_evict_key() anytime after the last + * bio_endio(). Therefore, the keyslot must be released before that. + */ + blk_crypto_rq_put_keyslot(req); + blk_account_io_completion(req, total_bytes);

do { @@ -905,6 +911,13 @@ 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)) && !test_bit(GD_DEAD, &req->q->disk->state)) { @@ -2967,7 +2980,7 @@ void 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);