Hi Eric,

On Thu, Mar 2, 2023 at 11:23 PM Eric Biggers ebiggers@kernel.org wrote:

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 Signed-off-by: Eric Biggers ebiggers@google.com

---

block/blk-crypto-internal.h | 15 +++++++++++---- block/blk-crypto.c | 24 ++++++++++++------------ block/blk-mq.c | 15 ++++++++++++++- 3 files changed, 37 insertions(+), 17 deletions(-)

diff --git a/block/blk-crypto-internal.h b/block/blk-crypto-internal.h index a8cdaf26851e1..73609902349b6 100644 --- a/block/blk-crypto-internal.h +++ b/block/blk-crypto-internal.h @@ -153,14 +153,21 @@ 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_is_encrypted(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 +206,7 @@ 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..8e5612364c48c 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) +{ mempool_free(rq->crypt_ctx, bio_crypt_ctx_pool);

•   blk_crypto_rq_set_defaults(rq);
  

•   rq->crypt_ctx = NULL;
  

•   /* The keyslot, if one was needed, should have been released earlier. */
  

•   if (WARN_ON_ONCE(rq->crypt_keyslot))
  

•           __blk_crypto_rq_put_keyslot(rq);
  

}

/** diff --git a/block/blk-mq.c b/block/blk-mq.c index d3494a796ba80..738e81f518227 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_is_encrypted(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);
  

-- 2.39.2

Thanks for the updated patchset. This patch looks good to me.

Reviewed-by: Nathan Huckleberry nhuck@google.com

Thanks, Huck