diff mbox series

[1/3] blk-mq: release crypto keyslot before reporting I/O complete

Message ID 20230303071959.144604-2-ebiggers@kernel.org (mailing list archive)
State New, archived
Headers show
Series Fix blk-crypto keyslot race condition | expand

Commit Message

Eric Biggers March 3, 2023, 7:19 a.m. UTC 
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(-)

Comments

Nathan Huckleberry March 3, 2023, 7:29 p.m. UTC | #1 
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
Eric Biggers March 8, 2023, 6:21 p.m. UTC | #2 
On Thu, Mar 02, 2023 at 11:19:57PM -0800, Eric Biggers wrote:
> +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);
>  }

I received a report that this WARN_ON_ONCE can be hit.

To fix this, attempt_merge() will need to release the keyslot too.

- Eric
diff mbox series

Patch

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);