blk-mq: release crypto keyslot before reporting I/O complete

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>

diff --git a/block/blk-crypto-internal.h b/block/blk-crypto-internal.h
index a8cdaf26851e18e882b65c001c4897135b74fb76..4f1de2495f0c391aa2d62701761de7610e1acab3 100644 (file)
--- 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 45378586151f78572d77c47be4d220c30c2995e8..d0c7feb447e966faa4969bd31a0d21ab407ad2e9 100644 (file)
--- 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 6460abdb24267cc054350b44781a4d386f8e1edf..65e75efa9bd3663c787b4b0c5b310479419467a2 100644 (file)
--- 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 d0cb2ef18fe21dfa07fe4eec5c76bde6d6286f05..49825538d932d75869d7dc1a6d57c6415166aa9d 100644 (file)
--- 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);