From: Eric Biggers ebiggers@google.com
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 --- block/blk-crypto-profile.c | 46 +++++++++++++++++--------------------- block/blk-crypto.c | 28 ++++++++++++++++------- 2 files changed, 41 insertions(+), 33 deletions(-)
diff --git a/block/blk-crypto-profile.c b/block/blk-crypto-profile.c index 0307fb0d95d34..3290c03c9918d 100644 --- a/block/blk-crypto-profile.c +++ b/block/blk-crypto-profile.c @@ -354,28 +354,16 @@ bool __blk_crypto_cfg_supported(struct blk_crypto_profile *profile, return true; }
-/** - * __blk_crypto_evict_key() - Evict a key from a device. - * @profile: the crypto profile of the device - * @key: the key to evict. It must not still be used in any I/O. - * - * If the device has keyslots, this finds the keyslot (if any) that contains the - * specified key and calls the driver's keyslot_evict function to evict it. - * - * Otherwise, this just calls the driver's keyslot_evict function if it is - * implemented, passing just the key (without any particular keyslot). This - * allows layered devices to evict the key from their underlying devices. - * - * Context: Process context. Takes and releases profile->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_crypto_evict_key(struct blk_crypto_profile *profile, const struct blk_crypto_key *key) { struct blk_crypto_keyslot *slot; - int err = 0; + int err;
if (profile->num_slots == 0) { if (profile->ll_ops.keyslot_evict) { @@ -389,22 +377,30 @@ int __blk_crypto_evict_key(struct blk_crypto_profile *profile,
blk_crypto_hw_enter(profile); slot = blk_crypto_find_keyslot(profile, 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 = profile->ll_ops.keyslot_evict(profile, key, blk_crypto_keyslot_index(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_crypto_hw_exit(profile); return err; } diff --git a/block/blk-crypto.c b/block/blk-crypto.c index e800f305e9eda..4d760b092deb9 100644 --- a/block/blk-crypto.c +++ b/block/blk-crypto.c @@ -400,15 +400,19 @@ int blk_crypto_start_using_key(struct block_device *bdev, }
/** - * blk_crypto_evict_key() - Evict a key from any inline encryption hardware - * it may have been programmed into - * @bdev: The block_device 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 block_device + * @bdev: a block_device 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 block_device, 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 block_device 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 block_device *bdev, const struct blk_crypto_key *key) @@ -420,6 +424,14 @@ void blk_crypto_evict_key(struct block_device *bdev, err = __blk_crypto_evict_key(q->crypto_profile, 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("%pg: error %d evicting key\n", bdev, err); }