From: Eric Biggers <ebiggers@xxxxxxxxxx>
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 an error
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.
Fixes: 1b2628397058 ("block: Keyslot Manager for Inline Encryption")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
block/blk-crypto-profile.c | 50 +++++++++++++++-----------------------
block/blk-crypto.c | 23 +++++++++++-------
2 files changed, 33 insertions(+), 40 deletions(-)
diff --git a/block/blk-crypto-profile.c b/block/blk-crypto-profile.c
index 0307fb0d95d34..1b20ead59f39b 100644
--- a/block/blk-crypto-profile.c
+++ b/block/blk-crypto-profile.c
@@ -354,22 +354,10 @@ 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)
@@ -389,22 +377,22 @@ 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 (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) {
- err = -EBUSY;
- goto out_unlock;
+ if (slot) {
+ if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) {
+ /* BUG: key is still in use by I/O */
+ err = -EBUSY;
+ } else {
+ err = profile->ll_ops.keyslot_evict(
+ profile, key,
+ blk_crypto_keyslot_index(slot));
+ }
+ /*
+ * Callers may 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 = profile->ll_ops.keyslot_evict(profile, key,
- blk_crypto_keyslot_index(slot));
- if (err)
- goto out_unlock;
-
- hlist_del(&slot->hash_node);
- slot->key = NULL;
- err = 0;
-out_unlock:
blk_crypto_hw_exit(profile);
return err;
}
diff --git a/block/blk-crypto.c b/block/blk-crypto.c
index 8e5612364c48c..caa86a210cb6c 100644
--- a/block/blk-crypto.c
+++ b/block/blk-crypto.c
@@ -399,17 +399,22 @@ 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.
*
- * Return: 0 on success or if the key wasn't in any keyslot; -errno on error.
+ * 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.
+ * Return: 0 on success or if the key wasn't in any keyslot; -errno if the key
+ * failed to be evicted from a keyslot or is still in-use. Even on
+ * "failure", the key is removed from the keyslot management structures.
*/
int blk_crypto_evict_key(struct block_device *bdev,
const struct blk_crypto_key *key)
--
2.39.2
