tree 5ff534692506594efb7fa3ec0f8e2f34b9808d8b
parent 0bf3d5c1604ecbbd4e49e9f5b3c79152b87adb0d
author Eric Biggers <ebiggers@google.com> 1553107152 -0700
committer Theodore Ts'o <tytso@mit.edu> 1555509992 -0400

fscrypt: only set dentry_operations on ciphertext dentries

Plaintext dentries are always valid, so only set fscrypt_d_ops on
ciphertext dentries.

Besides marginally improved performance, this allows overlayfs to use an
fscrypt-encrypted upperdir, provided that all the following are true:

    (1) The fscrypt encryption key is placed in the keyring before
	mounting overlayfs, and remains while the overlayfs is mounted.

    (2) The overlayfs workdir uses the same encryption policy.

    (3) No dentries for the ciphertext names of subdirectories have been
	created in the upperdir or workdir yet.  (Since otherwise
	d_splice_alias() will reuse the old dentry with ->d_op set.)

One potential use case is using an ephemeral encryption key to encrypt
all files created or changed by a container, so that they can be
securely erased ("crypto-shredded") after the container stops.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>