[PATCH v2 4/5] fscrypt: only set dentry_operations on ciphertext dentries

Theodore Ts'o tytso at mit.edu
Wed Apr 17 07:07:01 PDT 2019


On Wed, Mar 20, 2019 at 11:39:12AM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers at google.com>
> 
> 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 at google.com>

Looks good, applied.

					- Ted



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