linux-ext4 - Re: [PATCH v2 4/5] fscrypt: only set dentry

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Date:   Wed, 17 Apr 2019 10:07:01 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-mtd@...ts.infradead.org, linux-unionfs@...r.kernel.org,
        Sarthak Kukreti <sarthakkukreti@...omium.org>,
        Gao Xiang <gaoxiang25@...wei.com>
Subject: Re: [PATCH v2 4/5] fscrypt: only set dentry_operations on ciphertext
 dentries

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

Looks good, applied.

					- Ted