Re: [PATCH 2/4] fscrypt: add fscrypt_add_test_dummy_key()

["Theodore Y. Ts'o" <tytso@mit.edu>]

On Tue, May 12, 2020 at 04:32:49PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> Currently, the test_dummy_encryption mount option (which is used for
> encryption I/O testing with xfstests) uses v1 encryption policies, and
> it relies on userspace inserting a test key into the session keyring.
> 
> We need test_dummy_encryption to support v2 encryption policies too.
> Requiring userspace to add the test key doesn't work well with v2
> policies, since v2 policies only support the filesystem keyring (not the
> session keyring), and keys in the filesystem keyring are lost when the
> filesystem is unmounted.  Hooking all test code that unmounts and
> re-mounts the filesystem would be difficult.
> 
> Instead, let's make the filesystem automatically add the test key to its
> keyring when test_dummy_encryption is enabled.
> 
> That puts the responsibility for choosing the test key on the kernel.
> We could just hard-code a key.  But out of paranoia, let's first try
> using a per-boot random key, to prevent this code from being misused.
> A per-boot key will work as long as no one expects dummy-encrypted files
> to remain accessible after a reboot.  (gce-xfstests doesn't.)
> 
> Therefore, this patch adds a function fscrypt_add_test_dummy_key() which
> implements the above.  The next patch will use it.
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Reviewed-by: Theodore Ts'o <tytso@mit.edu>