Re: RFC: what to do about fscrypt vs block device interaction

[Eric Biggers <ebiggers@kernel.org>]

On Fri, Jul 22, 2022 at 06:03:49PM +0200, Christoph Hellwig wrote:
> > To avoid that, I think we could go through and evict all the
> > blk_crypto_keys (i.e. call fscrypt_destroy_prepared_key() on the
> > fscrypt_prepared_keys embedded in each fscrypt_master_key) during the
> > unmount itself, separating it from the destruction of the key objects
> > from the keyring subsystem's perspective. That could happen in the
> > moved call to fscrypt_sb_free().

Note: for iterating through the keys in ->s_master_keys, I'd try something like
assoc_array_iterate(&sb->s_master_keys->keys, fscrypt_teardown_key, sb)

> 
> I'll give this a try.
> 
> What would be a good test suite or set of tests to make sure I don't
> break fscrypt operation?

You can run xfstests on ext4 and f2fs with "-g encrypt", both with and without
the inlinecrypt mount option.
https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#tests shows the
commands to do this with kvm-xfstests, but it can also be done with regular
xfstests.  Note that for the inlinecrypt mount option to work you'll need a
kernel with CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK=y and
CONFIG_FS_ENCRYPTION_INLINE_CRYPT=y.

There are relevant things that aren't tested by this, such as f2fs's
multi-device support and whether the blk-crypto keys really get evicted, but
that's the best we have.

- Eric