Re: [PATCH 06/22] ext4 crypto: add encryption policy checking

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

On Wed, Apr 08, 2015 at 12:07:16PM -0600, Andreas Dilger wrote:
> > +/* Policy provided via an ioctl on the topmost directory */
> > +struct ext4_encryption_policy {
> > +	char version;
> > +	char contents_encryption_mode;
> > +	char filenames_encryption_mode;
> > +	char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
> > +} __attribute__((__packed__));
> 
> It wouldn't be bad to add a padding byte before master_key_descriptor,
> even if this is only passed from the ioctl.  That allows casting the
> key to a numeric value if desired without problems on some arches.

This data structure is only used for the ioctl interface.  The on-disk
format is the struct ext4_encryption_context, where we do have the
padding.

> > +#define EXT4_ENCRYPTION_CONTEXT_FORMAT_V0 0
> 
> Per comments in the call, it is better not to use "0" as a defined
> version, since this is much more likely to be seen accidentally
> (e.g. uninitialized buffer, memory corruption, etc).  Better to
> start with version 1.

I'll make this change.

						- Ted