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

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Date:	Sat, 11 Apr 2015 09:10:52 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	jaegeuk@...nel.org, mhalcrow@...gle.com,
	Ildar Muslukhov <muslukhovi@...il.com>
Subject: Re: [PATCH 06/22] ext4 crypto: add encryption policy checking

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

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