linux-kernel - Re: [PATCH RFC 3/8] fs/ext4: Disallow encryption if inode is DAX

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200415160307.GJ90651@mit.edu>
Date:   Wed, 15 Apr 2020 12:03:07 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFC 3/8] fs/ext4: Disallow encryption if inode is DAX

On Mon, Apr 13, 2020 at 09:00:25PM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> Encryption and DAX are incompatible.  Changing the DAX mode due to a
> change in Encryption mode is wrong without a corresponding
> address_space_operations update.
> 
> Make the 2 options mutually exclusive by returning an error if DAX was
> set first.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

The encryption flag is inherited from the containing directory, and
directories can't have the DAX flag set, so anything we do in
ext4_set_context() will be safety belt / sanity checking in nature.

But we *do* need to figure out what we do with mount -o dax=always
when the file system might have encrypted files.  My previous comments
about the verity flag and dax flag applies here.

Also note that encrypted files are read/write so we must never allow
the combination of ENCRPYT_FL and DAX_FL.  So that may be something
where we should teach __ext4_iget() to check for this, and declare the
file system as corrupted if it sees this combination.  (For VERITY_FL
&& DAX_FL that is a combo that we might want to support in the future,
so that's probably a case where arguably, we should just ignore the
DAX_FL for now.)

					- Ted