Re: [PATCH] fscrypt: add a documentation file for filesystem-level encryption

From: Anand Jain <anand.jain@oracle.com>
To: Eric Biggers <ebiggers3@gmail.com>
Cc: linux-fscrypt@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
	"Theodore Y . Ts'o" <tytso@mit.edu>,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	Richard Weinberger <richard@nod.at>,
	Michael Halcrow <mhalcrow@google.com>,
	Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH] fscrypt: add a documentation file for filesystem-level encryption
Date: Mon, 28 Aug 2017 20:18:46 +0800	[thread overview]
Message-ID: <9e3f608d-5410-b8f7-cdf0-93045be7a995@oracle.com> (raw)
In-Reply-To: <20170822170720.GA9587@gmail.com>

On 08/23/2017 01:07 AM, Eric Biggers wrote:
> On Tue, Aug 22, 2017 at 11:33:51PM +0800, Anand Jain wrote:
>>
>>
>> On 08/22/2017 10:55 AM, Eric Biggers wrote:
>>> On Tue, Aug 22, 2017 at 10:22:30AM +0800, Anand Jain wrote:
>>>>
>>>> Hi Eric,
>>>>
>>>>    How about a section on the threat model specific to the file-name ?
>>>>
>>>>    (Sorry if I am missing something).
>>>>
>>>> Thanks, Anand
>>>
>>> It's already mentioned that filenames are encrypted: "fscrypt protects the
>>> confidentiality of file contents and filenames in the event of a single
>>> point-in-time permanent offline compromise of the block device content."
>>> There's not much more to it than that; all the other points in the "Threat
>>> model" section (offline manipulations, timing attacks, access control, key
>>> eviction, etc.) are essentially the same between contents and filenames
>>> encryption.
>>
>>   Do you think if application does not keep the sensitive information
>> in the file-name, would that remove the file-name from the list of
>> items that should be protected ?
>>
> 
> If *no* applications care whether the filenames are encrypted or not, sure.
> But are you absolutely sure that no applications care?  How do you know?  And what
> is the advantage of not encrypting the filenames anyway?  It is better to
> encrypt by default.
> 
> Eric

  (sorry for the delay in reply due to my vacation).

  It all depends on the use case, Android is one such use case. Some 
data center use a known set of application. Again it all depends on the 
use case.

  File-name is a kind of File-system semantic and altering based on the 
on the user key context does not guarantee the system will be compatible 
with all their legacy applications.

  Also a section on backup and restore in this doc will be a good idea. 
As I think that will be affected IMO. And needing to have the user 
master key to restore encrypted file isn't practical in some data center 
multi tenanted solutions. Albeit it may work in some cases but hard to 
generalize.

Thanks, Anand