linux-kernel - Re: security module question

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Date:	Thu, 06 Aug 2009 14:45:29 -0400
From:	Shaya Potter <spotter@...columbia.edu>
To:	Eric Paris <eparis@...hat.com>
CC:	James Morris <jmorris@...ei.org>,
	Justin Banks <justinb@...bone.com>,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: security module question

Eric Paris wrote:
> On Wed, 2009-08-05 at 12:02 +1000, James Morris wrote:
>> On Tue, 4 Aug 2009, Justin Banks wrote:
>>
>>> Hello - I'm trying to implement a security module that will allow or
>>> disallow writes on files by byte ranges. Is there a way to use
>>> inode_permission() to do this, or is there an alternative route I should
>>> take? It doesn't look like inode_permission() will give me the data I
>>> need (offset + length of write).
> 
> There is nothing that can do that.  Neither fanotify nor the LSM.
> Biggest problem is mmap.....
> 
> I think there was past kernel module which did this, but I don't
> remember what they were called.  Nothing which tracks this and could be
> used was ever reasonable for the mainline kernel.

stackable file-system could do it (ala ecryptfs).  You'd end up with
double page table usage (as they don't stack well), but you'd be able to
catch all mmap writes to disk.
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