Date: Mon, 18 Aug 2008 16:31:48 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: tvrtko.ursulin@sophos.com
Cc: Theodore Tso <tytso@mit.edu>, Arjan van de Ven <arjan@infradead.org>,
       Adrian Bunk <bunk@kernel.org>, capibara@xs4all.nl,
       Casey Schaufler <casey@schaufler-ca.com>, davecb@sun.com, david@lang.hm,
       linux-kernel <linux-kernel@vger.kernel.org>,
       linux-security-module@vger.kernel.org, malware-list@lists.printk.net,
       malware-list-bounces@dmesg.printk.net,
       Mihai Don??u <mdontu@bitdefender.com>, Peter Dolding <oiaohm@gmail.com>,
       Pavel Machek <pavel@suse.cz>, rmeijer@xs4all.nl
Subject: Re: [malware-list] scanner interface proposal was: [TALPA] Intro	to
 a linux interface for on access scanning
Message-ID: <20080818163148.0ef3e383@lxorguk.ukuu.org.uk>
In-Reply-To: <20080818153212.6A6FD33687F@pmx1.sophos.com>
References: <20080818142511.GC8184@mit.edu>
	<20080818153212.6A6FD33687F@pmx1.sophos.com>
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> Huh? I was never advocating re-scan after each modification and I even 
> explicitly said it does not make sense for AV not only for performance but 
> because it will be useless most of the time. I thought sending out 
> modified notification on close makes sense because it is a natural point, 
> unless someone is trying to subvert which is out of scope. Other have 
> suggested time delay and lumping up.

You need a bit more than close I imagine, otherwise I can simply keep the
file open forever. There are lots of cases where that would be natural
behaviour - eg if I was to attack some kind of web forum and insert a
windows worm into the forum which was database backed the file would
probably never be closed. That seems to be one of the more common attack
vectors nowdays.

> 
> Also, just to double-check, you don't think AV scanning would read the 
> whole file on every write?

So you need the system to accumulate some kind of complete in memory set
of 'dirty' range lists on all I/O ? That is going to have pretty bad
performance impacts and serialization.
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