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SubjectRe: [malware-list] scanner interface proposal was: [TALPA] Intro to a linux interface for on access scanning
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Alan Cox <alan@lxorguk.ukuu.org.uk> wrote on 18/08/2008 16:31:48:

> > 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.

Yes, I agree that modification notifications are needed in some cases.

> > 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.

No, I was just saying scanning is pretty smart, it's not some brute force
method of scan all data that is there. It has a file type detection and
what and how to scan is determined by that. If a file does not resemble
any file type I don't think it gets scanned. For example take couple of
gigabytes of zeros and try to scan that with some products. I don't think
they will try to read the whole file.

--
Tvrtko A. Ursulin
Senior Software Engineer, Sophos

"Views and opinions expressed in this email are strictly those of the
author.
The contents has not been reviewed or approved by Sophos."


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