linux-kernel - Re: [malware-list] [RFC 0/5] [TALPA] Intro to a linux interfaceforon access scanning

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Date:	Tue, 05 Aug 2008 21:55:19 -0400
From:	Eric Paris <eparis@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	"Press, Jonathan" <Jonathan.Press@...com>,
	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	malware-list@...ts.printk.net,
	linux-security-module@...r.kernel.org
Subject: Re: [malware-list] [RFC 0/5] [TALPA] Intro to a linux
	interfaceforon access scanning

On Tue, 2008-08-05 at 20:30 -0400, Rik van Riel wrote:
> On Tue, 05 Aug 2008 14:39:34 -0400
> Eric Paris <eparis@...hat.com> wrote:
> > On Tue, 2008-08-05 at 11:27 -0700, Arjan van de Ven wrote:
> 
> > > but close is... very limited in value. Open is a discrete event
> > > traditionally associated withh permission checks.
> > > Close... not so.  (And if you mmap memory, you can then close the file
> > > and still write to it via the mmap)
> > 
> > Thankfully my implementation will invalidate that close time check and
> > caching result.  It does the invalidating the same place we update mtime
> > and my understanding is that mmap has been updating mtime for quite a
> > while now. 
> 
> Then isn't the close time check superfluous, since you do the
> checks at change time already?

In the patches I posted, "checks" are done at open and close if the
result is not already in the cache.  Every write invalidates the cache
and thus the next open/close will do a "check."

So the longer a process keeps a file open the longer it is susceptible
to "unclean" data existing in that file.

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