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Message-ID: <20120118204328.GU2618@outflux.net>
Date: Wed, 18 Jan 2012 12:43:28 -0800
From: Kees Cook <kees@...ntu.com>
To: oss-security@...ts.openwall.com
Cc: "Steven M. Christey" <coley@...us.mitre.org>
Subject: Re: CVE request: kernel: proc: clean up and fix
/proc/<pid>/mem handling
What's the problem with the old logic in the mem handling? (Why does this
need a CVE?)
On Wed, Jan 18, 2012 at 10:25:55AM +0800, Eugene Teo wrote:
> "Jüri Aedla reported that the /proc/<pid>/mem handling really isn't very
> robust, and it also doesn't match the permission checking of any of the
> other related files.
>
> This changes it to do the permission checks at open time, and instead of
> tracking the process, it tracks the VM at the time of the open. That
> simplifies the code a lot, but does mean that if you hold the file
> descriptor open over an execve(), you'll continue to read from the _old_ VM.
>
> That is different from our previous behavior, but much simpler. If
> somebody actually finds a load where this matters, we'll need to revert
> this commit.
>
> I suspect that nobody will ever notice - because the process mapping
> addresses will also have changed as part of the execve. So you cannot
> actually usefully access the fd across a VM change simply because all
> the offsets for IO would have changed too."
>
> http://git.kernel.org/linus/e268337dfe26dfc7efd422a804dbb27977a3cccc
>
> Thanks, Eugene
--
Kees Cook
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