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Re: CVE request: kernel: proc: clean up and fix /proc/<pid>/mem handling
From: Kees Cook <kees () ubuntu com>
Date: Wed, 18 Jan 2012 12:43:28 -0800

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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