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Date:	Tue, 8 Feb 2011 11:44:40 +1100 (EST)
From:	James Morris <jmorris@...ei.org>
To:	Kees Cook <kees.cook@...onical.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [SECURITY] /proc/$pid/ leaks contents across setuid exec

On Mon, 7 Feb 2011, Kees Cook wrote:

> $ ./procleak.py auxv,syscall /usr/bin/passwd
> running
> AT_BASE:   0x7f2828bde000
> AT_RANDOM: 0x7fff80bde7c9
> Changing password for kees.
> (current) UNIX password: 0 0x0 0x7fff80bdda90 0x1ff 0x7fff80bdd580 0x7f2828dc57c0 0x7f28287cec1d 0x7fff80bdd088 0x7f28282fe6c0
> 
> There needs to be some way to break the connection to these files across
> the setuid exec, or perform some sort of revalidation of permissions. (Maybe
> check dumpable?)

The way to do this is to set O_CLOEXEC.

See: 

http://udrepper.livejournal.com/20407.html
https://www.securecoding.cert.org/confluence/display/seccode/FIO42-C.+Ensure+files+are+properly+closed+when+they+are+no+longer+needed

Changing the behavior in the core kernel will break userspace.



- James
-- 
James Morris
<jmorris@...ei.org>
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