linux-kernel - Re: [PATCH 1/2] proc: restrict access to /proc/PID/io

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Date:	Tue, 28 Jun 2011 11:50:27 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Balbir Singh <bsingharora@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	David Rientjes <rientjes@...gle.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	security@...nel.org, Eric Paris <eparis@...hat.com>,
	Solar Designer <solar@...nwall.com>
Subject: Re: [PATCH 1/2] proc: restrict access to /proc/PID/io

On Tue, Jun 28, 2011 at 06:43 +0530, Balbir Singh wrote:
> On Fri, Jun 24, 2011 at 5:38 PM, Vasiliy Kulikov <segoon@...nwall.com> wrote:
> > /proc/PID/io may be used for gathering private information.  E.g. for
> > openssh and vsftpd daemons wchars/rchars may be used to learn the
> > precise password length.  Restrict it to processes being able to ptrace
> > the target process.
> >
> 
> Hmm.. How do I reproduce this,

Just register taskstats listener and wait for "vsftpd" process.
read_characters = strlen("USER username\r\n") + strlen("PASSWD
pass\r\n") + 1.

> won't they be enough randomness around
> rchar/wchar by the time the attacker reads it?

No, if you set "UsePrivilegeSeparation yes" in /etc/sshd/sshd_config or
similar setting in vsftpd config (set by default), one process will
have very small io activity, which is 100% related to the io in
question.

http://www.openwall.com/lists/oss-security/2011/06/24/6

So, the total io = io with the network + io with privileged parent.


Thanks,

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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