linux-kernel - Re: Security: information leaks in /proc enable keystroke recovery

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Message-ID: <alpine.DEB.2.00.0908160116330.30426@asgard.lang.hm>
Date:	Sun, 16 Aug 2009 01:18:07 -0700 (PDT)
From:	david@...g.hm
To:	Theodore Tso <tytso@....edu>
cc:	David Wagner <daw-news@...berkeley.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: Security: information leaks in /proc enable keystroke recovery

On Sat, 15 Aug 2009, Theodore Tso wrote:

> On Sun, Aug 16, 2009 at 12:44:14AM +0000, David Wagner wrote:
>> Theodore Tso  wrote:
>>> A configuration option which defaults to disabling ESP and EIP would
>>> be a simple way to prevent this specific instance of information
>>> leakage.  The problem is there are other files that might reveal
>>> timing information, but which are very useful for a system
>>> administrator.  A key example of this is /proc/$pid/wchan, which is
>>> responsible for the WCHAN column is a ps listing.
>>
>> If they're useful for system administrators, would making them
>> readable to root (but not everyone) be enough?
>
> I suppose sysadmins use "sudo ps" instead of "ps", but that would be a
> bit inconvenient and would certainly clutter the sudo logs.  It might
> also cause people to decide it's more trouble than it's worth, and
> configure their system not restrict the various proc files.
>
> That's why I think it would be useful to restrict the number of times
> any process in the system can sample the files before the system
> starts inserting random delays, thus destroying the usefulness of
> using wchan for mounting timing attacks, without removing system
> functionality.

would it make sense to limit the precision of the times reported? or cache 
the results for some time period?

David Lang
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