linux-kernel - Re: O_NOLINK for open()

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Message-ID: <20070912184601.M37791@pkunk.americas.sgi.com>
Date:	Wed, 12 Sep 2007 18:48:52 -0500 (CDT)
From:	Brent Casavant <bcasavan@....com>
To:	Al Viro <viro@....linux.org.uk>
cc:	linux-kernel@...r.kernel.org
Subject: Re: O_NOLINK for open()

On Wed, 12 Sep 2007, Brent Casavant wrote:

> On Wed, 12 Sep 2007, Al Viro wrote:
> 
> > Give me a break.  And learn about ptrace(2).  This "unlinking" bullshit
> > buys you zero additional security, both for /proc/*/mem and for /dev/mem
> > (see mknod(2)).
> 
> My (limited) understanding of ptrace is that a parent-child
> relationship is needed between the tracing process and the traced
> process (at least that's what I gather from the man page).  This
> does give cause for concern, and I might have to see what can be
> done to alleviate this concern.  I fully realize that making this
> design completely unassilable is a fools errand, but closing off
> as many attack vectors as possible seems prudent.

Hmm.  The solution would appear to be as simple as making the
target program set-user-id.  As long as as the attacker isn't
the superuser (or has CAP_SYS_PTRACE) we should be OK.

Thanks for the heads-up,
Brent

-- 
Brent Casavant                          All music is folk music.  I ain't
bcasavan@....com                        never heard a horse sing a song.
Silicon Graphics, Inc.                    -- Louis Armstrong
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