Date: Wed, 19 Mar 2008 16:20:07 -0500
From: "Serge E. Hallyn" <serue@us.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Serge E. Hallyn" <serue@us.ibm.com>, linux-kernel@vger.kernel.org,
       torvalds@linux-foundation.org, morgan@kernel.org,
       buraphalinuxserver@gmail.com, lcapitulino@mandriva.com.br,
       stable@kernel.org
Subject: Re: [PATCH 1/1] file capabilities: remove cap_task_kill() (-git)
Message-ID: <20080319212007.GA12217@sergelap.austin.ibm.com>
References: <20080319165635.GH5935@sergelap.ibm.com> <20080319141112.02981daf.akpm@linux-foundation.org>
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Quoting Andrew Morton (akpm@linux-foundation.org):
> On Wed, 19 Mar 2008 11:56:35 -0500
> "Serge E. Hallyn" <serue@us.ibm.com> wrote:
> 
> > (resending once against -git.  I had sent against -stable in
> > http://lkml.org/lkml/2008/2/28/225.  Without this patch,
> > atd is broken at least on some distros.)
> 
> So this fix is needed in 2.6.24.x?

Yes it is.

> > The original justification for cap_task_kill() was as follows:
> > 
> > 	check_kill_permission() does appropriate uid equivalence checks.
> > 	However with file capabilities it becomes possible for an
> > 	unprivileged user to execute a file with file capabilities
> > 	resulting in a more privileged task with the same uid.
> > 
> > However now that cap_task_kill() always returns 0 (permission
> > granted) when p->uid==current->uid, the whole hook is worthless,
> > and only likely to create more subtle problems in the corner cases
> > where it might still be called but return -EPERM.  Those cases
> > are basically when uids are different but euid/suid is equivalent
> > as per the check in check_kill_permission().
> > 
> > One example of a still-broken application is 'at' for non-root users.
> 
> This 2.6.25-rc6 patch doesn't apply correctly to 2.6.24.  I can't find a
> *formal* copy of your 2.6.24 patch on stable@kernel.org, so perhaps a
> resend for -stable is in order.

Argh, yes, will do.  Thanks.

-serge
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