linux-kernel - Re: [PATCH 1/1] file capabilities: remove cap_task

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Message-Id: <20080319141112.02981daf.akpm@linux-foundation.org>
Date:	Wed, 19 Mar 2008 14:11:12 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	morgan@...nel.org, buraphalinuxserver@...il.com,
	lcapitulino@...driva.com.br, stable@...nel.org
Subject: Re: [PATCH 1/1] file capabilities: remove cap_task_kill() (-git)

On Wed, 19 Mar 2008 11:56:35 -0500
"Serge E. Hallyn" <serue@...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?

> 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@...nel.org, so perhaps a
resend for -stable is in order.

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