linux-kernel - Re: [PATCH -v2] capabilites: allow the application of capability limits to usermode helpers

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Date:	Wed, 09 Mar 2011 20:47:21 +0000
From:	David Howells <dhowells@...hat.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, jmorris@...ei.org,
	serge.hallyn@...onical.com, morgan@...nel.org
Subject: Re: [PATCH -v2] capabilites: allow the application of capability limits to usermode helpers

Eric Paris <eparis@...hat.com> wrote:

> There is no way to limit the capabilities of usermodehelpers. This problem
> reared its head recently when someone complained that any user with
> cap_net_admin was able to load arbitrary kernel modules, even though the user
> didn't have cap_sys_module.  The reason is because the actual load is done by
> a usermode helper and those always have the full cap set.  This patch addes new
> sysctls which allow us to bound the permissions of usermode helpers.
> 
> /proc/sys/kernel/usermodehelper/bset
> /proc/sys/kernel/usermodehelper/inheritable
> 
> You must have CAP_SYS_MODULE to change these (changes are &= ONLY).
> When the kernel launches a usermodehelper it will do so with these as
> the bset and pI.
> 
> -v2:	make globals static
> 	create spinlock to protect globals
> 
> Signed-off-by: Eric Paris <eparis@...hat.com>
> No-objection-from: Serge E. Hallyn <serge.hallyn@...onical.com>

Acked-by: David Howells <dhowells@...hat.com>
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