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

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Date:	Wed, 9 Mar 2011 13:38:13 -0800
From:	Greg KH <greg@...ah.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, dhowells@...hat.com,
	jmorris@...ei.org, serge.hallyn@...onical.com, morgan@...nel.org
Subject: Re: [PATCH -v2] capabilites: allow the application of capability
 limits to usermode helpers

On Wed, Mar 09, 2011 at 02:33:31PM -0500, Eric Paris 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

Shouldn't these be documented somewhere?  Documentation/ABI?

> You must have CAP_SYS_MODULE to change these (changes are &= ONLY).

Why that permission?  Just because 'modprobe' is usually run from this
callback?  Or some other reason?

> When the kernel launches a usermodehelper it will do so with these as
> the bset and pI.

Shouldn't the caller of these functions be the ones dictating the
capabilities it should be run with?

thanks,

greg k-h
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