From: NeilBrown <neilb@suse.com>
To: Greg KH <gregkh@linuxfoundation.org>,
kernel-hardening@lists.openwall.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: [RFC 0/4] make call_usermodehelper a bit more "safe"
Date: Fri, 16 Dec 2016 12:02:33 +1100 [thread overview]
Message-ID: <87k2b0wus6.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20161214185000.GA3930@kroah.com>
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On Thu, Dec 15 2016, Greg KH wrote:
> Hi all,
>
> Here's a proof-of-concept patch series that tries to work to address the
> issue of call_usermodehelper being abused to have the kernel call any
> userspace binary with full root permissions.
>
> The issue is that if you end up getting write access to kernel memory,
> if you change the string '/sbin/hotplug' to point to
> '/home/hacked/my_binary', then the next uevent that the system makes
> will call this binary instead of the "trusted" one.
You seem to be targeting a situation where the kernel memory can be
easily changed, but filesystem content cannot (if it could - the
attacker would simply replace /sbin/hotplug).
If that is a credible threat scenario, it seems to me that the simplest
mitigation is to have call_usermodehelper always call a single
compiled-in path - e.g. /sbin/usermode-helper - and rely on that
program to validate argv[0] and call it if it is deemed safe.
i.e. get the policy out of the kernel.
Just a thought,
NeilBrown
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next prev parent reply other threads:[~2016-12-16 1:03 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-14 18:50 [RFC 0/4] make call_usermodehelper a bit more "safe" Greg KH
2016-12-14 18:50 ` [PATCH 1/4] kmod: make usermodehelper path a const string Greg KH
2016-12-14 18:50 ` [PATCH 2/4] drbd: rename "usermode_helper" to "drbd_usermode_helper" Greg KH
2016-12-14 18:50 ` [PATCH 3/4] Make static usermode helper binaries constant Greg KH
2016-12-14 19:11 ` [kernel-hardening] " Greg KH
2016-12-14 20:29 ` Rich Felker
2016-12-14 20:54 ` Greg KH
2016-12-15 17:54 ` Greg KH
2016-12-15 20:51 ` Daniel Micay
2016-12-15 21:18 ` Greg KH
2016-12-16 0:05 ` Daniel Micay
2016-12-16 0:14 ` Daniel Micay
2016-12-14 18:51 ` [RFC 4/4] Introduce CONFIG_READONLY_USERMODEHELPER Greg KH
2016-12-14 20:31 ` Kees Cook
2016-12-14 20:57 ` Greg KH
2016-12-14 19:25 ` [kernel-hardening] [RFC 0/4] make call_usermodehelper a bit more "safe" Mark Rutland
2016-12-14 20:16 ` Kees Cook
2016-12-14 21:28 ` Jason A. Donenfeld
2016-12-14 23:16 ` Greg Kroah-Hartman
2016-12-16 1:02 ` NeilBrown [this message]
2016-12-16 12:49 ` Greg KH
2016-12-19 13:34 ` Jiri Kosina
2016-12-20 9:27 ` Greg KH
2016-12-20 10:27 ` Jiri Kosina
2016-12-20 10:31 ` Jiri Kosina
2016-12-20 10:48 ` Greg KH
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