linux-kernel - Re: kdbus_proc_permission (Re: [GIT PULL] kdbus updates for Greg)

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Message-ID: <CALCETrV_s1i0ttc+tgH=Un0WsPv3-otsq4uEdDLZXJWPCqbdxA@mail.gmail.com>
Date:	Mon, 31 Aug 2015 12:09:53 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: kdbus_proc_permission (Re: [GIT PULL] kdbus updates for Greg)

On Mon, Aug 31, 2015 at 9:22 AM, David Herrmann <dh.herrmann@...il.com> wrote:
> Hi
>
> On Mon, Aug 31, 2015 at 5:37 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Mon, Aug 24, 2015 at 2:52 AM, David Herrmann <dh.herrmann@...il.com> wrote:
>>> On Mon, Aug 10, 2015 at 4:42 AM, Andy Lutomirski <luto@...capital.net> wrote:
>>>> I haven't checked the context in which it's used, but in order for
>>>> kdbus_proc_permission to do what it claims to do, it appears to be
>>>> missing calls to security_inode_permission and
>>>> security_file_permission.
>>>
>>> Both are expected to be added by lsm patches (both hooks you mentioned
>>> are empty if no lsm is selected).
>>
>> Will that mean that existing MAC policies stop being fully enforced
>> (in effect) if kdbus is installed?
>
> It means kdbus messages carry information about the sender, which LSMs
> might prevent you to read via /proc. Just like you can send dbus
> messages to a peer, which LSM-enhanced dbus-daemon might not allow.

It's a security-sensitive function that doesn't do what the name and
description suggest.  Whether that's an active problem or not is
unknown, but it's certainly a maintainability problem.

> If
> you use LSMs, we clearly advise you to wait for kdbus to gain LSM
> support. We explicitly support legacy dbus1-compat for exactly such
> reasons.

This is not an acceptable attitude for security.

There are so many things wrong with your statement that I'll limit
myself to one of them: Fedora 23/Rawhide, which is the *reference*
platform, uses SELinux.

--Andy

>
> Thanks
> David



-- 
Andy Lutomirski
AMA Capital Management, LLC
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