netdev - Re: [PATCH 0/8] SECURITY ISSUE with connector

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Date:	Fri, 2 Oct 2009 17:54:12 +0200
From:	Philipp Reisner <philipp.reisner@...bit.com>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>, dm-devel@...hat.com,
	Evgeniy Polyakov <zbr@...emap.net>,
	linux-fbdev-devel@...ts.sourceforge.net
Subject: Re: [PATCH 0/8] SECURITY ISSUE with connector

> On Fri, Oct 02, 2009 at 02:40:03PM +0200, Philipp Reisner wrote:
> > Affected: All code that uses connector, in kernel and out of mainline
> >
> > The connector, as it is today, does not allow the in kernel receiving
> > parts to do any checks on privileges of a message's sender.
>
> So, assume I know nothing about the connector architecture, what does
> this mean in a security context?
>

Think of the connector as a layer on top of netlink that allows more
than a hard coded number of subsystems to use netlink.

Netlink is used e.g. to modify routing tables in the kernel.

As it is today, subsystem utilising the connector can not examine
the capabilities of the user/program that sent the netlink message.

If the same would be true for netlink, than every unprivileged user
could change the routing tables on your box.

> > I know, there are not many out there that like connector, but as
> > long as it is in the kernel, we have to fix the security issues it has!
>
> And what specifically are the security issues?
>

unprivileged users can trigger operations that are supposed to be only
accessible to users having CAP_SYS_ADMIN (or some other CAP_XXX)

> > Please either drop connector, or someone who feels a bit responsible
> > and has our beloved dictator's blessing, PLEASE PLEASE PLEASE take
> > this into your tree, and send the pull request to Linus.
> >
> > Patches 1 to 4 are already Acked-by Evgeny, the connector's maintainer.
> > Patches 5 to 7 are the obvious fixes to the connector user's code.
>
> Obvious in what way?
>

They limit processing of connector/netlink messages in these subsystems
to messages sent from root (or some user having CAP_SYS_ADMIN).

That is obvious for dst, because device setup and destruction is done by
connector messages.

This is obvious for pohmelfs becuase these connector messages are
used there to change some configuration.

This is obvious for uvesafb because the connector messages are used 
there to delegate some video bios emulation to userspace. 

Last not least dm's dirty logging in user space, should be immune to
some crafted netlink packets sent by some unprivileged user.

Patches 1 to 4 fix the framework, should be merged as soon as possible.

Patches 5 to 8 (not 7) should probably be blessed by the affected
subsystem's maintainers. I think I have put all on CC. 

HTH.

-phil
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