netdev - Re: [PATCH net] ipvlan: disallow userns cap_net

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Message-Id: <20190222.112809.149058047808664396.davem@davemloft.net>
Date:   Fri, 22 Feb 2019 11:28:09 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     daniel@...earbox.net
Cc:     maheshb@...gle.com, m@...bda.lt, netdev@...r.kernel.org
Subject: Re: [PATCH net] ipvlan: disallow userns cap_net_admin to change
 global mode/flags

From: Daniel Borkmann <daniel@...earbox.net>
Date: Wed, 20 Feb 2019 00:15:30 +0100

> When running Docker with userns isolation e.g. --userns-remap="default"
> and spawning up some containers with CAP_NET_ADMIN under this realm, I
> noticed that link changes on ipvlan slave device inside that container
> can affect all devices from this ipvlan group which are in other net
> namespaces where the container should have no permission to make changes
> to, such as the init netns, for example.
> 
> This effectively allows to undo ipvlan private mode and switch globally to
> bridge mode where slaves can communicate directly without going through
> hostns, or it allows to switch between global operation mode (l2/l3/l3s)
> for everyone bound to the given ipvlan master device. libnetwork plugin
> here is creating an ipvlan master and ipvlan slave in hostns and a slave
> each that is moved into the container's netns upon creation event.
 ...
> One way to mitigate it is to check CAP_NET_ADMIN permissions of
> the ipvlan master device's ns, and only then allow to change
> mode or flags for all devices bound to it. Above two cases are
> then disallowed after the patch.
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

Applied and queued up for -stable.

Thanks.