netdev - Re: AF_UNIX sockets crossing namespace based boundaries

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Message-ID: <20190102160221.GB2446@lunn.ch>
Date:   Wed, 2 Jan 2019 17:02:21 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Donald Sharp <sharpd@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, David Ahern <dsa@...ulusnetworks.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: AF_UNIX sockets crossing namespace based boundaries

On Wed, Jan 02, 2019 at 10:22:36AM -0500, Donald Sharp wrote:
> I am only creating a network namespace, but I don't think this changes
> my core question.
> 
> Suppose I am running FRR/zebra in the default namespace and I startup
> a BGP instance in namespace one.  BGP will connect to the default
> namespaces zebra instance.

Hi David.

We are talking about AF_UNIX here. By default, the name of the socket
is a path on a filesystem. So to me, netns plays no role here when you
reference the socket via its filesystem name. The path exists in the
filesystem namespace, and in your case with only netns, the same path
exists in all your netns.

Linux has multiple namespaces, which in theory should be
orthogonal. However in practice, they do sometime overlap, and this is
one example. There are other examples, /proc files are also netns
unaware. It seems like having an object depend on two different
namespaces at the same time is simply not supported.

	   Andrew