netdev - Re: IPv4/IPv6 sysctl defaults in new namespace

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Date:	Mon, 15 Feb 2016 15:26:07 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Vasily Averin <vvs@...tuozzo.com>,
	David Miller <davem@...emloft.net>,
	Pavel Emelyanov <xemul@...tuozzo.com>
Subject: Re: IPv4/IPv6 sysctl defaults in new namespace

Konstantin Khlebnikov <koct9i@...il.com> writes:

> IPv6 initialized with default. That's ok.
> IPv4 makes a copy from init_net. Looks like a bug, here
> v2.6.24-2577-g752d14dc6aa9
>
> root@...g:~# sysctl net.ipv4.conf.all.forwarding=0
> net.ipv6.conf.all.forwarding=0
> net.ipv4.conf.all.forwarding = 0
> net.ipv6.conf.all.forwarding = 0
> root@...g:~# unshare -n sysctl net.ipv4.conf.all.forwarding
> net.ipv6.conf.all.forwarding
> net.ipv4.conf.all.forwarding = 0
> net.ipv6.conf.all.forwarding = 0
> root@...g:~# sysctl net.ipv4.conf.all.forwarding=1
> net.ipv6.conf.all.forwarding=1
> net.ipv4.conf.all.forwarding = 1
> net.ipv6.conf.all.forwarding = 1
> root@...g:~# unshare -n sysctl net.ipv4.conf.all.forwarding
> net.ipv6.conf.all.forwarding
> net.ipv4.conf.all.forwarding = 1
> net.ipv6.conf.all.forwarding = 0
>
> This is nasty. Could we fix this or this bug set in stone?

The test is do we break anyone, and the initial network namespace
is arbitrary enough I don't think anyone can depend upon a specific
value when creating a new network namespace.  So if someone is willing
to do the work we can fix this.

Of course the fixes would have to made against a recent kernel not
something as ancient as 2.6.24.

Eric