netdev - Re: [PATCH next] net: add option to not create fall-back tunnels in root-ns as well

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Date:   Fri, 21 Aug 2020 14:03:23 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     maheshb@...gle.com
Cc:     netdev@...r.kernel.org, kuba@...nel.org, edumazet@...gle.com,
        mahesh@...dewar.net, maze@...gle.com, jianyang@...gle.com
Subject: Re: [PATCH next] net: add option to not create fall-back tunnels
 in root-ns as well

From: Mahesh Bandewar <maheshb@...gle.com>
Date: Tue, 18 Aug 2020 17:51:23 -0700

> The sysctl that was added  earlier by commit 79134e6ce2c ("net: do
> not create fallback tunnels for non-default namespaces") to create
> fall-back only in root-ns. This patch enhances that behavior to provide
> option not to create fallback tunnels in root-ns as well. Since modules
> that create fallback tunnels could be built-in and setting the sysctl
> value after booting is pointless, so added a config option which defaults
> to zero (to preserve backward compatibility) but also takes values "1" and
> "2" which don't create fallback tunnels in non-root namespaces
> only and no-where respectively.
> 
> Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
 ...
> +config SYSCTL_FB_TUNNEL
 ...
> -int sysctl_fb_tunnels_only_for_init_net __read_mostly = 0;
> +int sysctl_fb_tunnels_only_for_init_net __read_mostly = CONFIG_SYSCTL_FB_TUNNEL;

I can't allow this.  This requires a kernel rebuild when none is
really necessary.  You're also forcing distributions to make a choice
they have no place making at all.

You have two ways to handle this situation already:

1) Kernel command line

2) initrd

I'm not allowing to add a third.  And if I had, then that sets
precedence and others will want to do this as well for their
favorite sysctl that has implications as soon as modules get
loaded.