netdev - Re: [PATCH] ipv4: in new netns initialize sysctls in net.ipv4.conf.* with defaults

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Date:	Sun, 21 Feb 2016 12:25:17 +0300
From:	Vasily Averin <vvs@...tuozzo.com>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Cc:	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] ipv4: in new netns initialize sysctls in net.ipv4.conf.*
 with defaults

Konstantin,
I've investigated question with sysctls initialization inside namespaces some time ago.
IIRC I've found people expect that sysctl values should be inherited from parent namespace.
It allows node admin to adjust unsafe pre-compiled settings, and prepare adequate defaults 
before creation of namespaces.

However, there is corner case:
module with sysctl can be loaded after creation of namespaces.
In this case namespaces will get pre-compiled sysctl defaults, 
and are not be able to adjust them even if they want to do it.

Thank you,
	Vasily Averin

On 21.02.2016 10:11, Konstantin Khlebnikov wrote:
> Currently initial net.ipv4.conf.all.* and net.ipv4.conf.default.* are
> copied from init network namespace because static structures are used
> for init_net. This makes no sense because new netns might be created
> from any netns. This patch makes private copy also for init netns if
> network namespaces are enabled. Other sysctls in net.ipv4 and net.ipv6
> already initialized with default values at namespace creation.
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Fixes: 752d14dc6aa9 ("[IPV4]: Move the devinet pointers on the struct net")
> ---
>  net/ipv4/devinet.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index cebd9d31e65a..9d73d4bbdba3 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -2290,7 +2290,7 @@ static __net_init int devinet_init_net(struct net *net)
>  	all = &ipv4_devconf;
>  	dflt = &ipv4_devconf_dflt;
>  
> -	if (!net_eq(net, &init_net)) {
> +	if (IS_ENABLED(CONFIG_NET_NS)) {
>  		all = kmemdup(all, sizeof(ipv4_devconf), GFP_KERNEL);
>  		if (!all)
>  			goto err_alloc_all;
> 
>