netdev - Re: [PATCH net-next] net-loopback: allow lo dev initial state to be controlled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 14 Nov 2020 10:17:09 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jian Yang <jianyang.kernel@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        Mahesh Bandewar <maheshb@...gle.com>,
        Jian Yang <jianyang@...gle.com>
Subject: Re: [PATCH net-next] net-loopback: allow lo dev initial state to be
 controlled

On Wed, 11 Nov 2020 12:43:08 -0800 Jian Yang wrote:
> From: Mahesh Bandewar <maheshb@...gle.com>
> 
> Traditionally loopback devices comes up with initial state as DOWN for
> any new network-namespace. This would mean that anyone needing this
> device (which is mostly true except sandboxes where networking in not
> needed at all), would have to bring this UP by issuing something like
> 'ip link set lo up' which can be avoided if the initial state can be set
> as UP. Also ICMP error propagation needs loopback to be UP.
> 
> The default value for this sysctl is set to ZERO which will preserve the
> backward compatible behavior for the root-netns while changing the
> sysctl will only alter the behavior of the newer network namespaces.

Any reason why the new sysctl itself is not per netns?

> +netdev_loopback_state
> +---------------------

loopback_init_state ?

> +Controls the loopback device initial state for any new network namespaces. By
> +default, we keep the initial state as DOWN.
> +
> +If set to 1, the loopback device will be brought UP during namespace creation.
> +This will only apply to all new network namespaces.
> +
> +Default : 0  (for compatibility reasons)
> +
>  netdev_max_backlog
>  ------------------
>  
> diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
> index a1c77cc00416..76dc92ac65a2 100644
> --- a/drivers/net/loopback.c
> +++ b/drivers/net/loopback.c
> @@ -219,6 +219,13 @@ static __net_init int loopback_net_init(struct net *net)
>  
>  	BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
>  	net->loopback_dev = dev;
> +
> +	if (sysctl_netdev_loopback_state) {
> +		/* Bring loopback device UP */
> +		rtnl_lock();
> +		dev_open(dev, NULL);
> +		rtnl_unlock();
> +	}

The only concern I have here is that it breaks notification ordering.
Is there precedent for NETDEV_UP to be generated before all pernet ops
->init was called?