Subject: Re: [PATCH v2 net-next] net/ipv6: Do not allow route add with a device that is down

From: Eric Dumazet <[email-masked]>
Date: Wed, 24 Jan 2018 09:23:34 -0800

On Wed, 2018-01-24 at 08:29 -0800, David Ahern wrote:
> IPv6 allows routes to be installed when the device is not up (admin up).
> Worse, it does not mark it as LINKDOWN. IPv4 does not allow it and really
> there is no reason for IPv6 to allow it, so check the flags and deny if
> device is admin down.
> 
> Signed-off-by: David Ahern <[email-masked]>
> ---
> v2
> - missed setting err to -ENETDOWN (thanks for catching that Roopa)
> 
>  net/ipv6/route.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index f85da2f1e729..4e8fab766018 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -2734,6 +2734,12 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg,
>  	if (!dev)
>  		goto out;
>  
> +	err = -ENETDOWN;
> +	if (!(dev->flags & IFF_UP)) {
> +		NL_SET_ERR_MSG(extack, "Nexthop device is not up");
> +		goto out;
> +	}

Note that since you have to take a branch, you can move the 
err = -ENETDOWN inside the branch.

The trick of setting err before doing :

if (cond)
   goto xxxx;

Is only relevant if the goto is naked.

By looking at your patch without more context, it is not clear that the
"err = -ENETDOWN" has no side effect.