Subject: Re: [PATCH 1/3] dev: Prevent creating network devices with negative ifindex

From: Stephen Hemminger <[email-masked]>
Date: Fri, 16 Jun 2017 09:18:06 -0700

On Fri, 16 Jun 2017 17:23:51 +0300
Serhey Popovych <[email-masked]> wrote:

> Interface index is signed integer, we can pass ifm->ifi_index
> from userspace via netlink and create network device with
> negative ifindex value.
> 
> Fixes: 9c7dafbfab15 ("net: Allow to create links with given ifindex")
> Signed-off-by: Serhey Popovych <[email-masked]>
> ---
>  net/core/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 8658074..dae8010 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -7491,7 +7491,7 @@ int register_netdevice(struct net_device *dev)
>  	}
>  
>  	ret = -EBUSY;
> -	if (!dev->ifindex)
> +	if (dev->ifindex <= 0)
>  		dev->ifindex = dev_new_index(net);
>  	else if (__dev_get_by_index(net, dev->ifindex))
>  		goto err_uninit;

You should fix this by adding error check in the netlink portion
that allows creating devices with given ifindex. Passing < 0
should be an error.