[PATCH] Check CAP_NET_ADMIN in old and new ns before changing network ns.

[Maarten de Vries]

On Mon, 4 Feb 2019 at 01:11, Maarten de Vries <maarten at de-vri.es> wrote:
>
> ---
>
> Forgot to check for CAP_NET_ADMIN. Quite important actually :)
>
>  src/netlink.c | 60 +++++++++++++++++++++++++++++----------------------
>  1 file changed, 34 insertions(+), 26 deletions(-)
>
> diff --git a/src/netlink.c b/src/netlink.c
> index 82e9030..2999593 100644
> --- a/src/netlink.c
> +++ b/src/netlink.c
> @@ -473,30 +473,10 @@ out:
>         return ret;
>  }
>
> -static int set_tunnel_netns(struct wg_device *wg, u32 fd)
> -{
> -       struct net *new_net;
> -
> -       if (wg->sock4 != NULL || wg->sock6 != NULL)
> -               return -EINVAL;
> -
> -       new_net = get_net_ns_by_fd(fd);
> -
> -       if (IS_ERR(new_net))
> -               return PTR_ERR(new_net);
> -
> -       if (wg->have_creating_net_ref)
> -               put_net(wg->creating_net);
> -
> -       wg->have_creating_net_ref = true;
> -       wg->creating_net = new_net;
> -
> -       return 0;
> -}
> -
>  static int wg_set_device(struct sk_buff *skb, struct genl_info *info)
>  {
>         struct wg_device *wg = lookup_interface(info->attrs, skb);
> +       struct net *new_net = NULL;
>         int ret;
>
>         if (IS_ERR(wg)) {
> @@ -509,10 +489,34 @@ static int wg_set_device(struct sk_buff *skb, struct genl_info *info)
>
>         ret = -EPERM;
>         if ((info->attrs[WGDEVICE_A_LISTEN_PORT] ||
> -            info->attrs[WGDEVICE_A_FWMARK]) &&
> +            info->attrs[WGDEVICE_A_FWMARK] ||
> +            info->attrs[WGDEVICE_A_TUNNEL_NETNS_FD]) &&
>             !ns_capable(wg->creating_net->user_ns, CAP_NET_ADMIN))
>                 goto out;
>
> +       if (info->attrs[WGDEVICE_A_TUNNEL_NETNS_FD]) {
> +               int fd = nla_get_u32(info->attrs[WGDEVICE_A_TUNNEL_NETNS_FD]);
> +               new_net = get_net_ns_by_fd(fd);
> +
> +               if (IS_ERR(new_net)) {
> +                       ret = PTR_ERR(new_net);
> +                       new_net = NULL;
> +                       goto out;
> +               }
> +
> +               /* Also check that we've got CAP_NET_ADMIN in the new namespace. */
> +               if (!ns_capable(new_net->user_ns, CAP_NET_ADMIN)) {
> +                       ret = -EPERM;
> +                       goto out;
> +               }
> +
> +               /* And check that there are no initialized sockets. */
> +               if (wg->sock4 != NULL || wg->sock6 != NULL) {
> +                       ret = -EINVAL;
> +                       goto out;
> +               }
> +       }
> +
>         ++wg->device_update_gen;
>
>         if (info->attrs[WGDEVICE_A_FWMARK]) {
> @@ -582,15 +586,19 @@ static int wg_set_device(struct sk_buff *skb, struct genl_info *info)
>         }
>
>         if (info->attrs[WGDEVICE_A_TUNNEL_NETNS_FD]) {
> -               int fd = nla_get_u32(info->attrs[WGDEVICE_A_TUNNEL_NETNS_FD]);
> -               ret = set_tunnel_netns(wg, fd);
> -               if (ret < 0)
> -                       goto out;
> +               if (wg->have_creating_net_ref)
> +                       put_net(wg->creating_net);
> +
> +               wg->have_creating_net_ref = true;
> +               wg->creating_net = new_net;
> +               new_net = NULL;
>         }
>
>         ret = 0;
>
>  out:
> +       if (new_net)
> +               put_net(new_net);
>         mutex_unlock(&wg->device_update_lock);
>         rtnl_unlock();
>         dev_put(wg->dev);
> --
> 2.20.1
>
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Hmm, I did send this with --in-reply-to, but at least in gmail it is
treated as a separate thread. This was meant to be a reply to [PATCH]
Allow changing `creator_net` after interface creation.