Subject: Re: [PATCH net-next 2/2 v3] netns: restrict uevents

From: [email-masked] (Eric W. Biederman)
Date: Fri, 27 Apr 2018 11:30:26 -0500

Christian Brauner <[email-masked]> writes:
> ---
>  lib/kobject_uevent.c | 140 ++++++++++++++++++++++++++++++-------------
>  1 file changed, 99 insertions(+), 41 deletions(-)
>
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index c3cb110f663b..d8ce5e6d83af 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
>  
> +static int uevent_net_broadcast_tagged(struct sock *usk,
> +				       struct kobj_uevent_env *env,
> +				       const char *action_string,
> +				       const char *devpath)
> +{
> +	struct user_namespace *owning_user_ns = sock_net(usk)->user_ns;
> +	struct sk_buff *skb = NULL;
> +	int ret;
> +
> +	skb = alloc_uevent_skb(env, action_string, devpath);
> +	if (!skb)
> +		return -ENOMEM;
> +
> +	/* fix credentials */
> +	if (owning_user_ns != &init_user_ns) {

Nit: This test is just a performance optimization as such is not
      necessary.  That is we can safely unconditionally set the
      credentials this way.

> +		struct netlink_skb_parms *parms = &NETLINK_CB(skb);
> +		kuid_t root_uid;
> +		kgid_t root_gid;
> +
> +		/* fix uid */
> +		root_uid = make_kuid(owning_user_ns, 0);
> +		if (!uid_valid(root_uid))
> +			root_uid = GLOBAL_ROOT_UID;
> +		parms->creds.uid = root_uid;
> +
> +		/* fix gid */
> +		root_gid = make_kgid(owning_user_ns, 0);
> +		if (!gid_valid(root_gid))
> +			root_gid = GLOBAL_ROOT_GID;
> +		parms->creds.gid = root_gid;
> +	}
> +
> +	ret = netlink_broadcast(usk, skb, 0, 1, GFP_KERNEL);
> +	/* ENOBUFS should be handled in userspace */
> +	if (ret == -ENOBUFS || ret == -ESRCH)
> +		ret = 0;
> +
> +	return ret;
> +}
> +#endif