Subject: Re: [PATCH v6 5/6] net: ipv4, ipv6: run cgroup eBPF egress programs

From: Pablo Neira Ayuso <[email-masked]>
Date: Mon, 19 Sep 2016 21:19:10 +0200

On Mon, Sep 19, 2016 at 06:44:00PM +0200, Daniel Mack wrote:
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 6001e78..5dc90aa 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -39,6 +39,7 @@
>  #include <linux/module.h>
>  #include <linux/slab.h>
>  
> +#include <linux/bpf-cgroup.h>
>  #include <linux/netfilter.h>
>  #include <linux/netfilter_ipv6.h>
>  
> @@ -143,6 +144,7 @@ int ip6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  {
>  	struct net_device *dev = skb_dst(skb)->dev;
>  	struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));
> +	int ret;
>  
>  	if (unlikely(idev->cnf.disable_ipv6)) {
>  		IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
> @@ -150,6 +152,12 @@ int ip6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  		return 0;
>  	}
>  
> +	ret = cgroup_bpf_run_filter(sk, skb, BPF_CGROUP_INET_EGRESS);
> +	if (ret) {
> +		kfree_skb(skb);
> +		return ret;
> +	}

1) If your goal is to filter packets, why so late? The sooner you
   enforce your policy, the less cycles you waste.

Actually, did you look at Google's approach to this problem?  They
want to control this at socket level, so you restrict what the process
can actually bind. That is enforcing the policy way before you even
send packets. On top of that, what they submitted is infrastructured
so any process with CAP_NET_ADMIN can access that policy that is being
applied and fetch a readable policy through kernel interface.

2) This will turn the stack into a nightmare to debug I predict. If
   any process with CAP_NET_ADMIN can potentially attach bpf blobs
   via these hooks, we will have to include in the network stack
   traveling documentation something like: "Probably you have to check
   that your orchestrator is not dropping your packets for some
   reason". So I wonder how users will debug this and how the policy that
   your orchestrator applies will be exposed to userspace.

>  	return NF_HOOK_COND(NFPROTO_IPV6, NF_INET_POST_ROUTING,
>  			    net, sk, skb, NULL, dev,
>  			    ip6_finish_output,
> -- 
> 2.5.5
>