netdev - Re: [PATCH bpf-next 1/2] bpf: add BPF_LWT_ENCAP_IP option to bpf_lwt_push

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Message-ID: <7c92e102-3e1f-04e3-5387-1616baaa6430@gmail.com>
Date:   Wed, 28 Nov 2018 17:47:46 -0700
From:   David Ahern <dsahern@...il.com>
To:     Peter Oskolkov <posk@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org
Cc:     Peter Oskolkov <posk.devel@...il.com>
Subject: Re: [PATCH bpf-next 1/2] bpf: add BPF_LWT_ENCAP_IP option to
 bpf_lwt_push_encap

On 11/28/18 5:22 PM, Peter Oskolkov wrote:
> diff --git a/net/core/filter.c b/net/core/filter.c
> index bd0df75dc7b6..17f3c37218e5 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4793,6 +4793,60 @@ static int bpf_push_seg6_encap(struct sk_buff *skb, u32 type, void *hdr, u32 len
>  }
>  #endif /* CONFIG_IPV6_SEG6_BPF */
>  
> +static int bpf_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len)
> +{
> +	struct dst_entry *dst;
> +	struct rtable *rt;
> +	struct iphdr *iph;
> +	struct net *net;
> +	int err;
> +
> +	if (skb->protocol != htons(ETH_P_IP))
> +		return -EINVAL;  /* ETH_P_IPV6 not yet supported */
> +
> +	iph = (struct iphdr *)hdr;
> +
> +	if (unlikely(len < sizeof(struct iphdr) || len > LWTUNNEL_MAX_ENCAP_HSIZE))
> +		return -EINVAL;
> +	if (unlikely(iph->version != 4 || iph->ihl * 4 > len))
> +		return -EINVAL;
> +
> +	if (skb->sk)
> +		net = sock_net(skb->sk);
> +	else {
> +		net = dev_net(skb_dst(skb)->dev);
> +	}
> +	rt = ip_route_output(net, iph->daddr, 0, 0, 0);

That is a very limited use case. e.g., oif = 0 means you are not
considering any kind of policy routing (e.g., VRF).