netdev - Re: [PATCH bpf-next v9 5/7] bpf: add handling of BPF_LWT_REROUTE to lwt

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Date:   Mon, 11 Feb 2019 21:39:59 -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@...k.io>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH bpf-next v9 5/7] bpf: add handling of BPF_LWT_REROUTE to
 lwt_bpf.c

On 2/11/19 5:42 PM, Peter Oskolkov wrote:
> @@ -88,6 +90,35 @@ static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
>  	return ret;
>  }
>  
> +static int bpf_lwt_input_reroute(struct sk_buff *skb)
> +{
> +	int err = -EINVAL;
> +
> +	if (skb->protocol == htons(ETH_P_IP)) {
> +		struct iphdr *iph = ip_hdr(skb);
> +
> +		err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
> +					   iph->tos, skb_dst(skb)->dev);
> +	} else if (skb->protocol == htons(ETH_P_IPV6)) {
> +#if IS_ENABLED(CONFIG_IPV6)
> +		err = ipv6_stub->ipv6_route_input(skb);
> +#else
> +		pr_warn_once("BPF_LWT_REROUTE input: IPV6 not available\n");
> +#endif

The stub defines ipv6_route_input when IPv6 is not enabled.
addrconf_core.o is compiled in if NET is enabled irregardless of
CONFIG_IPV6. ie., you don't need the IS_ENABLED check here.

If a bpf program pushes a v6 header the stub returns -EAFNOSUPPORT based
on patch 4.


> +	} else {
> +		pr_warn_once("BPF_LWT_REROUTE input: unsupported proto %d\n",
> +			     skb->protocol);

You don't need a warn on here; just return -EAFNOSUPPORT.


> +	}
> +
> +	if (err)
> +		goto err;
> +	return dst_input(skb);
> +
> +err:
> +	kfree_skb(skb);
> +	return err;
> +}
> +
>  static int bpf_input(struct sk_buff *skb)
>  {
>  	struct dst_entry *dst = skb_dst(skb);
> @@ -99,6 +130,8 @@ static int bpf_input(struct sk_buff *skb)
>  		ret = run_lwt_bpf(skb, &bpf->in, dst, NO_REDIRECT);
>  		if (ret < 0)
>  			return ret;
> +		if (ret == BPF_LWT_REROUTE)
> +			return bpf_lwt_input_reroute(skb);
>  	}
>  
>  	if (unlikely(!dst->lwtstate->orig_input)) {
> @@ -148,6 +181,95 @@ static int xmit_check_hhlen(struct sk_buff *skb)
>  	return 0;
>  }
>  
> +static int bpf_lwt_xmit_reroute(struct sk_buff *skb)
> +{
> +	struct net_device *l3mdev = l3mdev_master_dev_rcu(skb_dst(skb)->dev);
> +	int oif = l3mdev ? l3mdev->ifindex : 0;
> +	struct dst_entry *dst = NULL;
> +	struct sock *sk;
> +	struct net *net;
> +	bool ipv4;
> +	int err;
> +
> +	if (skb->protocol == htons(ETH_P_IP)) {
> +		ipv4 = true;
> +	} else if (skb->protocol == htons(ETH_P_IPV6)) {
> +		ipv4 = false;
> +	} else {
> +		pr_warn_once("BPF_LWT_REROUTE xmit: unsupported proto %d\n",
> +			     skb->protocol);

same here - no warn on.

> +		return -EINVAL;
> +	}
> +
> +	sk = sk_to_full_sk(skb->sk);
> +	if (sk) {
> +		if (sk->sk_bound_dev_if)
> +			oif = sk->sk_bound_dev_if;
> +		net = sock_net(sk);
> +	} else {
> +		net = dev_net(skb_dst(skb)->dev);
> +	}
> +
> +	if (ipv4) {
> +		struct iphdr *iph = ip_hdr(skb);
> +		struct flowi4 fl4 = {};
> +		struct rtable *rt;
> +
> +		fl4.flowi4_oif = oif;
> +		fl4.flowi4_mark = skb->mark;
> +		fl4.flowi4_uid = sock_net_uid(net, sk);
> +		fl4.flowi4_tos = RT_TOS(iph->tos);
> +		fl4.flowi4_flags = FLOWI_FLAG_ANYSRC;
> +		fl4.flowi4_proto = iph->protocol;
> +		fl4.daddr = iph->daddr;
> +		fl4.saddr = iph->saddr;
> +
> +		rt = ip_route_output_key(net, &fl4);
> +		if (IS_ERR(rt) || rt->dst.error)
> +			return -EINVAL;
> +		dst = &rt->dst;
> +	} else {
> +#if IS_ENABLED(CONFIG_IPV6)
> +		struct ipv6hdr *iph6 = ipv6_hdr(skb);
> +		struct flowi6 fl6 = {};
> +
> +		fl6.flowi6_oif = oif;
> +		fl6.flowi6_mark = skb->mark;
> +		fl6.flowi6_uid = sock_net_uid(net, sk);
> +		fl6.flowlabel = ip6_flowinfo(iph6);
> +		fl6.flowi6_proto = iph6->nexthdr;
> +		fl6.daddr = iph6->daddr;
> +		fl6.saddr = iph6->saddr;
> +
> +		err = ipv6_stub->ipv6_dst_lookup(net, skb->sk, &dst, &fl6);
> +		if (err || IS_ERR(dst) || dst->error)
> +			return -EINVAL;
> +#else
> +		pr_warn_once("BPF_LWT_REROUTE xmit: IPV6 not available\n");
> +		return -EINVAL;
> +#endif

No #if .. #endif needed. The stub handles it.