net/core/lwt_bpf.c - kernel/msm-5.4 - Gitiles

 /* Copyright (c) 2016 Thomas Graf <tgraf@tgraf.ch>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of version 2 of the GNU General Public
  * License as published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful, but
  * WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  * General Public License for more details.
  */

 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/skbuff.h>
 #include <linux/types.h>
 #include <linux/bpf.h>
 #include <net/lwtunnel.h>
 #include <net/gre.h>
 #include <net/ip6_route.h>
 #include <net/ipv6_stubs.h>

 struct bpf_lwt_prog {
 	struct bpf_prog *prog;
 	char *name;
 };

 struct bpf_lwt {
 	struct bpf_lwt_prog in;
 	struct bpf_lwt_prog out;
 	struct bpf_lwt_prog xmit;
 	int family;
 };

 #define MAX_PROG_NAME 256

 static inline struct bpf_lwt *bpf_lwt_lwtunnel(struct lwtunnel_state *lwt)
 {
 	return (struct bpf_lwt *)lwt->data;
 }

 #define NO_REDIRECT false
 #define CAN_REDIRECT true

 static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
 		       struct dst_entry *dst, bool can_redirect)
 {
 	int ret;

 	/* Preempt disable is needed to protect per-cpu redirect_info between
 	 * BPF prog and skb_do_redirect(). The call_rcu in bpf_prog_put() and
 	 * access to maps strictly require a rcu_read_lock() for protection,
 	 * mixing with BH RCU lock doesn't work.
 	 */
 	preempt_disable();
 	bpf_compute_data_pointers(skb);
 	ret = bpf_prog_run_save_cb(lwt->prog, skb);

 	switch (ret) {
 	case BPF_OK:
 	case BPF_LWT_REROUTE:
 		break;

 	case BPF_REDIRECT:
 		if (unlikely(!can_redirect)) {
 			pr_warn_once("Illegal redirect return code in prog %s\n",
 				     lwt->name ? : "<unknown>");
 			ret = BPF_OK;
 		} else {
 			skb_reset_mac_header(skb);
 			ret = skb_do_redirect(skb);
 			if (ret == 0)
 				ret = BPF_REDIRECT;
 		}
 		break;

 	case BPF_DROP:
 		kfree_skb(skb);
 		ret = -EPERM;
 		break;

 	default:
 		pr_warn_once("bpf-lwt: Illegal return value %u, expect packet loss\n", ret);
 		kfree_skb(skb);
 		ret = -EINVAL;
 		break;
 	}

 	preempt_enable();

 	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)) {
 		err = ipv6_stub->ipv6_route_input(skb);
 	} else {
 		err = -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);
 	struct bpf_lwt *bpf;
 	int ret;

 	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
 	if (bpf->in.prog) {
 		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)) {
 		kfree_skb(skb);
 		return -EINVAL;
 	}

 	return dst->lwtstate->orig_input(skb);
 }

 static int bpf_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
 	struct dst_entry *dst = skb_dst(skb);
 	struct bpf_lwt *bpf;
 	int ret;

 	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
 	if (bpf->out.prog) {
 		ret = run_lwt_bpf(skb, &bpf->out, dst, NO_REDIRECT);
 		if (ret < 0)
 			return ret;
 	}

 	if (unlikely(!dst->lwtstate->orig_output)) {
 		pr_warn_once("orig_output not set on dst for prog %s\n",
 			     bpf->out.name);
 		kfree_skb(skb);
 		return -EINVAL;
 	}

 	return dst->lwtstate->orig_output(net, sk, skb);
 }

 static int xmit_check_hhlen(struct sk_buff *skb)
 {
 	int hh_len = skb_dst(skb)->dev->hard_header_len;

 	if (skb_headroom(skb) < hh_len) {
 		int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));

 		if (pskb_expand_head(skb, nhead, 0, GFP_ATOMIC))
 			return -ENOMEM;
 	}

 	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;
 	int err = -EAFNOSUPPORT;
 	struct sock *sk;
 	struct net *net;
 	bool ipv4;

 	if (skb->protocol == htons(ETH_P_IP))
 		ipv4 = true;
 	else if (skb->protocol == htons(ETH_P_IPV6))
 		ipv4 = false;
 	else
 		goto err;

 	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)) {
 			err = PTR_ERR(rt);
 			goto err;
 		}
 		dst = &rt->dst;
 	} else {
 		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 (unlikely(err))
 			goto err;
 		if (IS_ERR(dst)) {
 			err = PTR_ERR(dst);
 			goto err;
 		}
 	}
 	if (unlikely(dst->error)) {
 		err = dst->error;
 		dst_release(dst);
 		goto err;
 	}

 	/* Although skb header was reserved in bpf_lwt_push_ip_encap(), it
 	 * was done for the previous dst, so we are doing it here again, in
 	 * case the new dst needs much more space. The call below is a noop
 	 * if there is enough header space in skb.
 	 */
 	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
 	if (unlikely(err))
 		goto err;

 	skb_dst_drop(skb);
 	skb_dst_set(skb, dst);

 	err = dst_output(dev_net(skb_dst(skb)->dev), skb->sk, skb);
 	if (unlikely(err))
 		return err;

 	/* ip[6]_finish_output2 understand LWTUNNEL_XMIT_DONE */
 	return LWTUNNEL_XMIT_DONE;

 err:
 	kfree_skb(skb);
 	return err;
 }

 static int bpf_xmit(struct sk_buff *skb)
 {
 	struct dst_entry *dst = skb_dst(skb);
 	struct bpf_lwt *bpf;

 	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
 	if (bpf->xmit.prog) {
 		__be16 proto = skb->protocol;
 		int ret;

 		ret = run_lwt_bpf(skb, &bpf->xmit, dst, CAN_REDIRECT);
 		switch (ret) {
 		case BPF_OK:
 			/* If the header changed, e.g. via bpf_lwt_push_encap,
 			 * BPF_LWT_REROUTE below should have been used if the
 			 * protocol was also changed.
 			 */
 			if (skb->protocol != proto) {
 				kfree_skb(skb);
 				return -EINVAL;
 			}
 			/* If the header was expanded, headroom might be too
 			 * small for L2 header to come, expand as needed.
 			 */
 			ret = xmit_check_hhlen(skb);
 			if (unlikely(ret))
 				return ret;

 			return LWTUNNEL_XMIT_CONTINUE;
 		case BPF_REDIRECT:
 			return LWTUNNEL_XMIT_DONE;
 		case BPF_LWT_REROUTE:
 			return bpf_lwt_xmit_reroute(skb);
 		default:
 			return ret;
 		}
 	}

 	return LWTUNNEL_XMIT_CONTINUE;
 }

 static void bpf_lwt_prog_destroy(struct bpf_lwt_prog *prog)
 {
 	if (prog->prog)
 		bpf_prog_put(prog->prog);

 	kfree(prog->name);
 }

 static void bpf_destroy_state(struct lwtunnel_state *lwt)
 {
 	struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);

 	bpf_lwt_prog_destroy(&bpf->in);
 	bpf_lwt_prog_destroy(&bpf->out);
 	bpf_lwt_prog_destroy(&bpf->xmit);
 }

 static const struct nla_policy bpf_prog_policy[LWT_BPF_PROG_MAX + 1] = {
 	[LWT_BPF_PROG_FD]   = { .type = NLA_U32, },
 	[LWT_BPF_PROG_NAME] = { .type = NLA_NUL_STRING,
 				.len = MAX_PROG_NAME },
 };

 static int bpf_parse_prog(struct nlattr *attr, struct bpf_lwt_prog *prog,
 			  enum bpf_prog_type type)
 {
 	struct nlattr *tb[LWT_BPF_PROG_MAX + 1];
 	struct bpf_prog *p;
 	int ret;
 	u32 fd;

 	ret = nla_parse_nested_deprecated(tb, LWT_BPF_PROG_MAX, attr,
 					  bpf_prog_policy, NULL);
 	if (ret < 0)
 		return ret;

 	if (!tb[LWT_BPF_PROG_FD] || !tb[LWT_BPF_PROG_NAME])
 		return -EINVAL;

 	prog->name = nla_memdup(tb[LWT_BPF_PROG_NAME], GFP_ATOMIC);
 	if (!prog->name)
 		return -ENOMEM;

 	fd = nla_get_u32(tb[LWT_BPF_PROG_FD]);
 	p = bpf_prog_get_type(fd, type);
 	if (IS_ERR(p))
 		return PTR_ERR(p);

 	prog->prog = p;

 	return 0;
 }

 static const struct nla_policy bpf_nl_policy[LWT_BPF_MAX + 1] = {
 	[LWT_BPF_IN]		= { .type = NLA_NESTED, },
 	[LWT_BPF_OUT]		= { .type = NLA_NESTED, },
 	[LWT_BPF_XMIT]		= { .type = NLA_NESTED, },
 	[LWT_BPF_XMIT_HEADROOM]	= { .type = NLA_U32 },
 };

 static int bpf_build_state(struct nlattr *nla,
 			   unsigned int family, const void *cfg,
 			   struct lwtunnel_state **ts,
 			   struct netlink_ext_ack *extack)
 {
 	struct nlattr *tb[LWT_BPF_MAX + 1];
 	struct lwtunnel_state *newts;
 	struct bpf_lwt *bpf;
 	int ret;

 	if (family != AF_INET && family != AF_INET6)
 		return -EAFNOSUPPORT;

 	ret = nla_parse_nested_deprecated(tb, LWT_BPF_MAX, nla, bpf_nl_policy,
 					  extack);
 	if (ret < 0)
 		return ret;

 	if (!tb[LWT_BPF_IN] && !tb[LWT_BPF_OUT] && !tb[LWT_BPF_XMIT])
 		return -EINVAL;

 	newts = lwtunnel_state_alloc(sizeof(*bpf));
 	if (!newts)
 		return -ENOMEM;

 	newts->type = LWTUNNEL_ENCAP_BPF;
 	bpf = bpf_lwt_lwtunnel(newts);

 	if (tb[LWT_BPF_IN]) {
 		newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
 		ret = bpf_parse_prog(tb[LWT_BPF_IN], &bpf->in,
 				     BPF_PROG_TYPE_LWT_IN);
 		if (ret  < 0)
 			goto errout;
 	}

 	if (tb[LWT_BPF_OUT]) {
 		newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
 		ret = bpf_parse_prog(tb[LWT_BPF_OUT], &bpf->out,
 				     BPF_PROG_TYPE_LWT_OUT);
 		if (ret < 0)
 			goto errout;
 	}

 	if (tb[LWT_BPF_XMIT]) {
 		newts->flags |= LWTUNNEL_STATE_XMIT_REDIRECT;
 		ret = bpf_parse_prog(tb[LWT_BPF_XMIT], &bpf->xmit,
 				     BPF_PROG_TYPE_LWT_XMIT);
 		if (ret < 0)
 			goto errout;
 	}

 	if (tb[LWT_BPF_XMIT_HEADROOM]) {
 		u32 headroom = nla_get_u32(tb[LWT_BPF_XMIT_HEADROOM]);

 		if (headroom > LWT_BPF_MAX_HEADROOM) {
 			ret = -ERANGE;
 			goto errout;
 		}

 		newts->headroom = headroom;
 	}

 	bpf->family = family;
 	*ts = newts;

 	return 0;

 errout:
 	bpf_destroy_state(newts);
 	kfree(newts);
 	return ret;
 }

 static int bpf_fill_lwt_prog(struct sk_buff *skb, int attr,
 			     struct bpf_lwt_prog *prog)
 {
 	struct nlattr *nest;

 	if (!prog->prog)
 		return 0;

 	nest = nla_nest_start_noflag(skb, attr);
 	if (!nest)
 		return -EMSGSIZE;

 	if (prog->name &&
 	    nla_put_string(skb, LWT_BPF_PROG_NAME, prog->name))
 		return -EMSGSIZE;

 	return nla_nest_end(skb, nest);
 }

 static int bpf_fill_encap_info(struct sk_buff *skb, struct lwtunnel_state *lwt)
 {
 	struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);

 	if (bpf_fill_lwt_prog(skb, LWT_BPF_IN, &bpf->in) < 0 ||
 	    bpf_fill_lwt_prog(skb, LWT_BPF_OUT, &bpf->out) < 0 ||
 	    bpf_fill_lwt_prog(skb, LWT_BPF_XMIT, &bpf->xmit) < 0)
 		return -EMSGSIZE;

 	return 0;
 }

 static int bpf_encap_nlsize(struct lwtunnel_state *lwtstate)
 {
 	int nest_len = nla_total_size(sizeof(struct nlattr)) +
 		       nla_total_size(MAX_PROG_NAME) + /* LWT_BPF_PROG_NAME */
 		       0;

 	return nest_len + /* LWT_BPF_IN */
 	       nest_len + /* LWT_BPF_OUT */
 	       nest_len + /* LWT_BPF_XMIT */
 	       0;
 }

 static int bpf_lwt_prog_cmp(struct bpf_lwt_prog *a, struct bpf_lwt_prog *b)
 {
 	/* FIXME:
 	 * The LWT state is currently rebuilt for delete requests which
 	 * results in a new bpf_prog instance. Comparing names for now.
 	 */
 	if (!a->name && !b->name)
 		return 0;

 	if (!a->name || !b->name)
 		return 1;

 	return strcmp(a->name, b->name);
 }

 static int bpf_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
 {
 	struct bpf_lwt *a_bpf = bpf_lwt_lwtunnel(a);
 	struct bpf_lwt *b_bpf = bpf_lwt_lwtunnel(b);

 	return bpf_lwt_prog_cmp(&a_bpf->in, &b_bpf->in) ||
 	       bpf_lwt_prog_cmp(&a_bpf->out, &b_bpf->out) ||
 	       bpf_lwt_prog_cmp(&a_bpf->xmit, &b_bpf->xmit);
 }

 static const struct lwtunnel_encap_ops bpf_encap_ops = {
 	.build_state	= bpf_build_state,
 	.destroy_state	= bpf_destroy_state,
 	.input		= bpf_input,
 	.output		= bpf_output,
 	.xmit		= bpf_xmit,
 	.fill_encap	= bpf_fill_encap_info,
 	.get_encap_size = bpf_encap_nlsize,
 	.cmp_encap	= bpf_encap_cmp,
 	.owner		= THIS_MODULE,
 };

 static int handle_gso_type(struct sk_buff *skb, unsigned int gso_type,
 			   int encap_len)
 {
 	struct skb_shared_info *shinfo = skb_shinfo(skb);

 	gso_type |= SKB_GSO_DODGY;
 	shinfo->gso_type |= gso_type;
 	skb_decrease_gso_size(shinfo, encap_len);
 	shinfo->gso_segs = 0;
 	return 0;
 }

 static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len)
 {
 	int next_hdr_offset;
 	void *next_hdr;
 	__u8 protocol;

 	/* SCTP and UDP_L4 gso need more nuanced handling than what
 	 * handle_gso_type() does above: skb_decrease_gso_size() is not enough.
 	 * So at the moment only TCP GSO packets are let through.
 	 */
 	if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
 		return -ENOTSUPP;

 	if (ipv4) {
 		protocol = ip_hdr(skb)->protocol;
 		next_hdr_offset = sizeof(struct iphdr);
 		next_hdr = skb_network_header(skb) + next_hdr_offset;
 	} else {
 		protocol = ipv6_hdr(skb)->nexthdr;
 		next_hdr_offset = sizeof(struct ipv6hdr);
 		next_hdr = skb_network_header(skb) + next_hdr_offset;
 	}

 	switch (protocol) {
 	case IPPROTO_GRE:
 		next_hdr_offset += sizeof(struct gre_base_hdr);
 		if (next_hdr_offset > encap_len)
 			return -EINVAL;

 		if (((struct gre_base_hdr *)next_hdr)->flags & GRE_CSUM)
 			return handle_gso_type(skb, SKB_GSO_GRE_CSUM,
 					       encap_len);
 		return handle_gso_type(skb, SKB_GSO_GRE, encap_len);

 	case IPPROTO_UDP:
 		next_hdr_offset += sizeof(struct udphdr);
 		if (next_hdr_offset > encap_len)
 			return -EINVAL;

 		if (((struct udphdr *)next_hdr)->check)
 			return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL_CSUM,
 					       encap_len);
 		return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL, encap_len);

 	case IPPROTO_IP:
 	case IPPROTO_IPV6:
 		if (ipv4)
 			return handle_gso_type(skb, SKB_GSO_IPXIP4, encap_len);
 		else
 			return handle_gso_type(skb, SKB_GSO_IPXIP6, encap_len);

 	default:
 		return -EPROTONOSUPPORT;
 	}
 }

 int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress)
 {
 	struct iphdr *iph;
 	bool ipv4;
 	int err;

 	if (unlikely(len < sizeof(struct iphdr) || len > LWT_BPF_MAX_HEADROOM))
 		return -EINVAL;

 	/* validate protocol and length */
 	iph = (struct iphdr *)hdr;
 	if (iph->version == 4) {
 		ipv4 = true;
 		if (unlikely(len < iph->ihl * 4))
 			return -EINVAL;
 	} else if (iph->version == 6) {
 		ipv4 = false;
 		if (unlikely(len < sizeof(struct ipv6hdr)))
 			return -EINVAL;
 	} else {
 		return -EINVAL;
 	}

 	if (ingress)
 		err = skb_cow_head(skb, len + skb->mac_len);
 	else
 		err = skb_cow_head(skb,
 				   len + LL_RESERVED_SPACE(skb_dst(skb)->dev));
 	if (unlikely(err))
 		return err;

 	/* push the encap headers and fix pointers */
 	skb_reset_inner_headers(skb);
 	skb_reset_inner_mac_header(skb);  /* mac header is not yet set */
 	skb_set_inner_protocol(skb, skb->protocol);
 	skb->encapsulation = 1;
 	skb_push(skb, len);
 	if (ingress)
 		skb_postpush_rcsum(skb, iph, len);
 	skb_reset_network_header(skb);
 	memcpy(skb_network_header(skb), hdr, len);
 	bpf_compute_data_pointers(skb);
 	skb_clear_hash(skb);

 	if (ipv4) {
 		skb->protocol = htons(ETH_P_IP);
 		iph = ip_hdr(skb);

 		if (!iph->check)
 			iph->check = ip_fast_csum((unsigned char *)iph,
 						  iph->ihl);
 	} else {
 		skb->protocol = htons(ETH_P_IPV6);
 	}

 	if (skb_is_gso(skb))
 		return handle_gso_encap(skb, ipv4, len);

 	return 0;
 }

 static int __init bpf_lwt_init(void)
 {
 	return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
 }

 subsys_initcall(bpf_lwt_init)
	/* Copyright (c) 2016 Thomas Graf <tgraf@tgraf.ch>
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of version 2 of the GNU General Public
	* License as published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*/

	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/skbuff.h>
	#include <linux/types.h>
	#include <linux/bpf.h>
	#include <net/lwtunnel.h>
	#include <net/gre.h>
	#include <net/ip6_route.h>
	#include <net/ipv6_stubs.h>

	struct bpf_lwt_prog {
	struct bpf_prog *prog;
	char *name;
	};

	struct bpf_lwt {
	struct bpf_lwt_prog in;
	struct bpf_lwt_prog out;
	struct bpf_lwt_prog xmit;
	int family;
	};

	#define MAX_PROG_NAME 256

	static inline struct bpf_lwt bpf_lwt_lwtunnel(struct lwtunnel_state lwt)
	{
	return (struct bpf_lwt *)lwt->data;
	}

	#define NO_REDIRECT false
	#define CAN_REDIRECT true

	static int run_lwt_bpf(struct sk_buff skb, struct bpf_lwt_prog lwt,
	struct dst_entry *dst, bool can_redirect)
	{
	int ret;

	/* Preempt disable is needed to protect per-cpu redirect_info between
	* BPF prog and skb_do_redirect(). The call_rcu in bpf_prog_put() and
	* access to maps strictly require a rcu_read_lock() for protection,
	* mixing with BH RCU lock doesn't work.
	*/
	preempt_disable();
	bpf_compute_data_pointers(skb);
	ret = bpf_prog_run_save_cb(lwt->prog, skb);

	switch (ret) {
	case BPF_OK:
	case BPF_LWT_REROUTE:
	break;

	case BPF_REDIRECT:
	if (unlikely(!can_redirect)) {
	pr_warn_once("Illegal redirect return code in prog %s\n",
	lwt->name ? : "<unknown>");
	ret = BPF_OK;
	} else {
	skb_reset_mac_header(skb);
	ret = skb_do_redirect(skb);
	if (ret == 0)
	ret = BPF_REDIRECT;
	}
	break;

	case BPF_DROP:
	kfree_skb(skb);
	ret = -EPERM;
	break;

	default:
	pr_warn_once("bpf-lwt: Illegal return value %u, expect packet loss\n", ret);
	kfree_skb(skb);
	ret = -EINVAL;
	break;
	}

	preempt_enable();

	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)) {
	err = ipv6_stub->ipv6_route_input(skb);
	} else {
	err = -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);
	struct bpf_lwt *bpf;
	int ret;

	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
	if (bpf->in.prog) {
	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)) {
	kfree_skb(skb);
	return -EINVAL;
	}

	return dst->lwtstate->orig_input(skb);
	}

	static int bpf_output(struct net net, struct sock sk, struct sk_buff *skb)
	{
	struct dst_entry *dst = skb_dst(skb);
	struct bpf_lwt *bpf;
	int ret;

	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
	if (bpf->out.prog) {
	ret = run_lwt_bpf(skb, &bpf->out, dst, NO_REDIRECT);
	if (ret < 0)
	return ret;
	}

	if (unlikely(!dst->lwtstate->orig_output)) {
	pr_warn_once("orig_output not set on dst for prog %s\n",
	bpf->out.name);
	kfree_skb(skb);
	return -EINVAL;
	}

	return dst->lwtstate->orig_output(net, sk, skb);
	}

	static int xmit_check_hhlen(struct sk_buff *skb)
	{
	int hh_len = skb_dst(skb)->dev->hard_header_len;

	if (skb_headroom(skb) < hh_len) {
	int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));

	if (pskb_expand_head(skb, nhead, 0, GFP_ATOMIC))
	return -ENOMEM;
	}

	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;
	int err = -EAFNOSUPPORT;
	struct sock *sk;
	struct net *net;
	bool ipv4;

	if (skb->protocol == htons(ETH_P_IP))
	ipv4 = true;
	else if (skb->protocol == htons(ETH_P_IPV6))
	ipv4 = false;
	else
	goto err;

	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)) {
	err = PTR_ERR(rt);
	goto err;
	}
	dst = &rt->dst;
	} else {
	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 (unlikely(err))
	goto err;
	if (IS_ERR(dst)) {
	err = PTR_ERR(dst);
	goto err;
	}
	}
	if (unlikely(dst->error)) {
	err = dst->error;
	dst_release(dst);
	goto err;
	}

	/* Although skb header was reserved in bpf_lwt_push_ip_encap(), it
	* was done for the previous dst, so we are doing it here again, in
	* case the new dst needs much more space. The call below is a noop
	* if there is enough header space in skb.
	*/
	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
	if (unlikely(err))
	goto err;

	skb_dst_drop(skb);
	skb_dst_set(skb, dst);

	err = dst_output(dev_net(skb_dst(skb)->dev), skb->sk, skb);
	if (unlikely(err))
	return err;

	/* ip[6]_finish_output2 understand LWTUNNEL_XMIT_DONE */
	return LWTUNNEL_XMIT_DONE;

	err:
	kfree_skb(skb);
	return err;
	}

	static int bpf_xmit(struct sk_buff *skb)
	{
	struct dst_entry *dst = skb_dst(skb);
	struct bpf_lwt *bpf;

	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
	if (bpf->xmit.prog) {
	__be16 proto = skb->protocol;
	int ret;

	ret = run_lwt_bpf(skb, &bpf->xmit, dst, CAN_REDIRECT);
	switch (ret) {
	case BPF_OK:
	/* If the header changed, e.g. via bpf_lwt_push_encap,
	* BPF_LWT_REROUTE below should have been used if the
	* protocol was also changed.
	*/
	if (skb->protocol != proto) {
	kfree_skb(skb);
	return -EINVAL;
	}
	/* If the header was expanded, headroom might be too
	* small for L2 header to come, expand as needed.
	*/
	ret = xmit_check_hhlen(skb);
	if (unlikely(ret))
	return ret;

	return LWTUNNEL_XMIT_CONTINUE;
	case BPF_REDIRECT:
	return LWTUNNEL_XMIT_DONE;
	case BPF_LWT_REROUTE:
	return bpf_lwt_xmit_reroute(skb);
	default:
	return ret;
	}
	}

	return LWTUNNEL_XMIT_CONTINUE;
	}

	static void bpf_lwt_prog_destroy(struct bpf_lwt_prog *prog)
	{
	if (prog->prog)
	bpf_prog_put(prog->prog);

	kfree(prog->name);
	}

	static void bpf_destroy_state(struct lwtunnel_state *lwt)
	{
	struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);

	bpf_lwt_prog_destroy(&bpf->in);
	bpf_lwt_prog_destroy(&bpf->out);
	bpf_lwt_prog_destroy(&bpf->xmit);
	}

	static const struct nla_policy bpf_prog_policy[LWT_BPF_PROG_MAX + 1] = {
	[LWT_BPF_PROG_FD] = { .type = NLA_U32, },
	[LWT_BPF_PROG_NAME] = { .type = NLA_NUL_STRING,
	.len = MAX_PROG_NAME },
	};

	static int bpf_parse_prog(struct nlattr attr, struct bpf_lwt_prog prog,
	enum bpf_prog_type type)
	{
	struct nlattr *tb[LWT_BPF_PROG_MAX + 1];
	struct bpf_prog *p;
	int ret;
	u32 fd;

	ret = nla_parse_nested_deprecated(tb, LWT_BPF_PROG_MAX, attr,
	bpf_prog_policy, NULL);
	if (ret < 0)
	return ret;

	if (!tb[LWT_BPF_PROG_FD] \|\| !tb[LWT_BPF_PROG_NAME])
	return -EINVAL;

	prog->name = nla_memdup(tb[LWT_BPF_PROG_NAME], GFP_ATOMIC);
	if (!prog->name)
	return -ENOMEM;

	fd = nla_get_u32(tb[LWT_BPF_PROG_FD]);
	p = bpf_prog_get_type(fd, type);
	if (IS_ERR(p))
	return PTR_ERR(p);

	prog->prog = p;

	return 0;
	}

	static const struct nla_policy bpf_nl_policy[LWT_BPF_MAX + 1] = {
	[LWT_BPF_IN] = { .type = NLA_NESTED, },
	[LWT_BPF_OUT] = { .type = NLA_NESTED, },
	[LWT_BPF_XMIT] = { .type = NLA_NESTED, },
	[LWT_BPF_XMIT_HEADROOM] = { .type = NLA_U32 },
	};

	static int bpf_build_state(struct nlattr *nla,
	unsigned int family, const void *cfg,
	struct lwtunnel_state **ts,
	struct netlink_ext_ack *extack)
	{
	struct nlattr *tb[LWT_BPF_MAX + 1];
	struct lwtunnel_state *newts;
	struct bpf_lwt *bpf;
	int ret;

	if (family != AF_INET && family != AF_INET6)
	return -EAFNOSUPPORT;

	ret = nla_parse_nested_deprecated(tb, LWT_BPF_MAX, nla, bpf_nl_policy,
	extack);
	if (ret < 0)
	return ret;

	if (!tb[LWT_BPF_IN] && !tb[LWT_BPF_OUT] && !tb[LWT_BPF_XMIT])
	return -EINVAL;

	newts = lwtunnel_state_alloc(sizeof(*bpf));
	if (!newts)
	return -ENOMEM;

	newts->type = LWTUNNEL_ENCAP_BPF;
	bpf = bpf_lwt_lwtunnel(newts);

	if (tb[LWT_BPF_IN]) {
	newts->flags \|= LWTUNNEL_STATE_INPUT_REDIRECT;
	ret = bpf_parse_prog(tb[LWT_BPF_IN], &bpf->in,
	BPF_PROG_TYPE_LWT_IN);
	if (ret < 0)
	goto errout;
	}

	if (tb[LWT_BPF_OUT]) {
	newts->flags \|= LWTUNNEL_STATE_OUTPUT_REDIRECT;
	ret = bpf_parse_prog(tb[LWT_BPF_OUT], &bpf->out,
	BPF_PROG_TYPE_LWT_OUT);
	if (ret < 0)
	goto errout;
	}

	if (tb[LWT_BPF_XMIT]) {
	newts->flags \|= LWTUNNEL_STATE_XMIT_REDIRECT;
	ret = bpf_parse_prog(tb[LWT_BPF_XMIT], &bpf->xmit,
	BPF_PROG_TYPE_LWT_XMIT);
	if (ret < 0)
	goto errout;
	}

	if (tb[LWT_BPF_XMIT_HEADROOM]) {
	u32 headroom = nla_get_u32(tb[LWT_BPF_XMIT_HEADROOM]);

	if (headroom > LWT_BPF_MAX_HEADROOM) {
	ret = -ERANGE;
	goto errout;
	}

	newts->headroom = headroom;
	}

	bpf->family = family;
	*ts = newts;

	return 0;

	errout:
	bpf_destroy_state(newts);
	kfree(newts);
	return ret;
	}

	static int bpf_fill_lwt_prog(struct sk_buff *skb, int attr,
	struct bpf_lwt_prog *prog)
	{
	struct nlattr *nest;

	if (!prog->prog)
	return 0;

	nest = nla_nest_start_noflag(skb, attr);
	if (!nest)
	return -EMSGSIZE;

	if (prog->name &&
	nla_put_string(skb, LWT_BPF_PROG_NAME, prog->name))
	return -EMSGSIZE;

	return nla_nest_end(skb, nest);
	}

	static int bpf_fill_encap_info(struct sk_buff skb, struct lwtunnel_state lwt)
	{
	struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);

	if (bpf_fill_lwt_prog(skb, LWT_BPF_IN, &bpf->in) < 0 \|\|
	bpf_fill_lwt_prog(skb, LWT_BPF_OUT, &bpf->out) < 0 \|\|
	bpf_fill_lwt_prog(skb, LWT_BPF_XMIT, &bpf->xmit) < 0)
	return -EMSGSIZE;

	return 0;
	}

	static int bpf_encap_nlsize(struct lwtunnel_state *lwtstate)
	{
	int nest_len = nla_total_size(sizeof(struct nlattr)) +
	nla_total_size(MAX_PROG_NAME) + /* LWT_BPF_PROG_NAME */
	0;

	return nest_len + /* LWT_BPF_IN */
	nest_len + /* LWT_BPF_OUT */
	nest_len + /* LWT_BPF_XMIT */
	0;
	}

	static int bpf_lwt_prog_cmp(struct bpf_lwt_prog a, struct bpf_lwt_prog b)
	{
	/* FIXME:
	* The LWT state is currently rebuilt for delete requests which
	* results in a new bpf_prog instance. Comparing names for now.
	*/
	if (!a->name && !b->name)
	return 0;

	if (!a->name \|\| !b->name)
	return 1;

	return strcmp(a->name, b->name);
	}

	static int bpf_encap_cmp(struct lwtunnel_state a, struct lwtunnel_state b)
	{
	struct bpf_lwt *a_bpf = bpf_lwt_lwtunnel(a);
	struct bpf_lwt *b_bpf = bpf_lwt_lwtunnel(b);

	return bpf_lwt_prog_cmp(&a_bpf->in, &b_bpf->in) \|\|
	bpf_lwt_prog_cmp(&a_bpf->out, &b_bpf->out) \|\|
	bpf_lwt_prog_cmp(&a_bpf->xmit, &b_bpf->xmit);
	}

	static const struct lwtunnel_encap_ops bpf_encap_ops = {
	.build_state = bpf_build_state,
	.destroy_state = bpf_destroy_state,
	.input = bpf_input,
	.output = bpf_output,
	.xmit = bpf_xmit,
	.fill_encap = bpf_fill_encap_info,
	.get_encap_size = bpf_encap_nlsize,
	.cmp_encap = bpf_encap_cmp,
	.owner = THIS_MODULE,
	};

	static int handle_gso_type(struct sk_buff *skb, unsigned int gso_type,
	int encap_len)
	{
	struct skb_shared_info *shinfo = skb_shinfo(skb);

	gso_type \|= SKB_GSO_DODGY;
	shinfo->gso_type \|= gso_type;
	skb_decrease_gso_size(shinfo, encap_len);
	shinfo->gso_segs = 0;
	return 0;
	}

	static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len)
	{
	int next_hdr_offset;
	void *next_hdr;
	__u8 protocol;

	/* SCTP and UDP_L4 gso need more nuanced handling than what
	* handle_gso_type() does above: skb_decrease_gso_size() is not enough.
	* So at the moment only TCP GSO packets are let through.
	*/
	if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 \| SKB_GSO_TCPV6)))
	return -ENOTSUPP;

	if (ipv4) {
	protocol = ip_hdr(skb)->protocol;
	next_hdr_offset = sizeof(struct iphdr);
	next_hdr = skb_network_header(skb) + next_hdr_offset;
	} else {
	protocol = ipv6_hdr(skb)->nexthdr;
	next_hdr_offset = sizeof(struct ipv6hdr);
	next_hdr = skb_network_header(skb) + next_hdr_offset;
	}

	switch (protocol) {
	case IPPROTO_GRE:
	next_hdr_offset += sizeof(struct gre_base_hdr);
	if (next_hdr_offset > encap_len)
	return -EINVAL;

	if (((struct gre_base_hdr *)next_hdr)->flags & GRE_CSUM)
	return handle_gso_type(skb, SKB_GSO_GRE_CSUM,
	encap_len);
	return handle_gso_type(skb, SKB_GSO_GRE, encap_len);

	case IPPROTO_UDP:
	next_hdr_offset += sizeof(struct udphdr);
	if (next_hdr_offset > encap_len)
	return -EINVAL;

	if (((struct udphdr *)next_hdr)->check)
	return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL_CSUM,
	encap_len);
	return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL, encap_len);

	case IPPROTO_IP:
	case IPPROTO_IPV6:
	if (ipv4)
	return handle_gso_type(skb, SKB_GSO_IPXIP4, encap_len);
	else
	return handle_gso_type(skb, SKB_GSO_IPXIP6, encap_len);

	default:
	return -EPROTONOSUPPORT;
	}
	}

	int bpf_lwt_push_ip_encap(struct sk_buff skb, void hdr, u32 len, bool ingress)
	{
	struct iphdr *iph;
	bool ipv4;
	int err;

	if (unlikely(len < sizeof(struct iphdr) \|\| len > LWT_BPF_MAX_HEADROOM))
	return -EINVAL;

	/* validate protocol and length */
	iph = (struct iphdr *)hdr;
	if (iph->version == 4) {
	ipv4 = true;
	if (unlikely(len < iph->ihl * 4))
	return -EINVAL;
	} else if (iph->version == 6) {
	ipv4 = false;
	if (unlikely(len < sizeof(struct ipv6hdr)))
	return -EINVAL;
	} else {
	return -EINVAL;
	}

	if (ingress)
	err = skb_cow_head(skb, len + skb->mac_len);
	else
	err = skb_cow_head(skb,
	len + LL_RESERVED_SPACE(skb_dst(skb)->dev));
	if (unlikely(err))
	return err;

	/* push the encap headers and fix pointers */
	skb_reset_inner_headers(skb);
	skb_reset_inner_mac_header(skb); /* mac header is not yet set */
	skb_set_inner_protocol(skb, skb->protocol);
	skb->encapsulation = 1;
	skb_push(skb, len);
	if (ingress)
	skb_postpush_rcsum(skb, iph, len);
	skb_reset_network_header(skb);
	memcpy(skb_network_header(skb), hdr, len);
	bpf_compute_data_pointers(skb);
	skb_clear_hash(skb);

	if (ipv4) {
	skb->protocol = htons(ETH_P_IP);
	iph = ip_hdr(skb);

	if (!iph->check)
	iph->check = ip_fast_csum((unsigned char *)iph,
	iph->ihl);
	} else {
	skb->protocol = htons(ETH_P_IPV6);
	}

	if (skb_is_gso(skb))
	return handle_gso_encap(skb, ipv4, len);

	return 0;
	}

	static int __init bpf_lwt_init(void)
	{
	return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
	}

	subsys_initcall(bpf_lwt_init)