Commit 52f27877 authored by Peter Oskolkov's avatar Peter Oskolkov Committed by Alexei Starovoitov
Browse files

bpf: implement BPF_LWT_ENCAP_IP mode in bpf_lwt_push_encap 



Implement BPF_LWT_ENCAP_IP mode in bpf_lwt_push_encap BPF helper.
It enables BPF programs (specifically, BPF_PROG_TYPE_LWT_IN and
BPF_PROG_TYPE_LWT_XMIT prog types) to add IP encapsulation headers
to packets (e.g. IP/GRE, GUE, IPIP).

This is useful when thousands of different short-lived flows should be
encapped, each with different and dynamically determined destination.
Although lwtunnels can be used in some of these scenarios, the ability
to dynamically generate encap headers adds more flexibility, e.g.
when routing depends on the state of the host (reflected in global bpf
maps).

v7 changes:
 - added a call skb_clear_hash();
 - removed calls to skb_set_transport_header();
 - refuse to encap GSO-enabled packets.

v8 changes:
 - fix build errors when LWT is not enabled.

Note: the next patch in the patchset with deal with GSO-enabled packets,
which are currently rejected at encapping attempt.

Signed-off-by: default avatarPeter Oskolkov <posk@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 3e0bd37c

include/net/lwtunnel.h

+2 −0
Original line number Original line Diff line number Diff line
@@ -126,6 +126,8 @@ int lwtunnel_cmp_encap(struct lwtunnel_state *a, struct lwtunnel_state *b); 
int lwtunnel_output(struct net *net, struct sock *sk, struct sk_buff *skb);

int lwtunnel_output(struct net *net, struct sock *sk, struct sk_buff *skb);

int lwtunnel_input(struct sk_buff *skb);

int lwtunnel_input(struct sk_buff *skb);

int lwtunnel_xmit(struct sk_buff *skb);

int lwtunnel_xmit(struct sk_buff *skb);

int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len,

			  bool ingress);





static inline void lwtunnel_set_redirect(struct dst_entry *dst)

static inline void lwtunnel_set_redirect(struct dst_entry *dst)

{

{

net/core/filter.c

+2 −1
Original line number Original line Diff line number Diff line
@@ -73,6 +73,7 @@ 
#include <linux/seg6_local.h>

#include <linux/seg6_local.h>

#include <net/seg6.h>

#include <net/seg6.h>

#include <net/seg6_local.h>

#include <net/seg6_local.h>

#include <net/lwtunnel.h>





/**

/**

 *	sk_filter_trim_cap - run a packet through a socket filter

 *	sk_filter_trim_cap - run a packet through a socket filter
@@ -4819,7 +4820,7 @@ static int bpf_push_seg6_encap(struct sk_buff *skb, u32 type, void *hdr, u32 len 
static int bpf_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len,

static int bpf_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len,

			     bool ingress)

			     bool ingress)

{

{

	return -EINVAL;  /* Implemented in the next patch. */

	return bpf_lwt_push_ip_encap(skb, hdr, len, ingress);

}

}

#endif

#endif

net/core/lwt_bpf.c

+65 −0
Original line number Original line Diff line number Diff line
@@ -390,6 +390,71 @@ static const struct lwtunnel_encap_ops bpf_encap_ops = { 
	.owner		= THIS_MODULE,

	.owner		= THIS_MODULE,

};

};





static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len)

{

	/* Handling of GSO-enabled packets is added in the next patch. */

	return -EOPNOTSUPP;

}



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->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)

static int __init bpf_lwt_init(void)

{

{

	return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);

	return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);

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