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// SPDX-License-Identifier: GPL-2.0
/* In-place tunneling */
#include <linux/stddef.h>
#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/pkt_cls.h>
#include <linux/types.h>
#include "bpf_endian.h"
#include "bpf_helpers.h"
static const int cfg_port = 8000;
static __always_inline void set_ipv4_csum(struct iphdr *iph)
{
__u16 *iph16 = (__u16 *)iph;
__u32 csum;
int i;
iph->check = 0;
#pragma clang loop unroll(full)
for (i = 0, csum = 0; i < sizeof(*iph) >> 1; i++)
csum += *iph16++;
iph->check = ~((csum & 0xffff) + (csum >> 16));
}
SEC("encap")
int encap_f(struct __sk_buff *skb)
{
struct iphdr iph_outer, iph_inner;
struct tcphdr tcph;
if (skb->protocol != __bpf_constant_htons(ETH_P_IP))
return TC_ACT_OK;
if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_inner,
sizeof(iph_inner)) < 0)
return TC_ACT_OK;
/* filter only packets we want */
if (iph_inner.ihl != 5 || iph_inner.protocol != IPPROTO_TCP)
return TC_ACT_OK;
if (bpf_skb_load_bytes(skb, ETH_HLEN + sizeof(iph_inner),
&tcph, sizeof(tcph)) < 0)
return TC_ACT_OK;
if (tcph.dest != __bpf_constant_htons(cfg_port))
return TC_ACT_OK;
/* add room between mac and network header */
if (bpf_skb_adjust_room(skb, sizeof(iph_outer), BPF_ADJ_ROOM_NET, 0))
return TC_ACT_SHOT;
/* prepare new outer network header */
iph_outer = iph_inner;
iph_outer.protocol = IPPROTO_IPIP;
iph_outer.tot_len = bpf_htons(sizeof(iph_outer) +
bpf_htons(iph_outer.tot_len));
set_ipv4_csum(&iph_outer);
/* store new outer network header */
if (bpf_skb_store_bytes(skb, ETH_HLEN, &iph_outer, sizeof(iph_outer),
BPF_F_INVALIDATE_HASH) < 0)
return TC_ACT_SHOT;
/* bpf_skb_adjust_room has moved header to start of room: restore */
if (bpf_skb_store_bytes(skb, ETH_HLEN + sizeof(iph_outer),
&iph_inner, sizeof(iph_inner),
BPF_F_INVALIDATE_HASH) < 0)
return TC_ACT_SHOT;
return TC_ACT_OK;
}
SEC("decap")
int decap_f(struct __sk_buff *skb)
{
struct iphdr iph_outer, iph_inner;
if (skb->protocol != __bpf_constant_htons(ETH_P_IP))
return TC_ACT_OK;
if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_outer,
sizeof(iph_outer)) < 0)
return TC_ACT_OK;
if (iph_outer.ihl != 5 || iph_outer.protocol != IPPROTO_IPIP)
return TC_ACT_OK;
if (bpf_skb_load_bytes(skb, ETH_HLEN + sizeof(iph_outer),
&iph_inner, sizeof(iph_inner)) < 0)
return TC_ACT_OK;
if (bpf_skb_adjust_room(skb, -(int)sizeof(iph_outer),
BPF_ADJ_ROOM_NET, 0))
return TC_ACT_SHOT;
/* bpf_skb_adjust_room has moved outer over inner header: restore */
if (bpf_skb_store_bytes(skb, ETH_HLEN, &iph_inner, sizeof(iph_inner),
BPF_F_INVALIDATE_HASH) < 0)
return TC_ACT_SHOT;
return TC_ACT_OK;
}
char __license[] SEC("license") = "GPL";
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