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// SPDX-License-Identifier: GPL-2.0
#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>
#include <linux/bpf.h>
#include <linux/stddef.h>
#include <linux/pkt_cls.h>
#include <linux/if_ether.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#ifndef ctx_ptr
# define ctx_ptr(field) (void *)(long)(field)
#endif
#define ip4_src 0xac100164 /* 172.16.1.100 */
#define ip4_dst 0xac100264 /* 172.16.2.100 */
#define ip6_src { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, \
0x00, 0x01, 0xde, 0xad, 0xbe, 0xef, 0xca, 0xfe }
#define ip6_dst { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, \
0x00, 0x02, 0xde, 0xad, 0xbe, 0xef, 0xca, 0xfe }
#ifndef v6_equal
# define v6_equal(a, b) (a.s6_addr32[0] == b.s6_addr32[0] && \
a.s6_addr32[1] == b.s6_addr32[1] && \
a.s6_addr32[2] == b.s6_addr32[2] && \
a.s6_addr32[3] == b.s6_addr32[3])
#endif
volatile const __u32 IFINDEX_SRC;
volatile const __u32 IFINDEX_DST;
static __always_inline bool is_remote_ep_v4(struct __sk_buff *skb,
__be32 addr)
{
void *data_end = ctx_ptr(skb->data_end);
void *data = ctx_ptr(skb->data);
struct iphdr *ip4h;
if (data + sizeof(struct ethhdr) > data_end)
return false;
ip4h = (struct iphdr *)(data + sizeof(struct ethhdr));
if ((void *)(ip4h + 1) > data_end)
return false;
return ip4h->daddr == addr;
}
static __always_inline bool is_remote_ep_v6(struct __sk_buff *skb,
struct in6_addr addr)
{
void *data_end = ctx_ptr(skb->data_end);
void *data = ctx_ptr(skb->data);
struct ipv6hdr *ip6h;
if (data + sizeof(struct ethhdr) > data_end)
return false;
ip6h = (struct ipv6hdr *)(data + sizeof(struct ethhdr));
if ((void *)(ip6h + 1) > data_end)
return false;
return v6_equal(ip6h->daddr, addr);
}
SEC("tc")
int tc_chk(struct __sk_buff *skb)
{
void *data_end = ctx_ptr(skb->data_end);
void *data = ctx_ptr(skb->data);
__u32 *raw = data;
if (data + sizeof(struct ethhdr) > data_end)
return TC_ACT_SHOT;
return !raw[0] && !raw[1] && !raw[2] ? TC_ACT_SHOT : TC_ACT_OK;
}
SEC("tc")
int tc_dst(struct __sk_buff *skb)
{
__u8 zero[ETH_ALEN * 2];
bool redirect = false;
switch (skb->protocol) {
case __bpf_constant_htons(ETH_P_IP):
redirect = is_remote_ep_v4(skb, __bpf_constant_htonl(ip4_src));
break;
case __bpf_constant_htons(ETH_P_IPV6):
redirect = is_remote_ep_v6(skb, (struct in6_addr)ip6_src);
break;
}
if (!redirect)
return TC_ACT_OK;
__builtin_memset(&zero, 0, sizeof(zero));
if (bpf_skb_store_bytes(skb, 0, &zero, sizeof(zero), 0) < 0)
return TC_ACT_SHOT;
return bpf_redirect_neigh(IFINDEX_SRC, NULL, 0, 0);
}
SEC("tc")
int tc_src(struct __sk_buff *skb)
{
__u8 zero[ETH_ALEN * 2];
bool redirect = false;
switch (skb->protocol) {
case __bpf_constant_htons(ETH_P_IP):
redirect = is_remote_ep_v4(skb, __bpf_constant_htonl(ip4_dst));
break;
case __bpf_constant_htons(ETH_P_IPV6):
redirect = is_remote_ep_v6(skb, (struct in6_addr)ip6_dst);
break;
}
if (!redirect)
return TC_ACT_OK;
__builtin_memset(&zero, 0, sizeof(zero));
if (bpf_skb_store_bytes(skb, 0, &zero, sizeof(zero), 0) < 0)
return TC_ACT_SHOT;
return bpf_redirect_neigh(IFINDEX_DST, NULL, 0, 0);
}
char __license[] SEC("license") = "GPL";
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