1 #include <uapi/linux/bpf.h>
2 #include <uapi/linux/if_ether.h>
3 #include <uapi/linux/if_packet.h>
4 #include <uapi/linux/ip.h>
5 #include <uapi/linux/in.h>
6 #include <uapi/linux/tcp.h>
7 #include <uapi/linux/filter.h>
8 #include <uapi/linux/pkt_cls.h>
9 #include <bpf/bpf_helpers.h>
10 #include "bpf_legacy.h"
11
12 /* compiler workaround */
13 #define _htonl __builtin_bswap32
14
15 #define IP_CSUM_OFF (ETH_HLEN + offsetof(struct iphdr, check))
16 #define TCP_CSUM_OFF (ETH_HLEN + sizeof(struct iphdr) + offsetof(struct tcphdr, check))
17 #define IP_DST_OFF (ETH_HLEN + offsetof(struct iphdr, daddr))
18
19 #define IS_PSEUDO 0x10
20
set_tcp_ip_dst(struct __sk_buff * skb,__u32 new_ip)21 static inline int set_tcp_ip_dst(struct __sk_buff *skb, __u32 new_ip)
22 {
23 __u32 old_ip = _htonl(load_word(skb, IP_DST_OFF));
24 if (old_ip != 0x0A010A0A) return 0;
25 bpf_printk("redirect from %x to %x\n", old_ip, new_ip);
26 bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_ip, new_ip, IS_PSEUDO | sizeof(new_ip));
27 bpf_l3_csum_replace(skb, IP_CSUM_OFF, old_ip, new_ip, sizeof(new_ip));
28 bpf_skb_store_bytes(skb, IP_DST_OFF, &new_ip, sizeof(new_ip), 0);
29 return 1;
30 }
31
32 SEC("tclb")
bpf_prog(struct __sk_buff * skb)33 int bpf_prog(struct __sk_buff *skb)
34 {
35 __u8 proto = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol));
36
37 if (proto == IPPROTO_TCP) {
38 if (set_tcp_ip_dst(skb, 0x030112ac)) return TC_ACT_REPEAT;
39 }
40
41 return TC_ACT_OK;
42 }
43
44 char _license[] SEC("license") = "GPL";
45