samples/bpf/tcbpf1_kern.c

   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
   9 #include "bpf_helpers.h"
  10
  11 /* compiler workaround */
  12 #define _htonl __builtin_bswap32
  13
  14 static inline void set_dst_mac(struct __sk_buff *skb, char *mac)
  15 {
  16         bpf_skb_store_bytes(skb, 0, mac, ETH_ALEN, 1);
  17 }
  18
  19 #define IP_CSUM_OFF (ETH_HLEN + offsetof(struct iphdr, check))
  20 #define TOS_OFF (ETH_HLEN + offsetof(struct iphdr, tos))
  21
  22 static inline void set_ip_tos(struct __sk_buff *skb, __u8 new_tos)
  23 {
  24         __u8 old_tos = load_byte(skb, BPF_LL_OFF + TOS_OFF);
  25
  26         bpf_l3_csum_replace(skb, IP_CSUM_OFF, htons(old_tos), htons(new_tos), 2);
  27         bpf_skb_store_bytes(skb, TOS_OFF, &new_tos, sizeof(new_tos), 0);
  28 }
  29
  30 #define TCP_CSUM_OFF (ETH_HLEN + sizeof(struct iphdr) + offsetof(struct tcphdr, check))
  31 #define IP_SRC_OFF (ETH_HLEN + offsetof(struct iphdr, saddr))
  32
  33 #define IS_PSEUDO 0x10
  34
  35 static inline void set_tcp_ip_src(struct __sk_buff *skb, __u32 new_ip)
  36 {
  37         __u32 old_ip = _htonl(load_word(skb, BPF_LL_OFF + IP_SRC_OFF));
  38
  39         bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_ip, new_ip, IS_PSEUDO | sizeof(new_ip));
  40         bpf_l3_csum_replace(skb, IP_CSUM_OFF, old_ip, new_ip, sizeof(new_ip));
  41         bpf_skb_store_bytes(skb, IP_SRC_OFF, &new_ip, sizeof(new_ip), 0);
  42 }
  43
  44 #define TCP_DPORT_OFF (ETH_HLEN + sizeof(struct iphdr) + offsetof(struct tcphdr, dest))
  45 static inline void set_tcp_dest_port(struct __sk_buff *skb, __u16 new_port)
  46 {
  47         __u16 old_port = htons(load_half(skb, BPF_LL_OFF + TCP_DPORT_OFF));
  48
  49         bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_port, new_port, sizeof(new_port));
  50         bpf_skb_store_bytes(skb, TCP_DPORT_OFF, &new_port, sizeof(new_port), 0);
  51 }
  52
  53 SEC("classifier")
  54 int bpf_prog1(struct __sk_buff *skb)
  55 {
  56         __u8 proto = load_byte(skb, BPF_LL_OFF + ETH_HLEN + offsetof(struct iphdr, protocol));
  57         long *value;
  58
  59         if (proto == IPPROTO_TCP) {
  60                 set_ip_tos(skb, 8);
  61                 set_tcp_ip_src(skb, 0xA010101);
  62                 set_tcp_dest_port(skb, 5001);
  63         }
  64
  65         return 0;
  66 }
  67 char _license[] SEC("license") = "GPL";