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, 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, 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, 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, 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"; 68