1 // SPDX-License-Identifier: (APACHE-2.0 OR MIT) 2 // Copyright 2016 6WIND S.A. <quentin.monnet@6wind.com> 3 4 // Block TCP packets on source or destination port 0x9999. 5 6 #include <linux/ip.h> 7 #include <linux/in.h> 8 #include <linux/tcp.h> 9 #include <linux/bpf.h> 10 11 #define ETH_ALEN 6 12 #define ETH_P_IP 0x0008 /* htons(0x0800) */ 13 #define TCP_HDR_LEN 20 14 15 #define BLOCKED_TCP_PORT 0x9999 16 17 struct eth_hdr { 18 unsigned char h_dest[ETH_ALEN]; 19 unsigned char h_source[ETH_ALEN]; 20 unsigned short h_proto; 21 }; 22 23 #define SEC(NAME) __attribute__((section(NAME), used)) 24 SEC(".classifier") handle_ingress(struct __sk_buff * skb)25int handle_ingress(struct __sk_buff *skb) 26 { 27 void *data = (void *)(long)skb->data; 28 void *data_end = (void *)(long)skb->data_end; 29 struct eth_hdr *eth = data; 30 struct iphdr *iph = data + sizeof(*eth); 31 struct tcphdr *tcp = data + sizeof(*eth) + sizeof(*iph); 32 33 /* single length check */ 34 if (data + sizeof(*eth) + sizeof(*iph) + sizeof(*tcp) > data_end) 35 return 0; 36 if (eth->h_proto != ETH_P_IP) 37 return 0; 38 if (iph->protocol != IPPROTO_TCP) 39 return 0; 40 if (tcp->source == BLOCKED_TCP_PORT || tcp->dest == BLOCKED_TCP_PORT) 41 return -1; 42 return 0; 43 } 44