1 // SPDX-License-Identifier: GPL-2.0 2 #ifndef BPF_NO_PRESERVE_ACCESS_INDEX 3 #define BPF_NO_PRESERVE_ACCESS_INDEX 4 #endif 5 #include <vmlinux.h> 6 #include <bpf/bpf_core_read.h> 7 #include <bpf/bpf_helpers.h> 8 9 #define INLINE __always_inline 10 11 #define skb_shorter(skb, len) ((void *)(long)(skb)->data + (len) > (void *)(long)skb->data_end) 12 13 #define ETH_IPV4_TCP_SIZE (14 + sizeof(struct iphdr) + sizeof(struct tcphdr)) 14 get_iphdr(struct __sk_buff * skb)15static INLINE struct iphdr *get_iphdr(struct __sk_buff *skb) 16 { 17 struct iphdr *ip = NULL; 18 struct ethhdr *eth; 19 20 if (skb_shorter(skb, ETH_IPV4_TCP_SIZE)) 21 goto out; 22 23 eth = (void *)(long)skb->data; 24 ip = (void *)(eth + 1); 25 26 out: 27 return ip; 28 } 29 30 SEC("tc") main_prog(struct __sk_buff * skb)31int main_prog(struct __sk_buff *skb) 32 { 33 struct iphdr *ip = NULL; 34 struct tcphdr *tcp; 35 __u8 proto = 0; 36 int urg_ptr; 37 u32 offset; 38 39 if (!(ip = get_iphdr(skb))) 40 goto out; 41 42 proto = ip->protocol; 43 44 if (proto != IPPROTO_TCP) 45 goto out; 46 47 tcp = (void*)(ip + 1); 48 if (tcp->dest != 0) 49 goto out; 50 if (!tcp) 51 goto out; 52 53 urg_ptr = tcp->urg_ptr; 54 55 /* Checksum validation part */ 56 proto++; 57 offset = sizeof(struct ethhdr) + offsetof(struct iphdr, protocol); 58 bpf_skb_store_bytes(skb, offset, &proto, sizeof(proto), BPF_F_RECOMPUTE_CSUM); 59 60 return urg_ptr; 61 out: 62 return -1; 63 } 64 char _license[] SEC("license") = "GPL"; 65