// SPDX-License-Identifier: GPL-2.0 #define BPF_NO_PRESERVE_ACCESS_INDEX #include <vmlinux.h> #include <bpf/bpf_core_read.h> #include <bpf/bpf_helpers.h> #define INLINE __always_inline #define skb_shorter(skb, len) ((void *)(long)(skb)->data + (len) > (void *)(long)skb->data_end) #define ETH_IPV4_TCP_SIZE (14 + sizeof(struct iphdr) + sizeof(struct tcphdr)) static INLINE struct iphdr *get_iphdr(struct __sk_buff *skb) { struct iphdr *ip = NULL; struct ethhdr *eth; if (skb_shorter(skb, ETH_IPV4_TCP_SIZE)) goto out; eth = (void *)(long)skb->data; ip = (void *)(eth + 1); out: return ip; } SEC("tc") int main_prog(struct __sk_buff *skb) { struct iphdr *ip = NULL; struct tcphdr *tcp; __u8 proto = 0; if (!(ip = get_iphdr(skb))) goto out; proto = ip->protocol; if (proto != IPPROTO_TCP) goto out; tcp = (void*)(ip + 1); if (tcp->dest != 0) goto out; if (!tcp) goto out; return tcp->urg_ptr; out: return -1; } char _license[] SEC("license") = "GPL";