/* Copyright (c) 2016 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */
#define KBUILD_MODNAME "foo"
#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/in.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <uapi/linux/bpf.h>
#include <net/ip.h>
#include <bpf/bpf_helpers.h>

#define DEFAULT_PKTGEN_UDP_PORT 9
#define DEBUG 0

static int tcp(void *data, uint64_t tp_off, void *data_end)
{
        struct tcphdr *tcp = data + tp_off;

        if (tcp + 1 > data_end)
                return 0;
        if (tcp->dest == htons(80) || tcp->source == htons(80))
                return TC_ACT_SHOT;
        return 0;
}

static int udp(void *data, uint64_t tp_off, void *data_end)
{
        struct udphdr *udp = data + tp_off;

        if (udp + 1 > data_end)
                return 0;
        if (udp->dest == htons(DEFAULT_PKTGEN_UDP_PORT) ||
            udp->source == htons(DEFAULT_PKTGEN_UDP_PORT)) {
                if (DEBUG) {
                        char fmt[] = "udp port 9 indeed\n";

                        bpf_trace_printk(fmt, sizeof(fmt));
                }
                return TC_ACT_SHOT;
        }
        return 0;
}

static int parse_ipv4(void *data, uint64_t nh_off, void *data_end)
{
        struct iphdr *iph;
        uint64_t ihl_len;

        iph = data + nh_off;
        if (iph + 1 > data_end)
                return 0;

        if (ip_is_fragment(iph))
                return 0;
        ihl_len = iph->ihl * 4;

        if (iph->protocol == IPPROTO_IPIP) {
                iph = data + nh_off + ihl_len;
                if (iph + 1 > data_end)
                        return 0;
                ihl_len += iph->ihl * 4;
        }

        if (iph->protocol == IPPROTO_TCP)
                return tcp(data, nh_off + ihl_len, data_end);
        else if (iph->protocol == IPPROTO_UDP)
                return udp(data, nh_off + ihl_len, data_end);
        return 0;
}

static int parse_ipv6(void *data, uint64_t nh_off, void *data_end)
{
        struct ipv6hdr *ip6h;
        struct iphdr *iph;
        uint64_t ihl_len = sizeof(struct ipv6hdr);
        uint64_t nexthdr;

        ip6h = data + nh_off;
        if (ip6h + 1 > data_end)
                return 0;

        nexthdr = ip6h->nexthdr;

        if (nexthdr == IPPROTO_IPIP) {
                iph = data + nh_off + ihl_len;
                if (iph + 1 > data_end)
                        return 0;
                ihl_len += iph->ihl * 4;
                nexthdr = iph->protocol;
        } else if (nexthdr == IPPROTO_IPV6) {
                ip6h = data + nh_off + ihl_len;
                if (ip6h + 1 > data_end)
                        return 0;
                ihl_len += sizeof(struct ipv6hdr);
                nexthdr = ip6h->nexthdr;
        }

        if (nexthdr == IPPROTO_TCP)
                return tcp(data, nh_off + ihl_len, data_end);
        else if (nexthdr == IPPROTO_UDP)
                return udp(data, nh_off + ihl_len, data_end);
        return 0;
}

SEC("varlen")
int handle_ingress(struct __sk_buff *skb)
{
        void *data = (void *)(long)skb->data;
        struct ethhdr *eth = data;
        void *data_end = (void *)(long)skb->data_end;
        uint64_t h_proto, nh_off;

        nh_off = sizeof(*eth);
        if (data + nh_off > data_end)
                return 0;

        h_proto = eth->h_proto;

        if (h_proto == ETH_P_8021Q || h_proto == ETH_P_8021AD) {
                struct vlan_hdr *vhdr;

                vhdr = data + nh_off;
                nh_off += sizeof(struct vlan_hdr);
                if (data + nh_off > data_end)
                        return 0;
                h_proto = vhdr->h_vlan_encapsulated_proto;
        }
        if (h_proto == ETH_P_8021Q || h_proto == ETH_P_8021AD) {
                struct vlan_hdr *vhdr;

                vhdr = data + nh_off;
                nh_off += sizeof(struct vlan_hdr);
                if (data + nh_off > data_end)
                        return 0;
                h_proto = vhdr->h_vlan_encapsulated_proto;
        }
        if (h_proto == htons(ETH_P_IP))
                return parse_ipv4(data, nh_off, data_end);
        else if (h_proto == htons(ETH_P_IPV6))
                return parse_ipv6(data, nh_off, data_end);
        return 0;
}
char _license[] SEC("license") = "GPL";