null.go

// Copyright 2017 Politecnico di Torino
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package null

var null_code = `
#include <bcc/proto.h>
#include <bcc/helpers.h>

#include <uapi/linux/bpf.h>
#include <uapi/linux/icmp.h>
#include <uapi/linux/if_ether.h>
#include <uapi/linux/if_packet.h>
#include <uapi/linux/ip.h>
#include <uapi/linux/in.h>
#include <uapi/linux/filter.h>
#include <uapi/linux/pkt_cls.h>

#define ICMP_CSUM_OFFSET (sizeof(struct eth_hdr) + sizeof(struct iphdr) + offsetof(struct icmphdr, checksum))

#define IP (0x0701A8C0) // 192.168.1.7

struct eth_hdr {
  __be64   dst:48;
  __be64   src:48;
  __be16   proto;
} __attribute__((packed));

static int handle_rx(void *skb, struct metadata *md) {
  struct __sk_buff *skb2 = (struct __sk_buff *)skb;
  void *data = (void *)(long)skb2->data;
  void *data_end = (void *)(long)skb2->data_end;

  struct eth_hdr *eth = data;
  struct iphdr *ip = data + sizeof(*eth);
  struct icmphdr *icmp = data + sizeof(*eth) + sizeof(*ip);
  if (data + sizeof(*eth) + sizeof(*ip) + sizeof(*icmp) > data_end)
    goto DROP;

  if (eth->proto != htons(ETH_P_IP))
    goto DROP;

  if (ip->protocol != IPPROTO_ICMP)
    goto DROP;

  if (icmp->type != ICMP_ECHO)
    goto DROP;

  if (ip->daddr != IP)
    goto DROP;

  //__u8 old_type = icmp->type;
  //__u8 new_type = (__u8) ICMP_ECHOREPLY;
  //bpf_l4_csum_replace(skb2, ICMP_CSUM_OFFSET, old_type, new_type, 2);
  int r = bpf_csum_update(skb2, 0xFFFF);
  bpf_trace_printk("r is %d\n", r);
  bpf_trace_printk("r is %x\n", r);

  //icmp->type = new_type;

  //__be32 old_src = ip->saddr;
  //__be32 old_dst = ip->daddr;
  //
  //ip->daddr = old_src;
  //ip->saddr = old_dst;
  //
  //__be64 old_src_mac = eth->src;
  //__be64 old_dst_mac = eth->dst;
  //eth->src = old_dst_mac;
  //eth->dst = old_src_mac;



  pkt_redirect(skb, md, md->in_ifc);
  return RX_REDIRECT;

DROP:
  return RX_DROP;
}
`