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/* MERD - MacVTap Egress and Routing Daemon
*
* arp.c - ARP implementation
*
* Author: Stefano Brivio <sbrivio@redhat.com>
* License: GPLv2
*
*/
#include <stdio.h>
#include <stddef.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <arpa/inet.h>
#include "merd.h"
#include "dhcp.h"
#include "util.h"
/**
* struct arpmsg - 802.2 ARP IPv4 payload
* @sha: Sender hardware address
* @sip: Sender IP address
* @tha: Target hardware address
* @tip: Target IP address
*/
struct arpmsg {
unsigned char sha[ETH_ALEN];
unsigned char sip[4];
unsigned char tha[ETH_ALEN];
unsigned char tip[4];
} __attribute__((__packed__));
/**
* dhcp() - Check if this is an ARP message, reply as needed
* @c: Execution context
* @len: Total L2 packet length
* @eh: Packet buffer, Ethernet header
*
* Return: 0 if it's not an ARP message, 1 if handled, -1 on failure
*/
int arp(struct ctx *c, unsigned len, struct ethhdr *eh)
{
struct arphdr *ah = (struct arphdr *)(eh + 1);
struct arpmsg *am = (struct arpmsg *)(ah + 1);
unsigned char swap[4];
if (eh->h_proto != htons(ETH_P_ARP))
return 0;
if (len < sizeof(*eh) + sizeof(*ah) + sizeof(*am))
return -1;
if (ah->ar_hrd != htons(ARPHRD_ETHER) ||
ah->ar_pro != htons(ETH_P_IP) ||
ah->ar_hln != ETH_ALEN || ah->ar_pln != 4 ||
ah->ar_op != htons(ARPOP_REQUEST))
return 1;
ah->ar_op = htons(ARPOP_REPLY);
memcpy(am->tha, am->sha, ETH_ALEN);
memcpy(am->sha, c->mac, ETH_ALEN);
memcpy(swap, am->tip, 4);
memcpy(am->tip, am->sip, 4);
memcpy(am->sip, swap, 4);
len = sizeof(*eh) + sizeof(*ah) + sizeof(*am);
memcpy(eh->h_dest, eh->h_source, ETH_ALEN);
memcpy(eh->h_source, c->mac, ETH_ALEN);
if (send(c->fd_unix, eh, len, 0) < 0)
perror("ARP: send");
return 1;
}
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