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// SPDX-License-Identifier: AGPL-3.0-or-later
/* PASST - Plug A Simple Socket Transport
* for qemu/UNIX domain socket mode
*
* PASTA - Pack A Subtle Tap Abstraction
* for network namespace/tap device mode
*
* arp.c - ARP implementation
*
* Copyright (c) 2020-2021 Red Hat GmbH
* Author: Stefano Brivio <sbrivio@redhat.com>
*/
#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/ipv6.h>
#include <linux/udp.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <arpa/inet.h>
#include "util.h"
#include "passt.h"
#include "dhcp.h"
#include "tap.h"
#include "arp.h"
/**
* arp() - 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, struct ethhdr *eh, size_t len)
{
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;
/* Discard announcements (but not 0.0.0.0 "probes"): we might have the
* same IP address, hide that.
*/
if (*((uint32_t *)&am->sip) && !memcmp(am->sip, am->tip, 4))
return 1;
/* Don't resolve our own address, either. */
if (!memcmp(am->tip, &c->addr4, 4))
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 (tap_send(c, eh, len, 0) < 0)
perror("ARP: send");
return 1;
}
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