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// SPDX-License-Identifier: GPL-2.0-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 <arpa/inet.h>
#include <limits.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <netinet/if_ether.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include "util.h"
#include "log.h"
#include "arp.h"
#include "dhcp.h"
#include "passt.h"
#include "tap.h"
/**
* arp() - Check if this is a supported ARP message, reply as needed
* @c: Execution context
* @p: Packet pool, single packet with Ethernet buffer
*
* Return: 1 if handled, -1 on failure
*/
int arp(const struct ctx *c, const struct pool *p)
{
unsigned char swap[4];
struct ethhdr *eh;
struct arphdr *ah;
struct arpmsg *am;
size_t l2len;
eh = packet_get(p, 0, 0, sizeof(*eh), NULL);
ah = packet_get(p, 0, sizeof(*eh), sizeof(*ah), NULL);
am = packet_get(p, 0, sizeof(*eh) + sizeof(*ah), sizeof(*am), NULL);
if (!eh || !ah || !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 (memcmp(am->sip, (unsigned char[4]){ 0 }, sizeof(am->tip)) &&
!memcmp(am->sip, am->tip, sizeof(am->sip)))
return 1;
/* Don't resolve our own address, either. */
if (!memcmp(am->tip, &c->ip4.addr, sizeof(am->tip)))
return 1;
ah->ar_op = htons(ARPOP_REPLY);
memcpy(am->tha, am->sha, sizeof(am->tha));
memcpy(am->sha, c->our_tap_mac, sizeof(am->sha));
memcpy(swap, am->tip, sizeof(am->tip));
memcpy(am->tip, am->sip, sizeof(am->tip));
memcpy(am->sip, swap, sizeof(am->sip));
l2len = sizeof(*eh) + sizeof(*ah) + sizeof(*am);
memcpy(eh->h_dest, eh->h_source, sizeof(eh->h_dest));
memcpy(eh->h_source, c->our_tap_mac, sizeof(eh->h_source));
tap_send_single(c, eh, l2len);
return 1;
}
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