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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"
/**
* ignore_arp() - Check if we should ignore this ARP message
* @c: Execution context
* @ah: ARP header
* @am: ARP message
*
* Return: true if the ARP message should be ignored, false otherwise
*/
static bool ignore_arp(const struct ctx *c,
const struct arphdr *ah, const struct arpmsg *am)
{
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 true;
/* Discard announcements, but not 0.0.0.0 "probes" */
if (memcmp(am->sip, &in4addr_any, sizeof(am->sip)) &&
!memcmp(am->sip, am->tip, sizeof(am->sip)))
return true;
/* Don't resolve the guest's assigned address, either. */
if (!memcmp(am->tip, &c->ip4.addr, sizeof(am->tip)))
return true;
return false;
}
/**
* arp() - Check if this is a supported ARP message, reply as needed
* @c: Execution context
* @data: Single packet with Ethernet buffer
*
* Return: 1 if handled, -1 on failure
*/
int arp(const struct ctx *c, struct iov_tail *data)
{
struct {
struct ethhdr eh;
struct arphdr ah;
struct arpmsg am;
} __attribute__((__packed__)) resp;
struct arphdr ah_storage;
struct ethhdr eh_storage;
struct arpmsg am_storage;
const struct ethhdr *eh;
const struct arphdr *ah;
const struct arpmsg *am;
eh = IOV_REMOVE_HEADER(data, eh_storage);
ah = IOV_REMOVE_HEADER(data, ah_storage);
am = IOV_REMOVE_HEADER(data, am_storage);
if (!eh || !ah || !am)
return -1;
if (ignore_arp(c, ah, am))
return 1;
/* Ethernet header */
resp.eh.h_proto = htons(ETH_P_ARP);
memcpy(resp.eh.h_dest, eh->h_source, sizeof(resp.eh.h_dest));
memcpy(resp.eh.h_source, c->our_tap_mac, sizeof(resp.eh.h_source));
/* ARP header */
resp.ah.ar_op = htons(ARPOP_REPLY);
resp.ah.ar_hrd = ah->ar_hrd;
resp.ah.ar_pro = ah->ar_pro;
resp.ah.ar_hln = ah->ar_hln;
resp.ah.ar_pln = ah->ar_pln;
/* ARP message */
memcpy(resp.am.sha, c->our_tap_mac, sizeof(resp.am.sha));
memcpy(resp.am.sip, am->tip, sizeof(resp.am.sip));
memcpy(resp.am.tha, am->sha, sizeof(resp.am.tha));
memcpy(resp.am.tip, am->sip, sizeof(resp.am.tip));
tap_send_single(c, &resp, sizeof(resp));
return 1;
}
/**
* arp_send_init_req() - Send initial ARP request to retrieve guest MAC address
* @c: Execution context
*/
void arp_send_init_req(const struct ctx *c)
{
struct {
struct ethhdr eh;
struct arphdr ah;
struct arpmsg am;
} __attribute__((__packed__)) req;
/* Ethernet header */
req.eh.h_proto = htons(ETH_P_ARP);
memcpy(req.eh.h_dest, MAC_BROADCAST, sizeof(req.eh.h_dest));
memcpy(req.eh.h_source, c->our_tap_mac, sizeof(req.eh.h_source));
/* ARP header */
req.ah.ar_op = htons(ARPOP_REQUEST);
req.ah.ar_hrd = htons(ARPHRD_ETHER);
req.ah.ar_pro = htons(ETH_P_IP);
req.ah.ar_hln = ETH_ALEN;
req.ah.ar_pln = 4;
/* ARP message */
memcpy(req.am.sha, c->our_tap_mac, sizeof(req.am.sha));
memcpy(req.am.sip, &c->ip4.our_tap_addr, sizeof(req.am.sip));
memcpy(req.am.tha, MAC_BROADCAST, sizeof(req.am.tha));
memcpy(req.am.tip, &c->ip4.addr, sizeof(req.am.tip));
debug("Sending initial ARP request for guest MAC address");
tap_send_single(c, &req, sizeof(req));
}
/**
* arp_announce() - Send an ARP announcement for an IPv4 host
* @c: Execution context
* @ip: IPv4 address we announce as owned by @mac
* @mac: MAC address to advertise for @ip
*/
void arp_announce(const struct ctx *c, struct in_addr *ip,
const unsigned char *mac)
{
char ip_str[INET_ADDRSTRLEN];
char mac_str[ETH_ADDRSTRLEN];
struct {
struct ethhdr eh;
struct arphdr ah;
struct arpmsg am;
} __attribute__((__packed__)) annc;
/* Ethernet header */
annc.eh.h_proto = htons(ETH_P_ARP);
memcpy(annc.eh.h_dest, MAC_BROADCAST, sizeof(annc.eh.h_dest));
memcpy(annc.eh.h_source, mac, sizeof(annc.eh.h_source));
/* ARP header */
annc.ah.ar_op = htons(ARPOP_REQUEST);
annc.ah.ar_hrd = htons(ARPHRD_ETHER);
annc.ah.ar_pro = htons(ETH_P_IP);
annc.ah.ar_hln = ETH_ALEN;
annc.ah.ar_pln = 4;
/* ARP message */
memcpy(annc.am.sha, mac, sizeof(annc.am.sha));
memcpy(annc.am.sip, ip, sizeof(annc.am.sip));
memcpy(annc.am.tha, MAC_BROADCAST, sizeof(annc.am.tha));
memcpy(annc.am.tip, ip, sizeof(annc.am.tip));
inet_ntop(AF_INET, ip, ip_str, sizeof(ip_str));
eth_ntop(mac, mac_str, sizeof(mac_str));
debug("Announcing ARP for %s / %s", ip_str, mac_str);
tap_send_single(c, &annc, sizeof(annc));
}
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