85 lines
2 KiB
C
85 lines
2 KiB
C
// SPDX-License-Identifier: AGPL-3.0-or-later
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/* PASST - Plug A Simple Socket Transport
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* for qemu/UNIX domain socket mode
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*
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* PASTA - Pack A Subtle Tap Abstraction
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* for network namespace/tap device mode
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*
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* arp.c - ARP implementation
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*
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* Copyright (c) 2020-2021 Red Hat GmbH
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* Author: Stefano Brivio <sbrivio@redhat.com>
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*/
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#include <arpa/inet.h>
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#include <limits.h>
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#include <net/if.h>
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#include <net/if_arp.h>
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#include <netinet/if_ether.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <string.h>
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#include "util.h"
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#include "arp.h"
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#include "dhcp.h"
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#include "passt.h"
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#include "tap.h"
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/**
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* arp() - Check if this is an ARP message, reply as needed
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* @c: Execution context
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* @len: Total L2 packet length
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* @eh: Packet buffer, Ethernet header
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*
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* Return: 0 if it's not an ARP message, 1 if handled, -1 on failure
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*/
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int arp(struct ctx *c, struct ethhdr *eh, size_t len)
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{
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struct arphdr *ah = (struct arphdr *)(eh + 1);
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struct arpmsg *am = (struct arpmsg *)(ah + 1);
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unsigned char swap[4];
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if (eh->h_proto != htons(ETH_P_ARP))
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return 0;
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if (len < sizeof(*eh) + sizeof(*ah) + sizeof(*am))
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return -1;
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if (ah->ar_hrd != htons(ARPHRD_ETHER) ||
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ah->ar_pro != htons(ETH_P_IP) ||
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ah->ar_hln != ETH_ALEN || ah->ar_pln != 4 ||
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ah->ar_op != htons(ARPOP_REQUEST))
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return 1;
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/* Discard announcements (but not 0.0.0.0 "probes"): we might have the
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* same IP address, hide that.
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*/
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if (memcmp(am->sip, (unsigned char[4]){ 0, 0, 0, 0 }, 4) &&
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!memcmp(am->sip, am->tip, 4))
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return 1;
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/* Don't resolve our own address, either. */
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if (!memcmp(am->tip, &c->addr4, 4))
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return 1;
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ah->ar_op = htons(ARPOP_REPLY);
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memcpy(am->tha, am->sha, ETH_ALEN);
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memcpy(am->sha, c->mac, ETH_ALEN);
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memcpy(swap, am->tip, 4);
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memcpy(am->tip, am->sip, 4);
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memcpy(am->sip, swap, 4);
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len = sizeof(*eh) + sizeof(*ah) + sizeof(*am);
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memcpy(eh->h_dest, eh->h_source, ETH_ALEN);
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memcpy(eh->h_source, c->mac, ETH_ALEN);
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if (tap_send(c, eh, len, 0) < 0)
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perror("ARP: send");
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return 1;
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}
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