// 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 */ #include #include #include #include #include #include #include #include #include #include #include "util.h" #include "arp.h" #include "dhcp.h" #include "passt.h" #include "tap.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 (memcmp(am->sip, (unsigned char[4]){ 0, 0, 0, 0 }, 4) && !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; }