83 lines
1.8 KiB
C
83 lines
1.8 KiB
C
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/* MERD - MacVTap Egress and Routing Daemon
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*
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* arp.c - ARP implementation
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*
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* Author: Stefano Brivio <sbrivio@redhat.com>
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* License: GPLv2
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*
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*/
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#include <stdio.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <unistd.h>
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#include <string.h>
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#include <linux/if_ether.h>
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#include <linux/ip.h>
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#include <linux/udp.h>
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#include <net/if.h>
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#include <net/if_arp.h>
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#include <arpa/inet.h>
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#include "merd.h"
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#include "dhcp.h"
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#include "util.h"
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/**
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* struct arpmsg - 802.2 ARP IPv4 payload
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* @sha: Sender hardware address
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* @sip: Sender IP address
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* @tha: Target hardware address
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* @tip: Target IP address
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*/
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struct arpmsg {
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unsigned char sha[ETH_ALEN];
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unsigned char sip[4];
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unsigned char tha[ETH_ALEN];
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unsigned char tip[4];
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} __attribute__((__packed__));
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/**
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* dhcp() - 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, unsigned len, struct ethhdr *eh)
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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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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 (send(c->fd_unix, 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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