Processing of ARP packets

src/Makefile.am

@@ -1,6 +1,7 @@
 sbin_PROGRAMS = wrapsix-dnsproxy wrapsix-wrapper
 wrapsix_dnsproxy_SOURCES = dnsproxy.c
 wrapsix_wrapper_SOURCES = \
+			  arp.c arp.h \
 			  ipv6.c ipv6.h \
 			  ipv4.h \
 			  nat.c nat.h \

src/arp.c

@@ -0,0 +1,92 @@
+/*
+ *  WrapSix
+ *  Copyright (C) 2008-2012  Michal Zima <xhire@mujmalysvet.cz>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as
+ *  published by the Free Software Foundation, either version 3 of the
+ *  License, or (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <net/ethernet.h>	/* ETHERTYPE_* */
+#include <netinet/in.h>		/* htons */
+#include <stdio.h>
+#include <stdlib.h>		/* malloc */
+#include <string.h>		/* memcmp, memset */
+
+#include "arp.h"
+#include "transmitter.h"
+#include "wrapper.h"
+
+/**
+ * Process ARP packets and reply to them.
+ *
+ * @param	ethq	Ethernet header of the packet
+ * @param	payload	Data of the packet
+ *
+ * @return		0 for success
+ * @return		1 for failure
+ */
+int arp(struct s_ethernet *ethq, char *payload)
+{
+	struct s_arp *arpq, *arpr;	/* request and reply */
+	struct s_ethernet *ethr;
+	unsigned char *packet;
+
+	arpq = (struct s_arp *) payload;
+
+	/* process only requests */
+	if (htons(arpq->opcode) != ARP_OP_REQUEST) {
+		/* not an ARP request */
+		return 1;
+	}
+
+	/* test if this packet belongs to us */
+	if (memcmp(&wrapsix_ipv4_addr, &arpq->ip_dest, 4)) {
+		printf("[Debug] This is unfamiliar packet\n");
+		return 1;
+	}
+
+	/* compute the packet size */
+	#define ARP_PACKET_SIZE sizeof(struct s_ethernet) + sizeof(struct s_arp)
+
+	/* allocate enough memory */
+	if ((packet = (unsigned char *) malloc(ARP_PACKET_SIZE)) == NULL) {
+		fprintf(stderr, "[Error] Lack of free memory\n");
+		return 1;
+	}
+	memset(packet, 0x0, ARP_PACKET_SIZE);
+
+	/* define ethernet header and ARP offsets */
+	ethr = (struct s_ethernet *) packet;
+	arpr = (struct s_arp *) (packet + sizeof(struct s_ethernet));
+
+	/* assemble the ethernet header */
+	ethr->dest = ethq->src;
+	ethr->src  = mac;
+	ethr->type = htons(ETHERTYPE_ARP);
+
+	/* assemble the ARP reply part */
+	arpr->hw        = htons(ARP_HDR_ETHER);
+	arpr->proto     = htons(ETHERTYPE_IP);
+	arpr->hw_len    = 0x06;
+	arpr->proto_len = 0x04;
+	arpr->opcode    = htons(ARP_OP_REPLY);
+	arpr->mac_src   = ethr->src;
+	arpr->mac_dest  = ethr->dest;
+	arpr->ip_src    = wrapsix_ipv4_addr;
+	arpr->ip_dest   = arpq->ip_src;
+
+	/* send ARP reply */
+	transmit_raw(packet, ARP_PACKET_SIZE);
+
+	return 0;
+}

src/arp.h

@@ -0,0 +1,46 @@
+/*
+ *  WrapSix
+ *  Copyright (C) 2008-2012  Michal Zima <xhire@mujmalysvet.cz>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as
+ *  published by the Free Software Foundation, either version 3 of the
+ *  License, or (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef ARP_H
+#define ARP_H
+
+#include "ipv4.h"
+#include "ipv6.h"
+
+/* ARP opcodes */
+#define ARP_OP_REQUEST	0x0001
+#define ARP_OP_REPLY	0x0002
+
+#define ARP_HDR_ETHER	0x0001
+
+/* ARP structure */
+struct s_arp {
+	unsigned short		hw;		/* 16 b; hardware type [0x0001] */
+	unsigned short		proto;		/* 16 b; protocol type [0x0800] */
+	unsigned char		hw_len;		/*  8 b; length of hardware address in bytes [0x06] */
+	unsigned char		proto_len;	/*  8 b; length of protocol address in bytes [0x04] */
+	unsigned short		opcode;		/* 16 b; operation code: [0x0001] or [0x0002] */
+	struct s_mac_addr	mac_src;	/* 48 b; sender hardware address */
+	struct s_ipv4_addr	ip_src;		/* 32 b; sender protocol address */
+	struct s_mac_addr	mac_dest;	/* 48 b; target hardware address */
+	struct s_ipv4_addr	ip_dest;	/* 32 b; target protocol address */
+}__attribute__((__packed__));
+
+int arp(struct s_ethernet *ethq, char *payload);
+
+#endif /* ARP_H */

src/wrapper.c

@@ -29,6 +29,7 @@
 #include <time.h>		/* time */
 #include <unistd.h>		/* close */
 
+#include "arp.h"
 #include "ethernet.h"
 #include "ipv4.h"
 #include "ipv6.h"
@@ -166,7 +167,7 @@ int process(char *packet)
 			return ipv6(eth, payload);
 		case ETHERTYPE_ARP:
 			printf("[Debug] HW Protocol: ARP\n");
-			return -1;
+			return arp(eth, payload);
 		default:
 			printf("[Debug] HW Protocol: unknown [%d/0x%04x]\n",
 			       htons(eth->type), htons(eth->type));