extensions/ebt_arp.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <getopt.h>
#include "../include/ebtables_u.h"
#include <linux/netfilter_bridge/ebt_arp.h>

#define ARP_OPCODE '1'
#define ARP_HTYPE  '2'
#define ARP_PTYPE  '3'
#define ARP_IP_S   '4'
#define ARP_IP_D   '5'
static struct option opts[] =
{
	{ "arp-opcode"    , required_argument, 0, ARP_OPCODE },
	{ "arp-op"        , required_argument, 0, ARP_OPCODE },
	{ "arp-htype"     , required_argument, 0, ARP_HTYPE  },
	{ "arp-ptype"     , required_argument, 0, ARP_PTYPE  },
	{ "arp-ip-src"    , required_argument, 0, ARP_IP_S   },
	{ "arp-ip-dst"    , required_argument, 0, ARP_IP_D   },
	{ 0 }
};

// a few names
static char *opcodes[] =
{
	"Request",
	"Reply",
	"Request Reverse",
	"Reply Reverse",
	"DRARP Request",
	"DRARP Reply",
	"DRARP Error",
	"InARP Request",
	"ARP NAK",
	""
};

static void print_help()
{
	int i = 0;

	printf(
"arp options:\n"
"--arp-opcode opcode            : ARP opcode (integer or string)\n"
"--arp-htype type               : ARP hardware type (integer or string)\n"
"--arp-ptype type               : ARP protocol type (hexadecimal or string)\n"
"--arp-ip-src [!] address[/mask]: ARP ip source specification\n"
"--arp-ip-dst [!] address[/mask]: ARP ip target specification\n"
" opcode strings: \n");
	while (strcmp(opcodes[i], "")) {
		printf("%d = %s\n", i + 1, opcodes[i]);
		i++;
	}
	printf(
" hardware type string: \n 1 = Ethernet\n"
" protocol type string: \n 0x0800 = IPv4\n");
}

static void init(struct ebt_entry_match *match)
{
	struct ebt_arp_info *arpinfo = (struct ebt_arp_info *)match->data;

	arpinfo->invflags = 0;
	arpinfo->bitmask = 0;
}

// defined in ebt_ip.c
void parse_ip_address(char *address, __u32 *addr, __u32 *msk);

#define OPT_OPCODE 0x01
#define OPT_HTYPE  0x02
#define OPT_PTYPE  0x04
#define OPT_IP_S   0x08
#define OPT_IP_D   0x10
static int parse(int c, char **argv, int argc, const struct ebt_u_entry *entry,
   unsigned int *flags, struct ebt_entry_match **match)
{
	struct ebt_arp_info *arpinfo = (struct ebt_arp_info *)(*match)->data;
	int i;
	char *end;
	__u32 *addr;
	__u32 *mask;

	switch (c) {
	case ARP_OPCODE:
		check_option(flags, OPT_OPCODE);
		if (check_inverse(optarg))
			arpinfo->invflags |= EBT_ARP_OPCODE;

		if (optind > argc)
			print_error("Missing arp opcode argument");
		i = strtol(argv[optind - 1], &end, 10);
		if (i < 0 || i >= (0x1 << 16) || *end !='\0') {
			i = 0;
			while (strcmp(opcodes[i], "")) {
				if (!strcasecmp(opcodes[i], optarg))
					break;
				i++;
			}
			if (!strcmp(opcodes[i], ""))
				print_error("Problem with specified "
				            "arp opcode");
		}
		arpinfo->opcode = htons(i);
		arpinfo->bitmask |= EBT_ARP_OPCODE;
		break;

	case ARP_HTYPE:
		check_option(flags, OPT_HTYPE);
		if (check_inverse(optarg))
			arpinfo->invflags |= EBT_ARP_HTYPE;

		if (optind > argc)
			print_error("Missing arp hardware type argument");
		i = strtol(argv[optind - 1], &end, 10);
		if (i < 0 || i >= (0x1 << 16) || *end !='\0') {
			if (!strcasecmp("Ethernet", argv[optind - 1]))
				i = 1;
			else
				print_error("Problem with specified arp "
				            "hardware type");
		}
		arpinfo->htype = htons(i);
		arpinfo->bitmask |= EBT_ARP_HTYPE;
		break;

	case ARP_PTYPE:
		check_option(flags, OPT_PTYPE);
		if (check_inverse(optarg))
			arpinfo->invflags |= EBT_ARP_PTYPE;

		if (optind > argc)
			print_error("Missing arp protocol type argument");
		i = strtol(argv[optind - 1], &end, 16);
		if (i < 0 || i >= (0x1 << 16) || *end !='\0') {
			if (!strcasecmp("IPv4", argv[optind - 1]))
				i = 0x0800;
			else
				print_error("Problem with specified arp "
				            "protocol type");
		}
		arpinfo->ptype = htons(i);
		arpinfo->bitmask |= EBT_ARP_PTYPE;
		break;

	case ARP_IP_S:
	case ARP_IP_D:
		if (c == ARP_IP_S) {
			check_option(flags, OPT_IP_S);
			addr = &arpinfo->saddr;
			mask = &arpinfo->smsk;
			arpinfo->bitmask |= EBT_ARP_SRC_IP;
		} else {
			check_option(flags, OPT_IP_D);
			addr = &arpinfo->daddr;
			mask = &arpinfo->dmsk;
			arpinfo->bitmask |= EBT_ARP_DST_IP;
		}
		if (check_inverse(optarg)) {
			if (c == ARP_IP_S)
				arpinfo->invflags |= EBT_ARP_SRC_IP;
			else
				arpinfo->invflags |= EBT_ARP_DST_IP;
		}
		if (optind > argc)
			print_error("Missing ip address argument");
		parse_ip_address(argv[optind - 1], addr, mask);
		break;
	default:
		return 0;
	}
	return 1;
}

static void final_check(const struct ebt_u_entry *entry,
   const struct ebt_entry_match *match, const char *name,
   unsigned int hook_mask, unsigned int time)
{
	if (entry->bitmask & EBT_NOPROTO || entry->bitmask & EBT_802_3 ||
	   (entry->ethproto != ETH_P_ARP && entry->ethproto != ETH_P_RARP))
		print_error("For (R)ARP filtering the protocol must be "
		            "specified as ARP or RARP");
}

// defined in the ebt_ip.c
char *mask_to_dotted(__u32 mask);
static void print(const struct ebt_u_entry *entry,
   const struct ebt_entry_match *match)
{
	struct ebt_arp_info *arpinfo = (struct ebt_arp_info *)match->data;
	int i;

	if (arpinfo->bitmask & EBT_ARP_OPCODE) {
		printf("--arp-op ");
		if (arpinfo->invflags & EBT_ARP_OPCODE)
			printf("! ");
		printf("%d ", ntohs(arpinfo->opcode));
	}
	if (arpinfo->bitmask & EBT_ARP_HTYPE) {
		printf("--arp-htype ");
		if (arpinfo->invflags & EBT_ARP_HTYPE)
			printf("! ");
		printf("%d ", ntohs(arpinfo->htype));
	}
	if (arpinfo->bitmask & EBT_ARP_PTYPE) {
		printf("--arp-ptype ");
		if (arpinfo->invflags & EBT_ARP_PTYPE)
			printf("! ");
		printf("0x%x ", ntohs(arpinfo->ptype));
	}
	if (arpinfo->bitmask & EBT_ARP_SRC_IP) {
		printf("--arp-ip-src ");
		if (arpinfo->invflags & EBT_ARP_SRC_IP)
			printf("! ");
		for (i = 0; i < 4; i++)
			printf("%d%s", ((unsigned char *)&arpinfo->saddr)[i],
			   (i == 3) ? "" : ".");
		printf("%s ", mask_to_dotted(arpinfo->smsk));
	}
	if (arpinfo->bitmask & EBT_ARP_DST_IP) {
		printf("--arp-ip-dst ");
		if (arpinfo->invflags & EBT_ARP_DST_IP)
			printf("! ");
		for (i = 0; i < 4; i++)
			printf("%d%s", ((unsigned char *)&arpinfo->daddr)[i],
			   (i == 3) ? "" : ".");
		printf("%s ", mask_to_dotted(arpinfo->dmsk));
	}
}

static int compare(const struct ebt_entry_match *m1,
   const struct ebt_entry_match *m2)
{
	struct ebt_arp_info *arpinfo1 = (struct ebt_arp_info *)m1->data;
	struct ebt_arp_info *arpinfo2 = (struct ebt_arp_info *)m2->data;

	if (arpinfo1->bitmask != arpinfo2->bitmask)
		return 0;
	if (arpinfo1->invflags != arpinfo2->invflags)
		return 0;
	if (arpinfo1->bitmask & EBT_ARP_OPCODE) {
		if (arpinfo1->opcode != arpinfo2->opcode)
			return 0;
	}
	if (arpinfo1->bitmask & EBT_ARP_HTYPE) {
		if (arpinfo1->htype != arpinfo2->htype)
			return 0;
	}
	if (arpinfo1->bitmask & EBT_ARP_PTYPE) {
		if (arpinfo1->ptype != arpinfo2->ptype)
			return 0;
	}
	if (arpinfo1->bitmask & EBT_ARP_SRC_IP) {
		if (arpinfo1->saddr != arpinfo2->saddr)
			return 0;
		if (arpinfo1->smsk != arpinfo2->smsk)
			return 0;
	}
	if (arpinfo1->bitmask & EBT_ARP_DST_IP) {
		if (arpinfo1->daddr != arpinfo2->daddr)
			return 0;
		if (arpinfo1->dmsk != arpinfo2->dmsk)
			return 0;
	}
	return 1;
}

static struct ebt_u_match arp_match =
{
	EBT_ARP_MATCH,
	sizeof(struct ebt_arp_info),
	print_help,
	init,
	parse,
	final_check,
	print,
	compare,
	opts,
};

static void _init(void) __attribute__ ((constructor));
static void _init(void)
{
	register_match(&arp_match);
}