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/*
* Copyright (C) 2010 Martin Willi
* Copyright (C) 2010 revosec AG
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
*
* 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 General Public License
* for more details.
*/
#include "farp_spoofer.h"
#include <errno.h>
#include <unistd.h>
#include <sys/socket.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/filter.h>
#include <sys/ioctl.h>
#include <daemon.h>
#include <threading/thread.h>
#include <processing/jobs/callback_job.h>
typedef struct private_farp_spoofer_t private_farp_spoofer_t;
/**
* Private data of an farp_spoofer_t object.
*/
struct private_farp_spoofer_t {
/**
* Public farp_spoofer_t interface.
*/
farp_spoofer_t public;
/**
* Listener that knows active addresses
*/
farp_listener_t *listener;
/**
* RAW socket for ARP requests
*/
int skt;
};
/**
* IP over Ethernet ARP message
*/
typedef struct __attribute__((packed)) {
u_int16_t hardware_type;
u_int16_t protocol_type;
u_int8_t hardware_size;
u_int8_t protocol_size;
u_int16_t opcode;
u_int8_t sender_mac[6];
u_int8_t sender_ip[4];
u_int8_t target_mac[6];
u_int8_t target_ip[4];
} arp_t;
/**
* Send faked ARP response
*/
static void send_arp(private_farp_spoofer_t *this,
arp_t *arp, struct sockaddr_ll *addr)
{
struct ifreq req;
char tmp[4];
req.ifr_ifindex = addr->sll_ifindex;
if (ioctl(this->skt, SIOCGIFNAME, &req) == 0 &&
ioctl(this->skt, SIOCGIFHWADDR, &req) == 0 &&
req.ifr_hwaddr.sa_family == ARPHRD_ETHER)
{
memcpy(arp->target_mac, arp->sender_mac, 6);
memcpy(arp->sender_mac, req.ifr_hwaddr.sa_data, 6);
memcpy(tmp, arp->sender_ip, 4);
memcpy(arp->sender_ip, arp->target_ip, 4);
memcpy(arp->target_ip, tmp, 4);
arp->opcode = htons(ARPOP_REPLY);
sendto(this->skt, arp, sizeof(*arp), 0,
(struct sockaddr*)addr, sizeof(*addr));
}
}
/**
* ARP request receiving
*/
static bool receive_arp(private_farp_spoofer_t *this)
{
struct sockaddr_ll addr;
socklen_t addr_len = sizeof(addr);
arp_t arp;
ssize_t len;
host_t *local, *remote;
len = recvfrom(this->skt, &arp, sizeof(arp), MSG_DONTWAIT,
(struct sockaddr*)&addr, &addr_len);
if (len == sizeof(arp))
{
local = host_create_from_chunk(AF_INET,
chunk_create((char*)&arp.sender_ip, 4), 0);
remote = host_create_from_chunk(AF_INET,
chunk_create((char*)&arp.target_ip, 4), 0);
if (this->listener->has_tunnel(this->listener, local, remote))
{
send_arp(this, &arp, &addr);
}
local->destroy(local);
remote->destroy(remote);
}
return TRUE;
}
METHOD(farp_spoofer_t, destroy, void,
private_farp_spoofer_t *this)
{
lib->watcher->remove(lib->watcher, this->skt);
close(this->skt);
free(this);
}
/**
* See header
*/
farp_spoofer_t *farp_spoofer_create(farp_listener_t *listener)
{
private_farp_spoofer_t *this;
struct sock_filter arp_request_filter_code[] = {
BPF_STMT(BPF_LD+BPF_H+BPF_ABS, offsetof(arp_t, protocol_type)),
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, ETH_P_IP, 0, 9),
BPF_STMT(BPF_LD+BPF_B+BPF_ABS, offsetof(arp_t, hardware_size)),
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 6, 0, 7),
BPF_STMT(BPF_LD+BPF_B+BPF_ABS, offsetof(arp_t, protocol_size)),
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 4, 0, 4),
BPF_STMT(BPF_LD+BPF_H+BPF_ABS, offsetof(arp_t, opcode)),
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, ARPOP_REQUEST, 0, 3),
BPF_STMT(BPF_LD+BPF_W+BPF_LEN, 0),
BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, sizeof(arp_t), 0, 1),
BPF_STMT(BPF_RET+BPF_K, sizeof(arp_t)),
BPF_STMT(BPF_RET+BPF_K, 0),
};
struct sock_fprog arp_request_filter = {
sizeof(arp_request_filter_code) / sizeof(struct sock_filter),
arp_request_filter_code,
};
INIT(this,
.public = {
.destroy = _destroy,
},
.listener = listener,
);
this->skt = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ARP));
if (this->skt == -1)
{
DBG1(DBG_NET, "opening ARP packet socket failed: %s", strerror(errno));
free(this);
return NULL;
}
if (setsockopt(this->skt, SOL_SOCKET, SO_ATTACH_FILTER,
&arp_request_filter, sizeof(arp_request_filter)) < 0)
{
DBG1(DBG_NET, "installing ARP packet filter failed: %s", strerror(errno));
close(this->skt);
free(this);
return NULL;
}
lib->watcher->add(lib->watcher, this->skt, WATCHER_READ,
(watcher_cb_t)receive_arp, this);
return &this->public;
}
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