iface.c File Reference

Network interface and socket setup. More...

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/ether.h>
#include <linux/filter.h>
#include <linux/if_packet.h>
#include <sys/epoll.h>
#include <sys/ioctl.h>
#include "iface.h"
#include "log.h"

Include dependency graph for iface.c:

Functions
static int	validate (struct iface_t *iface)
	Check that a network interface is up and get its MTU. More...
static int	epoll_register (int epfd, struct iface_t *iface)
	Register the skt field of iface with an epoll instance. More...
static u_char *	get_mac (struct iface_t *iface)
	Query the kernel for the MAC address of a network interface. More...
static int	sockopt (struct iface_t *iface)
	Set socket options for the skt field of a struct iface_t. More...
int	iface_init (struct iface_t *ifaces, int epfd)
	Create raw sockets for interfaces in a list and add them to an epoll instance. More...
int	iface_count (struct iface_t *ifaces)
	Count number of items in a list of struct iface_t. More...
int	iface_set_mac (struct iface_t *iface, u_char *src_mac)
	Set the MAC address of a network interface. More...
char *	iface_strmac (u_char *mac)
	Convert a MAC address to a string. More...

Variables
static const u_char	eapol_grp_mac [3][ETH_ALEN]
	EAPOL multicast group MAC addresses. More...
BPF filter for EAPOL packets
Scenario - Create a socket with ETH_P_PAE as the protocol. Set the PACKET_AUXDATA option on the socket. Receive tpacket_auxdata structures with recvmsg(2) that contain 802.1Q tag info. Just kidding! ETH_P_PAE means no tpacket_auxdata structures. Thanks, Linux! Providing our own bpf filter, however, works fine. Note The filter checks bytes 12:13 - after Linux strips out the tag. That's actually convenient. See also socket(7), "Socket options" bpf(2)
static struct sock_filter	eapol_sock_filter []
	A simple bpf filter for EAPOL packets. More...
static const struct sock_fprog	eapol_fprog
	The complete bpf filter program provided to setsockopt(3) More...

Detailed Description

Network interface and socket setup.

Function Documentation

static int validate ( struct iface_t *  iface )

static

Check that a network interface is up and get its MTU.

Also sets the mtu field of iface to the interface's current MTU.

Parameters

iface

Pointer to a struct iface_t representing an interface

Returns

0 if successful, or -1 if unsuccessful

static int epoll_register ( int  epfd, struct iface_t *  iface  )

static

Register the skt field of iface with an epoll instance.

Provide iface itself as the event data, so we know on which interface an EPOLLIN event occurred.

Parameters

epfd	File descriptor for an epoll instance
iface	Pointer to a struct iface_t representing an interface

Returns

0 if successful, or -1 if unsuccessful

static u_char * get_mac ( struct iface_t *  iface )

static

Query the kernel for the MAC address of a network interface.

Parameters

iface

Pointer to a struct iface_t representing an interface

Returns

Pointer to a static buffer containing ETH_ALEN bytes if successful, or NULL if unsuccessful

Note

For this to succeed, the interface must be an Ethernet interface

static int sockopt ( struct iface_t *  iface )

static

Set socket options for the skt field of a struct iface_t.

Attaches a bpf filter for the 802.1X EtherType, sets multicast or promiscuous mode, and requests a PACKET_AUXDATA cmsg from the kernel.

Parameters

iface

Pointer to a struct iface_t representing an interface

Returns

0 if successful, or -1 if unsuccessful

See also

cmsg(3)

int iface_init	(	struct iface_t *	ifaces,
		int	epfd
	)

Create raw sockets for interfaces in a list and add them to an epoll instance.

Also set interface MAC if set-mac was specified in the config file.

Parameters

ifaces	Pointer to a list of struct iface_t structures representing network interfaces
epfd	File descriptor for an epoll instance

Returns

The number of interfaces added to epoll

int iface_count

(

struct iface_t *

ifaces

)

Count number of items in a list of struct iface_t.

Parameters

ifaces

Pointer to a list of struct iface_t structures representing network interfaces

Returns

The length of the list

int iface_set_mac	(	struct iface_t *	iface,
		u_char *	src_mac
	)

Set the MAC address of a network interface.

Parameters

iface	Pointer to a struct iface_t representing an interface
src_mac	Pointer to ETH_ALEN bytes containing a MAC address

Returns

0 if successful, or -1 if unsuccessful

Note

Brings the interface down and back up, invalidating all sockets on it

char* iface_strmac

(

u_char *

mac

)

Convert a MAC address to a string.

Parameters

mac	Pointer to ETH_ALEN bytes containing a MAC address

Returns

Static buffer containing mac converted to a human-readable, colon-delimited MAC address

Note

Like ether_ntoa(3)

See also

ether_ntoa(3)

Variable Documentation

const u_char eapol_grp_mac[3][ETH_ALEN]

static

Initial value:

= {
        { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x00 },         
        { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x03 },         
        { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x0e }          
}

EAPOL multicast group MAC addresses.

See also

IEEE Std 802.1X-2010 §11.1.1

struct sock_filter eapol_sock_filter[]

static

Initial value:

= {
        { 0x28, 0, 0, 0x0000000c },
        { 0x15, 0, 1, 0x0000888e },
        { 0x6, 0, 0, 0xbef001ed },
        { 0x6, 0, 0, 0x00000000 }
}

A simple bpf filter for EAPOL packets.

The tcpdump-style bpf assembly equivalent is:

(000) ldh       [12]
(001) jeq       #0x888e                         jt 2    jf 3
(002) ret       #<decently big nonzero>
(003) ret       #0

const struct sock_fprog eapol_fprog

static

Initial value:

= {
        .len = 4,
        .filter = eapol_sock_filter
}

The complete bpf filter program provided to setsockopt(3)