/*

  fakeif - Sets the apparent hardware address of a network interface

  To compile: 
              gcc -shared -o fakeif.so fakeif.c

  To run: 

              HWADDR_eth0=11:22:33:44:55:66 export HWADDR_eth0
              LD_PRELOAD=/path/to/fakeif.so program args...

*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/syscall.h>
#include <netinet/in.h>
#include <linux/sockios.h>
#include <net/if.h>
#include <string.h>
#include <errno.h>

#define __NR_real_ioctl  __NR_ioctl

static inline _syscall3(int,real_ioctl,int,fd,unsigned int,cmd,unsigned long,arg);

int ioctl(int fd, unsigned int cmd, unsigned long arg)
{
	char var[IFNAMSIZ+8], *endptr;
	const char *hwtxt, *ptr;
	struct ifreq *req=(struct ifreq *)arg;
	unsigned char hwaddr[6]={0,0,0,0,0,0};
	int byte;

	if (cmd!=SIOCGIFHWADDR) goto out;

	sprintf(var, "HWADDR_%.*s", IFNAMSIZ, req->ifr_name);
	if (!(ptr=hwtxt=getenv(var))) goto out;
	
	for (byte=0; byte<6; byte++)
	{
		unsigned long l=strtoul(ptr, &endptr, 16);
		hwaddr[byte]=l;
		if (ptr==endptr || l>255) goto fail;
		ptr=endptr;
		if (*ptr==':' || *ptr=='-') ptr++;
	}
	if (*endptr) goto fail;
	memcpy(&req->ifr_hwaddr.sa_data, hwaddr, 6);
	return 0;
 fail:
	fprintf(stderr, "fakeif: WARNING: %s is invalid (%s)\n", var, hwtxt);
 out:
	return real_ioctl(fd, cmd, arg);
}