randomize_mac_address.sh

gistfile1.sh

#!/bin/sh

#
# randomize the WAN mac address on a DD-WRT based router, save it to nvram
# then restart. this was a bit of a challenge since $RANDOM doesn't exist,
# and none of the standard GNU random utilities are installed by default.
# 
# this isn't bash. it's like going back to 1978. ;)
#
# i'm sure this could be written to be more efficient. not really a huge
# concern, since this only runs once every few days, if that often.
#
# use full paths, since there's no guarantee our PATH will be valid or
# exist if this runs outside of a user shell
#
# put this in /jffs or in /opt if you've got memory backing. this reboots
# the router, so you're going to lose any changes made anywhere else on
# the file system.
#

randnum() {
	/bin/grep -m1 -ao "[0-9]" /dev/urandom | /usr/bin/head -n1
}

get_octet() {
	R1=-1
	R2=-1
	R3=-1
	while [[ $R1 -lt 0 || $R1 -gt 2 ]]; do
		R1=$( randnum 2 )
	done
	if [[ $R1 == 2 ]]; then
		MAXR2=5
	else
		MAXR2=9
	fi
	while [[ $R2 -lt 0 || $R2 -gt $MAXR2 ]]; do
		R2=$( randnum $MAXR2 )
	done

	if [[ $R1 == 2 && $R2 == 5 ]]; then
		MAXR3=4
	else
		MAXR3=9
	fi
	while [[ $R3 -lt 0 || $R3 -gt $MAXR3 ]]; do
		R3=$( randnum $MAXR3 )
	done

	if [[ $R1 != 0 ]]; then
		OUT=$R1
	fi
	if [[ $R1 != 0 && $R2 != 0 ]]; then
		OUT=${OUT}${R2}
	fi
	OUT=${OUT}$R3

	/bin/echo -n $OUT

}

old_mac="$( /usr/sbin/nvram get def_hwaddr )"
O1=$( get_octet )
O2=$( get_octet )
O3=$( get_octet )
old_mac_prefix="$( /bin/echo $old_mac | /usr/bin/cut -d ":" -f 1-3 )"

new_mac=$( /usr/bin/printf "%s:%02X:%02X:%02X" $old_mac_prefix $O1 $O2 $O3 )

echo "###"
echo "###"
echo "### Changing WAN MAC to: $new_mac"
echo "###"
echo "###"
echo ""
echo "Ctrl-C within 10 seconds to abort..."
sleep 10
echo ""
echo "Setting new MAC and rebooting."

/usr/sbin/nvram set def_hwaddr=$new_mac
/usr/sbin/nvram commit

/bin/sync
/bin/sync
/bin/sync

echo "Bye... see you in 2 minutes"

/sbin/reboot