This general thing has been posted around a fair bit, including here and here.  I don't recommend going to them, because they are long and rambly, but they did help me fix my problem.  I'm going to include the instructions for flashing firmware on linux with tftp, as much so I can remember next time I brick the router.

You will need tftp installed.  These instructions worked on Fedora 17.

First, as root, (sudo -i)

# Stop network manager from messing up our flashing
systemctl stop NetworkManager.service

# Give your computer an ip address
ifconfig eth0 && ifconfig eth0 netmask

# Point it where your router will be
arp -s 02:AA:BB:CC:DD:1A

At this point, you should have your router plugged into the computer, but not powered on. Download an appropriate firmware and, in another non-root terminal
# Your router is always
rexmt 1
timeout 60

put ./wzr-something.enc

Naturally, you need to put in the appropriate filename after 'put'.  Plug in your router after you've entered that command.  After retrying a dozen or so times, it should transfer.  Let the router reboot and enjoy.