Remotely triggerable ICMP buffer underwrite in the FreeBSD kernel

>[Feel free to send this to the FreeBSD lists or whatever to get it fixed. I honestly can't be bothered making a throwaway email and going through the subscription process, nor do I want "TheGrandSchlonging" to appear in FreeBSD commit logs.]

Amazing.

Edit: The reporter has been credited as "A reddit user": https://reviews.freebsd.org/rS340260

Since the exploit in question requires non default settings which most people won't use this part is actually far scarier:

> P.S. I recommend setting net.inet.ip.maxfragsperpacket to 0 to prepare for what's coming next.