I guess a binpatch is better late than never.
Quote from the henning@'s commit message:
MFC, initial fix by Chris Cappucino, more complete fix by me: make sure users of rtlabel_id2name() can deal with no label present, by not calling it when the label id is 0 (initial fix) and also checking for rtlabel_id2name() returning NULL (complete fix). original rtlabel code had that all right, the newer rtlabel bound to an interface code not. impact: local users can cause a kernel panic by using the SIOCGIFRTLABEL ioctl on interfaces with no route label assigned.
I've made binpatches for i386, amd64 and sparc64.