Executive brief
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nfnetlink_log: cope with concurrent instance destruction
Instances are refcounted. However, only memory release happens on the 1 -> 0 transition; the unlink from hashes can occur with any refcount.
Uncooperative userspace can force a situation where a queue is pending for destruction from netlink event while a different socket with same portid processes an UNBIND request.
With right timing, this will unhash the instance again:
Oops: general protection fault, [..] Call Trace: <TASK> nfulnl_recv_config+0x31a/0xd50 nfnetlink_rcv_msg+0x7c2/0xeb0