In the Linux kernel, the following vulnerability has been resolved:
net: rswitch: Avoid use-after-free in rswitch_poll()
The use-after-free is actually in rswitchtxfree(), which is inlined in
rswitchpoll(). Since skb
and gq->skbs[gq->dirty]
are in fact the
same pointer, the skb is first freed using devkfreeskbany(), then the
value in skb->len is used to update the interface statistics.
Let's move around the instructions to use skb->len before the skb is freed.
This bug is trivial to reproduce using KFENCE. It will trigger a splat every few packets. A simple ARP request or ICMP echo request is enough.