net: rswitch: Avoid use-after-free in rswitch_poll()

Vulnerability Description

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 rswitch_tx_free(), which is inlined in rswitch_poll(). Since `skb` and `gq->skbs[gq->dirty]` are in fact the same pointer, the skb is first freed using dev_kfree_skb_any(), 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.

References

• https://git.kernel.org/stable/c/4a41bb9f2b402469d425a1c13359d3b3ea4e6403
• https://git.kernel.org/stable/c/92cbbe7759193e3418f38d0d73f8fe125312c58b
• https://git.kernel.org/stable/c/9a0c28efeec6383ef22e97437616b920e7320b67