CVE-2021-47232

In the Linux kernel, the following vulnerability has been resolved:

can: j1939: fix Use-after-Free, hold skb ref while in use

This patch fixes a Use-after-Free found by the syzbot.

The problem is that a skb is taken from the per-session skb queue,
without incrementing the ref count. This leads to a Use-after-Free if
the skb is taken concurrently from the session queue due to a CTS.