CVE-2022-49975

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

bpf: Don't redirect packets with invalid pkt_len

Syzbot found an issue [1]: fqcodeldrop() try to drop a flow whitout any skbs, that is, the flow->head is null. The root cause, as the [2] says, is because that bpfprogtestrunskb() run a bpf prog which redirects empty skbs. So we should determine whether the length of the packet modified by bpf prog or others like bpfprogtest is valid before forwarding it directly.