bpf: expose prog id for cls_bpf and act_bpf

In order to be able to retrieve the attached programs from cls_bpf
and act_bpf, we need to expose the prog ids via netlink so that
an application can later on get an fd based on the id through the
BPF_PROG_GET_FD_BY_ID command, and dump related prog info via
BPF_OBJ_GET_INFO_BY_FD command for bpf(2).

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_bpf.c

@@ -566,6 +566,9 @@ static int cls_bpf_dump_ebpf_info(const struct cls_bpf_prog *prog,
 	    nla_put_string(skb, TCA_BPF_NAME, prog->bpf_name))
 		return -EMSGSIZE;
 
+	if (nla_put_u32(skb, TCA_BPF_ID, prog->filter->aux->id))
+		return -EMSGSIZE;
+
 	nla = nla_reserve(skb, TCA_BPF_TAG, sizeof(prog->filter->tag));
 	if (nla == NULL)
 		return -EMSGSIZE;