net: act_bpf: fix size mismatch on filter preparation

Similarly as in cls_bpf, also this code needs to reject mismatches.

Reference: http://article.gmane.org/gmane.linux.network/347406
Fixes: d23b8ad8 ("tc: add BPF based action")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_bpf.c

@@ -122,6 +122,9 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
 		return -EINVAL;
 
 	bpf_size = bpf_num_ops * sizeof(*bpf_ops);
+	if (bpf_size != nla_len(tb[TCA_ACT_BPF_OPS]))
+		return -EINVAL;
+
 	bpf_ops = kzalloc(bpf_size, GFP_KERNEL);
 	if (!bpf_ops)
 		return -ENOMEM;