cls_cgroup: Fix oops when user send improperly 'tc filter add' request

I found a bug in cls_cgroup_change() in cls_cgroup.c.
cls_cgroup_change() expected tca[TCA_OPTIONS] was set from user space properly,
but tc in iproute2-2.6.29-1 (which I used) didn't set it.

In the current source code of tc in git, it set tca[TCA_OPTIONS].

git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git

If we always use a newest iproute2 in git when we use cls_cgroup,
we don't face this oops probably.
But I think, kernel shouldn't panic regardless of use program's behaviour.

Signed-off-by: Minoru Usui <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/sched/cls_cgroup.c

···
 	struct tcf_exts e;
 	int err;
 
+	if (!tca[TCA_OPTIONS])
+		return -EINVAL;
+
 	if (head == NULL) {
 		if (!handle)
 			return -EINVAL;