bpf: Do not dereference user pointer in bpf_test_finish().

Instead, pass the kattr in which has a kernel side copy of this
data structure from userspace already.

Fix based upon a suggestion from Alexei Starovoitov.

Signed-off-by: David S. Miller <[e-mail]>
Acked-by: Daniel Borkmann <[e-mail]>

net/bpf/test_run.c

···
 	return ret;
 }
 
-static int bpf_test_finish(union bpf_attr __user *uattr, const void *data,
+static int bpf_test_finish(const union bpf_attr *kattr,
+			   union bpf_attr __user *uattr, const void *data,
 			   u32 size, u32 retval, u32 duration)
 {
-	void __user *data_out = u64_to_user_ptr(uattr->test.data_out);
+	void __user *data_out = u64_to_user_ptr(kattr->test.data_out);
 	int err = -EFAULT;
 
 	if (data_out && copy_to_user(data_out, data, size))
···
 	/* bpf program can never convert linear skb to non-linear */
 	if (WARN_ON_ONCE(skb_is_nonlinear(skb)))
 		size = skb_headlen(skb);
-	ret = bpf_test_finish(uattr, skb->data, size, retval, duration);
+	ret = bpf_test_finish(kattr, uattr, skb->data, size, retval, duration);
 	kfree_skb(skb);
 	return ret;
 }
···
 	retval = bpf_test_run(prog, &xdp, repeat, &duration);
 	if (xdp.data != data + XDP_PACKET_HEADROOM)
 		size = xdp.data_end - xdp.data;
-	ret = bpf_test_finish(uattr, xdp.data, size, retval, duration);
+	ret = bpf_test_finish(kattr, uattr, xdp.data, size, retval, duration);
 	kfree(data);
 	return ret;
 }