clk: check ops pointer on clock register

Nothing really prevents a provider from (trying to) register a clock
without providing the clock ops structure.

We do check the individual fields before using them, but not the
structure pointer itself. This may have the usual nasty consequences when
the pointer is dereferenced, most likely when checking one the field
during the initialization.

This is fixed by returning an error on clock register if the ops pointer
is NULL.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20171219083329.24746-1-jbrunet@baylibre.com

drivers/clk/clk.c

@@ -2678,7 +2678,13 @@ struct clk *clk_register(struct device *dev, struct clk_hw *hw)
 		ret = -ENOMEM;
 		goto fail_name;
 	}
+
+	if (WARN_ON(!hw->init->ops)) {
+		ret = -EINVAL;
+		goto fail_ops;
+	}
 	core->ops = hw->init->ops;
+
 	if (dev && pm_runtime_enabled(dev))
 		core->dev = dev;
 	if (dev && dev->driver)
@@ -2740,6 +2746,7 @@ fail_parent_names_copy:
 		kfree_const(core->parent_names[i]);
 	kfree(core->parent_names);
 fail_parent_names:
+fail_ops:
 	kfree_const(core->name);
 fail_name:
 	kfree(core);