Input: uinput - sanity check on ff_effects_max and EV_FF

Currently the user can set ff_effects_max to zero with the EV_FF bit (and
the FF_GAIN and/or FF_AUTOCENTER bits) set, in this case the uninitialized
methods ff->set_gain and/or ff->set_autocenter can be dereferenced,
resulting in a kernel oops.

Check in uinput_create_device() and print a helpful message and return
-EINVAL in case the check fails.

Signed-off-by: Elias Vanderstuyft <elias.vds@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/misc/uinput.c

@@ -272,6 +272,13 @@ static int uinput_create_device(struct uinput_device *udev)
 		input_set_events_per_packet(dev, 60);
 	}
 
+	if (test_bit(EV_FF, dev->evbit) && !udev->ff_effects_max) {
+		printk(KERN_DEBUG "%s: ff_effects_max should be non-zero when FF_BIT is set\n",
+			UINPUT_NAME);
+		error = -EINVAL;
+		goto fail1;
+	}
+
 	if (udev->ff_effects_max) {
 		error = input_ff_create(dev, udev->ff_effects_max);
 		if (error)