platform/chrome: cros_ec_chardev: fix kernel data leak from ioctl

It is possible to peep kernel page's data by providing larger `insize`
in struct cros_ec_command[1] when invoking EC host commands.

Fix it by using zeroed memory.

[1]: https://elixir.bootlin.com/linux/v6.2/source/include/linux/platform_data/cros_ec_proto.h#L74

Fixes: eda2e30c ("mfd / platform: cros_ec: Miscellaneous character device to talk with the EC")
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Link: https://lore.kernel.org/r/20230324010658.1082361-1-tzungbi@kernel.org

drivers/platform/chrome/cros_ec_chardev.c

@@ -284,7 +284,7 @@ static long cros_ec_chardev_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg)
 	    u_cmd.insize > EC_MAX_MSG_BYTES)
 		return -EINVAL;
 
-	s_cmd = kmalloc(sizeof(*s_cmd) + max(u_cmd.outsize, u_cmd.insize),
+	s_cmd = kzalloc(sizeof(*s_cmd) + max(u_cmd.outsize, u_cmd.insize),
 			GFP_KERNEL);
 	if (!s_cmd)
 		return -ENOMEM;