firmware_class: make sure fw requests contain a name

commit 471b095d upstream.

An empty firmware request name will trigger warnings when building
device names. Make sure this is caught earlier and rejected.

The warning was visible via the test_firmware.ko module interface:

echo -ne "\x00" > /sys/devices/virtual/misc/test_firmware/trigger_request
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

drivers/base/firmware_class.c

@@ -1063,6 +1063,9 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
 	if (!firmware_p)
 		return -EINVAL;
 
+	if (!name || name[0] == '\0')
+		return -EINVAL;
+
 	ret = _request_firmware_prepare(&fw, name, device);
 	if (ret <= 0) /* error or already assigned */
 		goto out;