usb: gadget: f_rndis: Protect RNDIS options with mutex

The class/subclass/protocol options are suspectible to race conditions
as they can be accessed concurrently through configfs.

Use existing mutex to protect these options. This issue was identified
during code inspection.

Fixes: 73517cf ("usb: gadget: add RNDIS configfs options for class/subclass/protocol")
Cc: stable@vger.kernel.org
Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://patch.msgid.link/20260320-usb-net-lifecycle-v1-2-4886b578161b@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Kuen-Han Tsai

drivers/usb/gadget/function/f_rndis.c

@@ -11,6 +11,7 @@
 
 /* #define VERBOSE_DEBUG */
 
+#include <linux/cleanup.h>
 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -678,9 +679,11 @@ rndis_bind(struct usb_configuration *c, struct usb_function *f)
 			return -ENOMEM;
 	}
 
-	rndis_iad_descriptor.bFunctionClass = rndis_opts->class;
-	rndis_iad_descriptor.bFunctionSubClass = rndis_opts->subclass;
-	rndis_iad_descriptor.bFunctionProtocol = rndis_opts->protocol;
+	scoped_guard(mutex, &rndis_opts->lock) {
+		rndis_iad_descriptor.bFunctionClass = rndis_opts->class;
+		rndis_iad_descriptor.bFunctionSubClass = rndis_opts->subclass;
+		rndis_iad_descriptor.bFunctionProtocol = rndis_opts->protocol;
+	}
 
 	/*
 	 * in drivers/usb/gadget/configfs.c:configfs_composite_bind()