USB: properly lock dynamic id list when showing an id

JIRA: https://issues.redhat.com/browse/RHEL-78828

commit 81f5c72
Author: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Wed, 13 Nov 2024 07:49:23 +0100

  When walking the list of dynamic ids for a driver, no lock was being
  held, which meant that an id could be removed or added while the list
  was being iterated.  Fix this up by properly grabing the lock while we
  walk the list.

  Reported-by: Alan Stern <stern@rowland.harvard.edu>
  Cc: linux-usb@vger.kernel.org
  Link: https://lore.kernel.org/r/2024111324-tubby-facecloth-d4a0@gregkh
  Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Desnes Nunes <desnesn@redhat.com>

Author: Desnes Nunes

drivers/usb/core/driver.c

@@ -116,6 +116,7 @@ ssize_t usb_show_dynids(struct usb_dynids *dynids, char *buf)
 	struct usb_dynid *dynid;
 	size_t count = 0;
 
+	guard(mutex)(&usb_dynids_lock);
 	list_for_each_entry(dynid, &dynids->list, node)
 		if (dynid->id.bInterfaceClass != 0)
 			count += scnprintf(&buf[count], PAGE_SIZE - count, "%04x %04x %02x\n",