On Tue, Jun 22, 2021 at 07:16:34PM +0200, Greg KH wrote:

On Tue, Jun 22, 2021 at 09:32:08AM -0700, Luis Chamberlain wrote:

quoted

On Tue, Jun 22, 2021 at 09:45:39AM +0200, Greg KH wrote:

quoted

On Mon, Jun 21, 2021 at 04:36:34PM -0700, Luis Chamberlain wrote:

quoted

@@ -2048,13 +2048,19 @@ static ssize_t hot_add_show(struct class *class,
 {
 	int ret;
 
+	if (!try_module_get(THIS_MODULE))
+		return -ENODEV;
+

You can not increment/decrement your own module's reference count and
expect it to work properly, as it is still a race.

The goal here is to prevent an rmmod call if this succeeds. If it
succeeds then any subsequent rmmod will fail. Can you explain how
this is still racy?

{sigh}

What happens if the driver core is just about to call hot_add_show() and
the module is removed from the system.  It then calls to the memory
location that hot_add_show() was previously at, but now that is not a
valid pointer to code, and boom.

The new kobject_get() on patch 3/3 ensures that the device will be up
throughout the entire life of the store call, and thus prevent the
code being executed being removed, no?

  Luis