Re: [PATCH v11 4/7] iommufd: Use iommufd_access_change_ioas in iommufd_access_destroy_object

[Jason Gunthorpe]

On Thu, Jul 27, 2023 at 11:33:26PM -0700, Nicolin Chen wrote:
> Update the unprotect routine in iommufd_access_destroy_object() to calling
> the new iommufd_access_change_ioas() helper. This will reduce some risk of
> race condition with another concurrent iommufd_access_replace/detach call.
> 
> Note that the behavior of this function call is changed: a WARN_ON will be
> triggered by a -EBUSY return code if there is another ongoing detach.

This should be completely impossible, at this point the object must
have a refcount of 0 so if another thread is concurrently detaching it
we are already UAFing.

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason