Re: [PATCH] iommufd: Reject opens until module initialization succeeds

[Jason Gunthorpe]

On Thu, Oct 29, 2026 at 09:23:45PM -0700, Kyle Zeng wrote:
> iommufd_init() publishes /dev/iommu before registering the optional
> /dev/vfio/vfio compatibility node and running the optional self-test
> initialization. Either later operation can fail. Since file operations
> can acquire a reference to a COMING module, an already-open file can
> survive the failed initialization and refer to freed iommufd module
> memory.

What? This seems like a core bug not iommufd.

files take refcounts on their modules when they open via this:

static const struct file_operations iommufd_fops = {
	.owner = THIS_MODULE,

If the module hasn't even loaded yet I would rather expect the core
code to not allow the module refcount to be taken, and if it somehow
succeeds then it shouldn't allow the module to get yanked out from
under it.

It is hard to guess what crashes to be more specific, but
at least misc_deregister() is safe while files are open.

Though I wonder how module auto loading works..

Jason