Re: [PATCH] RDMA/uverbs: Consider capability of the process that opens the file

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Apr 25, 2025 at 09:01:44AM -0500, Serge E. Hallyn wrote:
> On Fri, Apr 25, 2025 at 10:29:30AM -0300, Jason Gunthorpe wrote:
> > On Fri, Apr 25, 2025 at 01:14:35PM +0000, Parav Pandit wrote:
> > 
> > > 1. In uobject creation syscall, I will add the check current->nsproxy->net->user_ns capability using ns_capable().
> > > And we don't hold any reference for user ns.
> > 
> > This is the thing that makes my head ache.. Is that really the right
> > way to get the user_ns of current? Is it possible that current has
> > multiple user_ns's? We are picking nsproxy because ib_dev has a net
> > namespace affiliation?
> 
> It's not that "current has multiple user_ns's", it's that the various
> resources, including other namespaces, which current has or belongs
> to have associated namespaces.

That seems like splitting nits. Can I do current->XXX->user_ns and get
different answers? Sounds like yes?

> current_user_ns() is the user namespace to which current belongs.
> But if you want to check if it can have privilege over a resource,
> you have to check whether current has ns_capable(resource->userns, CAP_X).

So what is the resource here?

It is definitely not the file descriptor.

Is it the kernel's struct ib_device? It has a netns that is captured
at its creation time.

Jason