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

[Serge E. Hallyn]

On Fri, Apr 04, 2025 at 12:13:47PM -0300, Jason Gunthorpe wrote:
> On Fri, Apr 04, 2025 at 02:53:30PM +0000, Parav Pandit wrote:
> > To summarize,
> > 
> > 1. A process can open an RDMA resource (such as a raw QP, raw flow entry, or similar 'raw' resource)
> > through the fd using ioctl(), if it has the appropriate capability, which in this case is CAP_NET_RAW.
> > This is similar to a process that opens a raw socket.
> > 
> > 2. Given that RDMA uses ioctl() for resource creation, there isn't a security concern surrounding
> > the read()/write() system calls.
> > 
> > 3. If process A, which does not have CAP_NET_RAW, passes the opened fd to another privileged
> > process B, which has CAP_NET_RAW, process B can open the raw RDMA resource.
> > This is still within the kernel-defined security boundary, similar to a raw socket.
> > 
> > 4. If process A, which has the CAP_NET_RAW capability, passes the file descriptor to Process B, which does not have CAP_NET_RAW, Process B will not be able to open the raw RDMA resource.
> > 
> > Do we agree on this Eric?
> 
> This is our model, I consider it uAPI, so I don't belive we can change
> it without an extreme reason..
> 
> > 5. the process's capability check should be done in the right user namespace.
> > (instead of current in default user ns).
> > The right user namespace is the one which created the net namespace.
> > This is because rdma networking resources are governed by the net namespace.
> 
> This all makes my head hurt. The right user namespace is the one that
> is currently active for the invoking process, I couldn't understand
> why we have net namespaces refer to user namespaces :\

A user at any time can create a new user namespace, without creating a
new network namespace, and have privilege in that user namespace, over
resources owned by the user namespace.

So if a user can create a new user namespace, then say "hey I have
CAP_NET_ADMIN over current_user_ns, so give me access to the RDMA
resources belonging to my current_net_ns", that's a problem.

So that's why the check should be ns_capable(device->net->user-ns, CAP_NET_ADMIN)
and not ns_capable(current_user_ns, CAP_NET_ADMIN).

-serge