[PATCH review 52/85] sunrpc: Properly encode kuids and kgids in auth.unix.gid rpc pipe upcalls.

[J. Bruce Fields]

On Wed, Feb 13, 2013 at 01:29:35PM -0800, Eric W. Biederman wrote:
> "J. Bruce Fields" <bfields at fieldses.org> writes:
> 
> > On Wed, Feb 13, 2013 at 09:51:41AM -0800, Eric W. Biederman wrote:
> >> From: "Eric W. Biederman" <ebiederm at xmission.com>
> >> 
> >> When a new rpc connection is established with an in-kernel server, the
> >> traffic passes through svc_process_common, and svc_set_client and down
> >> into svcauth_unix_set_client if it is of type RPC_AUTH_NULL or
> >> RPC_AUTH_UNIX.
> >> 
> >> svcauth_unix_set_client then looks at the uid of the credential we
> >> have assigned to the incomming client and if we don't have the groups
> >> already cached makes an upcall to get a list of groups that the client
> >> can use.
> >> 
> >> The upcall encodes send a rpc message to user space encoding the uid
> >> of the user whose groups we want to know.  Encode the kuid of the user
> >> in the initial user namespace as nfs mounts can only happen today in
> >> the initial user namespace.
> >
> > OK, I didn't know that.
> >
> > (Though I'm unclear how it should matter to the server what user
> > namespace the client is in?)
> 
> Perhaps I have the description a little scrambled.  The short version
> is that to start I only support the initial network namespace.
> 
> If I haven't succeeded it is my intent to initially limit the servers
> to the initial user namespace as well.  I should see if I can figure
> that out.
> 
> >> When a reply to an upcall comes in convert interpret the uid and gid values
> >> from the rpc pipe as uids and gids in the initial user namespace and convert
> >> them into kuids and kgids before processing them further.
> >> 
> >> When reading proc files listing the uid to gid list cache convert the
> >> kuids and kgids from into uids and gids the initial user namespace.  As we are
> >> displaying server internal details it makes sense to display these values
> >> from the servers perspective.
> >
> > All of these caches are already per-network-namespace.  Ideally wouldn't
> > we also like to associate a user namespace with each cache somehow?
> 
> Ideally yes.  I read through the caches enough to figure out where there
> user space interfaces were, and to make certain we had conversions
> to/from kuids and kgids.
> 
> I haven't looked at what user namespace makes sense for these
> caches.  For this cache my first guess is that net->user_ns
> is what we want as it will be shared by all users in network namespace I
> presume.

Oh, I didn't know about net->user_ns--so each network namespace is
associated with a single user namespace, great, that simplifies life.
Yes, that sounds exactly right.

--b.