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SubjectRe: [PATCH review 52/85] sunrpc: Properly encode kuids and kgids in auth.unix.gid rpc pipe upcalls.
"J. Bruce Fields" <> writes:

> On Wed, Feb 13, 2013 at 01:29:35PM -0800, Eric W. Biederman wrote:
>> "J. Bruce Fields" <> writes:
>> > On Wed, Feb 13, 2013 at 09:51:41AM -0800, Eric W. Biederman wrote:
>> >> From: "Eric W. Biederman" <>
>> >>
>> >> 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
>> >>
>> >> 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.

Yes. net->user_ns is the user namespace the network namespace was
created in. And it is the user namespace that is used in test
like ns_capable(net->user_ns, CAP_NET_ADMIN) to see if you are allowed
to manipulate the network namespace. So looks like exactly what we
want for that cache.

Could you double check my understanding of the code?

I want to be certain that I can't _yet_ start an sunrpc server process
outside of the initial user namespace. While writing an earlier reply I
realized that I hadn't thought about where sunrpc server processes come

Reading through the code it looks like we can have nfs mounts outside of
the initial network namespace. But because they are mounts they are
still limited to the initial user namespace.

Now looking at the nfs server, seems to be hard coded to only start
in the initial network namespace despite almost having support for
starting in more.

Even more the nfs server is controlled and started through the "nfsd"
filesystem. Which has to be mounted before you can start the server.
So you can only start the server through a mount in the initial user

lockd is started by either the nfs server or the nfs client.

There are no other sunrpc servers in the kernel.

I think all of that is enough to reasonably claim that you can't have
any sunrpc server processes outside of the initial user namespace. But
if I am wrong I would to find an appropriate spot to put in a line
that says:
if (current_user_ns() != &init_user)


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