Re: [PATCH] NFSv4: use unique client identifiers in network namespaces

[Trond Myklebust <trondmy@hammerspace.com>]

On Tue, 2022-02-08 at 15:03 -0500, Benjamin Coddington wrote:
> In order to differentiate client state, assign a random uuid to the
> uniquifing portion of the client identifier when a network namespace
> is
> created.  Containers may still override this value if they wish to
> maintain
> stable client identifiers by writing to
> /sys/fs/nfs/net/client/identifier,
> either by udev rules or other means.
> 
> Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
> ---
>  fs/nfs/sysfs.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/fs/nfs/sysfs.c b/fs/nfs/sysfs.c
> index 8cb70755e3c9..9b811323fd7f 100644
> --- a/fs/nfs/sysfs.c
> +++ b/fs/nfs/sysfs.c
> @@ -167,6 +167,18 @@ static struct nfs_netns_client
> *nfs_netns_client_alloc(struct kobject *parent,
>         return NULL;
>  }
>  
> +static void assign_unique_clientid(struct nfs_netns_client *clp)
> +{
> +       unsigned char client_uuid[16];
> +       char *uuid_str = kmalloc(UUID_STRING_LEN + 1, GFP_KERNEL);
> +
> +       if (uuid_str) {
> +               generate_random_uuid(client_uuid);
> +               sprintf(uuid_str, "%pU", client_uuid);
> +               rcu_assign_pointer(clp->identifier, uuid_str);
> +       }
> +}
> +
>  void nfs_netns_sysfs_setup(struct nfs_net *netns, struct net *net)
>  {
>         struct nfs_netns_client *clp;
> @@ -174,6 +186,8 @@ void nfs_netns_sysfs_setup(struct nfs_net *netns,
> struct net *net)
>         clp = nfs_netns_client_alloc(nfs_client_kobj, net);
>         if (clp) {
>                 netns->nfs_client = clp;
> +               if (net != &init_net)
> +                       assign_unique_clientid(clp);

Why shouldn't this go in nfs_netns_client_alloc? At this point you've
already published the pointer in netns, so you're prone to races.

Also, why the exclusion of init_net?

>                 kobject_uevent(&clp->kobject, KOBJ_ADD);
>         }
>  }

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com