nfs: implement client support for NFS_LOCALIO_PROGRAM

The LOCALIO auxiliary RPC protocol consists of a single "UUID_IS_LOCAL"
RPC method that allows the Linux NFS client to verify the local Linux
NFS server can see the nonce (single-use UUID) the client generated and
made available in nfs_common for subsequent lookup and verification
by the NFS server.  If matched, the NFS server populates members in the
nfs_uuid_t struct.  The NFS client then transfers these nfs_uuid_t
struct member pointers to the nfs_client struct and cleans up the
nfs_uuid_t struct.  See: fs/nfs/localio.c:nfs_local_probe()

This protocol isn't part of an IETF standard, nor does it need to be
considering it is Linux-to-Linux auxiliary RPC protocol that amounts
to an implementation detail.

Localio is only supported when UNIX-style authentication (AUTH_UNIX, aka
AUTH_SYS) is used (enforced by fs/nfs/localio.c:nfs_local_probe()).

The UUID_IS_LOCAL method encodes the client generated uuid_t in terms of
the fixed UUID_SIZE (16 bytes).  The fixed size opaque encode and decode
XDR methods are used instead of the less efficient variable sized
methods.

Having a nonce (single-use uuid) is better than using the same uuid
for the life of the server, and sending it proactively by client
rather than reactively by the server is also safer.

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Co-developed-by: NeilBrown <neilb@suse.de>
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

Author: Mike Snitzer

fs/nfs/client.c

@@ -434,8 +434,10 @@ struct nfs_client *nfs_get_client(const struct nfs_client_initdata *cl_init)
 			list_add_tail(&new->cl_share_link,
 					&nn->nfs_client_list);
 			spin_unlock(&nn->nfs_client_lock);
-			nfs_local_probe(new);
-			return rpc_ops->init_client(new, cl_init);
+			new = rpc_ops->init_client(new, cl_init);
+			if (!IS_ERR(new))
+				 nfs_local_probe(new);
+			return new;
 		}
 
 		spin_unlock(&nn->nfs_client_lock);

fs/nfs/localio.c

@@ -51,17 +51,77 @@ static void nfs_local_fsync_work(struct work_struct *work);
 static bool localio_enabled __read_mostly = true;
 module_param(localio_enabled, bool, 0644);
 
+static inline bool nfs_client_is_local(const struct nfs_client *clp)
+{
+	return !!test_bit(NFS_CS_LOCAL_IO, &clp->cl_flags);
+}
+
 bool nfs_server_is_local(const struct nfs_client *clp)
 {
-	return test_bit(NFS_CS_LOCAL_IO, &clp->cl_flags) != 0 &&
-		localio_enabled;
+	return nfs_client_is_local(clp) && localio_enabled;
 }
 EXPORT_SYMBOL_GPL(nfs_server_is_local);
 
+/*
+ * UUID_IS_LOCAL XDR functions
+ */
+
+static void localio_xdr_enc_uuidargs(struct rpc_rqst *req,
+				     struct xdr_stream *xdr,
+				     const void *data)
+{
+	const u8 *uuid = data;
+
+	encode_opaque_fixed(xdr, uuid, UUID_SIZE);
+}
+
+static int localio_xdr_dec_uuidres(struct rpc_rqst *req,
+				   struct xdr_stream *xdr,
+				   void *result)
+{
+	/* void return */
+	return 0;
+}
+
+static const struct rpc_procinfo nfs_localio_procedures[] = {
+	[LOCALIOPROC_UUID_IS_LOCAL] = {
+		.p_proc = LOCALIOPROC_UUID_IS_LOCAL,
+		.p_encode = localio_xdr_enc_uuidargs,
+		.p_decode = localio_xdr_dec_uuidres,
+		.p_arglen = XDR_QUADLEN(UUID_SIZE),
+		.p_replen = 0,
+		.p_statidx = LOCALIOPROC_UUID_IS_LOCAL,
+		.p_name = "UUID_IS_LOCAL",
+	},
+};
+
+static unsigned int nfs_localio_counts[ARRAY_SIZE(nfs_localio_procedures)];
+static const struct rpc_version nfslocalio_version1 = {
+	.number			= 1,
+	.nrprocs		= ARRAY_SIZE(nfs_localio_procedures),
+	.procs			= nfs_localio_procedures,
+	.counts			= nfs_localio_counts,
+};
+
+static const struct rpc_version *nfslocalio_version[] = {
+       [1]			= &nfslocalio_version1,
+};
+
+extern const struct rpc_program nfslocalio_program;
+static struct rpc_stat		nfslocalio_rpcstat = { &nfslocalio_program };
+
+const struct rpc_program nfslocalio_program = {
+	.name			= "nfslocalio",
+	.number			= NFS_LOCALIO_PROGRAM,
+	.nrvers			= ARRAY_SIZE(nfslocalio_version),
+	.version		= nfslocalio_version,
+	.stats			= &nfslocalio_rpcstat,
+};
+
 /*
  * nfs_local_enable - enable local i/o for an nfs_client
  */
-static __maybe_unused void nfs_local_enable(struct nfs_client *clp)
+static void nfs_local_enable(struct nfs_client *clp)
 {
 	spin_lock(&clp->cl_localio_lock);
 	set_bit(NFS_CS_LOCAL_IO, &clp->cl_flags);
@@ -82,11 +142,74 @@ void nfs_local_disable(struct nfs_client *clp)
 	spin_unlock(&clp->cl_localio_lock);
 }
 
+/*
+ * nfs_init_localioclient - Initialise an NFS localio client connection
+ */
+static struct rpc_clnt *nfs_init_localioclient(struct nfs_client *clp)
+{
+	struct rpc_clnt *rpcclient_localio;
+
+	rpcclient_localio = rpc_bind_new_program(clp->cl_rpcclient,
+						 &nfslocalio_program, 1);
+
+	dprintk_rcu("%s: server (%s) %s NFS LOCALIO.\n",
+		__func__, rpc_peeraddr2str(clp->cl_rpcclient, RPC_DISPLAY_ADDR),
+		(IS_ERR(rpcclient_localio) ? "does not support" : "supports"));
+
+	return rpcclient_localio;
+}
+
+static bool nfs_server_uuid_is_local(struct nfs_client *clp)
+{
+	u8 uuid[UUID_SIZE];
+	struct rpc_message msg = {
+		.rpc_argp = &uuid,
+	};
+	struct rpc_clnt *rpcclient_localio;
+	int status;
+
+	rpcclient_localio = nfs_init_localioclient(clp);
+	if (IS_ERR(rpcclient_localio))
+		return false;
+
+	export_uuid(uuid, &clp->cl_uuid.uuid);
+
+	msg.rpc_proc = &nfs_localio_procedures[LOCALIOPROC_UUID_IS_LOCAL];
+	status = rpc_call_sync(rpcclient_localio, &msg, 0);
+	dprintk("%s: NFS reply UUID_IS_LOCAL: status=%d\n",
+		__func__, status);
+	rpc_shutdown_client(rpcclient_localio);
+
+	/* Server is only local if it initialized required struct members */
+	if (status || !clp->cl_uuid.net || !clp->cl_uuid.dom)
+		return false;
+
+	return true;
+}
+
 /*
  * nfs_local_probe - probe local i/o support for an nfs_server and nfs_client
+ * - called after alloc_client and init_client (so cl_rpcclient exists)
+ * - this function is idempotent, it can be called for old or new clients
  */
 void nfs_local_probe(struct nfs_client *clp)
 {
+	/* Disallow localio if disabled via sysfs or AUTH_SYS isn't used */
+	if (!localio_enabled ||
+	    clp->cl_rpcclient->cl_auth->au_flavor != RPC_AUTH_UNIX) {
+		nfs_local_disable(clp);
+		return;
+	}
+
+	if (nfs_client_is_local(clp)) {
+		/* If already enabled, disable and re-enable */
+		nfs_local_disable(clp);
+	}
+
+	nfs_uuid_begin(&clp->cl_uuid);
+	if (nfs_server_uuid_is_local(clp))
+		nfs_local_enable(clp);
+	nfs_uuid_end(&clp->cl_uuid);
 }
 EXPORT_SYMBOL_GPL(nfs_local_probe);
 
@@ -116,7 +239,8 @@ nfs_local_open_fh(struct nfs_client *clp, const struct cred *cred,
 		case -ENOMEM:
 		case -ENXIO:
 		case -ENOENT:
-			nfs_local_disable(clp);
+			/* Revalidate localio, will disable if unsupported */
+			nfs_local_probe(clp);
 		}
 		return NULL;
 	}