SUNRPC: Ensure that rpc_mkpipe returns a refcounted dentry

If not, we cannot guarantee that idmap->idmap_dentry, gss_auth->dentry and
clnt->cl_dentry are valid dentries.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth_gss/auth_gss.c

@@ -721,6 +721,8 @@ gss_destroy(struct rpc_auth *auth)
 
 	gss_auth = container_of(auth, struct gss_auth, rpc_auth);
 	rpc_unlink(gss_auth->path);
+	dput(gss_auth->dentry);
+	gss_auth->dentry = NULL;
 	gss_mech_put(gss_auth->mech);
 
 	rpcauth_free_credcache(auth);