NFSv4: Reintroduce machine creds

We need to try to ensure that we always use the same credentials whenever
we re-establish the clientid on the server. If not, the server won't
recognise that we're the same client, and so may not allow us to recover
state.

Signed-off-by: Trond Myklebust <[e-mail]>

fs/nfs/client.c

···
 static struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_init)
 {
 	struct nfs_client *clp;
+	struct rpc_cred *cred;
 
 	if ((clp = kzalloc(sizeof(*clp), GFP_KERNEL)) == NULL)
 		goto error_0;
···
 	clp->cl_boot_time = CURRENT_TIME;
 	clp->cl_state = 1 << NFS4CLNT_LEASE_EXPIRED;
 #endif
+	cred = rpc_lookup_machine_cred();
+	if (!IS_ERR(cred))
+		clp->cl_machine_cred = cred;
 
 	return clp;
 
···
 
 	if (__test_and_clear_bit(NFS_CS_CALLBACK, &clp->cl_res_state))
 		nfs_callback_down();
+
+	if (clp->cl_machine_cred != NULL)
+		put_rpccred(clp->cl_machine_cred);
 
 	kfree(clp->cl_hostname);
 	kfree(clp);

include/linux/nfs_fs_sb.h

···
 	const struct nfs_rpc_ops *rpc_ops;	/* NFS protocol vector */
 	int			cl_proto;	/* Network transport protocol */
 
+	struct rpc_cred		*cl_machine_cred;
+
 #ifdef CONFIG_NFS_V4
 	u64			cl_clientid;	/* constant */
 	nfs4_verifier		cl_confirm;

include/linux/sunrpc/auth.h

···
 	uid_t	uid;
 	gid_t	gid;
 	struct group_info *group_info;
+	unsigned char machine_cred : 1;
 };
 
 /*
···
 void __exit		rpc_destroy_generic_auth(void);
 
 struct rpc_cred *	rpc_lookup_cred(void);
+struct rpc_cred *	rpc_lookup_machine_cred(void);
 int			rpcauth_register(const struct rpc_authops *);
 int			rpcauth_unregister(const struct rpc_authops *);
 struct rpc_auth *	rpcauth_create(rpc_authflavor_t, struct rpc_clnt *);

include/linux/sunrpc/auth_gss.h

···
 	enum rpc_gss_svc	gc_service;
 	struct gss_cl_ctx	*gc_ctx;
 	struct gss_upcall_msg	*gc_upcall;
+	unsigned char		gc_machine_cred : 1;
 };
 
 #endif /* __KERNEL__ */

net/sunrpc/auth_generic.c

···
 # define RPCDBG_FACILITY	RPCDBG_AUTH
 #endif
 
+#define RPC_ANONYMOUS_USERID	((uid_t)-2)
+#define RPC_ANONYMOUS_GROUPID	((gid_t)-2)
+
 struct generic_cred {
 	struct rpc_cred gc_base;
 	struct auth_cred acred;
···
 	return rpcauth_lookupcred(&generic_auth, 0);
 }
 EXPORT_SYMBOL_GPL(rpc_lookup_cred);
+
+/*
+ * Public call interface for looking up machine creds.
+ */
+struct rpc_cred *rpc_lookup_machine_cred(void)
+{
+	struct auth_cred acred = {
+		.uid = RPC_ANONYMOUS_USERID,
+		.gid = RPC_ANONYMOUS_GROUPID,
+		.machine_cred = 1,
+	};
+
+	dprintk("RPC:       looking up machine cred\n");
+	return generic_auth.au_ops->lookup_cred(&generic_auth, &acred, 0);
+}
+EXPORT_SYMBOL_GPL(rpc_lookup_machine_cred);
 
 static void
 generic_bind_cred(struct rpc_task *task, struct rpc_cred *cred)
···
 	gcred->acred.group_info = acred->group_info;
 	if (gcred->acred.group_info != NULL)
 		get_group_info(gcred->acred.group_info);
+	gcred->acred.machine_cred = acred->machine_cred;
 
-	dprintk("RPC:       allocated generic cred %p for uid %d gid %d\n",
+	dprintk("RPC:       allocated %s cred %p for uid %d gid %d\n",
+			gcred->acred.machine_cred ? "machine" : "generic",
 			gcred, acred->uid, acred->gid);
 	return &gcred->gc_base;
 }
···
 
 	if (gcred->acred.uid != acred->uid ||
 	    gcred->acred.gid != acred->gid ||
-	    gcred->acred.group_info != acred->group_info)
+	    gcred->acred.group_info != acred->group_info ||
+	    gcred->acred.machine_cred != acred->machine_cred)
 		return 0;
 	return 1;
 }

net/sunrpc/auth_gss/auth_gss.c

···
 static struct gss_upcall_msg *
 gss_setup_upcall(struct rpc_clnt *clnt, struct gss_auth *gss_auth, struct rpc_cred *cred)
 {
+	struct gss_cred *gss_cred = container_of(cred,
+			struct gss_cred, gc_base);
 	struct gss_upcall_msg *gss_new, *gss_msg;
+	uid_t uid = cred->cr_uid;
 
-	gss_new = gss_alloc_msg(gss_auth, cred->cr_uid);
+	/* Special case: rpc.gssd assumes that uid == 0 implies machine creds */
+	if (gss_cred->gc_machine_cred != 0)
+		uid = 0;
+
+	gss_new = gss_alloc_msg(gss_auth, uid);
 	if (gss_new == NULL)
 		return ERR_PTR(-ENOMEM);
 	gss_msg = gss_add_msg(gss_auth, gss_new);
···
 	 */
 	cred->gc_base.cr_flags = 1UL << RPCAUTH_CRED_NEW;
 	cred->gc_service = gss_auth->service;
+	cred->gc_machine_cred = acred->machine_cred;
 	kref_get(&gss_auth->kref);
 	return &cred->gc_base;
 
···
 	if (gss_cred->gc_ctx && time_after(jiffies, gss_cred->gc_ctx->gc_expiry))
 		return 0;
 out:
+	if (acred->machine_cred != gss_cred->gc_machine_cred)
+		return 0;
 	return (rc->cr_uid == acred->uid);
 }