NFS/SUNRPC: don't lookup machine credential until rpcauth_bindcred().

When NFS creates a machine credential, it is a "generic" credential,
not tied to any auth protocol, and is really just a container for
the princpal name.
This doesn't get linked to a genuine credential until rpcauth_bindcred()
is called.
The lookup always succeeds, so various places that test if the machine
credential is NULL, are pointless.

As a step towards getting rid of generic credentials, this patch gets
rid of generic machine credentials.  The nfs_client and rpc_client
just hold a pointer to a constant principal name.
When a machine credential is wanted, a special static 'struct rpc_cred'
pointer is used. rpcauth_bindcred() recognizes this, finds the
principal from the client, and binds the correct credential.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

10 files changed, 55 insertions, 69 deletions

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index cce151776709..fb1cf1a4bda2 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -151,7 +151,6 @@ EXPORT_SYMBOL_GPL(unregister_nfs_version);
 struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_init)
 {
         struct nfs_client *clp;
-        struct rpc_cred *cred;
         int err = -ENOMEM;
 
         if ((clp = kzalloc(sizeof(*clp), GFP_KERNEL)) == NULL)
@@ -182,9 +181,7 @@ struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_init)
         clp->cl_proto = cl_init->proto;
         clp->cl_net = get_net(cl_init->net);
 
-        cred = rpc_lookup_machine_cred("*");
-        if (!IS_ERR(cred))
-                clp->cl_machine_cred = cred;
+        clp->cl_principal = "*";
         nfs_fscache_get_client_cookie(clp);
 
         return clp;
@@ -246,11 +243,6 @@ void nfs_free_client(struct nfs_client *clp)
         if (!IS_ERR(clp->cl_rpcclient))
                 rpc_shutdown_client(clp->cl_rpcclient);
 
-        if (clp->cl_machine_cred != NULL)
-                put_rpccred(clp->cl_machine_cred);
-        if (clp->cl_root_cred != NULL)
-                put_rpccred(clp->cl_root_cred);
-
         put_net(clp->cl_net);
         put_nfs_version(clp->cl_nfs_mod);
         kfree(clp->cl_hostname);
@@ -529,6 +521,7 @@ int nfs_create_rpc_client(struct nfs_client *clp,
                 return PTR_ERR(clnt);
         }
 
+        clnt->cl_principal = clp->cl_principal;
         clp->cl_rpcclient = clnt;
         return 0;
 }
diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index ad649a49822f..eab41490ce58 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -338,7 +338,6 @@ static inline bool
 _nfs4_state_protect(struct nfs_client *clp, unsigned long sp4_mode,
                     struct rpc_clnt **clntp, struct rpc_message *msg)
 {
-        struct rpc_cred *newcred = NULL;
         rpc_authflavor_t flavor;
 
         if (sp4_mode == NFS_SP4_MACH_CRED_CLEANUP ||
@@ -353,13 +352,7 @@ _nfs4_state_protect(struct nfs_client *clp, unsigned long sp4_mode,
                         return false;
         }
         if (test_bit(sp4_mode, &clp->cl_sp4_flags)) {
-                spin_lock(&clp->cl_lock);
-                if (clp->cl_machine_cred != NULL)
-                        /* don't call get_rpccred on the machine cred -
-                         * a reference will be held for life of clp */
-                        newcred = clp->cl_machine_cred;
-                spin_unlock(&clp->cl_lock);
-                msg->rpc_cred = newcred;
+                msg->rpc_cred = rpc_machine_cred();
 
                 flavor = clp->cl_rpcclient->cl_auth->au_flavor;
                 WARN_ON_ONCE(flavor != RPC_AUTH_GSS_KRB5I &&
diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index f142fca6995b..6304c79dbcd1 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -166,28 +166,15 @@ out:
 
 struct rpc_cred *nfs4_get_machine_cred(struct nfs_client *clp)
 {
-        struct rpc_cred *cred = clp->cl_root_cred;
-
-        if (!cred)
-                cred = clp->cl_machine_cred;
-        if (cred)
-                return get_rpccred(cred);
-        return cred;
+        return get_rpccred(rpc_machine_cred());
 }
 
 static void nfs4_root_machine_cred(struct nfs_client *clp)
 {
-        struct rpc_cred *new;
 
-        new = rpc_lookup_machine_cred(NULL);
-        spin_lock(&clp->cl_lock);
-        if (clp->cl_root_cred == NULL) {
-                clp->cl_root_cred = new;
-                new = NULL;
-        }
-        spin_unlock(&clp->cl_lock);
-        if (new != NULL)
-                put_rpccred(new);
+        /* Force root creds instead of machine */
+        clp->cl_principal = NULL;
+        clp->cl_rpcclient->cl_principal = NULL;
 }
 
 static struct rpc_cred *
diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index c032e4c24a8d..1dcee1fd32d9 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -847,14 +847,10 @@ static int max_cb_time(struct net *net)
 static struct rpc_cred *get_backchannel_cred(struct nfs4_client *clp, struct rpc_clnt *client, struct nfsd4_session *ses)
 {
         if (clp->cl_minorversion == 0) {
-                char *principal = clp->cl_cred.cr_targ_princ ?
-                                        clp->cl_cred.cr_targ_princ : "nfs";
-                struct rpc_cred *cred;
-
-                cred = rpc_lookup_machine_cred(principal);
-                if (!IS_ERR(cred))
-                        get_rpccred(cred);
-                return cred;
+                client->cl_principal = clp->cl_cred.cr_targ_princ ?
+                        clp->cl_cred.cr_targ_princ : "nfs";
+
+                return get_rpccred(rpc_machine_cred());
         } else {
                 struct rpc_auth *auth = client->cl_auth;
                 struct auth_cred acred = {};
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index fea51b44fe50..6aa8cc83c3b6 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -58,8 +58,7 @@ struct nfs_client {
         struct nfs_subversion * cl_nfs_mod;     /* pointer to nfs version module */
 
         u32                     cl_minorversion;/* NFSv4 minorversion */
-        struct rpc_cred         *cl_machine_cred;
-        struct rpc_cred         *cl_root_cred;  /* Use when machine_cred is ineffective */
+        const char *            cl_principal;  /* used for machine cred */
 
 #if IS_ENABLED(CONFIG_NFS_V4)
         struct list_head        cl_ds_clients; /* auth flavor data servers */
diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index 1c0468f39479..28b34c740c43 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -75,6 +75,8 @@ struct rpc_cred {
 #define RPCAUTH_CRED_HASHED     2
 #define RPCAUTH_CRED_NEGATIVE   3
 
+struct rpc_cred *rpc_machine_cred(void);
+
 /* rpc_auth au_flags */
 #define RPCAUTH_AUTH_NO_CRKEY_TIMEOUT   0x0001 /* underlying cred has no key timeout */
 
@@ -170,7 +172,6 @@ void 			rpc_destroy_authunix(void);
 struct rpc_cred *       rpc_lookup_cred(void);
 struct rpc_cred *       rpc_lookup_cred_nonblock(void);
 struct rpc_cred *       rpc_lookup_generic_cred(struct auth_cred *, int, gfp_t);
-struct rpc_cred *       rpc_lookup_machine_cred(const char *service_name);
 int                     rpcauth_register(const struct rpc_authops *);
 int                     rpcauth_unregister(const struct rpc_authops *);
 struct rpc_auth *       rpcauth_create(const struct rpc_auth_create_args *,
diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
index 73d5c4a870fa..fc6dfbf77a9d 100644
--- a/include/linux/sunrpc/clnt.h
+++ b/include/linux/sunrpc/clnt.h
@@ -66,6 +66,7 @@ struct rpc_clnt {
         struct rpc_rtt          cl_rtt_default;
         struct rpc_timeout      cl_timeout_default;
         const struct rpc_program *cl_program;
+        const char *            cl_principal;   /* use for machine cred */
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
         struct dentry           *cl_debugfs;    /* debugfs directory */
 #endif
diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
index 63e2d35c10d5..9e709dcc8c39 100644
--- a/net/sunrpc/auth.c
+++ b/net/sunrpc/auth.c
@@ -39,6 +39,20 @@ static const struct rpc_authops __rcu *auth_flavors[RPC_AUTH_MAXFLAVOR] = {
 static LIST_HEAD(cred_unused);
 static unsigned long number_cred_unused;
 
+static struct rpc_cred machine_cred = {
+        .cr_count = REFCOUNT_INIT(1),
+};
+
+/*
+ * Return the machine_cred pointer to be used whenever
+ * the a generic machine credential is needed.
+ */
+struct rpc_cred *rpc_machine_cred(void)
+{
+        return &machine_cred;
+}
+EXPORT_SYMBOL_GPL(rpc_machine_cred);
+
 #define MAX_HASHTABLE_BITS (14)
 static int param_set_hashtbl_sz(const char *val, const struct kernel_param *kp)
 {
@@ -703,6 +717,22 @@ rpcauth_bind_root_cred(struct rpc_task *task, int lookupflags)
 }
 
 static struct rpc_cred *
+rpcauth_bind_machine_cred(struct rpc_task *task, int lookupflags)
+{
+        struct rpc_auth *auth = task->tk_client->cl_auth;
+        struct auth_cred acred = {
+                .principal = task->tk_client->cl_principal,
+                .cred = init_task.cred,
+        };
+
+        if (!acred.principal)
+                return NULL;
+        dprintk("RPC: %5u looking up %s machine cred\n",
+                task->tk_pid, task->tk_client->cl_auth->au_ops->au_name);
+        return auth->au_ops->lookup_cred(auth, &acred, lookupflags);
+}
+
+static struct rpc_cred *
 rpcauth_bind_new_cred(struct rpc_task *task, int lookupflags)
 {
         struct rpc_auth *auth = task->tk_client->cl_auth;
@@ -716,14 +746,20 @@ static int
 rpcauth_bindcred(struct rpc_task *task, struct rpc_cred *cred, int flags)
 {
         struct rpc_rqst *req = task->tk_rqstp;
-        struct rpc_cred *new;
+        struct rpc_cred *new = NULL;
         int lookupflags = 0;
 
         if (flags & RPC_TASK_ASYNC)
                 lookupflags |= RPCAUTH_LOOKUP_NEW;
-        if (cred != NULL)
+        if (cred != NULL && cred != &machine_cred)
                 new = cred->cr_ops->crbind(task, cred, lookupflags);
-        else if (flags & RPC_TASK_ROOTCREDS)
+        else if (cred == &machine_cred)
+                new = rpcauth_bind_machine_cred(task, lookupflags);
+
+        /* If machine cred couldn't be bound, try a root cred */
+        if (new)
+                ;
+        else if (cred == &machine_cred || (flags & RPC_TASK_ROOTCREDS))
                 new = rpcauth_bind_root_cred(task, lookupflags);
         else
                 new = rpcauth_bind_new_cred(task, lookupflags);
diff --git a/net/sunrpc/auth_generic.c b/net/sunrpc/auth_generic.c
index 7d1a8f45726c..5f7aa6324b78 100644
--- a/net/sunrpc/auth_generic.c
+++ b/net/sunrpc/auth_generic.c
@@ -48,27 +48,6 @@ struct rpc_cred *rpc_lookup_cred_nonblock(void)
 }
 EXPORT_SYMBOL_GPL(rpc_lookup_cred_nonblock);
 
-/*
- * Public call interface for looking up machine creds.
- * Note that if service_name is NULL, we actually look up
- * "root" credential.
- */
-struct rpc_cred *rpc_lookup_machine_cred(const char *service_name)
-{
-        struct auth_cred acred = {
-                .principal = service_name,
-                .cred = get_task_cred(&init_task),
-        };
-        struct rpc_cred *ret;
-
-        dprintk("RPC:       looking up machine cred for service %s\n",
-                        service_name);
-        ret = generic_auth.au_ops->lookup_cred(&generic_auth, &acred, 0);
-        put_cred(acred.cred);
-        return ret;
-}
-EXPORT_SYMBOL_GPL(rpc_lookup_machine_cred);
-
 static struct rpc_cred *generic_bind_cred(struct rpc_task *task,
                 struct rpc_cred *cred, int lookupflags)
 {
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 24cbddc44c88..c5bf56abf266 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -627,6 +627,7 @@ static struct rpc_clnt *__rpc_clone_client(struct rpc_create_args *args,
         new->cl_noretranstimeo = clnt->cl_noretranstimeo;
         new->cl_discrtry = clnt->cl_discrtry;
         new->cl_chatty = clnt->cl_chatty;
+        new->cl_principal = clnt->cl_principal;
         return new;
 
 out_err: