SUNRPC: Introduce rpcauth_get_pseudoflavor()

A SECINFO reply may contain flavors whose kernel module is not
yet loaded by the client's kernel.  A new RPC client API, called
rpcauth_get_pseudoflavor(), is introduced to do proper checking
for support of a security flavor.

When this API is invoked, the RPC client now tries to load the
module for each flavor first before performing the "is this
supported?" check.  This means if a module is available on the
client, but has not been loaded yet, it will be loaded and
registered automatically when the SECINFO reply is processed.

The new API can take a full GSS tuple (OID, QoP, and service).
Previously only the OID and service were considered.

nfs_find_best_sec() is updated to verify all flavors requested in a
SECINFO reply, including AUTH_NULL and AUTH_UNIX.  Previously these
two flavors were simply assumed to be supported without consulting
the RPC client.

Note that the replaced version of nfs_find_best_sec() can return
RPC_AUTH_MAXFLAVOR if the server returns a recognized OID but an
unsupported "service" value.  nfs_find_best_sec() now returns
RPC_AUTH_UNIX in this case.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4namespace.c

@@ -134,33 +134,38 @@ static size_t nfs_parse_server_name(char *string, size_t len,
 	return ret;
 }
 
+/**
+ * nfs_find_best_sec - Find a security mechanism supported locally
+ * @flavors: List of security tuples returned by SECINFO procedure
+ *
+ * Return the pseudoflavor of the first security mechanism in
+ * "flavors" that is locally supported.  Return RPC_AUTH_UNIX if
+ * no matching flavor is found in the array.  The "flavors" array
+ * is searched in the order returned from the server, per RFC 3530
+ * recommendation.
+ */
 rpc_authflavor_t nfs_find_best_sec(struct nfs4_secinfo_flavors *flavors)
 {
-	struct gss_api_mech *mech;
-	struct xdr_netobj oid;
+	rpc_authflavor_t pseudoflavor;
+	struct nfs4_secinfo4 *secinfo;
 	unsigned int i;
-	rpc_authflavor_t pseudoflavor = RPC_AUTH_UNIX;
 
 	for (i = 0; i < flavors->num_flavors; i++) {
-		struct nfs4_secinfo4 *flavor = &flavors->flavors[i];
-
-		if (flavor->flavor == RPC_AUTH_NULL || flavor->flavor == RPC_AUTH_UNIX) {
-			pseudoflavor = flavor->flavor;
-			break;
-		} else if (flavor->flavor == RPC_AUTH_GSS) {
-			oid.len  = flavor->flavor_info.oid.len;
-			oid.data = flavor->flavor_info.oid.data;
-			mech = gss_mech_get_by_OID(&oid);
-			if (!mech)
-				continue;
-			pseudoflavor = gss_svc_to_pseudoflavor(mech,
-						flavor->flavor_info.service);
-			gss_mech_put(mech);
+		secinfo = &flavors->flavors[i];
+
+		switch (secinfo->flavor) {
+		case RPC_AUTH_NULL:
+		case RPC_AUTH_UNIX:
+		case RPC_AUTH_GSS:
+			pseudoflavor = rpcauth_get_pseudoflavor(secinfo->flavor,
+							&secinfo->flavor_info);
+			if (pseudoflavor != RPC_AUTH_MAXFLAVOR)
+				return pseudoflavor;
 			break;
 		}
 	}
 
-	return pseudoflavor;
+	return RPC_AUTH_UNIX;
 }
 
 static rpc_authflavor_t nfs4_negotiate_security(struct inode *inode, struct qstr *name)

include/linux/sunrpc/auth.h

@@ -22,6 +22,8 @@
 /* size of the nodename buffer */
 #define UNX_MAXNODENAME	32
 
+struct rpcsec_gss_info;
+
 /* Work around the lack of a VFS credential */
 struct auth_cred {
 	kuid_t	uid;
@@ -103,6 +105,7 @@ struct rpc_authops {
 	int			(*pipes_create)(struct rpc_auth *);
 	void			(*pipes_destroy)(struct rpc_auth *);
 	int			(*list_pseudoflavors)(rpc_authflavor_t *, int);
+	rpc_authflavor_t	(*info2flavor)(struct rpcsec_gss_info *);
 };
 
 struct rpc_credops {
@@ -137,6 +140,8 @@ 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 *);
 void			rpcauth_release(struct rpc_auth *);
+rpc_authflavor_t	rpcauth_get_pseudoflavor(rpc_authflavor_t,
+				struct rpcsec_gss_info *);
 int			rpcauth_list_flavors(rpc_authflavor_t *, int);
 struct rpc_cred *	rpcauth_lookup_credcache(struct rpc_auth *, struct auth_cred *, int);
 void			rpcauth_init_cred(struct rpc_cred *, const struct auth_cred *, struct rpc_auth *, const struct rpc_credops *);

include/linux/sunrpc/gss_api.h

@@ -127,9 +127,8 @@ struct gss_api_ops {
 int gss_mech_register(struct gss_api_mech *);
 void gss_mech_unregister(struct gss_api_mech *);
 
-/* returns a mechanism descriptor given an OID, and increments the mechanism's
- * reference count. */
-struct gss_api_mech * gss_mech_get_by_OID(struct xdr_netobj *);
+/* Given a GSS security tuple, look up a pseudoflavor */
+rpc_authflavor_t gss_mech_info2flavor(struct rpcsec_gss_info *);
 
 /* Returns a reference to a mechanism, given a name like "krb5" etc. */
 struct gss_api_mech *gss_mech_get_by_name(const char *);

net/sunrpc/auth.c

@@ -123,6 +123,41 @@ rpcauth_unregister(const struct rpc_authops *ops)
 }
 EXPORT_SYMBOL_GPL(rpcauth_unregister);
 
+/**
+ * rpcauth_get_pseudoflavor - check if security flavor is supported
+ * @flavor: a security flavor
+ * @info: a GSS mech OID, quality of protection, and service value
+ *
+ * Verifies that an appropriate kernel module is available or already loaded.
+ * Returns an equivalent pseudoflavor, or RPC_AUTH_MAXFLAVOR if "flavor" is
+ * not supported locally.
+ */
+rpc_authflavor_t
+rpcauth_get_pseudoflavor(rpc_authflavor_t flavor, struct rpcsec_gss_info *info)
+{
+	const struct rpc_authops *ops;
+	rpc_authflavor_t pseudoflavor;
+
+	ops = auth_flavors[flavor];
+	if (ops == NULL)
+		request_module("rpc-auth-%u", flavor);
+	spin_lock(&rpc_authflavor_lock);
+	ops = auth_flavors[flavor];
+	if (ops == NULL || !try_module_get(ops->owner)) {
+		spin_unlock(&rpc_authflavor_lock);
+		return RPC_AUTH_MAXFLAVOR;
+	}
+	spin_unlock(&rpc_authflavor_lock);
+
+	pseudoflavor = flavor;
+	if (ops->info2flavor != NULL)
+		pseudoflavor = ops->info2flavor(info);
+
+	module_put(ops->owner);
+	return pseudoflavor;
+}
+EXPORT_SYMBOL_GPL(rpcauth_get_pseudoflavor);
+
 /**
  * rpcauth_list_flavors - discover registered flavors and pseudoflavors
  * @array: array to fill in

net/sunrpc/auth_gss/auth_gss.c

@@ -1641,6 +1641,7 @@ static const struct rpc_authops authgss_ops = {
 	.pipes_create	= gss_pipes_dentries_create,
 	.pipes_destroy	= gss_pipes_dentries_destroy,
 	.list_pseudoflavors = gss_mech_list_pseudoflavors,
+	.info2flavor	= gss_mech_info2flavor,
 };
 
 static const struct rpc_credops gss_credops = {

net/sunrpc/auth_gss/gss_mech_switch.c

@@ -171,8 +171,7 @@ struct gss_api_mech * gss_mech_get_by_name(const char *name)
 }
 EXPORT_SYMBOL_GPL(gss_mech_get_by_name);
 
-struct gss_api_mech *
-gss_mech_get_by_OID(struct xdr_netobj *obj)
+static struct gss_api_mech *gss_mech_get_by_OID(struct rpcsec_gss_oid *obj)
 {
 	struct gss_api_mech	*pos, *gm = NULL;
 
@@ -188,11 +187,8 @@ gss_mech_get_by_OID(struct xdr_netobj *obj)
 	}
 	spin_unlock(&registered_mechs_lock);
 	return gm;
-
 }
 
-EXPORT_SYMBOL_GPL(gss_mech_get_by_OID);
-
 static inline int
 mech_supports_pseudoflavor(struct gss_api_mech *gm, u32 pseudoflavor)
 {
@@ -282,6 +278,28 @@ gss_svc_to_pseudoflavor(struct gss_api_mech *gm, u32 service)
 }
 EXPORT_SYMBOL_GPL(gss_svc_to_pseudoflavor);
 
+/**
+ * gss_mech_info2flavor - look up a pseudoflavor given a GSS tuple
+ * @info: a GSS mech OID, quality of protection, and service value
+ *
+ * Returns a matching pseudoflavor, or RPC_AUTH_MAXFLAVOR if the tuple is
+ * not supported.
+ */
+rpc_authflavor_t gss_mech_info2flavor(struct rpcsec_gss_info *info)
+{
+	rpc_authflavor_t pseudoflavor;
+	struct gss_api_mech *gm;
+
+	gm = gss_mech_get_by_OID(&info->oid);
+	if (gm == NULL)
+		return RPC_AUTH_MAXFLAVOR;
+
+	pseudoflavor = gss_svc_to_pseudoflavor(gm, info->service);
+
+	gss_mech_put(gm);
+	return pseudoflavor;
+}
+
 u32
 gss_pseudoflavor_to_service(struct gss_api_mech *gm, u32 pseudoflavor)
 {