NFSv4: test SECINFO RPC_AUTH_GSS pseudoflavors for support

Fix nfs4_negotiate_security to create an rpc_clnt used to test each SECINFO
returned pseudoflavor. Check credential creation  (and gss_context creation)
which is important for RPC_AUTH_GSS pseudoflavors which can fail for multiple
reasons including mis-configuration.

Don't call nfs4_negotiate in nfs4_submount as it was just called by
nfs4_proc_lookup_mountpoint (nfs4_proc_lookup_common)

Signed-off-by: Andy Adamson <andros@netapp.com>
[Trond: fix corrupt return value from nfs_find_best_sec()]
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

3 files changed, 57 insertions, 45 deletions

diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index f63cb87..ba2affa 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -230,7 +230,7 @@ int nfs_atomic_open(struct inode *, struct dentry *, struct file *,
 extern struct file_system_type nfs4_fs_type;
 
 /* nfs4namespace.c */
-struct rpc_clnt *nfs4_create_sec_client(struct rpc_clnt *, struct inode *, struct qstr *);
+struct rpc_clnt *nfs4_negotiate_security(struct rpc_clnt *, struct inode *, struct qstr *);
 struct vfsmount *nfs4_submount(struct nfs_server *, struct dentry *,
 			       struct nfs_fh *, struct nfs_fattr *);
 int nfs4_replace_transport(struct nfs_server *server,
diff --git a/fs/nfs/nfs4namespace.c b/fs/nfs/nfs4namespace.c
index fd4dcb6..3d83cb1 100644
--- a/fs/nfs/nfs4namespace.c
+++ b/fs/nfs/nfs4namespace.c
@@ -139,17 +139,22 @@ static size_t nfs_parse_server_name(char *string, size_t len,
  * @server: NFS server struct
  * @flavors: List of security tuples returned by SECINFO procedure
  *
- * Return the pseudoflavor of the first security mechanism in
- * "flavors" that is locally supported. The "flavors" array
+ * Return an rpc client that uses the first security mechanism in
+ * "flavors" that is locally supported.  The "flavors" array
  * is searched in the order returned from the server, per RFC 3530
- * recommendation.
+ * recommendation and each flavor is checked for membership in the
+ * sec= mount option list if it exists.
  *
  * Return -EPERM if no matching flavor is found in the array.
+ *
+ * Please call rpc_shutdown_client() when you are done with this rpc client.
+ *
  */
-static rpc_authflavor_t nfs_find_best_sec(struct nfs_server *server,
+static struct rpc_clnt *nfs_find_best_sec(struct rpc_clnt *clnt,
+					  struct nfs_server *server,
 					  struct nfs4_secinfo_flavors *flavors)
 {
-	rpc_authflavor_t pseudoflavor;
+	rpc_authflavor_t pflavor;
 	struct nfs4_secinfo4 *secinfo;
 	unsigned int i;
 
@@ -160,58 +165,73 @@ static rpc_authflavor_t nfs_find_best_sec(struct nfs_server *server,
 		case RPC_AUTH_NULL:
 		case RPC_AUTH_UNIX:
 		case RPC_AUTH_GSS:
-			pseudoflavor = rpcauth_get_pseudoflavor(secinfo->flavor,
+			pflavor = rpcauth_get_pseudoflavor(secinfo->flavor,
 							&secinfo->flavor_info);
-			/* make sure pseudoflavor matches sec= mount opt */
-			if (pseudoflavor != RPC_AUTH_MAXFLAVOR &&
-			    nfs_auth_info_match(&server->auth_info,
-						pseudoflavor))
-				return pseudoflavor;
-			break;
+			/* does the pseudoflavor match a sec= mount opt? */
+			if (pflavor != RPC_AUTH_MAXFLAVOR &&
+			    nfs_auth_info_match(&server->auth_info, pflavor)) {
+				struct rpc_clnt *new;
+				struct rpc_cred *cred;
+
+				/* Cloning creates an rpc_auth for the flavor */
+				new = rpc_clone_client_set_auth(clnt, pflavor);
+				if (IS_ERR(new))
+					continue;
+				/**
+				* Check that the user actually can use the
+				* flavor. This is mostly for RPC_AUTH_GSS
+				* where cr_init obtains a gss context
+				*/
+				cred = rpcauth_lookupcred(new->cl_auth, 0);
+				if (IS_ERR(cred)) {
+					rpc_shutdown_client(new);
+					continue;
+				}
+				put_rpccred(cred);
+				return new;
+			}
 		}
 	}
-
-	return -EPERM;
+	return ERR_PTR(-EPERM);
 }
 
-static rpc_authflavor_t nfs4_negotiate_security(struct inode *inode, struct qstr *name)
+/**
+ * nfs4_negotiate_security - in response to an NFS4ERR_WRONGSEC on lookup,
+ * return an rpc_clnt that uses the best available security flavor with
+ * respect to the secinfo flavor list and the sec= mount options.
+ *
+ * @clnt: RPC client to clone
+ * @inode: directory inode
+ * @name: lookup name
+ *
+ * Please call rpc_shutdown_client() when you are done with this rpc client.
+ */
+struct rpc_clnt *
+nfs4_negotiate_security(struct rpc_clnt *clnt, struct inode *inode,
+					struct qstr *name)
 {
 	struct page *page;
 	struct nfs4_secinfo_flavors *flavors;
-	rpc_authflavor_t flavor;
+	struct rpc_clnt *new;
 	int err;
 
 	page = alloc_page(GFP_KERNEL);
 	if (!page)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
+
 	flavors = page_address(page);
 
 	err = nfs4_proc_secinfo(inode, name, flavors);
 	if (err < 0) {
-		flavor = err;
+		new = ERR_PTR(err);
 		goto out;
 	}
 
-	flavor = nfs_find_best_sec(NFS_SERVER(inode), flavors);
+	new = nfs_find_best_sec(clnt, NFS_SERVER(inode), flavors);
 
 out:
 	put_page(page);
-	return flavor;
-}
-
-/*
- * Please call rpc_shutdown_client() when you are done with this client.
- */
-struct rpc_clnt *nfs4_create_sec_client(struct rpc_clnt *clnt, struct inode *inode,
-					struct qstr *name)
-{
-	rpc_authflavor_t flavor;
-
-	flavor = nfs4_negotiate_security(inode, name);
-	if ((int)flavor < 0)
-		return ERR_PTR((int)flavor);
-
-	return rpc_clone_client_set_auth(clnt, flavor);
+	return new;
 }
 
 static struct vfsmount *try_location(struct nfs_clone_mount *mountdata,
@@ -394,14 +414,6 @@ struct vfsmount *nfs4_submount(struct nfs_server *server, struct dentry *dentry,
 
 	if (client->cl_auth->au_flavor != flavor)
 		flavor = client->cl_auth->au_flavor;
-	else {
-		rpc_authflavor_t new = nfs4_negotiate_security(dir, name);
-		if ((int)new < 0) {
-			mnt = ERR_PTR((int)new);
-			goto out;
-		}
-		flavor = new;
-	}
 	mnt = nfs_do_submount(dentry, fh, fattr, flavor);
 out:
 	rpc_shutdown_client(client);
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 285ad53..4bf3d97 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3247,7 +3247,7 @@ static int nfs4_proc_lookup_common(struct rpc_clnt **clnt, struct inode *dir,
 			err = -EPERM;
 			if (client != *clnt)
 				goto out;
-			client = nfs4_create_sec_client(client, dir, name);
+			client = nfs4_negotiate_security(client, dir, name);
 			if (IS_ERR(client))
 				return PTR_ERR(client);