vendor: vendor fscrypt integration dependencies

Signed-off-by: Marcel Lauhoff <marcel.lauhoff@suse.com>

vendor/github.com/google/fscrypt/security/cache.go

@@ -0,0 +1,49 @@
+/*
+ * cache.go - Handles cache clearing and management.
+ *
+ * Copyright 2017 Google Inc.
+ * Author: Joe Richey (joerichey@google.com)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package security
+
+import (
+	"log"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// DropFilesystemCache instructs the kernel to free the reclaimable inodes and
+// dentries. This has the effect of making encrypted directories whose keys are
+// not present no longer accessible. Requires root privileges.
+func DropFilesystemCache() error {
+	// Dirty reclaimable inodes must be synced so that they will be freed.
+	log.Print("syncing changes to filesystem")
+	unix.Sync()
+
+	// See: https://www.kernel.org/doc/Documentation/sysctl/vm.txt
+	log.Print("freeing reclaimable inodes and dentries")
+	file, err := os.OpenFile("/proc/sys/vm/drop_caches", os.O_WRONLY|os.O_SYNC, 0)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+	// "2" just frees the reclaimable inodes and dentries. The associated
+	// pages to these inodes will be freed. We do not need to free the
+	// entire pagecache (as this will severely impact performance).
+	_, err = file.WriteString("2")
+	return err
+}