Protection

Protection

• User information and data is stored in the secondary storage. It is necessary to provide security from physical damage and improper access.

Type of Access

• Access is limited or full access of data. User having full access can perform read, write and modify operation on the data and information. In limited access, user only read and executes the information.

• Protection mechanism provides controlled access. Following are some of the aw operation performed on the files.

1. Read: User can read a file.

2. Write: User can rewrite a file.

3. Delete: User can delete a file whenever space is required.

4. Execute: User execute a file after loading into the main memory.

5. List: User check attributes of the file and file/directory names.

Access Control

• Traditionally, a file object in Linux is associated with three sets of permissions. These sets assign read (r), write (w), and execute (x) permissions for the three user groups file owner group, and other.

• Nine bits are used to determine the characteristics of all objects in a Linux system. Additionally, the set user id, set group id and sticky bits can be set for special cases.

• ACLS can be used for situations where the traditional file permission concept does not suffice. They allow the assignment of permissions to individual users or groups even if these do not correspond to the owner or the owning group. Access Control Lists are a feature of the Linux kernel.

• There are two types of ACLS : Access ACLS and default ACLs. An access ACL is the access control list for a specific file or directory. A default ACL can only be associated with a directory; if a file within the directory does not have an access ACL, it uses the rules of the default ACL for the directory. Default ACL's are optional.

• ACL's can be configured:

1. Per user 2. Per group

3. Via the effective rights mask

4. For users not in the user group for the file.

Access determination

• When a process attempts to access a file, its effective UID is compared to the UID that owns the file. If they are the same, access is determined by the ACL's user permissions. Otherwise, if a matching user specific ACL entry exists, permissions are determined by that entry in combination with the ACL mask.

• If no specific entry is available, the file system tries to locate a valid group related b entry that provides the required access; these entries are processed in conjunction se with the ACL mask. If no matching entry can be found, the other entry prevails.

NFSv4 ACL

• The NFSv4 (Network File System - Version 4 protocol introduces a new ACL format that extends other existing ACL formats. NFSv4 ACL is easy to work with and introduces more detailed file security attributes, making NFSv4ACLs more

• NFSv4 ACL's are similar to Windows ACL's in structural perspective. In both the system, ACL stores this entity as a string.

The Windows and NFSv4 permission model is more granular than the traditional UNIX read-write-execute model.

1. NFSv4 distinguishes permissions to create files within a directory from permission to create subdirectories.

2. NFSv4 has a separate append permission bit.

3. NFSv4 has separate read and write permissions for data, file attributes, extended attributes, and ACLs.

4. NFSv4 controls a user's ability to change the ownership of a file through the standard ACL.

NFSv4 file permissions

Access Determination in NFS

• In the POSIX ACL system, the file system attempts to match the user's identity to the single most appropriate access control entry. The Access Control Entry (ACE) then provides a complete set of controlling permissions for the file.

• Each NFSv4 ACE is either an "allow" ACE or a "deny" ACE. When deciding whether to allow a particular operation, the file system reads the ACL in order, processing ACEs until either all requested permissions have been allowed or some requested permission has been denied.

ACL inheritance

• ACL inheritance is a mechanism that lets container objects pass access control information to their child objects. A container's child objects can be non-container objects as well as other container objects.

• From an administrator point of view, ACL inheritance simplifies access control management. An administrator can set the ACL on a parent object and if inheritance is enabled, he shouldn't need to set ACLS on each child object.