Access control list
An access control list (ACL), with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject and an operation. For instance, if a file has an ACL that contains (Alice, delete), this would give Alice permission to delete the file.
ACL-based security models 
When a subject requests an operation on an object in an ACL-based security model, the operating system first checks the ACL for an applicable entry to decide whether the requested operation is authorized. A key issue in the definition of any ACL-based security model is determining how access control lists are edited, namely which users and processes are granted ACL-modification access. ACL models may be applied to collections of objects as well as to individual entities within the system's hierarchy.
Filesystem ACLs 
A filesystem ACL is a data structure (usually a table) containing entries that specify individual user or group rights to specific system objects such as programs, processes, or files. These entries are known as access control entries (ACEs) in the Microsoft Windows NT, OpenVMS, Unix-like, and Mac OS X operating systems. Each accessible object contains an identifier to its ACL. The privileges or permissions determine specific access rights, such as whether a user can read from, write to, or execute an object. In some implementations, an ACE can control whether or not a user, or group of users, may alter the ACL on an object.
Most of the Unix and Unix-like operating systems (e.g. Linux, BSD, or Solaris) support POSIX.1e ACLs, based on an early POSIX draft that was abandoned. Many of them, for example AIX, FreeBSD, Mac OS X beginning with version 10.4 ("Tiger"), or Solaris with ZFS filesystem, support NFSv4 ACLs, which are part of the NFSv4 standard. There are two experimental implementations of NFSv4 ACLs for Linux: NFSv4 ACLs support for Ext3 filesystem and recent Richacls, which brings NFSv4 ACLs support for Ext4 filesystem.
Networking ACLs 
On some types of proprietary computer hardware (in particular routers and switches), an Access Control List refers to rules that are applied to port numbers or IP Addresses that are available on a host or other layer 3, each with a list of hosts and/or networks permitted to use the service. Although it is additionally possible to configure Access Control Lists based on network domain names, this is generally a questionable idea because individual TCP, UDP, and ICMP packets do not contain domain names. Consequently, the device enforcing the Access Control List must separately resolve names to numeric addresses. This presents an additional attack surface for an attacker who is seeking to compromise security of the system which the Access Control List is protecting. Both individual servers as well as routers can have network ACLs. Access control lists can generally be configured to control both inbound and outbound traffic, and in this context they are similar to firewalls. Like Firewalls, ACLs are subject to security regulations and standards such as PCI DSS.
See also 
- "Managing Authorization and Access Control". Microsoft Technet. 2005-11-03. Retrieved 2013-04-08.
- "Red Hat Enterprise Linux AS 3 Release Notes (x86 Edition)". Red Hat. 2003. Retrieved 2013-04-08. "EA (Extended Attributes) and ACL (Access Control Lists) functionality is now available for ext3 file systems. In addition, ACL functionality is available for NFS."
- "NFSv4 ACLs". FreeBSD. 2011-09-12. Retrieved 2013-04-08.
- "Chapter 8 Using ACLs and Attributes to Protect ZFS Files". Oracle Corporation. 2009-10-01. Retrieved 2013-04-08.
- Grünbacher, Andreas (May 2008). "Native NFSv4 ACLs on Linux". SUSE. Retrieved 2013-04-08.
- Grünbacher, Andreas (July-September 2010). "Richacls - Native NFSv4 ACLs on Linux". bestbits.at. Retrieved 2013-04-08.
Further reading 
- Rhodes, Tom. "File System Access Control Lists (ACLs)". FreeBSD Handbook. Retrieved 2013-04-08.
- Michael Fox, John Giordano, Lori Stotler, Arun Thomas (2005-08-24). "SELinux and grsecurity: A Case Study Comparing Linux Security Kernel Enhancements". University of Virginia. Retrieved 2013-04-08.
- Hinrichs, Susan (2005). "Operating System Security". CyberSecurity Spring 2005. University of Illinois. Retrieved 2013-04-08.
- Mitchell, John. "Access Control and Operating System Security". Stanford University. Retrieved 2013-04-08.
- Clarkson, Michael. "Access Control". Cornell University. Retrieved 2013-04-08.
- Klein, Helge (2009-03-12). "Permissions: A Primer, or: DACL, SACL, Owner, SID and ACE Explained". Retrieved 2013-04-08.
- "Access Control Lists". MSDN Library. 2012-10-26. Retrieved 2013-04-08.
- "How Permissions Work". Microsoft Technet. 2003-03-28. Retrieved 2013-04-08.