Module jcifs
Package org.codelibs.jcifs.smb.internal.dtyp

Class ACE

java.lang.Object
org.codelibs.jcifs.smb.internal.dtyp.ACE
All Implemented Interfaces:
ACE, Decodable
public class ACE extends Object implements ACE, Decodable
An Access Control Entry (ACE) is an element in a security descriptor such as those associated with files and directories. The Windows OS determines which users have the necessary permissions to access objects based on these entries.

To fully understand the information exposed by this class a description of the access check algorithm used by Windows is required. The following is a basic description of the algorithm. For a more complete description we recommend reading the section on Access Control in Keith Brown's "The .NET Developer's Guide to Windows Security" (which is also available online).

Direct ACEs are evaluated first in order. The SID of the user performing the operation and the desired access bits are compared to the SID and access mask of each ACE. If the SID matches, the allow/deny flags and access mask are considered. If the ACE is a "deny" ACE and any of the desired access bits match bits in the access mask of the ACE, the whole access check fails. If the ACE is an "allow" ACE and all of the bits in the desired access bits match bits in the access mask of the ACE, the access check is successful. Otherwise, more ACEs are evaluated until all desired access bits (combined) are "allowed". If all of the desired access bits are not "allowed" the then same process is repeated for inherited ACEs.

For example, if user WNET\alice tries to open a file with desired access bits 0x00000003 (FILE_READ_DATA | FILE_WRITE_DATA) and the target file has the following security descriptor ACEs: 

 Allow WNET\alice     0x001200A9  Direct
 Allow Administrators 0x001F01FF  Inherited
 Allow SYSTEM         0x001F01FF  Inherited
the access check would fail because the direct ACE has an access mask of 0x001200A9 which doesn't have the FILE_WRITE_DATA bit on (bit 0x00000002). Actually, this isn't quite correct. If WNET\alice is in the local Administrators group the access check will succeed because the inherited ACE allows local Administrators both FILE_READ_DATA and FILE_WRITE_DATA access.

  • Constructor Details

    • ACE

      public ACE()
      Default constructor for ACE

  • Method Details

    • isAllow

      public boolean isAllow()
      Description copied from interface: ACE
      Returns true if this ACE is an allow ACE and false if it is a deny ACE.
      Specified by:
      isAllow in interface ACE
      Returns:
      whether this in an allow ACE

    • isInherited

      public boolean isInherited()
      Description copied from interface: ACE
      Returns true if this ACE is an inherited ACE and false if it is a direct ACE.

      Note: For reasons not fully understood, FLAGS_INHERITED may not be set within all security descriptors even though the ACE was in face inherited. If an inherited ACE is added to a parent the Windows ACL editor will rebuild all children ACEs and set this flag accordingly.

      Specified by:
      isInherited in interface ACE
      Returns:
      whether this is an inherited ACE

    • getFlags

      public int getFlags()
      Description copied from interface: ACE
      Returns the flags for this ACE. The isInherited() method checks the FLAGS_INHERITED bit in these flags.
      Specified by:
      getFlags in interface ACE
      Returns:
      the ACE flags

    • getApplyToText

      public String getApplyToText()
      Description copied from interface: ACE
      Returns the 'Apply To' text for inheritance of ACEs on directories such as 'This folder, subfolder and files'. For files the text is always 'This object only'.
      Specified by:
      getApplyToText in interface ACE
      Returns:
      descriptive text for the ACE scope

    • getAccessMask

      public int getAccessMask()
      Description copied from interface: ACE
      Returns the access mask associated with this ACE. Use the constants for FILE_READ_DATA, FILE_WRITE_DATA, READ_CONTROL, GENERIC_ALL, etc with bitwise operators to determine which bits of the mask are on or off.
      Specified by:
      getAccessMask in interface ACE
      Returns:
      the access mask

    • getSID

      public SID getSID()
      Description copied from interface: ACE
      Return the SID associated with this ACE.
      Specified by:
      getSID in interface ACE
      Returns:
      ACE target SID

    • decode

      public int decode(byte[] buf, int bi, int len)
      Description copied from interface: Decodable
      Decode data from a byte buffer
      Specified by:
      decode in interface Decodable
      Parameters:
      buf - the byte buffer containing the data to decode
      bi - the starting index in the buffer
      len - the maximum length of data to decode
      Returns:
      decoded length

    • toString

      public String toString()
      Return a string represeting this ACE.

      Note: This function should probably be changed to return SDDL fragments but currently it does not.

      Overrides:
      toString in class Object