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getace (advapi32)
 
.
Summary
Get an Access Control Entry from a Access Control List.

C# Signature:

  [DllImport("advapi32.dll", SetLastError = true)]
  static extern int GetAce(IntPtr aclPtr, int aceIndex, out IntPtr acePtr);

  [DllImport("advapi32.dll", SetLastError = true)]
  static extern bool GetAce(IntPtr aclPtr, int aceIndex, out IntPtr acePtr); // returns bool per MS

VB Signature:

Declare Function GetAce Lib "advapi32.dll" (TODO) As TODO

User-Defined Types:

None.

Alternative Managed API:

Do you know one? Please contribute it!

Notes:

None.

Tips & Tricks:

Please add some!

Sample Code:

    [DllImport("Netapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    static extern int NetShareGetInfo(
        [MarshalAs(UnmanagedType.LPWStr)] string serverName,
        [MarshalAs(UnmanagedType.LPWStr)] string netName,
        Int32 level,
        out IntPtr bufPtr);

    [DllImport("advapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool GetSecurityDescriptorDacl(
        IntPtr pSecurityDescriptor,
        [MarshalAs(UnmanagedType.Bool)] out bool bDaclPresent,
        ref IntPtr pDacl,
        [MarshalAs(UnmanagedType.Bool)] out bool bDaclDefaulted
        );

    [DllImport("advapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool GetAclInformation(
        IntPtr pAcl,
        ref ACL_SIZE_INFORMATION pAclInformation,
        uint nAclInformationLength,
        ACL_INFORMATION_CLASS dwAclInformationClass
     );

    [DllImport("advapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    static extern int GetAce(
        IntPtr aclPtr,
        int aceIndex,
        out IntPtr acePtr
     );

    [DllImport("advapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    static extern int GetLengthSid(
        IntPtr pSID
     );

    [DllImport("advapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool ConvertSidToStringSid(
        [MarshalAs(UnmanagedType.LPArray)] byte[] pSID,
        out IntPtr ptrSid
     );

    [DllImport("netapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    static extern int NetApiBufferFree(
        IntPtr buffer
     );

    [StructLayout(LayoutKind.Sequential)]
    struct SHARE_INFO_502
    {
        [MarshalAs(UnmanagedType.LPWStr)]
        public string shi502_netname;
        public uint shi502_type;
        [MarshalAs(UnmanagedType.LPWStr)]
        public string shi502_remark;
        public Int32 shi502_permissions;
        public Int32 shi502_max_uses;
        public Int32 shi502_current_uses;
        [MarshalAs(UnmanagedType.LPWStr)]
        public string shi502_path;
        public IntPtr shi502_passwd;
        public Int32 shi502_reserved;
        public IntPtr shi502_security_descriptor;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct ACL_SIZE_INFORMATION
    {
        public uint AceCount;
        public uint AclBytesInUse;
        public uint AclBytesFree;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct ACE_HEADER
    {
        public byte AceType;
        public byte AceFlags;
        public short AceSize;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct ACCESS_ALLOWED_ACE
    {
        public ACE_HEADER Header;
        public int Mask;
        public int SidStart;
    }

    enum ACL_INFORMATION_CLASS
    {
        AclRevisionInformation = 1,
        AclSizeInformation
    }

    static void Main(string[] args)
    {
        IntPtr bufptr = IntPtr.Zero;
        int err = NetShareGetInfo(args[0], args[1], 502, out bufptr);
        if (0 == err)
        {
            SHARE_INFO_502 shareInfo = (SHARE_INFO_502)Marshal.PtrToStructure(bufptr, typeof(SHARE_INFO_502));

            bool bDaclPresent;
            bool bDaclDefaulted;
            IntPtr pAcl = IntPtr.Zero;
            GetSecurityDescriptorDacl(shareInfo.shi502_security_descriptor, out bDaclPresent, ref pAcl, out bDaclDefaulted);
            if (bDaclPresent)
            {
                ACL_SIZE_INFORMATION AclSize = new ACL_SIZE_INFORMATION();
                GetAclInformation(pAcl, ref AclSize, (uint)Marshal.SizeOf(typeof(ACL_SIZE_INFORMATION)), ACL_INFORMATION_CLASS.AclSizeInformation);
                for (int i = 0; i < AclSize.AceCount; i++)
                {
                    IntPtr pAce;
                    err = GetAce(pAcl, i, out pAce);
                    ACCESS_ALLOWED_ACE ace = (ACCESS_ALLOWED_ACE)Marshal.PtrToStructure(pAce, typeof(ACCESS_ALLOWED_ACE));

                    IntPtr iter = (IntPtr)((long)pAce + (long)Marshal.OffsetOf(typeof(ACCESS_ALLOWED_ACE), "SidStart"));
                    byte[] bSID = null;
                    int size = (int)GetLengthSid(iter);
                    bSID = new byte[size];
                    Marshal.Copy(iter, bSID, 0, size);
                    IntPtr ptrSid;
                    ConvertSidToStringSid(bSID, out ptrSid);
                    string strSID = Marshal.PtrToStringAuto(ptrSid);

                    Console.WriteLine("{0} : {1}/{2}/{3}", strSID, ace.Header.AceType.ToString(), ace.Mask.ToString(), ace.Header.AceFlags.ToString());
                }
            }
            err = NetApiBufferFree(bufptr);
        }
    }

Documentation
GetAce on MSDN

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