/// <summary>
/// The sub function of the AccessCheck algorithm
/// </summary>
/// <param name="objectType">The current ace objectType to be dealt with.</param>
/// <param name="localTree">
/// The current tree representation of the hierarchy of objects for which to check access.
/// </param>
private static void AncestorNodesAccessCheck(
Guid objectType,
ref AccessCheckObjectTree localTree)
{
Guid[] ancestor = localTree.GetAncestorNodes(objectType);
if (ancestor.Length > 0)
{
Guid currentNode = objectType;
for (int i = 0; i < ancestor.Length; i++)
{
Guid[] sibling = localTree.GetSiblingNodes(currentNode);
if (sibling.Length > 0)
{
uint currentRemaining = 0;
foreach (Guid node in sibling)
{
currentRemaining |= localTree.GetTreeNodeData(node);
}
if (currentRemaining != localTree.GetTreeNodeData(currentNode))
{
break;
}
}
localTree.SetTreeNodeData(ancestor[i], localTree.GetTreeNodeData(currentNode));
currentNode = ancestor[i];
}
}
}
/// <summary>
/// Access Check Algorithm. MS-DTYP section 2.5.4.1
/// </summary>
/// <param name="securityDescriptor">
/// SECURITY_DESCRIPTOR structure that is assigned to the object.
/// </param>
/// <param name="token">
/// Token is an authorization context containing all SIDs
/// that represent the security principal
/// </param>
/// <param name="accessRequestMask">
/// Set of permissions requested on the object.
/// </param>
/// <param name="objectTree">
/// A tree representation of the hierarchy of objects for which
/// to check access. Each node represents an object with two values.
/// A GUID that represents the object itself and a value called
/// Remaining, which indicates the user rights request for that
/// node that have not yet been satisfied. It can be null.
/// </param>
/// <param name="principalSelfSubstitudeSid">
/// A SID that logically replaces the SID in any ACE that contains
/// the well-known PRINCIPAL_SELF SID. It can be null.
/// </param>
/// <returns>
/// Returns TRUE if access is allowed. Otherwise, it returns FALSE if access is denied.
/// </returns>
/// <exception cref="ArgumentException">
/// Thrown when the Dacl field of securityDescriptor doesn't exist, but the DACLPresent flag is set.
/// Thrown when the Revision field of securityDescriptor is invalid
/// </exception>
public static bool AccessCheck(
_SECURITY_DESCRIPTOR securityDescriptor,
Token token,
uint accessRequestMask,
AccessCheckObjectTree objectTree,
_SID? principalSelfSubstitudeSid)
{
//MS-ADTS Section 5.1.3.3.1 Null vs. Empty DACLs
//The presence of a NULL DACL in the nTSecurityDescriptor attribute of an object grants full
//access to the object to any principal that requests it; normal access checks are not performed
//with respect to the object.
if (securityDescriptor.Revision != 0x1)
{
throw new ArgumentException("The Revision field is invalid.", "securityDescriptor");
}
if ((securityDescriptor.Control & SECURITY_DESCRIPTOR_Control.DACLPresent)
== SECURITY_DESCRIPTOR_Control.None)
{
return true;
}
else if (securityDescriptor.Dacl == null)
{
throw new ArgumentException(
"The Dacl field of securityDescriptor doesn't exist, but the DACLPresent flag is set.", "securityDescriptor");
}
//Pscudocode
//
//Set DACL to SecurityDescriptor Dacl field
//Set RemainingAccess to Access Request mask
//
//IF RemainingAccess contains ACCESS_SYSTEM_SECURITY access flag THEN
//IF Token.Privileges contains SeSecurityPrivilege THEN
//Remove ACCESS_SYSTEM_SECURITY access bit from RemainingAccess
//END IF
//END IF
//
//IF RemainingAccess contains WRITE_OWNER access bit THEN
//IF Token.Privileges contains SeTakeOwnershipPrivilege THEN
//Remove WRITE_OWNER access bit from RemainingAccess
//END IF
//END IF
//-- the owner of an object is always granted READ_CONTROL and WRITE_DAC.
//CALL SidInToken( Token, SecurityDescriptor.Owner, PrincipalSelfSubst)
//IF SidInToken returns True THEN
//Remove READ_CONTROL and WRITE_DAC from RemainingAccess
//END IF
_ACL? dacl = securityDescriptor.Dacl;
uint remainingAccess = accessRequestMask;
AccessCheckObjectTree localTree = new AccessCheckObjectTree();
Guid[] allNodes = new Guid[] { };
if ((remainingAccess & ACCESS_MASK_ACCESS_SYSTEM_SECURITY) != 0 && token.Privileges != null)
{
foreach (_LUID privilege in token.Privileges)
{
if (ObjectUtility.DeepCompare(privilege, GetPrivilegeLuid(PrivilegeName.SE_SECURITY_NAME)))
{
remainingAccess &= ~ACCESS_MASK_ACCESS_SYSTEM_SECURITY;
}
}
}
if ((remainingAccess & ACCESS_MASK_WRITE_OWNER) != 0 && token.Privileges != null)
{
foreach (_LUID privilege in token.Privileges)
{
if (ObjectUtility.DeepCompare(privilege, GetPrivilegeLuid(PrivilegeName.SE_TAKE_OWNERSHIP_NAME)))
{
remainingAccess &= ~ACCESS_MASK_WRITE_OWNER;
}
}
}
if (securityDescriptor.OwnerSid != null
&& SidInToken(token, securityDescriptor.OwnerSid.Value, principalSelfSubstitudeSid))
{
remainingAccess &= ~(uint)(ACCESS_MASK_READ_CONTROL | ACCESS_MASK_WRITE_DAC);
}
//IF Object Tree is not NULL THEN
//Set LocalTree to Object Tree
//FOR each node in LocalTree DO
//Set node.Remaining to RemainingAccess
//END FOR
//END IF
if (objectTree != null && objectTree.Root != null)
{
localTree = (AccessCheckObjectTree)ObjectUtility.DeepClone(objectTree);
List<Guid> tmpList = new List<Guid>();
tmpList.Add(localTree.Root.Value);
tmpList.AddRange(localTree.GetDescendentNodes(localTree.Root.Value));
allNodes = tmpList.ToArray();
foreach (Guid node in allNodes)
{
localTree.SetTreeNodeData(node, remainingAccess);
}
}
//FOR each ACE in DACL DO
//IF ACE.flag does not contain INHERIT_ONLY_ACE THEN
//CASE ACE.Type OF
//CASE Allow Access:
//CALL SidInToken( Token, ACE.Sid, and PrincipalSelfSubst )
//IF SidInToken returns True THEN
// Remove ACE.AccessMask from RemainingAccess
// FOR each node in LocalTree DO
// Remove ACE.AccessMask from node.Remaining
//END FOR
//END IF
//CASE Deny Access:
//CALL SidInToken( Token, ACE.Sid, PrincipalSelfSubst )
//IF SidInToken returns True THEN
// IF any bit of RemainingAccess is in ACE.AccessMask THEN
// Return access_denied
//END IF
//END IF
//CASE Object Allow Access:
//CALL SidInToken( Token, ACE.Sid, PrincipalSelfSubst )
//IF SidInToken returns True THEN
// IF ACE.Object is contained in LocalTree THEN
// Locate node n in LocalTree such that
// n.GUID is the same as ACE.Object
// Remove ACE.AccessMask from n.Remaining
// FOR each node ns such that ns is a descendent of n DO
// Remove ACE.AccessMask from ns.Remaining
// END FOR
// FOR each node np such that np is an ancestor of n DO
// Set np.Remaining = np.Remaining or np-1.Remaining
//END FOR
//END IF
//END IF
//CASE Object Deny Access:
//CALL SidInToken( Token, ACE.Sid, PrincipalSelfSubst )
//IF SidInToken returns True THEN
// Locate node n in LocalTree such that
// n.GUID is the same as ACE.Object
// IF n exists THEN
// If any bit of n.Remaining is in ACE.AccessMask THEN
// Return access_denied
//END IF
//END IF
//END IF
//END CASE
//END IF
//END FOR
if (dacl.Value.Aces != null)
{
foreach (object ace in dacl.Value.Aces)
{
_ACE_HEADER header = (_ACE_HEADER)ObjectUtility.GetFieldValue(ace, "Header");
_SID sid = (_SID)ObjectUtility.GetFieldValue(ace, "Sid");
if ((header.AceFlags & ACE_FLAGS.INHERIT_ONLY_ACE) == ACE_FLAGS.INHERIT_ONLY_ACE
|| !SidInToken(token, sid, principalSelfSubstitudeSid))
{
continue;
}
bool ret = DtypUtility.AceAccessCheck(ace, ref remainingAccess, ref localTree, allNodes);
if (ret == false)
{
return false;
}
}
}
//IF RemainingAccess = 0 THEN
//Return success
//Else
//Return access_denied
//END IF
bool status;
if (objectTree != null && objectTree.Root != null)
{
status = (localTree.GetTreeNodeData(localTree.Root.Value) == 0);
}
else
{
status = (remainingAccess == 0);
}
return status;
}
/// <summary>
/// The sub function of the AccessCheck algorithm
/// </summary>
/// <param name="ace">The current ace to be dealt with.</param>
/// <param name="remainingAccess">The current requested permissions. </param>
/// <param name="localTree">
/// The current tree representation of the hierarchy of objects for which to check access.
/// </param>
/// <param name="allNodes">All the nodes in the current tree.</param>
/// <returns>Return FALSE if access is denied. Otherwise, it returns TRUE.</returns>
private static bool AceAccessCheck(
object ace,
ref uint remainingAccess,
ref AccessCheckObjectTree localTree,
Guid[] allNodes)
{
if (localTree != null && localTree.Root != null)
{
List<Guid> tmpList = new List<Guid>();
tmpList.Add(localTree.Root.Value);
tmpList.AddRange(localTree.GetDescendentNodes(localTree.Root.Value));
allNodes = tmpList.ToArray();
}
_ACE_HEADER header = (_ACE_HEADER)ObjectUtility.GetFieldValue(ace, "Header");
uint mask = (uint)ObjectUtility.GetFieldValue(ace, "Mask");
ACCESS_OBJECT_ACE_Flags flags = ACCESS_OBJECT_ACE_Flags.None;
ACE_TYPE aceType = header.AceType;
if (header.AceType == ACE_TYPE.ACCESS_ALLOWED_OBJECT_ACE_TYPE
|| header.AceType == ACE_TYPE.ACCESS_DENIED_OBJECT_ACE_TYPE)
{
flags = (ACCESS_OBJECT_ACE_Flags)ObjectUtility.GetFieldValue(ace, "Flags");
if ((flags & ACCESS_OBJECT_ACE_Flags.ACE_OBJECT_TYPE_PRESENT)
!= ACCESS_OBJECT_ACE_Flags.ACE_OBJECT_TYPE_PRESENT)
{
aceType = (header.AceType == ACE_TYPE.ACCESS_ALLOWED_OBJECT_ACE_TYPE)
? ACE_TYPE.ACCESS_ALLOWED_ACE_TYPE
: ACE_TYPE.ACCESS_DENIED_ACE_TYPE;
}
}
switch (aceType)
{
//CASE ACE.Type OF
//CASE Allow Access:
//CALL SidInToken( Token, ACE.Sid, and PrincipalSelfSubst )
//IF SidInToken returns True THEN
// Remove ACE.AccessMask from RemainingAccess
// FOR each node in LocalTree DO
// Remove ACE.AccessMask from node.Remaining
// END FOR
//END IF
//CASE Deny Access:
//CALL SidInToken( Token, ACE.Sid, PrincipalSelfSubst )
//IF SidInToken returns True THEN
// IF any bit of RemainingAccess is in ACE.AccessMask THEN
// Return access_denied
//END IF
//END IF
case ACE_TYPE.ACCESS_ALLOWED_ACE_TYPE:
remainingAccess &= ~mask;
foreach (Guid node in allNodes)
{
uint newRemaining = localTree.GetTreeNodeData(node) & ~mask;
localTree.SetTreeNodeData(node, newRemaining);
}
break;
case ACE_TYPE.ACCESS_DENIED_ACE_TYPE:
if ((remainingAccess & mask) != 0)
{
return false;
}
break;
//CASE Object Allow Access:
//CALL SidInToken( Token, ACE.Sid, PrincipalSelfSubst )
//IF SidInToken returns True THEN
// IF ACE.Object is contained in LocalTree THEN
// Locate node n in LocalTree such that
// n.GUID is the same as ACE.Object
// Remove ACE.AccessMask from n.Remaining
// FOR each node ns such that ns is a descendent of n DO
// Remove ACE.AccessMask from ns.Remaining
// END FOR
// FOR each node np such that np is an ancestor of n DO
// Set np.Remaining = np.Remaining or np-1.Remaining //Filed TDI 55801
//END FOR
//END IF
//END IF
case ACE_TYPE.ACCESS_ALLOWED_OBJECT_ACE_TYPE:
Guid objectType = (Guid)ObjectUtility.GetFieldValue(ace, "ObjectType");
if (localTree.ContainsTreeNode(objectType))
{
uint newRemaining = localTree.GetTreeNodeData(objectType) & ~mask;
localTree.SetTreeNodeData(objectType, newRemaining);
Guid[] descendent = localTree.GetDescendentNodes(objectType);
if (descendent.Length > 0)
{
foreach (Guid nodeGuid in descendent)
{
newRemaining = localTree.GetTreeNodeData(nodeGuid) & ~mask;
localTree.SetTreeNodeData(nodeGuid, newRemaining);
}
}
DtypUtility.AncestorNodesAccessCheck(objectType, ref localTree);
}
break;
//CASE Object Deny Access:
//CALL SidInToken( Token, ACE.Sid, PrincipalSelfSubst )
//IF SidInToken returns True THEN
// Locate node n in LocalTree such that
// n.GUID is the same as ACE.Object
// IF n exists THEN
// If any bit of n.Remaining is in ACE.AccessMask THEN
// Return access_denied
//END IF
//END IF
//END IF
//END CASE
case ACE_TYPE.ACCESS_DENIED_OBJECT_ACE_TYPE:
Guid objectType2 = (Guid)ObjectUtility.GetFieldValue(ace, "ObjectType");
foreach (Guid node in allNodes)
{
if (node == objectType2 && (localTree.GetTreeNodeData(node) & mask) != 0)
{
return false;
}
}
break;
}
return true;
}
