NullReferenceException in Opc.Ua.Server.MasterNodeManager.ValidateRolePermissions()

[GhislainPr]

Type of issue

• Bug
• Enhancement
• Compliance
• Question
• Help wanted

Current Behavior

NullReferenceException in Opc.Ua.Server.MasterNodeManager.ValidateRolePermissions() method if Opc.Ua.NodeState.ClearChangeMasks() is called while Opc.Ua.Server.CustomNodeManager2.CreateMonitoredItems() is processing.
In this case, the Session property of MonitoredItem is null.

Expected Behavior

No exception attempted while changing nodes during monitoreditem creation.

Steps To Reproduce

It's difficult to reproduce because it's depend on thread synchronization.

Environment

- OS: Windows 11
- Environment: Visual Studio 2022
- Runtime: .NET 4.6.2,
- Nuget Version: 1.05.375.457
- Component: Opc.Ua.Server
- Server: Reference Server
- Client: UA Expert

Anything else?

Suggested solution in Libraries/Opc.Ua.Server/Diagnostics/MonitoredNode.cs :
295 : if (monitoredItem.Session != null && monitoredItem.AttributeId == Attributes.Value && (changes & NodeStateChangeMasks.Value) != 0)

instead of :
295 : if (monitoredItem.AttributeId == Attributes.Value && (changes & NodeStateChangeMasks.Value) != 0)

[romanett]

@GhislainPr I dont see MasterNodeManager.ValidateRolePermissions access the Session, validation should take place with the saved user identity:

UA-.NETStandard/Libraries/Opc.Ua.Server/NodeManager/MasterNodeManager.cs

Line 3434 in 66ba504

var currentRoleIds = context.UserIdentity.GrantedRoleIds;

MonitoredItem is expected to have a null Session in some cases

[GhislainPr]

Thanks for your interest.

I try to detail the technical context :
In one thread, Opc.Ua.NodeState.ClearChangeMasks() is called.
In the call stack of the Opc.Ua.Server.MasterNodeManager.ValidateRolePermissions() method is also called (MonitoredNode.cs line 298 : ServiceResult validationResult = NodeManager.ValidateRolePermissions(new OperationContext(monitoredItem), node.NodeId, PermissionType.Read);). At this step, A OperationContext is created from a monitoredItem, whith this Session property value equals to null. So, the value of the Identity property of OperationContext stills null. The processing continue until the crash in ValidateRolePermissions() method (MasterNodeManager.cs line 3323 : var currentRoleIds = context.UserIdentity.GrantedRoleIds;).

During this time, in another thread, Opc.Ua.Server.Subscription.CreateMonitoredItems() is locked (Subscription.cs line 1473 : lock (m_lock)). At this step, MonitoredItems are created, but their SubscriptionCallbacbk property still at null value. Their value is set some instructions after in Subscription.cs line 1499 : monitoredItem.SubscriptionCallback = this;.