1 files changed, 26 insertions, 1 deletions
diff --git a/src/Agent.Windows/Security/TaskAclManager.cs b/src/Agent.Windows/Security/TaskAclManager.cs
index be0080d..6534e5a 100644
--- a/src/Agent.Windows/Security/TaskAclManager.cs
+++ b/src/Agent.Windows/Security/TaskAclManager.cs
@@ -1,13 +1,34 @@
+using System.ComponentModel;
+using System.Runtime.InteropServices;
 using System.Security.AccessControl;
 using System.Security.Principal;
 using Agent.Windows.Recovery;
+using Microsoft.Win32.SafeHandles;
 
 namespace Agent.Windows.Security;
 
 public sealed record AclSnapshot(string Path, byte[] SecurityDescriptor, Guid? JournalEntryId = null);
 
-public sealed class TaskAclManager(SecurityIdentifier appContainerSid, ISecurityAuditSink audit, TaskResourceJournal? journal = null)
+public sealed partial class TaskAclManager(SecurityIdentifier appContainerSid, ISecurityAuditSink audit, TaskResourceJournal? journal = null)
 {
+    private const uint WriteDac = 0x00040000;
+    private const uint ShareReadWriteDelete = 0x00000007;
+    private const uint OpenExisting = 3;
+    private const uint BackupSemantics = 0x02000000;
+
+    public static void DemandWriteDac(string path)
+    {
+        string canonical = ResolvedPath.Resolve(path);
+        uint flags = Directory.Exists(canonical) ? BackupSemantics : 0;
+        using SafeFileHandle handle = CreateFile(canonical, WriteDac, ShareReadWriteDelete, 0, OpenExisting, flags, 0);
+        if (!handle.IsInvalid) return;
+        int error = Marshal.GetLastPInvokeError();
+        throw new SandboxPolicyException("sandbox.access_denied",
+            $"The current user cannot open '{canonical}' with WRITE_DAC ({new Win32Exception(error).Message}).",
+            "acl", canonical, "WRITE_DAC",
+            "Use a root owned by the current user or grant that user WRITE_DAC; elevation does not bypass this requirement.");
+    }
+
     public AclSnapshot Grant(Guid taskId, string path, FileCapability capabilities)
     {
         string canonical = ResolvedPath.Resolve(path);
@@ -112,4 +133,8 @@ public sealed class TaskAclManager(SecurityIdentifier appContainerSid, ISecurity
         if ((capabilities & FileCapability.Delete) != 0) rights |= FileSystemRights.Delete | FileSystemRights.DeleteSubdirectoriesAndFiles;
         return rights;
     }
+
+    [LibraryImport("kernel32.dll", EntryPoint = "CreateFileW", SetLastError = true, StringMarshalling = StringMarshalling.Utf16)]
+    private static partial SafeFileHandle CreateFile(string fileName, uint desiredAccess, uint shareMode,
+        nint securityAttributes, uint creationDisposition, uint flagsAndAttributes, nint templateFile);
 }