Fix ResourceUpdater.Dispose() (#120029)

The apphost ResourceUpdater doesn't dispose of the PEReader when leaveOpen is true, but the leaveOpen should only apply to the FileStream passed to the constructor. The PEReader is not accessible from the creator and cannot be disposed of elsewhere. This causes some race conditions, especially in cases where the PEReader ends up mapping the file into memory.

Fixes dotnet/sdk#50784

Author: jtschuster

src/installer/managed/Microsoft.NET.HostModel/ResourceUpdater.cs

@@ -13,7 +13,7 @@ namespace Microsoft.NET.HostModel
     /// <summary>
     /// Provides methods for modifying the embedded native resources in a PE image.
     /// </summary>
-    public class ResourceUpdater : IDisposable
+    public sealed class ResourceUpdater : IDisposable
     {
         private readonly FileStream stream;
         private readonly PEReader _reader;
@@ -331,12 +331,15 @@ public void Dispose()
             GC.SuppressFinalize(this);
         }
 
-        public void Dispose(bool disposing)
+        private void Dispose(bool disposing)
         {
-            if (disposing && !leaveOpen)
+            if (disposing)
             {
                 _reader.Dispose();
-                stream.Dispose();
+                if (!leaveOpen)
+                {
+                    stream.Dispose();
+                }
             }
         }
     }

src/installer/tests/Microsoft.NET.HostModel.Tests/ResourceUpdaterTests.cs

@@ -23,7 +23,7 @@ class TempFile : IDisposable
         public TempFile()
         {
             _path = Path.GetTempFileName();
-            Stream = new FileStream(_path, FileMode.Open);
+            Stream = new FileStream(_path, FileMode.Open, FileAccess.ReadWrite, FileShare.None);
         }
 
         public void Dispose()
@@ -169,6 +169,25 @@ void AddResource_AddTwoSameUShortTypeWithDifferName()
         }
     }
 
+    [Fact]
+    void DisposeWithLeaveOpenDisposesPEReader()
+    {
+        using var tempFile = GetCurrentAssemblyMemoryStream();
+        PEReader? peReader = null;
+
+        using (var updater = new ResourceUpdater(tempFile.Stream, leaveOpen: true))
+        {
+            FieldInfo? readerField = typeof(ResourceUpdater).GetField("_reader", BindingFlags.Instance | BindingFlags.NonPublic);
+            Assert.NotNull(readerField);
+            peReader = Assert.IsType<PEReader>(readerField.GetValue(updater));
+            _ = peReader.PEHeaders;
+        }
+
+        Assert.NotNull(peReader);
+
+        Assert.Throws<ObjectDisposedException>(() => _ = peReader!.PEHeaders);
+    }
+
     [Fact]
     void AddResourcesFromPEImage()
     {