Return a snapshot of handles and enforce ReadWrite in FUSE

Author: d2dyno1

src/Core/SecureFolderFS.Core.FUSE/OpenHandles/FuseHandlesManager.cs

@@ -13,12 +13,22 @@ public FuseHandlesManager(StreamsAccess streamsAccess, VirtualFileSystemOptions
         {
         }
 
+        /// <summary>
+        /// Provides an enumerable collection of all currently active handles managed by the instance.
+        /// </summary>
+        /// <remarks>
+        /// The handles are returned as a snapshot of the internal collection to prevent race conditions
+        /// when accessing or enumerating the data. Any modifications to the collection are thread-safe
+        /// and do not affect the snapshot returned by this property.
+        /// </remarks>
         public IEnumerable<IDisposable> OpenHandles
         {
             get
             {
+                // Return a snapshot - the live collection could be mutated
+                // by another thread while the caller is enumerating it
                 lock (handles)
-                    return handles.Values;
+                    return handles.Values.ToArray();
             }
         }
 
@@ -38,7 +48,11 @@ public override ulong OpenFileHandle(string ciphertextPath, FileMode mode, FileA
                 // A file cannot be opened with both FileMode.Append and FileMode.Read, but opening it with
                 // FileMode.Write would cause an error when writing, as the stream needs to be readable.
                 Mode = mode == FileMode.Append ? FileMode.Open : mode,
-                Access = FileAccess.ReadWrite,
+
+                // Writes require read access as well (chunks are read-modify-write), but read-only
+                // opens must not request write access. Otherwise, files with read-only permissions
+                // (or vaults on read-only media) could not be opened at all
+                Access = access == FileAccess.Read ? FileAccess.Read : FileAccess.ReadWrite,
                 Share = share | FileShare.Delete,
                 Options = options
             });