From 2a06b5901650d23eba75f211d5a4cf5d3522ad7c Mon Sep 17 00:00:00 2001
From: Hannah von Reth <hannah.vonreth@owncloud.com>
Date: Tue, 5 Oct 2021 11:45:30 +0200
Subject: Prevent downgrade of Windows VFS folders

---
 changelog/unreleased/9114 |  5 +++++
 src/gui/folder.cpp        | 11 ++++++-----
 src/gui/folder.h          |  3 ++-
 3 files changed, 13 insertions(+), 6 deletions(-)
 create mode 100644 changelog/unreleased/9114

diff --git a/changelog/unreleased/9114 b/changelog/unreleased/9114
new file mode 100644
index 000000000..39afc7d45
--- /dev/null
+++ b/changelog/unreleased/9114
@@ -0,0 +1,5 @@
+Bugfix: Downgrades could trigger deletion of virtual files
+
+We now prevent the downgrade of Windows VFS folders.
+
+https://github.com/owncloud/client/issues/9114
diff --git a/src/gui/folder.cpp b/src/gui/folder.cpp
index 31c11ebd9..b6c7afa4f 100644
--- a/src/gui/folder.cpp
+++ b/src/gui/folder.cpp
@@ -58,6 +58,9 @@ auto versionC()
 {
     return QStringLiteral("version");
 }
+
+constexpr int WinVfsSettingsVersion = 4;
+constexpr int SettingsVersion = 2;
 }
 
 namespace OCC {
@@ -1309,11 +1312,9 @@ void FolderDefinition::save(QSettings &settings, const FolderDefinition &folder)
     settings.setValue(QStringLiteral("virtualFilesMode"), Vfs::modeToString(folder.virtualFilesMode));
 
     // Ensure new vfs modes won't be attempted by older clients
-    if (folder.virtualFilesMode == Vfs::WindowsCfApi) {
-        settings.setValue(versionC(), 3);
-    } else {
-        settings.setValue(versionC(), 2);
-    }
+    const int version = folder.virtualFilesMode == Vfs::WindowsCfApi ? WinVfsSettingsVersion : SettingsVersion;
+    Q_ASSERT(version <= maxSettingsVersion());
+    settings.setValue(versionC(), version);
 
     // Happens only on Windows when the explorer integration is enabled.
     if (!folder.navigationPaneClsid.isNull())
diff --git a/src/gui/folder.h b/src/gui/folder.h
index ecd3327a9..3f7d30737 100644
--- a/src/gui/folder.h
+++ b/src/gui/folder.h
@@ -90,8 +90,9 @@ public:
      * Version 2: introduction of metadata_parent hash in 2.6.0
      *            (version remains readable by 2.5.1)
      * Version 3: introduction of new windows vfs mode in 2.6.0
+     * Version 4: until 2.9.1 windows vfs tried to unregister folders with a different id from windows.
      */
-    static int maxSettingsVersion() { return 3; }
+    static int maxSettingsVersion() { return 4; }
 
     /// Ensure / as separator and trailing /.
     static QString prepareLocalPath(const QString &path);
-- 
cgit v1.2.3