CrOS FilesApp: Comments and test to disallow sharing DriveFS .Trash with crostini

Bug: 878324
Change-Id: I2eaec453ff0555b6a77c8dd650a705f8be2d89bd
Reviewed-on: https://chromium-review.googlesource.com/c/1300818Reviewed-by: Timothy Loh <timloh@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603000}

chrome/browser/chromeos/crostini/crostini_share_path.cc

@@ -75,11 +75,12 @@ void CallSeneschalSharePath(
              base::FilePath("/media/fuse")
                  .AppendRelativePath(drivefs_mount_point_path,
                                      &drivefs_mount_name)) {
-    // Allow subdirs of DriveFS.
+    // Allow subdirs of DriveFS except .Trash.
     request.set_drivefs_mount_name(drivefs_mount_name.value());
     base::FilePath root("root");
     base::FilePath team_drives("team_drives");
     base::FilePath computers("Computers");
+    base::FilePath trash(".Trash");  // Not to be shared!
     if (root == drivefs_path ||
         root.AppendRelativePath(drivefs_path, &relative_path)) {
       // My Drive and subdirs.
@@ -98,6 +99,11 @@ void CallSeneschalSharePath(
       allowed_path = true;
       request.set_storage_location(
           vm_tools::seneschal::SharePathRequest::DRIVEFS_COMPUTERS);
+    } else if (trash == drivefs_path || trash.IsParent(drivefs_path)) {
+      // Note: Do not expose .Trash which would allow linux apps to make
+      // permanent deletes from Drive.  This branch is not especially required,
+      // but is included to make it explicit that .Trash should not be shared.
+      allowed_path = false;
     }
   } else if (base::FilePath("/media/removable")
                  .AppendRelativePath(path, &relative_path)) {

chrome/browser/chromeos/crostini/crostini_share_path_unittest.cc

@@ -271,6 +271,16 @@ TEST_F(CrostiniSharePathTest, SuccessDriveFsComputers) {
   run_loop()->Run();
 }
 
+TEST_F(CrostiniSharePathTest, FailDriveFsTrash) {
+  SharePath(
+      profile(), "vm-running", drivefs_.Append(".Trash").Append("in-the-trash"),
+      false,
+      base::BindOnce(&CrostiniSharePathTest::SharePathCallback,
+                     base::Unretained(this), false, false, nullptr, "", false,
+                     "Path is not allowed", run_loop()->QuitClosure()));
+  run_loop()->Run();
+}
+
 TEST_F(CrostiniSharePathTest, SuccessRemovable) {
   SharePath(profile(), "vm-running", base::FilePath("/media/removable/MyUSB"),
             false,