Only allow trusted overlays to specify FLAG_SLIPPERY

For all other requests, drop this flag.

Test: atest FlagSlipperyTest
Bug: 157929241
Change-Id: Ia30f1c38d5ddb351c90b748ea76448a76a9dde7b
Merged-In: Ia30f1c38d5ddb351c90b748ea76448a76a9dde7b

services/core/java/com/android/server/wm/DisplayPolicy.java

@@ -62,6 +62,7 @@ import static android.view.WindowManager.LayoutParams.FLAG_LAYOUT_INSET_DECOR;
 import static android.view.WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN;
 import static android.view.WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS;
 import static android.view.WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
+import static android.view.WindowManager.LayoutParams.FLAG_SLIPPERY;
 import static android.view.WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION;
 import static android.view.WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS;
 import static android.view.WindowManager.LayoutParams.LAST_APPLICATION_WINDOW;
@@ -833,6 +834,20 @@ public class DisplayPolicy {
                 == PackageManager.PERMISSION_GRANTED;
     }
 
+    /**
+     * Only trusted overlays are allowed to use FLAG_SLIPPERY.
+     */
+    static int sanitizeFlagSlippery(int flags, int privateFlags, String name) {
+        if ((flags & FLAG_SLIPPERY) == 0) {
+            return flags;
+        }
+        if ((privateFlags & PRIVATE_FLAG_TRUSTED_OVERLAY) != 0) {
+            return flags;
+        }
+        Slog.w(TAG, "Removing FLAG_SLIPPERY for non-trusted overlay " + name);
+        return flags & ~FLAG_SLIPPERY;
+    }
+
     /**
      * Sanitize the layout parameters coming from a client.  Allows the policy
      * to do things like ensure that windows of a specific type can't take
@@ -916,6 +931,7 @@ public class DisplayPolicy {
                 }
                 break;
         }
+        attrs.flags = sanitizeFlagSlippery(attrs.flags, attrs.privateFlags, win.getName());
     }
 
     /**

services/core/java/com/android/server/wm/WindowManagerService.java

@@ -55,6 +55,7 @@ import static android.view.WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
 import static android.view.WindowManager.LayoutParams.FLAG_SECURE;
 import static android.view.WindowManager.LayoutParams.FLAG_SHOW_WALLPAPER;
 import static android.view.WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED;
+import static android.view.WindowManager.LayoutParams.FLAG_SLIPPERY;
 import static android.view.WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL;
 import static android.view.WindowManager.LayoutParams.LAST_APPLICATION_WINDOW;
 import static android.view.WindowManager.LayoutParams.LAST_SUB_WINDOW;
@@ -8086,8 +8087,9 @@ public class WindowManagerService extends IWindowManager.Stub
         h.token = channelToken;
         h.name = name;
 
-        final int sanitizedFlags = flags & (LayoutParams.FLAG_NOT_TOUCHABLE
+        flags = DisplayPolicy.sanitizeFlagSlippery(flags, privateFlags, name);
-                | LayoutParams.FLAG_SLIPPERY);
+
+        final int sanitizedFlags = flags & (LayoutParams.FLAG_NOT_TOUCHABLE | FLAG_SLIPPERY);
         h.layoutParamsFlags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL | sanitizedFlags;
         h.layoutParamsType = type;
         h.dispatchingTimeoutNanos = DEFAULT_INPUT_DISPATCHING_TIMEOUT_NANOS;