From 7e0f84c7cefed3231921846996caaeefbf00ec5c Mon Sep 17 00:00:00 2001
From: Giovanni Campagna <gcampagna@src.gnome.org>
Date: Mon, 26 Nov 2012 20:18:57 +0100
Subject: [PATCH] ScreenShield: try harder to become modal, and catch failures

The screenshield was not checking the return value of pushModal(), meaning
that it believed it was fully locked when it was not. Later, calling
popModal() would fail, causing an exception and blocking the unlock.
Now we do nothing for user initiated actions, and fail with an explanatory
message at idle time.

https://bugzilla.gnome.org/show_bug.cgi?id=689106
---
 js/ui/screenShield.js | 43 ++++++++++++++++++++++++++++++++++---------
 1 file changed, 34 insertions(+), 9 deletions(-)

diff --git a/js/ui/screenShield.js b/js/ui/screenShield.js
index 278f7fbc9..4cacad3cc 100644
--- a/js/ui/screenShield.js
+++ b/js/ui/screenShield.js
@@ -442,6 +442,20 @@ const ScreenShield = new Lang.Class({
         this.idleMonitor = Shell.IdleMonitor.get();
     },
 
+    _becomeModal: function() {
+        if (this._isModal)
+            return true;
+
+        this._isModal = Main.pushModal(this.actor);
+        if (this._isModal)
+            return true;
+
+        // We failed to get a pointer grab, it means that
+        // something else has it. Try with a keyboard grab only
+        this._isModal = Main.pushModal(this.actor, { options: Meta.ModalOptions.POINTER_ALREADY_GRABBED });
+        return this._isModal;
+    },
+
     _onLockScreenKeyRelease: function(actor, event) {
         let symbol = event.get_key_symbol();
 
@@ -560,9 +574,17 @@ const ScreenShield = new Lang.Class({
             }
         }
 
-        if (!this._isModal) {
-            Main.pushModal(this.actor);
-            this._isModal = true;
+        if (!this._becomeModal()) {
+            // We could not become modal, so we can't activate the
+            // screenshield. The user is probably very upset at this
+            // point, but any application using global grabs is broken
+            // Just tell him to stop using this app
+            //
+            // XXX: another option is to kick the user into the gdm login
+            // screen, where we're not affected by grabs
+            Main.notifyError("Unable to lock",
+                             "Lock was blocked by an application");
+            return;
         }
 
         if (!this._isActive) {
@@ -604,9 +626,10 @@ const ScreenShield = new Lang.Class({
         // Ensure that the stage window is mapped, before taking a grab
         // otherwise X errors out
         Meta.later_add(Meta.LaterType.BEFORE_REDRAW, Lang.bind(this, function() {
-            if (!this._isModal) {
-                Main.pushModal(this.actor);
-                this._isModal = true;
+            if (!this._becomeModal()) {
+                // In the login screen, this is a hard error. Fail-whale
+                log('Could not acquire modal grab for the login screen. Aborting login process.');
+                Meta.quit(Meta.ExitCode.ERROR);
             }
 
             return false;
@@ -862,9 +885,11 @@ const ScreenShield = new Lang.Class({
     },
 
     lock: function(animate) {
-        if (!this._isModal) {
-            Main.pushModal(this.actor);
-            this._isModal = true;
+        // Warn the user if we can't become modal
+        if (!this._becomeModal()) {
+            Main.notifyError("Unable to lock",
+                             "Lock was blocked by an application");
+            return;
         }
 
         if (this._activationTime == 0)