Avoid null-pointer dereference for PPAPI Instance BindGraphics....

webkit/plugins/ppapi/ppapi_plugin_instance.cc

Index: webkit/plugins/ppapi/ppapi_plugin_instance.cc
===================================================================
--- webkit/plugins/ppapi/ppapi_plugin_instance.cc	(revision 72340)
+++ webkit/plugins/ppapi/ppapi_plugin_instance.cc	(working copy)
@@ -460,16 +460,18 @@
       // repaints.
       const SkBitmap* old_backing_bitmap =
           bound_graphics_2d()->image_data()->GetMappedBitmap();

[David Springer, 2011/01/24 20:19:29]

Is there any chance that these accessors could return a NULL ptr?  E.g. I can
imagine image_data() returning a NULL ptr while initialization is going on in
the NaCl process.  It seems to me that the chance of a NULL ptr is greater when
using a NaCl process than when using a trusted plugin.

-      SkRect old_size = SkRect::MakeWH(
-          SkScalar(static_cast<float>(old_backing_bitmap->width())),
-          SkScalar(static_cast<float>(old_backing_bitmap->height())));
+      if (old_backing_bitmap != NULL) {

[brettw, 2011/01/24 21:00:07]

Instead of checking to see if there's no mapped bitmap, this should just map the
data. Can you use an ImageDataAutoMapper on the image data? Then GetMappedBitmap
will always return success.

+        SkRect old_size = SkRect::MakeWH(
+            SkScalar(static_cast<float>(old_backing_bitmap->width())),
+            SkScalar(static_cast<float>(old_backing_bitmap->height())));
 
-      SkCanvas canvas(*graphics_2d->image_data()->GetMappedBitmap());
-      canvas.drawBitmap(*old_backing_bitmap, 0, 0);
+        SkCanvas canvas(*graphics_2d->image_data()->GetMappedBitmap());
+        canvas.drawBitmap(*old_backing_bitmap, 0, 0);
 
-      // Fill in any extra space with white.
-      canvas.clipRect(old_size, SkRegion::kDifference_Op);
-      canvas.drawARGB(255, 255, 255, 255);
+        // Fill in any extra space with white.
+        canvas.clipRect(old_size, SkRegion::kDifference_Op);
+        canvas.drawARGB(255, 255, 255, 255);
+      }
     }
 
     bound_graphics_ = graphics_2d;