Comment 4 for bug 1241465

so, in /DistUpgrade/DistUpgradeController.py

after line 381, inserting something like this would possibly patch this bug:

                while os.path.islink(fs_default_version) :
                    fs_default_version = os.readlink(fs_default_version)

It would be an endless loop if links are circular though. Adding a counter for a maximum depth is one way out...
Another would be to add the visited links to a list and checking it to see if the current link is already in the list. If so. break and return an error of some sort. But it would be a very unusual configuration to find.