Original owner did chmod 666... after making sure traditional unix
permissions protect the file. Please look at original mail; it was
subtle but I believe I got it right, and file would not be writable
with /proc unmounted.
I remember the original mail content. You're right, you can't reach
the file if the procfs is not mounted, but you forget about the
race, allowing the guest to create a hardlink to the file in an
unrestricted location before the directory access becomes
restricted. Again, procfs is just another, specific kind of
hardlinks.