explains why Linux allows users to escape a chroot() jail

Ah, but Linux, AFAIK, doesn't allow just any user to escape the chroot() environment. It only allows the super-user to escape it.

I think we might be referring to two different special cases.

As for when /.. = /. = / is implemented, I wouldn't think it would happen during mkfs because mkfs would have no way of knowing whether the filesystem in question would be used as the root fs or not. (Might there be something going on when the root fs is mounted?) My understanding of this stuff is admittedly weak; I'd be happy to receive some enlightenment.

-sauoq
"My two cents aren't worth a dime.";

The root file system is the only file system that doesn't need /. and /.. to be special.

The special case is when a file system is mounted as a non-root filesystem, as then /mount/point/.. needs to appear to refer to the same inode as /mount does. The same is true of chroot(). The Linux code seems to jump through quite a few hoops (with functions names like 'graft_tree()') to deal with mounts...