Yenya's World

Mon, 16 Jul 2007

Referer Abuse

Well, not really abuse, but a clever hack of a HTTP Referer: header. While looking for information about new "polyinstantiated directories" feature I have found the namespace.conf(5) manpage on some web site.

The URL is, and it looks as an ordinary page. However, when you do a Google search for polyinstantiated directories and follow the link to namespace.conf(5) (today it was in the middle of the search results page), the searched keywords get highlighted. The highlighting is done by the Javascript at

This cool hack aside, the subject itself (polyinstantiated directories) is interesting on its own. It seems that the support for this has been in the kernel for a while (check whether your /proc/mounts is in fact a symlink to /proc/self/mounts), the user-space (Fedora rawhide) now supports it via the pam_namespace PAM module. Further reading on this topic include the SAGE-2006 talk by Russel Coker, and the Documentation/sharedsubtree.txt file from the kernel sources.

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