Patch for the Linux Kernel to implement "SymlinksIfOwnerMatches" features

This is a patch that implements a symlink protection feature in the Linux kernel. For a configurable group all file accesses with symlinks will only be approved if the owner of the symlink target matches the owner of the symlink.

This prevents attacks with web servers on multiuser systems. This attack was used in the hack of Freedom Hosting II.

Background:

• https://blog.hboeck.de/archives/873-The-tricky-security-issue-with-FollowSymLinks-and-Apache.html
• https://securityaffairs.co/wordpress/55990/deep-web/freedom-hosting-ii-hack.html

If you get rejects when applying the latest patch to the latest upstream kernel please open an issue and I'll try to update it.

This patch is extracted from the grsecurity kernel patch. It is licensed (like the Linux kernel itself) under the GPL version 2.

Copyright 2014-2017 by Open Source Security, Inc., Brad Spengler [email protected] and PaX Team [email protected]

The only thing I did is extract the patch out of the larger grsecurity patchset.

Hanno Böck, https://hboeck.de/