Documentation Security Beat

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Beat Closed on Wiki
Work on beats has now moved to git. If you have changes or additions, please contact the docs team via #fedora-docs, docs@lists.fp.o, or with the fedora-release-notes BZ component.

Hardlink and symlink restrictions

A long-standing class of security issues is the link-based time-of-check-time-of-use race, most commonly seen in world-writable directories like /tmp. The common method of exploitation of this flaw is to cross privilege boundaries when following a given link (i.e. a root process follows a link belonging to another user). In Fedora 19, we permit links to only be followed when outside a sticky world-writable directory, or when the uid of the link and follower match, or when the directory owner matches the link's owner. In previous releases, this was enforced by SELinux policy and in this release, we have enabled these restrictions via the following sysctl settings in /usr/lib/sysctl.d/00-system.conf as an additional layer of protection:

fs.protected_hardlinks = 1
fs.protected_symlinks = 1

Refer to and for more detailed information about this change. Note that in addition to this,