Linux, politics, and other interesting things
The book SE Linux by Example has been reviewed on Slashdot.
The issue of Perl scripts was raised for discussion. It is of course true that a domain which is permitted to run the Perl interpreter can perform arbitrary system calls – it can therefore do anything that SE Linux permits that domain to do. This is in fact a demonstration of how SE Linux does the right thing! If you want to restrict what can be done when executing the Perl interpreter then you can have a domain_auto_trans() rule to have Perl run in a different domain.
Restricting Perl (as used by one particular program) is actually easier than restricting a complex application run by users such as Firefox. Users want to use Firefox for web browsing, local HTML file browsing, saving files that are downloaded from the web, running plugins, and more. Granting Firefox access to perform all those tasks means that it is not restricted from doing anything that the user can do.
A claim was made that a novice users would not understand how to use SE Linux. The fact is that they don’t need to. I know many novice computer users who are running SE Linux systems, it just works! It’s more advanced users that have to learn about SE Linux because they configure their machines more heavily.
The essential difference between path-based access control and Inode based access control is that the standard Unix commands to control file access (chmod, chown, and chgrp) all operate on Inodes. If a file has 1000 hard links then I can restrict access to all of them via a single chmod or chcon (the SE Linux command that is comparable to chmod) command. AppArmor does things differently and implements an access control model that is vastly different to the Unix traditions. SE Linux extends the Unix traditions with Mandatory Access Control.
Granting different levels of access to a file based on the name of the link which is used is a horror not a feature.
I wrote this as a blog entry rather than a /. comment because my lack of Karma means that less people will read my /. comments than my blog.Tags: Best Posts, Selinux