Kernel Korner - Filesystem Labeling in SELinux
Although it is possible to assign security context labels to NFS mounted filesystems, they operate only locally for access control decisions within the kernel. No labels are transmitted across the network with files. Work has been advancing in this area, with SELinux-specific modifications being made to the NFSv2/v3 protocols and code. Further down the track, NFSv4 integration is expected to involve labeling over the wire by way of named attributes, which are part of the more extensible NFSv4 specification. This would allow both the NFS client and server to implement SELinux security for networked files. Support for other networked filesystems also would be useful, as would interoperability with Trusted BSD's SELinux port.
Backup and Restoration
One of the many tasks that change for system administrators using SELinux is backup and restoration. When creating an archive, how will the security context labels be preserved within the archive? The answer is to use the highly flexible star(1) utility, which has extended attribute support.
To manipulate archives with security context labels, use the xattr option. When creating archives, you also need to specify the exustar format. For example:
$ star -xattr -H=exustar -c -f cups-log.star /var/log/cups
creates an archive of the /var/log/cups directory, retaining security context labels on the files.
To extract, simply use the xattr option:
$ star -xattr -x -f cups-log.star $ ls -Z var/log/cups/ -rw-r--r--+ root sys system_u:object_r:cupsd_log_t error_log -rw-r--r--+ root sys system_u:object_r:cupsd_log_t error_log.1
As you can see, the security context labels have been preserved.
Resources for this article: /article/7689.
James Morris (firstname.lastname@example.org) is a kernel hacker from Sydney, Australia, currently working for Red Hat in Boston. He is a kernel maintainer of SELinux, Networking and the Crypto API; an LSM developer and an Emeritus Netfilter Core Team member.
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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