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Question about a “Secure Filesystem”

I have just been asked for advice about “secure filesystem” and decided to blog my answers.

The first issue is what is meant by “secure filesystem, that could either mean the ability to restrict file access (EG by supporting SE Linux security contexts and using SE Linux for file access control) or the ability to encrypt data in case the machine is stolen. For access control I recommend SE Linux of course. For encryption on a local machine I mostly use dm-crypt which is configured with the cryptsetup utility. I encrypt at the LVM logical volume level as it is common that there are some LVs that don’t need to be encrypted. For files that need extra encryption or files that are shared between machines I use GPG.

A question was asked about kernel vs user-space filesystem encryption. AES is in the kernel so there is no lack in terms of strong encryption there. Also performance is pretty good (in most cases the CPU is fast enough that the hard drive is the bottleneck). For fine grained encryption (such as some of the experimental filesystems that encrypt data separately for each user) user-space is probably the only way to go.

If you want servers to be “high-security level” and protected from “hackers or unauthorised people” then it’s difficult to offer any advice that is smaller than a text book. I suggest that if you have such questions then you should do one of two things. If you are running a corporate IT department then hire an expert who can help with determine your specific requirements and meet them. If you want to learn about computer security and run your own systems in the best way possible then read as much from the experts as possible.

If you are looking for a project to contribute to related to security then if you choose SE Linux I could offer some specific advice on things that need work. I suggest not deciding on whether to do “kernel level or user level” work up front, but decide first which area of security you want to work on and then select a project which fits – then you should be able to determine whether your skills are best suited to kernel or user space coding. As for whether developing a new filesystem is necessary, I will note that SE Linux works well on Ext3 and XFS, it has just become usable on JFFS2, and it will work on other newer filesystems in the near future. Adding SE Linux support to a filesystem is not a difficult task if the filesystem supports XATTRs. I believe that there is a lot of scope for other access control systems to be developed which use XATTRs for security labels.

I can’t advise on e-books. I generally don’t read books, I read blogs and papers. Anything that I read which I consider to be worth recommending will probably have a link from my blog.

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