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07. Linux-VServer Security

Now that we know what the Linux-VServer framework provides and how some features work, let's have a word on security, because you should not rely on the framework to be secure per definition. Instead, you should exactly know what you are doing.

07.0. Secure Capabilities

Currently the following Linux Capabilities are considered secure for VPS use. If others are added, it will probably open some security hole.

CAP_NET_RAW for example is not considered secure although it is often used to allow the broken ping command to work, although there are better alternatives like the userspace ping command poink[U7] or the VXC_RAW_ICMP Context Capability.

07.1. The Chroot Barrier

Ensuring that the Barrier flag is set on the parent directory of each VPS is vital if you do not want VPS root to escape from the confinement and walk your Host's root filesystem.

07.2. Secure Device Nodes

The /dev directory of a VPS should not contain more than the following devices and the one directory for the unix pts tree.

Of course other device nodes like console, mem and kmem, even block and character devices can be added, but some expertise is required in order to ensure no security holes are opened.

07.3. Secure Proc-FS Entries

There has been no detailed evaluation of secure and unsecure entries in the proc filesystem, but there have been some incidents where unprotected (not protected via Linux Capabilities) writable proc entries caused mayhem.

For example, /proc/sysrq-trigger is something which should not be accessible inside a VPS without a very good reason.

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