Security Options

Singularity 3.0 introduces many new security related options to the container runtime. This document will describe the new methods users have for specifying the security scope and context when running Singularity containers.

Linux Capabilities

Singularity provides full support for granting and revoking Linux capabilities on a user or group basis. For example, let us suppose that an admin has decided to grant a user capabilities to open raw sockets so that they can use ping in a container where the binary is controlled via capabilities (i.e. a recent version of CentOS).

To do so, the admin would issue a command such as this:

$ sudo singularity capability add --user david CAP_NET_RAW

This means the user david has just been granted permissions (through Linux capabilities) to open raw sockets within Singularity containers.

The admin can check that this change is in effect with the capability list command.

$ sudo singularity capability list --user david

To take advantage of this new capability, the user david must also request the capability when executing a container with the --add-caps flag like so:

$ singularity exec --add-caps CAP_NET_RAW library://centos ping -c 1
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=128 time=18.3 ms

--- ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 18.320/18.320/18.320/0.000 ms

If the admin decides that it is no longer necessary to allow the user dave to open raw sockets within Singularity containers, they can revoke the appropriate Linux capability like so:

$ sudo singularity capability drop --user david CAP_NET_RAW

The capabiltiy add and drop subcommands will also accept the case insensitive keyword all to grant or revoke all Linux capabilities to a user or group. Similarly, the --add-caps option will accept the all keyword. Of course appropriate caution should be exercised when using this keyword.