Seccomp security profiles for Docker

Seccomp security profiles for Docker

Secure computing mode (Seccomp) is a Linux kernel feature. You can use it to restrict the actions available within the container. The seccomp() system call operates on the seccomp state of the calling process. You can use this feature to restrict your application’s access.

This feature is available only if Docker has been built with seccomp and the kernel is configured with CONFIG_SECCOMP enabled. To check if your kernel supports seccomp:

$ cat /boot/config-`uname -r` | grep CONFIG_SECCOMP=
CONFIG_SECCOMP=y

Note: seccomp profiles require seccomp 2.2.1 and are only available starting with Debian 9 “Stretch”, Ubuntu 15.10 “Wily”, and Fedora 22. To use this feature on Ubuntu 14.04, Debian Wheezy, or Debian Jessie, you must download the latest static Docker Linux binary. This feature is currently not available on other distributions.

Passing a profile for a container

The default seccomp profile provides a sane default for running containers with seccomp and disables around 44 system calls out of 300+. It is moderately protective while providing wide application compatibility. The default Docker profile (found here has a JSON layout in the following form:

{
	"defaultAction": "SCMP_ACT_ERRNO",
	"architectures": [
		"SCMP_ARCH_X86_64",
		"SCMP_ARCH_X86",
		"SCMP_ARCH_X32"
	],
	"syscalls": [
		{
			"name": "accept",
			"action": "SCMP_ACT_ALLOW",
			"args": []
		},
		{
			"name": "accept4",
			"action": "SCMP_ACT_ALLOW",
			"args": []
		},
		...
	]
}

When you run a container, it uses the default profile unless you override it with the security-opt option. For example, the following explicitly specifies the default policy:

$ docker run --rm -it --security-opt seccomp=/path/to/seccomp/profile.json hello-world

Significant syscalls blocked by the default profile

Docker’s default seccomp profile is a whitelist which specifies the calls that are allowed. The table below lists the significant (but not all) syscalls that are effectively blocked because they are not on the whitelist. The table includes the reason each syscall is blocked rather than white-listed.

Run without the default seccomp profile

You can pass unconfined to run a container without the default seccomp profile.

$ docker run --rm -it --security-opt seccomp=unconfined debian:jessie \
    unshare --map-root-user --user sh -c whoami