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Adam Ryczkowski
Asked: 2012-10-28 03:19:48 +0800 CST

How to create dm-crypt device in LXC?

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On one LXC container I need to put sensitive data, preferrably stored in dm-crypt encrypted filesystem.

When I write

sudo cryptsetup luksFormat --cipher aes-xts-plain --size 512 $MyDocsCryptDir/$MyDocsCryptFile,

after the confirmation dialog I've got the error:

Cannot find a free loopback device.

The LXC is installed on Ubuntu 12.04 with 3.6.3 kernel from kernel-ppa/mainline - Kernel Ubuntu

Container config:

lxc.network.type=veth
lxc.network.link=lxcbr0
lxc.network.flags=up
lxc.network.hwaddr= 00:16:3e:10:97:12
lxc.network.ipv4 = 10.0.3.11/24

lxc.devttydir = lxc
lxc.tty = 4
lxc.pts = 1024
lxc.arch = amd64
lxc.cap.drop = sys_module mac_admin

lxc.cgroup.devices.deny = a
# Allow any mknod (but not using the node)
lxc.cgroup.devices.allow = c *:* m
lxc.cgroup.devices.allow = b *:* m
# /dev/null and zero
lxc.cgroup.devices.allow = c 1:3 rwm
lxc.cgroup.devices.allow = c 1:5 rwm
# consoles
lxc.cgroup.devices.allow = c 5:1 rwm
lxc.cgroup.devices.allow = c 5:0 rwm
#lxc.cgroup.devices.allow = c 4:0 rwm
#lxc.cgroup.devices.allow = c 4:1 rwm
# /dev/{,u}random
lxc.cgroup.devices.allow = c 1:9 rwm
lxc.cgroup.devices.allow = c 1:8 rwm
lxc.cgroup.devices.allow = c 136:* rwm
lxc.cgroup.devices.allow = c 5:2 rwm
# rtc
lxc.cgroup.devices.allow = c 254:0 rwm
#fuse
lxc.cgroup.devices.allow = c 10:229 rwm
#tun
lxc.cgroup.devices.allow = c 10:200 rwm
#full
lxc.cgroup.devices.allow = c 1:7 rwm
#hpet
lxc.cgroup.devices.allow = c 10:228 rwm
#kvm
lxc.cgroup.devices.allow = c 10:232 rwm
lxc.utsname = statystyka
lxc.mount = /var/lib/lxc/statystyka/fstab
lxc.rootfs = /var/lib/lxc/statystyka/rootfs
12.04

1 Answers

  1. You can try to allow the container to use system module (by removing sys_module from being dropped):

    lxc.cap.drop = mac_admin

    Maybe also by allowing use of the device mapper block:

    lxc.cgroup.devices.allow = b 252:* rwm
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