Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces

[Richard Weinberger <richard@nod.at>]

Aditya,

I gave your patch set a try but it does not work for me.
Maybe you can bring some light into the issues I'm facing.
Sadly I still had no time to dig into your code.

Am 05.12.2014 um 02:55 schrieb Aditya Kali:
> Signed-off-by: Aditya Kali <adityakali@google.com>
> ---
>  Documentation/cgroups/namespace.txt | 147 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 147 insertions(+)
>  create mode 100644 Documentation/cgroups/namespace.txt
> 
> diff --git a/Documentation/cgroups/namespace.txt b/Documentation/cgroups/namespace.txt
> new file mode 100644
> index 0000000..6480379
> --- /dev/null
> +++ b/Documentation/cgroups/namespace.txt
> @@ -0,0 +1,147 @@
> +			CGroup Namespaces
> +
> +CGroup Namespace provides a mechanism to virtualize the view of the
> +/proc/<pid>/cgroup file. The CLONE_NEWCGROUP clone-flag can be used with
> +clone() and unshare() syscalls to create a new cgroup namespace.
> +The process running inside the cgroup namespace will have its /proc/<pid>/cgroup
> +output restricted to cgroupns-root. cgroupns-root is the cgroup of the process
> +at the time of creation of the cgroup namespace.
> +
> +Prior to CGroup Namespace, the /proc/<pid>/cgroup file used to show complete
> +path of the cgroup of a process. In a container setup (where a set of cgroups
> +and namespaces are intended to isolate processes), the /proc/<pid>/cgroup file
> +may leak potential system level information to the isolated processes.
> +
> +For Example:
> +  $ cat /proc/self/cgroup
> +  0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/batchjobs/container_id1
> +
> +The path '/batchjobs/container_id1' can generally be considered as system-data
> +and its desirable to not expose it to the isolated process.
> +
> +CGroup Namespaces can be used to restrict visibility of this path.
> +For Example:
> +  # Before creating cgroup namespace
> +  $ ls -l /proc/self/ns/cgroup
> +  lrwxrwxrwx 1 root root 0 2014-07-15 10:37 /proc/self/ns/cgroup -> cgroup:[4026531835]
> +  $ cat /proc/self/cgroup
> +  0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/batchjobs/container_id1
> +
> +  # unshare(CLONE_NEWCGROUP) and exec /bin/bash
> +  $ ~/unshare -c
> +  [ns]$ ls -l /proc/self/ns/cgroup
> +  lrwxrwxrwx 1 root root 0 2014-07-15 10:35 /proc/self/ns/cgroup -> cgroup:[4026532183]
> +  # From within new cgroupns, process sees that its in the root cgroup
> +  [ns]$ cat /proc/self/cgroup
> +  0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/
> +
> +  # From global cgroupns:
> +  $ cat /proc/<pid>/cgroup
> +  0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/batchjobs/container_id1
> +
> +  # Unshare cgroupns along with userns and mountns
> +  # Following calls unshare(CLONE_NEWCGROUP|CLONE_NEWUSER|CLONE_NEWNS), then
> +  # sets up uid/gid map and execs /bin/bash
> +  $ ~/unshare -c -u -m

This command does not issue CLONE_NEWUSER, -U does.

> +  # Originally, we were in /batchjobs/container_id1 cgroup. Mount our own cgroup
> +  # hierarchy.
> +  [ns]$ mount -t cgroup cgroup /tmp/cgroup
> +  [ns]$ ls -l /tmp/cgroup
> +  total 0
> +  -r--r--r-- 1 root root 0 2014-10-13 09:32 cgroup.controllers
> +  -r--r--r-- 1 root root 0 2014-10-13 09:32 cgroup.populated
> +  -rw-r--r-- 1 root root 0 2014-10-13 09:25 cgroup.procs
> +  -rw-r--r-- 1 root root 0 2014-10-13 09:32 cgroup.subtree_control

I've patched libvirt-lxc to issue CLONE_NEWCGROUP and not bind mount cgroupfs into a container.
But I'm unable to mount cgroupfs within the container, mount(2) is failing with EINVAL.
And /proc/self/cgroup still shows the cgroup from outside.

---cut---
container:/ # ls /sys/fs/cgroup/
container:/ # mount -t cgroup none /sys/fs/cgroup/
mount: wrong fs type, bad option, bad superblock on none,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.
container:/ # cat /proc/self/cgroup
8:memory:/machine/test00.libvirt-lxc
7:devices:/machine/test00.libvirt-lxc
6:hugetlb:/
5:cpuset:/machine/test00.libvirt-lxc
4:blkio:/machine/test00.libvirt-lxc
3:cpu,cpuacct:/machine/test00.libvirt-lxc
2:freezer:/machine/test00.libvirt-lxc
1:name=systemd:/user.slice/user-0.slice/session-c2.scope
container:/ # ls -la /proc/self/ns
total 0
dr-x--x--x 2 root root 0 Dec 14 23:02 .
dr-xr-xr-x 8 root root 0 Dec 14 23:02 ..
lrwxrwxrwx 1 root root 0 Dec 14 23:02 cgroup -> cgroup:[4026532240]
lrwxrwxrwx 1 root root 0 Dec 14 23:02 ipc -> ipc:[4026532238]
lrwxrwxrwx 1 root root 0 Dec 14 23:02 mnt -> mnt:[4026532235]
lrwxrwxrwx 1 root root 0 Dec 14 23:02 net -> net:[4026532242]
lrwxrwxrwx 1 root root 0 Dec 14 23:02 pid -> pid:[4026532239]
lrwxrwxrwx 1 root root 0 Dec 14 23:02 user -> user:[4026532234]
lrwxrwxrwx 1 root root 0 Dec 14 23:02 uts -> uts:[4026532236]
container:/ #

#host side
lxc-os132:~ # ls -la /proc/self/ns
total 0
dr-x--x--x 2 root root 0 Dec 14 23:56 .
dr-xr-xr-x 8 root root 0 Dec 14 23:56 ..
lrwxrwxrwx 1 root root 0 Dec 14 23:56 cgroup -> cgroup:[4026531835]
lrwxrwxrwx 1 root root 0 Dec 14 23:56 ipc -> ipc:[4026531839]
lrwxrwxrwx 1 root root 0 Dec 14 23:56 mnt -> mnt:[4026531840]
lrwxrwxrwx 1 root root 0 Dec 14 23:56 net -> net:[4026531957]
lrwxrwxrwx 1 root root 0 Dec 14 23:56 pid -> pid:[4026531836]
lrwxrwxrwx 1 root root 0 Dec 14 23:56 user -> user:[4026531837]
lrwxrwxrwx 1 root root 0 Dec 14 23:56 uts -> uts:[4026531838]
---cut---

Any ideas?

Thanks,
//richard