Richard Weinberger [off-list ref] writes:

Am 05.01.2015 um 23:48 schrieb Aditya Kali:

quoted

On Sun, Dec 14, 2014 at 3:05 PM, Richard Weinberger [off-list ref] wrote:

quoted

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:

quoted

Signed-off-by: Aditya Kali <redacted>
---
 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.

I was using a custom unshare binary. But I will update the command
line to be similar to the one in util-linux.

quoted

quoted

+  # 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/

You need to provide "-o __DEVEL_sane_behavior" flag. Inside the
container, only unified hierarchy can be mounted. So, for now, that
flag is needed. I will fix the documentation too.

quoted

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?

Please try with "-o __DEVEL_sane_behavior" flag to the mount command.

Ohh, this renders the whole patch useless for me as systemd needs the "old/default" behavior of cgroups. :-(
I really hoped that cgroup namespaces will help me running systemd in a sane way within Linux containers.

Ugh.  It sounds like there is a real mess here.  At the very least there
is misunderstanding.

I have a memory that systemd should have been able to use a unified
hierarchy.  As you could still mount the different controllers
independently (they just use the same directory structure on each
mount).

That said from a practical standpoint I am not certain that a cgroup
namespace is viable if it can not support the behavior of cgroupsfs
that everyone is using.

Eric