7:32 p.m.
Hi there!
I am trying to turn on user namespace by adding following lines to the
config:
<idmap>
<uid start='0' target='0' count='100000'/>
<gid start='0' target='0' count='100000'/>
</idmap>
As you can see the root in container is mapped to the root outside. I was
expected to see no difference after adding this lines, but unfortunately
there are some (see details below).
Am I missing something or is there a problem with system, libvirt or kernel?
Full libvirt config:
<domain type='lxc'>
<name>test_with_idmap</name>
<memory>102400</memory>
<os>
<type>exe</type>
<init>/usr/lib/systemd/systemd</init>
</os>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>destroy</on_crash>
<idmap>
<uid start='0' target='0' count='100000'/>
<gid start='0' target='0' count='100000'/>
</idmap>
<devices>
<console type='pty'/>
<filesystem type='mount'>
<source dir='/guest'/>
<target dir='/'/>
</filesystem>
</devices>
</domain>
root:~> uname -a
Linux localhost 3.10.19-01077-g4a19d28-dirty #5 SMP PREEMPT Mon Jan 13
12:56:09 CET 2014 armv7l GNU/Linux
root:~> libvirtd --version
libvirtd (libvirt) 1.2.1
root:~> systemd --version
systemd 204
After adding idmap to config systemd can't start many of its services, in
particular:
Failed to mount Debug File System.
Failed to mount Configuration File System.
Failed to mount FUSE Control File System.
Failed to start udev Kernel Device Manager.
Failed to start Remount Root and Kernel File Systems.
Failed to start Journal Service.
systemctl status says:
ExecMount=/bin/mount debugfs /sys/kernel/debug -t debugfs (code=exited,
status=32)
ExecMount=/bin/mount configfs /sys/kernel/config -t configfs (code=exited,
status=32) ExecMount=/bin/mount fusectl /sys/fs/fuse/connections -t fusectl
(code=exited, status=32) ExecStart=/usr/lib/systemd/systemd-udevd
(code=exited,status=206/OOM_ADJUST)
ExecStart=/usr/lib/systemd/systemd-remount-fs (code=exited,status=1/FAILURE)
ExecStart=/usr/lib/systemd/systemd-journald (code=exited,
status=218/CAPABILITIES)
Thanks!
7:46 p.m.
On Tue, Jan 28, 2014 at 12:32:41PM +0100, Jan Olszak wrote:
Hi there!
I am trying to turn on user namespace by adding following lines to the
config:
<idmap>
<uid start='0' target='0' count='100000'/>
<gid start='0' target='0' count='100000'/>
</idmap>
As you can see the root in container is mapped to the root outside. I was
expected to see no difference after adding this lines, but unfortunately
there are some (see details below).
Am I missing something or is there a problem with system, libvirt or kernel?
I've not had any chance to try LXC + user namespaces + systemd yet, but
based on the list of things which fail, it seems like it might not be
detecting that it is inside a container. Seems almost like it has still
got the CAP_MKNOD permission and so is strying to start things it should
not have like udev, and various filesystems.
Daniel
--
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org -o- http://virt-manager.org :|
|: http://autobuild.org -o- http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
7:35 p.m.
On 28.01.2014 12:46, Daniel P. Berrange wrote:
On Tue, Jan 28, 2014 at 12:32:41PM +0100, Jan Olszak wrote:
> Hi there!
>
> I am trying to turn on user namespace by adding following lines to the
> config:
>
>
>
> <idmap>
>
> <uid start='0' target='0' count='100000'/>
>
> <gid start='0' target='0' count='100000'/>
>
> </idmap>
>
>
>
> As you can see the root in container is mapped to the root outside. I was
> expected to see no difference after adding this lines, but unfortunately
> there are some (see details below).
>
> Am I missing something or is there a problem with system, libvirt or kernel?
I've not had any chance to try LXC + user namespaces + systemd yet, but
based on the list of things which fail, it seems like it might not be
detecting that it is inside a container. Seems almost like it has still
got the CAP_MKNOD permission and so is strying to start things it should
not have like udev, and various filesystems.
Daniel
I was able to reduce the problem by not using libvirt nor systemd.
I've created a bash process inside user namespace with mapping
root_inside<->root_outside.
I've used a program from https://lwn.net/Articles/532593/ :
./userns_child_exec -U -M '0 0 1' -G '0 0 1' bash
This program simply calls clone with CLONE_NEWUSER flag and set proper
uid_map and gid_map.
The test commands are as follows:
mkdir /test
mount debugfs /test -t debugfs
and strace shows:
mount("debugfs", "/test", "debugfs", MS_MGC_VAL, NULL) = -1
EPERM
(Operation not permitted)
Now the question is:
Is it a kernel bug or expected behavior ie. inside user namespace we
have always limited permissions even if uid=0 inside container is mapped
to uid=0 outside?
# cat /proc/$$/uid_map
0 0 1
# cat /proc/$$/gid_map
0 0 1
# cat /proc/$$/status | grep Cap
CapInh: 0000000000000000
CapPrm: 0000001fffffffff
CapEff: 0000001fffffffff
CapBnd: 0000001fffffffff
--
Piotr Bartosiewicz
7:40 p.m.
On Wed, Jan 29, 2014 at 12:35:25PM +0100, Piotr Bartosiewicz wrote:
On 28.01.2014 12:46, Daniel P. Berrange wrote:
>On Tue, Jan 28, 2014 at 12:32:41PM +0100, Jan Olszak wrote:
>>Hi there!
>>
>>I am trying to turn on user namespace by adding following lines to the
>>config:
>>
>>
>> <idmap>
>>
>> <uid start='0' target='0' count='100000'/>
>>
>> <gid start='0' target='0' count='100000'/>
>>
>> </idmap>
>>
>>
>>As you can see the root in container is mapped to the root outside. I was
>>expected to see no difference after adding this lines, but unfortunately
>>there are some (see details below).
>>
>>Am I missing something or is there a problem with system, libvirt or kernel?
>I've not had any chance to try LXC + user namespaces + systemd yet, but
>based on the list of things which fail, it seems like it might not be
>detecting that it is inside a container. Seems almost like it has still
>got the CAP_MKNOD permission and so is strying to start things it should
>not have like udev, and various filesystems.
>
>Daniel
I was able to reduce the problem by not using libvirt nor systemd.
I've created a bash process inside user namespace with mapping
root_inside<->root_outside.
I've used a program from https://lwn.net/Articles/532593/ :
./userns_child_exec -U -M '0 0 1' -G '0 0 1' bash
This program simply calls clone with CLONE_NEWUSER flag and set
proper uid_map and gid_map.
The test commands are as follows:
mkdir /test
mount debugfs /test -t debugfs
and strace shows:
mount("debugfs", "/test", "debugfs", MS_MGC_VAL, NULL) = -1
EPERM
(Operation not permitted)
Now the question is:
Is it a kernel bug or expected behavior ie. inside user namespace we
have always limited permissions even if uid=0 inside container is
mapped to uid=0 outside?
uid==0 inside the container will not have exactly the same
permissions as uid==0 in the host. The reason is due to the
way the kernel is checking capabilities. When a syscall
requires CAP_SYS_ADMIN, for example, the kernel will either
use capable(CAP_SYS_ADMIN) which only succeeds in the host,
or ns_capable(CAP_SYS_ADMIN) which is allowed to suceed in
the container.
Different filesystems have differing restrictions, but at
this time the vast majority of filesystems require that
capable(CAP_SYS_ADMIN) succeeed and thus you can only
mount them in the host.
Daniel
--
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org -o- http://virt-manager.org :|
|: http://autobuild.org -o- http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
3874
days inactive
3875
days old
3 comments
3 participants
participants (3)
-
Daniel P. Berrange -
Jan Olszak -
Piotr Bartosiewicz