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Re: [libvirt] [PATCH 2/2] lxc: Add virCgroupSetOwner()



Am 11.02.2014 13:05, schrieb Daniel P. Berrange:
> On Sat, Feb 08, 2014 at 06:37:43PM +0100, Richard Weinberger wrote:
>> Add a new helper function to change the permissions
>> of a control group.
>>
>> Signed-off-by: Richard Weinberger <richard nod at>
>> ---
>>  src/lxc/lxc_controller.c |  7 +++++++
>>  src/util/vircgroup.c     | 43 +++++++++++++++++++++++++++++++++++++++++++
>>  src/util/vircgroup.h     |  2 ++
>>  3 files changed, 52 insertions(+)
>>
>> diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
>> index f7b614b..6e348b3 100644
>> --- a/src/lxc/lxc_controller.c
>> +++ b/src/lxc/lxc_controller.c
>> @@ -2223,6 +2223,13 @@ virLXCControllerRun(virLXCControllerPtr ctrl)
>>          goto cleanup;
>>      }
>>  
>> +    /* setup control group permissions for user namespace */
>> +    if (ctrl->def->idmap.uidmap) {
>> +        if (virCgroupSetOwner(ctrl->cgroup, ctrl->def->idmap.uidmap[0].target,
>> +            ctrl->def->idmap.gidmap[0].target))
>> +            goto cleanup;
>> +    }
>> +
> 
> I wonder is it possible to just do the ownership change in the
> virLXCCgroupCreate method ?   When the container then does the
> bind mount, it should preserve the ownership correctly. This
> would avoid any need for the extra handshake synchronization.

Bah, I've overlooked that. Of course it works.
Much simplified patch is on its way.
Thanks for pointing this out!

>> diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
>> index a6d60c5..b66ffed 100644
>> --- a/src/util/vircgroup.c
>> +++ b/src/util/vircgroup.c
>> @@ -3252,6 +3252,49 @@ cleanup:
>>      return ret;
>>  }
>>  
>> +int virCgroupSetOwner(virCgroupPtr cgroup, uid_t uid, gid_t gid) {
>> +    size_t i;
>> +
>> +    for (i = 0; i < VIR_CGROUP_CONTROLLER_LAST; i++) {
> 
> I think we only want to set ownership for VIR_CGROUP_CONTROLLER_SYSTEMD.
> We don't want to give the container permission to change resource
> controllers, this that would allow it to potentially escape its resource
> limits. You might think the hierarchy would lock things down, but I
> believe the kernel developers still say it is unsafe to delegate cgroup
> resource controllers to unprivileged users.

That's right. But then we should generally only delegate the systemd cgroup
to a container.
...patch sent.

Thanks,
//richard


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