[libvirt] [PATCH] LXC: create a bind mount for sysfs when enable userns but disable netns

Daniel P. Berrange berrange at redhat.com
Fri Mar 20 08:45:24 UTC 2015


On Fri, Mar 20, 2015 at 02:14:04AM +0000, Chen, Hanxiao wrote:
> 
> 
> > -----Original Message-----
> > From: Richard Weinberger [mailto:richard at nod.at]
> > Sent: Friday, March 20, 2015 1:41 AM
> > To: Daniel P. Berrange
> > Cc: Chen, Hanxiao/陈 晗霄; libvir-list at redhat.com
> > Subject: Re: [libvirt] [PATCH] LXC: create a bind mount for sysfs when enable userns
> > but disable netns
> > 
> > Am 19.03.2015 um 18:28 schrieb Daniel P. Berrange:
> > > On Thu, Mar 19, 2015 at 06:04:57PM +0100, Richard Weinberger wrote:
> > >> Am 19.03.2015 um 17:58 schrieb Daniel P. Berrange:
> > >>> On Thu, Mar 19, 2015 at 05:54:32PM +0100, Richard Weinberger wrote:
> > >>>> Am 11.03.2015 um 10:36 schrieb Richard Weinberger:
> > >>>>> Am 11.03.2015 um 03:30 schrieb Chen, Hanxiao:
> > >>>>>>>> @@ -826,8 +829,25 @@ static int lxcContainerMountBasicFS(bool
> > userns_enabled)
> > >>>>>>>>          bool bindOverReadonly;
> > >>>>>>>>          virLXCBasicMountInfo const *mnt = &lxcBasicMounts[i];
> > >>>>>>>>
> > >>>>>>>> +        /* When enable userns but disable netns, kernel will
> > >>>>>>>> +         * forbid us doing a new fresh mount for sysfs.
> > >>>>>>>> +         * So we had to do a bind mount for sysfs instead.
> > >>>>>>>> +         */
> > >>>>>>>> +        if (userns_enabled && netns_disabled &&
> > >>>>>>>> +            STREQ(mnt->src, "sysfs")) {
> > >>>>>>>> +            if (VIR_STRDUP(mnt_src, "/sys") < 0) {
> > >>>>>>>> +                goto cleanup;
> > >>>>>>>> +            }
> > >>>>>>>
> > >>>>>>> This is clearly broken and looks very untested to me.
> > >>>>>>>
> > >>>>>> It's broken now.
> > >>>>>> But when I submitted this patch last year, it's not.
> > >>>>>
> > >>>>> Are you sure?
> > >>>>> Just built libvirt v1.2.6-222-ga86b621, head is
> > >>>>> commit a86b6215a74b1feb2667204e214fbfd2f7decc5c
> > >>>>> Author: Chen Hanxiao <chenhanxiao at cn.fujitsu.com>
> > >>>>> Date:   Mon Jul 14 18:01:51 2014 +0800
> > >>>>>
> > >>>>>     LXC: create a bind mount for sysfs when enable userns but disable netns
> > >>>>>
> > >>>>> /sys is still an empty directory but as at this time (most likely due to another
> > bug)
> > >>>>> libvirt was able to create /sys/fs/cgroup and mounted groups there.
> > >>>>> But no sysfs at all is at /sys.
> > >>>>>
> > >>>>> I mean, how is this supposed to work? You bind mount /sys over /sys...
> > >>>>
> > >>>> Any further comments on that?
> > >>>
> > >>> It just looks impossible for it to work in this way
> > >>
> > >> That's also my impression.
> > >>
> > >> Therefore containers without their own network namespace currently don't work
> > >> and have never worked as expected.
> > >
> > > No, it is only a problem if userns is used. If userns is not used then
> > > they do work
> > 
> > Agreed.
> > 
> That's what I tried to do.
> Sorry for my mistake.
> 
> > >> Shall we revert commit a86b6215a74b and try to bind mount
> > >> before the pivot_root()?
> > >
> > > Not sure if that works with userns is active either.
> > 
> > Fact is that commit a86b6215a74 is broken.
> > We could also refuse to create container with userns enabled but netns disabled...
> > 
> 
> I think we should refuse it too, rather than do something to work around.
> Dan, what's your opinion?

Yes, if we are unable to figure out how to make this work, then we should
report VIR_ERR_CONFIG_UNSUPPORTED for the combination of private userns +
shared netns


Regards,
Daniel
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