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

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> -----Original Message-----
> From: Richard Weinberger [mailto:richard@xxxxxx]
> Sent: Friday, March 20, 2015 1:41 AM
> To: Daniel P. Berrange
> Cc: Chen, Hanxiao/陈 晗霄; libvir-list@xxxxxxxxxx
> Subject: Re:  [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@xxxxxxxxxxxxxx>
> >>>>> 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?

Regards,
- Chen

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