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Re: [libvirt] [PATCH v2]LXC: Helper function for checking ownership of dir when userns enabled




> -----Original Message-----
> From: Daniel P. Berrange [mailto:berrange redhat com]
> Sent: Saturday, August 10, 2013 12:54 AM
> To: Chen Hanxiao
> Cc: libvir-list redhat com
> Subject: Re: [libvirt] [PATCH v2]LXC: Helper function for checking ownership of
> dir when userns enabled
> 
> On Fri, Aug 09, 2013 at 04:05:58PM +0800, Chen Hanxiao wrote:
> > From: Chen Hanxiao <chenhanxiao cn fujitsu com>
> >
> > If we enable userns, the ownership of dir we provided for containers
> > should match the uid/gid in idmap.
> > Currently, the debug log is very implicit or misleading sometimes.
> > This patch will help clarify this for us when using
> > debug log or virsh.
> 
> I do recall hitting some permission issue once, but can't remember
> just what it was. Can you describe exactly how to reproduce the
> problem ?
> 

1)  Enable user namespace in kernel
2)  Add idmap for container
3)  Don't change the ownership of devices/ filesystem/ source dir  ( leave them to 'root' for instance)
4)  Start the container

Usually I got an input/output error by virsh, which is not a good hint.


> > Signed-off-by: Chen Hanxiao <chenhanxiao cn fujitsu com>
> > ---
> >  src/lxc/lxc_container.c |   46
> ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 files changed, 46 insertions(+), 0 deletions(-)
> >
> > diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
> > index b910b10..2ccdc61 100644
> > --- a/src/lxc/lxc_container.c
> > +++ b/src/lxc/lxc_container.c
> > @@ -1815,6 +1815,49 @@ lxcNeedNetworkNamespace(virDomainDefPtr
> def)
> >      return false;
> >  }
> >
> > +/*
> > + * Helper function for helping check
> > + * whether we have enough privilege
> > + * to operate the source dir when userns enabled
> > + * @vmDef: pointer to vm definition structure
> > + * Returns 0 on success or -1 in case of error
> > + */
> > +static int
> > +lxcContainerUsernsSrcOwnershipCheck(virDomainDefPtr vmDef)
> > +{
> > +    struct stat buf;
> > +    size_t i;
> > +    uid_t uid;
> > +    gid_t gid;
> > +
> > +    VIR_DEBUG("vmDef->nfss %d", (int)vmDef->nfss);
> > +    for (i = 0; i < vmDef->nfss; i++) {
> > +        VIR_DEBUG("dst is %s, src is %s",
> > +                  vmDef->fss[i]->dst,
> > +                  vmDef->fss[i]->src);
> > +
> > +        uid = vmDef->idmap.uidmap[0].target;
> > +        gid = vmDef->idmap.gidmap[0].target;
> > +
> > +        if (lstat(vmDef->fss[i]->src, &buf) < 0) {
> > +            virReportSystemError(errno, _("Cannot access '%s'"),
> > +                                 vmDef->fss[i]->src);
> > +            return -1;
> > +        } else if (uid != buf.st_uid || gid != buf.st_gid) {
> > +            VIR_DEBUG("In userns uid is %d, gid is %d\n",
> > +                      uid, gid);
> > +            errno = EINVAL;
> > +
> > +            virReportSystemError(errno,
> > +                                  _("[userns] Src dir '%s' does not
> belong to uid/gid: %d/%d"),
> > +                                 vmDef->fss[i]->src, uid, gid);
> > +            return -1;
> > +        }
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> >  /**
> >   * lxcContainerStart:
> >   * @def: pointer to virtual machine structure
> > @@ -1866,6 +1909,9 @@ int lxcContainerStart(virDomainDefPtr def,
> >          if (userns_supported()) {
> >              VIR_DEBUG("Enable user namespace");
> >              cflags |= CLONE_NEWUSER;
> > +            if (lxcContainerUsernsSrcOwnershipCheck(def) < 0) {
> > +                return -1;
> > +            }
> >          } else {
> >              virReportSystemError(VIR_ERR_CONFIG_UNSUPPORTED,
> "%s",
> >                                   _("Kernel doesn't support user
> namespace"));
> 
> 
> Daniel
> --
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> |: http://libvirt.org              -o-
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