[libvirt] [PATCH 2/2] LXC: don't unmount mounts for shared root

[Daniel P. Berrange]

On Tue, Nov 19, 2013 at 05:53:21PM +0800, Gao feng wrote:
> Also after commit 5ff9d8a65ce80efb509ce4e8051394e9ed2cd942
> vfs: Lock in place mounts from more privileged users,
> 
> unprivileged user has no rights to umount the mounts that
> inherited from parent mountns.
> 
> right now, I have no good idea to fix this problem, we need
> to do more research. this patch just skip unmounting these
> mounts for shared root.
> 
> BTW, I think when libvirt lxc enables user namespace, the
> configuation that shares root with host is very rara.
> 
> Signed-off-by: Gao feng <gaofeng at cn.fujitsu.com>
> ---
>  src/lxc/lxc_container.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
> index 61283e4..8003594 100644
> --- a/src/lxc/lxc_container.c
> +++ b/src/lxc/lxc_container.c
> @@ -1591,7 +1591,9 @@ static int lxcContainerSetupPivotRoot(virDomainDefPtr vmDef,
>      if (lxcContainerPivotRoot(root) < 0)
>          goto cleanup;
>  
> -    if (STREQ(root->src, "/") &&
> +    /* FIXME: we should find a way to unmount these mounts for container
> +     * even user namespace is enabled. */
> +    if (STREQ(root->src, "/") && (!vmDef->idmap.nuidmap) &&
>          lxcContainerUnmountForSharedRoot(stateDir, vmDef->name) < 0)
>          goto cleanup;

If unmounting fails for these few temporary filesystems, then how is
unmount succeeding for everything under /.oldroot after we do the
pivot root ?  Does the pivot_root() confuse the kernel into thinking
stuff under /.oldroot was owned by this process & thus allowed to be
unmounted ?  Or is it falling back to the MNT_DETACH scenario instead ?


Daniel
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