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

On 11/19/2013 11:00 PM, Daniel P. Berrange wrote: > 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(a)cn.fujitsu.com&gt; >> --- >> 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 ? > > ./oldroot is mounted in container, so container has rights to umount it, but for sub mounts under ./oldroot, container has no rights to umount them, so it falls back to MNT_DETACH scenario. hmm, So I think for the [PATCH 1/2], use MS_BIND instead of MS_MOVE may be a simple way, since even we move the /dev /dev/pts on host side, the unmount ./oldroot will fall back to MNT_DETACH scenario too.