Seth Forshee <seth.forshee@xxxxxxxxxxxxx> writes: > Both of these filesystems already have use cases for mounting the > same super block from multiple user namespaces. For sysfs this > happens when using criu for snapshotting a container, where sysfs > is mnounted in the containers network ns but the hosts user ns. > The cgroup filesystem shares the same super block for all mounts > of the same hierarchy regardless of the namespace. > > As a result, the restriction on mounting a super block from a > single user namespace creates regressions for existing uses of > these filesystems. For these specific filesystems this > restriction isn't really necessary since the backing store is > objects in kernel memory and thus the ids assigned from inodes > is not subject to translation relative to s_user_ns. > > Add a new filesystem flag, FS_USERNS_SHARE_SB, which when set > causes sget_userns() to skip the check of s_user_ns. Set this > flag for the sysfs and cgroup filesystems to fix the > regressions. So this one needs to be sget_userns(..., &init_user_ns, ...). And not a new special case. Apologies for not catching this earlier. I am looking at folding all of this into the patch that introduces sget_userns so that even bisects won't have regresssions. We loose the ability to call mount -o remount and actually affect these filesystems (which we don't have without s_user_ns) but we gain a whole lot of simplicity, and we don't break the xattr and security label on sysfs code. Eric -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
