Code change:
} // apply volume ownership <del> if !c.readOnly && fsGroup != nil { err := volume.SetVolumeOwnership(c, fsGroup) if err != nil { // attempt to rollback mount. glog.Error(log("mounter.SetupAt failed to set fsgroup volume ownership for [%s]: %v", c.volumeID, err)) glog.V(4).Info(log("mounter.SetupAt attempting to unpublish volume %s due to previous error", c.volumeID)) if unpubErr := csi.NodeUnpublishVolume(ctx, c.volumeID, dir); unpubErr != nil { glog.Error(log( "mounter.SetupAt failed to unpublish volume [%s]: %v (caused by previous NodePublish error: %v)", c.volumeID, unpubErr, err, )) return fmt.Errorf("%v (caused by %v)", unpubErr, err) } </del> <ins> // The following logic is derived from https://github.com/kubernetes/kubernetes/issues/66323 // if fstype is "", then skip fsgroup (could be indication of non-block filesystem) // if fstype is provided and pv.AccessMode == ReadWriteOnly, then apply fsgroup </ins> <del> if unmountErr := removeMountDir(c.plugin, dir); unmountErr != nil { glog.Error(log( "mounter.SetupAt failed to clean mount dir [%s]: %v (caused by previous NodePublish error: %v)", dir, unmountErr, err, )) return fmt.Errorf("%v (caused by %v)", unmountErr, err) } </del> <ins> err = c.applyFSGroup(fsType, fsGroup) if err != nil { // attempt to rollback mount. fsGrpErr := fmt.Errorf("applyFSGroup failed for vol %s: %v", c.volumeID, err) if unpubErr := csi.NodeUnpublishVolume(ctx, c.volumeID, dir); unpubErr != nil { glog.Error(log("NodeUnpublishVolume failed for [%s]: %v", c.volumeID, unpubErr)) return fsGrpErr } </ins> <del> return err </del> <ins> if unmountErr := removeMountDir(c.plugin, dir); unmountErr != nil { glog.Error(log("removeMountDir failed for [%s]: %v", dir, unmountErr)) return fsGrpErr </ins> } <del> glog.V(4).Info(log("mounter.SetupAt sets fsGroup to [%d] for %s", *fsGroup, c.volumeID)) </del> <ins> return fsGrpErr </ins> } glog.V(4).Infof(log("mounter.SetUp successfully requested NodePublish [%s]", dir))

Related discussion:
text: Currently, this is what the code is doing which we knew needed to be revisited:
Users may not fully understand what fsgroup is and set it anyway, or a default psp with some fsgroup may be defined in which it will automatically be set on all pods. The first case we can attribute to user error, but the second case may not have a good workaround and could cause permission issues on rwx volumes. So I think we do need to solve this.
Yes, agreed this has to be solved. As you pointed out user error or improperly configured PSP can set value that does not match the correct attribute, causing permission issues. Here is what I think can be done without new CSI capabilities: , then do not apply fsgroup then: , apply fsgroup , do not apply fsgroup to void stated issue then: , apply fsgroup I think that may help deduce when to apply fsgroup.
If mount reference count <= 1, apply fsgroup If mount reference count 1, do not apply fsgroup to void stated issue A RWM volume (say NFS) can be mounted on multiple nodes. Do you have reliable count of mounts across all nodes?
In addition, that would be a change in semantics to how we support rwx volumes today. If we don't have a new CSI capability, then I think the best course of action is to only apply fsgroup for RWO volumes. Some questions remain: Do all RWO volumes support fsgroup? RWX is a superset of RWO. So if a user requests a RWO volume, it could still be satisfied by a RWX volume type. Can we detect this and still not apply the fsgroup even though the volume capability will say RWO?
If there's not a reliable way to enumerate node mounts (thinking about it, for CSI external drivers, the answer is NO). Theres is no reliable way to have k8s autocorrect a bad fsgroup/PV.AccessMode combo. So we would have to rely on the config provided by user/admin. I have come to similar conclusion as -- mainly, apply fsgroup only to volumes with access modes. The other k8s specified access modes, , cannot be reliably applied.