On Fri, May 3, 2019 at 12:03 PM J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > On Thu, May 02, 2019 at 12:02:33PM +1000, NeilBrown wrote: > > On Tue, Dec 06 2016, J. Bruce Fields wrote: > > > > > On Tue, Dec 06, 2016 at 02:18:31PM +0100, Andreas Gruenbacher wrote: > > >> On Tue, Dec 6, 2016 at 11:08 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > >> > On Tue, Dec 6, 2016 at 12:24 AM, Andreas Grünbacher > > >> > <andreas.gruenbacher@xxxxxxxxx> wrote: > > >> >> 2016-12-06 0:19 GMT+01:00 Andreas Grünbacher <andreas.gruenbacher@xxxxxxxxx>: > > >> > > > >> >>> It's not hard to come up with a heuristic that determines if a > > >> >>> system.nfs4_acl value is equivalent to a file mode, and to ignore the > > >> >>> attribute in that case. (The file mode is transmitted in its own > > >> >>> attribute already, so actually converting .) That way, overlayfs could > > >> >>> still fail copying up files that have an actual ACL. It's still an > > >> >>> ugly hack ... > > >> >> > > >> >> Actually, that kind of heuristic would make sense in the NFS client > > >> >> which could then hide the "system.nfs4_acl" attribute. > > >> > > > >> > Even simpler would be if knfsd didn't send the attribute if not > > >> > necessary. Looks like there's code actively creating the nfs4_acl on > > >> > the wire even if the filesystem had none: > > >> > > > >> > pacl = get_acl(inode, ACL_TYPE_ACCESS); > > >> > if (!pacl) > > >> > pacl = posix_acl_from_mode(inode->i_mode, GFP_KERNEL); > > >> > > > >> > What's the point? > > >> > > >> That's how the protocol is specified. > > > > > > Yep, even if we could make that change to nfsd it wouldn't help the > > > client with the large number of other servers that are out there > > > (including older knfsd's). > > > > > > --b. > > > > > >> (I'm not saying that that's very helpful.) > > >> > > >> Andreas > > > > Hi everyone..... > > I have a customer facing this problem, and so stumbled onto the email > > thread. > > Unfortunately it didn't resolve anything. Maybe I can help kick things > > along??? > > > > The core problem here is that NFSv4 and ext4 use different and largely > > incompatible ACL implementations. There is no way to accurately > > translate from one to the other in general (common specific examples > > can be converted). > > > > This means that either: > > 1/ overlayfs cannot use ext4 for upper and NFS for lower (or vice > > versa) or > > 2/ overlayfs need to accept that sometimes it cannot copy ACLs, and > > that is OK. > > > > Silently not copying the ACLs is probably not a good idea as it might > > result in inappropriate permissions being given away. So if the > > sysadmin wants this (and some clearly do), they need a way to > > explicitly say "I accept the risk". > > So, I feel like silently copying ACLs up *also* carries a risk, if that > means switching from server-enforcement to client-enforcement of those > permissions. > > Sorry, I know we had another thread recently about permissions in this > situation, and I've forgotten the conclusion. > > Out of curiosity, what's done with selinux labels? > overlayfs calls security_inode_copy_up_xattr(name) which can fail (<0) allow (0) or skip(1). selinux_inode_copy_up_xattr() as well as smack_inode_copy_up_xattr() skip their own xattr on copy up and fail any other xattr copy up. Thanks, Amir.
