On Fri, May 03 2019, J. Bruce Fields 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 <mik...@szeredi.hu> wrote: >> >> > On Tue, Dec 6, 2016 at 12:24 AM, Andreas Grünbacher >> >> > <andreas.gruenbac...@gmail.com> wrote: >> >> >> 2016-12-06 0:19 GMT+01:00 Andreas Grünbacher >> >> >> <andreas.gruenbac...@gmail.com>: >> >> > >> >> >>> 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.
Interesting perspective .... though doesn't NFSv4 explicitly allow
client-side ACL enforcement in the case of delegations?
Not sure how relevant that is....
It seems to me we have two options:
1/ declare the NFSv4 doesn't work as a lower layer for overlayfs and
recommend people use NFSv3, or
2/ Modify overlayfs to work with NFSv4 by ignoring nfsv4 ACLs either
2a/ always - and ignore all other acls and probably all system. xattrs,
or
2b/ based on a mount option that might be
2bi/ general "noacl" or might be
2bii/ explicit "noxattr=system.nfs4acl"
I think that continuing to discuss the miniature of the options isn't
going to help. No solution is perfect - we just need to clearly
document the implications of whatever we come up with.
I lean towards 2a, but I be happy with with any '2' and '1' won't kill
me.
Do we have a vote? Or does someone make an executive decision??
NeilBrown
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