On Wed, May 1, 2019 at 10:03 PM NeilBrown <neilb@xxxxxxxx> 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. For example? permissions given away to do what? Note that ovl_permission() only check permissions of *mounter* to read the lower NFS file and ovl_open()/ovl_read_iter() access the lower file with *mounter* credentials. I might be wrong, but seems to me that once admin mounted overlayfs with lower NFS, NFS ACLs are not being enforced at all even before copy up. > So if the > sysadmin wants this (and some clearly do), they need a way to > explicitly say "I accept the risk". If only standard Unix permissions > are used, there is no risk, so this seems reasonable. > > So I would like to propose a new option for overlayfs > nocopyupacl: when overlayfs is copying a file (or directory etc) > from the lower filesystem to the upper filesystem, it does not > copy extended attributes with the "system." prefix. These are > used for storing ACL information and this is sometimes not > compatible between different filesystem types (e.g. ext4 and > NFSv4). Standard Unix ownership permission flags (rwx) *are* > copied so this option does not risk giving away inappropriate > permissions unless the lowerfs uses unusual ACLs. > > I am wondering if it would make more sense for nfs to register a security_inode_copy_up_xattr() hook. That is the mechanism that prevents copying up other security.* xattrs? Thanks, Amir.
