On Thu, 2 May 2019 at 05:57, NeilBrown <neilb@xxxxxxxx> wrote: > On Wed, May 01 2019, Amir Goldstein wrote: > > 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. I still think the nfs client could make this problem mostly go away by not exposing "system.nfs4_acl" xattrs when the acl is equivalent to the file mode. The richacl patches contain a workable abgorithm for that. The problem would remain for files that have an actual NFS4 ACL, which just cannot be mapped to a file mode or to POSIX ACLs in the general case, as well as for files that have a POSIX ACL. Mapping NFS4 ACL that used to be a POSIX ACL back to POSIX ACLs could be achieved in many cases as well, but the code would be quite messy. A better way seems to be to using a filesystem that doesn't support POSIX ACLs in the first place. Unfortunately, xfs doesn't allow turning off POSIX ACLs, for example. Andreas > >> >> > 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. > > I guess it is just as well that copy-up fails then - if the lower-level > permission check is being ignored. > > > > >> 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? > > No, I don't think that would make sense. > Support some day support for nfs4 acls were added to ext4 (not a totally > ridiculous suggestion). We would then want NFS to allow it's ACLs to be > copied up. > > Thanks, > NeilBrown > > > > > > Thanks, > > Amir.
