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. >> >> > >> >> > 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.
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