On Tue, Oct 02, 2012 at 12:38:10PM +1000, NeilBrown wrote: > On Mon, 1 Oct 2012 11:43:10 -0400 "J. Bruce Fields" <bfields@xxxxxxxxxxxx> > wrote: > > > On Tue, Sep 18, 2012 at 11:23:29AM +1000, NeilBrown wrote: > > > > > > Suppose that on an NFS server I have a directory > > > /foo/bar/baz > > > > > > which I export, and that /foo/bar does not have world access. e.g. > > > permissions are '750' and everyone who owns files in there is a member of the > > > group which owns /foo/bar. > > > > > > Then with NFSv3 I can > > > mount server:/foo/bar/baz /somewhere > > > because the lookup of /foo/bar/baz happens as root on the server in mountd. > > > > > > With NFSv4 using 'sec=sys' I can only do this if I export with > > > "no_root_squash", as the lookup happens on the client as root, and if root > > > were squashed, it wouldn't have access beyond /foo/bar. > > > > > > But if I use NFSv4 using 'sec=krb5', the lookup happens on the client using a > > > machine credential which gets mapped to 'nobody/nogroup' (or whatever anonuid > > > and anongid are set to for the export). So I cannot perform the mount at all. > > > > > > This is - at best - inconsistent and can cause confusion (hey - I was > > > confused for a while there). > > > > > > Should something be done? Can anything be done? > > > > I think nfsd_lookup_dentry() would need a special exception for the > > NFSEXP_V4ROOT case. > > I don't think that would help in general. > If I export /foo and want to mount /foo/bar/baz, then for the last lookup at > least, NFSEXP_V4ROOT isn't set anywhere near. I'm not entirely clear why mountd even allows that, but no point trying to change it now anyway. > An exception would need to be made for every 'nfs4_lookup_dentry', provided > it found a directory, or nothing (or a symlink...). Possibly this could only > be done for anonymous credentials (as are used by the nfs4 mount operation). Yuch. > It would be nice if we could clearly differentiate a mount-time lookup from a > regular lookup, but I don't think the protocol allows for that. I guess you're right. So it starts to sound more like: "you have a confusing setup. Your export configuration says one thing, and your filesystem permissions say another. Under NFSv3 the confusion didn't matter, but now it does--time to fix it." --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
