On Thu, Jun 20, 2013 at 03:12:16PM -0400, Brian Foster wrote: > On 06/20/2013 01:39 PM, Dwight Engen wrote: > > On Thu, 20 Jun 2013 11:27:04 -0400 > > Brian Foster <bfoster@xxxxxxxxxx> wrote: > > > >> On 06/20/2013 09:54 AM, Dwight Engen wrote: > >>> On Thu, 20 Jun 2013 10:13:41 +1000 > >>> Dave Chinner <david@xxxxxxxxxxxxx> wrote: > >>> > >>>> On Wed, Jun 19, 2013 at 11:09:48AM -0400, Dwight Engen wrote: > ... > >> > >> Hi Dwight, > >> > >> If I understand correctly, the proposition is to turn > >> XFS_EOF_FREE_EOFBLOCKS into administrator only functionality and run > >> ns conversions on the inode uid/gid and associated eofb values for > >> the ID filtering functionality. > > > > Hi Brian, yeah that was the proposal :) I think there are really two > > issues here. One is that the uid_t/gid_t may come from a userns so we > > should be aware of that. Currently the ids passed in are used for > > *filtering* so a malicious user can't do anything more than they > > already can by not passing ids at all, but we should fix this so only > > the intended files are affected. Second is that currently the ioctl > > allows an unprivileged user to affect another user (as Eric pointed > > out): > > > >> I am little dubious about XFS_IOC_FREE_EOFBLOCKS allowing any > >> user to affect any other user. Your changes just seem to make > >> it guaranteed that when called from a user namespace the wrong > >> user will be affected. > > > > I don't think the nsown_capability() I proposed is enough to take care > > of this. Do you agree that if the caller is going to affect other > > users, they should be CAP_SYS_ADMIN (or maybe CAP_FOWNER) in > > init_user_ns? > > > > Yeah, that's what I was getting at below by restricting "global" scans > to admin privilege. Project quota scans are global scans, so user-based initiation through ioctls they should always be restricted to CAP_SYS_ADMIN. > >> The latter sounds reasonable to me, though I'm not so sure about the > >> CAP_SYS_ADMIN bit. For example, I think we'd expect a regular user to > >> be able to run an eofblocks scan against files covered under his > >> quota. > >> > >> Perhaps the right thing to do here is to restrict global (and project > >> quota?) scans to CAP_SYS_ADMIN and uid/gid based scans to processes > >> with the appropriate permissions (i.e., CAP_SYS_ADMIN, matching > >> uid/gid or CAP_FOWNER). Thoughts? > > > > That sounds good to me. Maybe for a regular user the appropriate > > permission check (at the top of xfs_inode_free_eofblocks()) could be > > something like: > > > > I think the various capability/permission checks should be in the ioctl > code. Yes, the cap/perm checks should be done before anything else in the ioctl. > This would still allow use cases such as the pending code I have that > invokes an eofblocks scan on write() failure due to EDQUOT/ENOSPC in the > case of project or user/group quotas. Right, we have to ensure this can occur without namespace restriction, because ENOSPC is not something that is bound by user namespaces. > I suspect adding the namespace > conversion stuff wouldn't break the typical user/group quota case, but For EDQUOT, no, but for a global ENOSPC scan I think it could cause problems. > we'd still require the ability to run a project quota scan from a > particular user context. I think the combined check you have > above would break that. Yup, that still needs to work, as does the background scanner which should not be subject to any restrictions at all ;) Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
