> On Nov 13, 2024, at 8:29 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > On Wed, 2024-11-13 at 11:17 +0100, Erin Shepherd wrote: >> On 13/11/2024 01:40, Darrick J. Wong wrote: >>>> Hmm, I guess I might have made that possible, though I'm certainly not >>>> familiar enough with the internals of nfsd to be able to test if I've done >>>> so. >>> AFAIK check_export() in fs/nfsd/export.c spells this it out: >>> >>> /* There are two requirements on a filesystem to be exportable. >>> * 1: We must be able to identify the filesystem from a number. >>> * either a device number (so FS_REQUIRES_DEV needed) >>> * or an FSID number (so NFSEXP_FSID or ->uuid is needed). >>> * 2: We must be able to find an inode from a filehandle. >>> * This means that s_export_op must be set. >>> * 3: We must not currently be on an idmapped mount. >>> */ >>> >>> Granted I've been wrong on account of stale docs before. :$ >>> >>> Though it would be kinda funny if you *could* mess with another >>> machine's processes over NFS. >>> >>> --D >> >> To be clear I'm not familiar enough with the workings of nfsd to tell if >> pidfs fails those requirements and therefore wouldn't become exportable as >> a result of this patch, though I gather from you're message that we're in the >> clear? >> >> Regardless I think my question is: do we think either those requirements could >> change in the future, or the properties of pidfs could change in the future, >> in ways that could accidentally make the filesystem exportable? >> >> I guess though that the same concern would apply to cgroupfs and it hasn't posed >> an issue so far. > > We have other filesystems that do this sort of thing (like cgroupfs), > and we don't allow them to be exportable. We'll need to make sure that > that's the case before we merge this, of course, as I forget the > details of how that works. It's far easier to add exportability later than it is to remove it if we think it was a mistake. I would err on the side of caution if there isn't an immediate need/use-case for exposure via NFS. -- Chuck Lever
