Quoting Miklos Szeredi (miklos@xxxxxxxxxx): > > > > > On mount propagation, let the owner of the clone be inherited from the > > > > > parent into which it has been propagated. Also if the parent has the > > > > > "nosuid" flag, set this flag for the child as well. > > > > > > > > What about nodev? > > > > > > Hmm, I think the nosuid thing is meant to prevent suid mounts being > > > introduced into a "suidless" namespace. This doesn't apply to dev > > > mounts, which are quite safe in a suidless environment, as long as the > > > user is not able to create devices. But that should be taken care of > > > by capability tests. > > > > > > I'll update the description. > > > > Hmm, > > > > Part of me wants to say the safest thing for now would be to refuse > > mounts propagation from non-user mounts to user mounts. > > > > I assume you're thinking about a fully user-mounted chroot, where > > the user woudl still want to be able to stick in a cdrom and have > > it automounted under /mnt/cdrom, propagated from the root mounts ns? > > Right. > > > But then are there no devices which the user could create on a floppy > > while inserted into his own laptop, owned by his own uid, then insert > > into this machine, and use the device under the auto-mounted /dev/floppy > > to gain inappropriate access? > > I assume, that the floppy and cdrom are already mounted with > nosuid,nodev. Yeah, of course, what I'm saying is no different whether the upper mount is a user mount or not. You're right. > The problem case is I think is if a sysadmin does some mounting in the > initial namespace, and this is propagated into the fully user-mounted > namespace (or chroot), so that a mount with suid binaries slips in. > Which is bad, because the user may be able rearange the namespace, to > trick the suid program to something it should not do. And really this shouldn't be an issue at all - the usermount chroot would be set up under something like /share/hallyn/root, so the admin would have to purposely set up propagation into that tree, so this won't be happening by accident. > OTOH, a mount with devices can't be abused this way, since it is not > possible to gain privileges to files/devices just by rearanging the > mounts. Thanks for humoring me, -serge - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
