> >> Arn't there ways to escape chroot jails? Serge had pointed me to a URL > >> which showed chroots can be escaped. And if that is true than having all > >> user's private mount tree in the same namespace can be a security issue? > > > > No. In fact chrooting the user into /share/$USER will actually > > _grant_ a privilege to the user, instead of taking it away. It allows > > the user to modify it's root namespace, which it wouldn't be able to > > in the initial namespace. > > > > So even if the user could escape from the chroot (which I doubt), s/he > > would not be able to do any harm, since unprivileged mounting would be > > restricted to /share. Also /share/$USER should only have read/search > > permission for $USER or no permissions at all, which would mean, that > > other users' namespaces would be safe from tampering as well. > > A couple of points. > - chroot can be escaped, it is just a chdir for the root directory > it is not a security feature. The only security is that you have to > be root to call chdir. A carefully done namespace setup won't have > that issue. > > - While it may not violate security as far as what a user is allowed > to modify it may violate security as far as what a user is allowed > to see. I think that's just up to the permissions in the global namespace. In this example if you 'chmod 0 /share' there won't be anything for the user to see. > There are interesting per login cases as well such as allowing a > user to replicate their mount tree from another machine when they > log in. When /home is on a network filesystem this can be very > practical and can allow propagation of mounts across machines not > just across a single login session. Yeah, sounds interesting, but I think it's better to get the basics working first, and then we can start to think about the extras. Btw, there's nothing that prevents cloning the namespace _after_ chrooting into the per-user tree. That would still be simpler than doing it the other way round: first creating per-session namespaces and then setting up mount propagation between them. Miklos - 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
