Messages in this thread | | | Date | Thu, 13 Jul 2006 12:47:21 -0500 | From | "Serge E. Hallyn" <> | Subject | Re: [PATCH -mm 5/7] add user namespace |
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Quoting Cedric Le Goater (clg@fr.ibm.com): > Eric W. Biederman wrote: > > >> I think user namespace should be unshared with filesystem. if not, the > >> user/admin should know what is doing. > > > > No. The uids in a filesystem are interpreted in some user namespace > > context. We can discover that context at the first mount of the > > filesystem. > > ok. so once you're in such a user namespace, you can't unshare from it > without loosing access to all your files ? > > > Assuming the uids on a filesystem are the same set of uids your process > > is using is just wrong. > > well, this is what is currently done without user namespaces. > > >>> I believe some of the key infrastructure which is roughly kerberos > >>> authentication tokens could be used for this purpose. > >> please elaborate ? i'm not sure to understand why you want to use the keys > >> to map users. > > > > keys are essentially security credentials for something besides the > > local kernel. Think kerberos tickets. That makes the keys the > > obvious place to say what uid you are in a different user namespace > > and similar things. > > what about performance ? wouldn't that slow the checking ?
Rather than try to store (uid, namespace) on the filesystem, I like the idea of doing something like
mount --bind -o ro --uidswap 500,1001 --uidswap 501,0 /home /home
In other words, when you unshare the user namespace, nothing filesystem-related changes unless you also unshare the fs-namespace and set uid info on the vfsmount. This is fully backward-compatible and should have no overhead if you don't need the feature.
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