James Morris wrote: > On Tue, 13 Oct 2009, Trond Myklebust wrote: > > [added the ecryptfs folk] > > >> On Tue, 2009-10-13 at 18:02 +1100, James Morris wrote: >> >>> This xattr approach would only cover the "dumb server" scenario, where the >>> server simply stores and retrieves security labels on behalf of the >>> client. It's intended primarily to enable things like nfsroot, backups, >>> serving virtualized file systems etc., and not for fully trusted sharing >>> like Labeled NFS. >>> >>> It is essentially just security label transport. >>> >>> Support for this feature would be configured at the server, possibly an >>> option in /etc/exports which enables specific security namespaces, e.g: >>> >>> /opt/share 10.0.0.0/8(rw,insecure,xattr="user.*,security.SMACK64") >>> >>> This says that the XATTR side protocol is enabled and clients can read and >>> write user and security.smack xattrs (local DAC would be applied to both). >>> >>> The server kernel would likely need to know that these are foreign labels, >>> and not necessarily 'trust' them for its own use, so a root_squash -like >>> option may be used to remap them to an 'untrusted' local label for local >>> enforcement purposes -- if it was running SELinux or Smack at all, which >>> it may not be. >>> >> Fair enough. That might indeed work. >> >> One simple alternative might be to just store the exported xattrs in >> something other than the 'security' extended attribute namespace so that >> your server processes don't have to deal with any conflicts. >> >> IOW: maybe add a 'nfs.security' xattr namespace, which would contain >> those security labels that are actually exported by this XATTR protocol, >> and which the clients could then translate into their local 'security' >> labels. >> > > This sounds like a really good idea, and may provide a general solution > for non-user xattrs. i.e. any system, security or trusted xattr is stored > in the 'nfs' namespace on the server, and these are always opaque to the > server -- semantics are managed at the client. > > The wire protocol would always carry the client view, for simplicity, and > there's no negotiation -- label mapping is always configured at the server > by the admin. > If you wanted to you could implement a mapping scheme of your choice on the server. A Smack server might be happy with mapping nfs.security.SMACK64 to security.SMACK64, while an HP/UX server might have a function to map nfs.security.selinux into security.BellAndLaPadula for its own nefarious purposes. Because you could do this strictly on the server you don't have to implement a negotiation protocol, although you could. > i.e. the client always sends and receives "security.selinux"; the > server by default maps these locally as "nfs.security.selinux"; and may be > optionally configured to map to "nfs.$(custom).security.selinux" > > I wonder how to handle ecryptfs -- it strikes me as a special case where > the semantics are always local i.e. files can always be decrypted locally > because of the crypto metatdata stored with them. > > >> You might even be able to store per-client security labels as something >> like 'nfs.$(hostname).security', or perhaps have a namespace like >> 'nfs.fedora11.security' that applies to all clients running fedora? >> > > I don't know if there's an established need for this, but some kind of > generalized mapping scheme might be useful, and I suspect it's pretty > simple to implement as long as the xattr values are always opaque to the > server. > > > - James > -- 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
