Messages in this thread | | | Date | Thu, 6 Oct 2005 10:58:17 -0700 | From | Chris Wright <> | Subject | Re: [Keyrings] [PATCH] Keys: Add LSM hooks for key management |
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* David Howells (dhowells@redhat.com) wrote: > James Morris <jmorris@namei.org> wrote: > > > What case causes context != current? > > > > Indeed, this is critical: we always need to know which task initiated the > > current action. If it's not current, then we need the calling task struct > > passed into the security hook. > > Surely you know the calling task struct: it's current, but I can pass it in > anyway if you wish. > > As I outlined in a previous email, this has to do with the way request_key() > works, and the need for the process actually instantiating the key to gain > access to the keyrings, ownership, group membership, etc. of the process that > created the key.
The security check is comparing key label to task label. If it's not done 100% in current context, then task must be passed to get access to proper label. So, for example, request-key is done by the special privileged /sbin/request-key via usermodehelper on behalf of someone else.
> > > > + /* do a final security check before publishing the key */ > > > > + ret = security_key_alloc(key); > > > > > > This may simply be allocating space for the label (and possibly labelling) > > > not necessarily a security check. > > > > Agree, in fact, I think we should always aim to keep housekeeping hooks > > separate from access control hooks. > > What do you mean by separate? And this provides a chance for the LSM to deny > the creation of a key before it's published.
Just remove the comment, and we'll all agree ;-)
> > Access checks seem to be usually done before this point via > > lookup_user_key(), which is ideal. > > Eh? lookup_user_key()? That's not necessarily called before, not if you're > creating a key. > > > > This is odd, esp since nothing could have failed between alloc and > > > publish. Only state change is serial number. Would you expect the > > > security module to update a label based on serial number? > > > > I don't think SELinux would care about this yet. If so, the hook can be > > added later. > > Auditing?
Hmm, suppose, but auditing is not the charter of LSM. So in this case, the previous hook can audit key creation if needed. Just looking to avoid hook proliferation if possible.
> > > Are you sure this is right? Normally I'd expect users can _not_ set the > > > security labels of their own keys. But perhaps I've missed the point > > > of this one, could you give a use case? > > > > I think this is like xattrs on files, where the user can set and view > > security attributes. > > That's what I was thinking of.
I see, what would they used for?
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