On Tue, Jun 4, 2019 at 1:31 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: > > n 6/4/2019 10:43 AM, Andy Lutomirski wrote: > > On Tue, Jun 4, 2019 at 9:35 AM David Howells <dhowells@xxxxxxxxxx> wrote: > >> > >> Hi Al, > >> > >> Here's a set of patches to add a general variable-length notification queue > >> concept and to add sources of events for: > > I asked before and didn't see a response, so I'll ask again. Why are > > you paying any attention at all to the creds that generate an event? > > It seems like the resulting security model will be vary hard to > > understand and probably buggy. Can't you define a sensible model in > > which only the listener creds matter? > > We've spent the last 18 months reeling from the implications > of what can happen when one process has the ability to snoop > on another. Introducing yet another mechanism that is trivial > to exploit is a very bad idea. If you're talking about Spectre, etc, this is IMO entirely irrelevant. Among other things, setting these watches can and should require some degree of privilege. > > I will try to explain the problem once again. If process A > sends a signal (writes information) to process B the kernel > checks that either process A has the same UID as process B > or that process A has privilege to override that policy. > Process B is passive in this access control decision, while > process A is active. Are you stating what you see to be a requirement? > Process A must have write access > (defined by some policy) to process B's event buffer. No, stop right here. Process B is monitoring some aspect of the system. Process A is doing something. Process B should need permission to monitor whatever it's monitoring, and process A should have permission to do whatever it's doing. I don't think it makes sense to try to ascribe an identity to the actor doing some action to decide to omit it from the watch -- this has all kinds of correctness issues. If you're writing a policy and you don't like letting process B spy on processes doing various things, then disallow that type of spying. > To > implement such a policy requires A's credential, You may not design a new mechanism that looks at the credential in a context where looking at a credential is invalid unless you have some very strong justification for why all of the known reasons that it's a bad idea don't apply to what you're doing. So, without a much stronger justification, NAK.
