[RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
luto at kernel.org
Tue Jun 4 21:05:57 UTC 2019
On Tue, Jun 4, 2019 at 1:31 PM Casey Schaufler <casey at schaufler-ca.com> wrote:
> n 6/4/2019 10:43 AM, Andy Lutomirski wrote:
> > On Tue, Jun 4, 2019 at 9:35 AM David Howells <dhowells at redhat.com> 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
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.
> 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.
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