Re: [Keyrings] [PATCH] Keys: Add LSM hooks for key management

[Chris Wright]

* David Howells (dhowells@xxxxxxxxxx) wrote:
> Chris Wright <chrisw@xxxxxxxx> wrote:
> 
> > BTW, /proc/keys should move, esp since it's a debugging interface.
> 
> Move where? Actually, it shouldn't exist, except that I need it for debugging.

Debugfs is logical spot.

> > It means the security modules have to be able to parse the data.  I
> > think that'd be the rough analog to updating file label based on file
> > contents, right?  And we definitely don't want that.
> 
> Okay, I'll not do that then.
> 
> > So this security information is COW?
> 
> That's a good point. I need to add a duplicate hook so that the LSM can copy
> or whatever the security information. Or maybe I should get rid of key
> duplication entirely since it's not available to userspace.

Yes, that's what I was trying to get at.

> > > The problem is that key_ref_t isn't available if CONFIG_KEYS is not defined,
> > > but it's still referenced in security.h. Would it be reasonable to make all
> > > the security_key_*() functions contingent on CONFIG_KEYS since they're only
> > > called from the key management code? That would mean I wouldn't need to do
> > > this.
> > 
> > I see.  I thought they already were conditional on CONFIG_KEYS.
> 
> No... You get either one set which works or another set which is a bunch of
> dummy functions, not neither. I should change that. I could ditch the
> security_*() stubs entirely; they're just magic fluff to appease those who
> feel queasy at the sight of #ifdefs in .c files.

Typically forward decl is enough, it's just that typedef that's
problematic.  But, it's not an issue, I was just clarifying that it
wasn't a core part of the patch, rather prep work.

> > So this is where 'rka->context = current' is established.  And since
> > call_usermodehelper is called with wait flag set, you're sure current
> > won't go away...OK scratch that worry of mine.
> 
> Even if that context could go away (say we made it request_key()
> interruptible), the authorisation key would be revoked _first_ with the key
> semaphore held, just to make sure there wouldn't be a race.

I was looking for places where rka->context is referrenced assuming it
didn't go away (i.e. Oops waiting to happen).  Given the non-interrupitble
wait, this isn't possible.

> > Ah, I saw that code and didn't grok why that bit was needed, thanks.
> 
> I should wrap this outline up and stick it in a document somewhere.

That's a good idea.  I do appreciate the nice explanation.

> > > At some point, I will have to make it so that I don't have to use
> > > /sbin/request-key, but can instead request an already running daemon assume
> > > the context from an auth key specified to it, say by passing the key serial
> > > number over a socket.
> > 
> > I can see the appeal, but actually current architecture makes it easier
> > to do checks against the caller that initiated the request.
> 
> It's going to be necessary. I've had requests for this from Trond (NFSv4)
> amongst others. We discussed it at OLS; it really slows things down to be
> forking off new processes regularly, so it needs to be done. I thought I
> should probably do the LSM patch first so I could then work out how to fit in
> with that - so there may be more key security hooks coming.

Hmm, so we'll need a way for it to assume an identity, label and all.

<snip>
> > You're right, somehow I thought it was newly introduced.
> 
> Well, you (or someone) did comment on the bit of the patch where I removed it
> from the header file...

Hehe, it was me, I blame overexposure to diapers ;-) 

thanks,
-chris
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