Re: Thoughts on credential switching

[Jeremy Allison <jra@samba.org>]

On Thu, Mar 27, 2014 at 11:46:39AM -0700, Andy Lutomirski wrote:
> On Thu, Mar 27, 2014 at 11:26 AM, Jeremy Allison <jra@samba.org> wrote:
> >
> > Amen to that :-).
> >
> > However, after talking with Jeff and Jim at CollabSummit,
> > I was 'encouraged' to make my opinions known on the list.
> >
> > To me, calling the creds handle a file descriptor just
> > feels wrong. IT *isn't* an fd, you can't read/write/poll
> > on it, and it's only done as a convenience to get the
> > close-on-exec semantics and the fact that the creds are
> > already hung off the fd's in kernel space.
> 
> Windows calls these things "handles."  Linux has "file descriptors,"
> and there's plenty of precedent for things that aren't files.

Sure, but there's a set of expectations around
fd's that these things don't satisfy - IO-ops.

> > That way we can also make it clear this thing only has
> > meaning to a thread group, and SHOULD NOT (and indeed
> > preferably CAN NOT) be passed between processes.
> >
> 
> If you want those semantics, then stick a struct pid * in there for
> the tgid of the cretor and make sure that current's tgid matches when
> you try to use it.
> 
> I think they'd be more useful without that check, though.

I'm more worried about leakage and unintended consequences
here.

> BTW, what do you want to have happen on fork?  I think they should keep working.

Yeah, that's true. I want them to keep
working across fork, but not across exec
or any other method of fd-passing.

Jeremy.