Date: Tue, 9 Oct 2001 13:05:11 -0700 (PDT) From: Julian Elischer <julian@elischer.org> To: John Baldwin <jhb@FreeBSD.org> Cc: arch@FreeBSD.org Subject: Re: ucred API Message-ID: <Pine.BSF.4.21.0110091301321.27416-100000@InterJet.elischer.org> In-Reply-To: <XFMail.011009112923.jhb@FreeBSD.org>
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On Tue, 9 Oct 2001, John Baldwin wrote:
>
> newcred = crget();
> PROC_LOCK(p);
> oldcred = p->p_ucred;
> error = suser(oldcred);
is suser being changed to take a cred?
> if (error == 0) {
> crcopy(newcred, oldcred);
>
> Stage 2:
> - Add a per-thread reference to the ucred that is created on syscall
> entry and released on syscall exit. It is also created and released
> if needed on trap enter/exit. It is _not_ created for interrupts since
> interrupts should not care about the ucred of their borrowed context.
> The per-thread ucred reference will then point to a ucred that won't
> ever change (setuid, etc. update the per-process ucred) and thus won't
> need any locking. Almost all references to ucreds for suser(), VOP's
> etc. will use the thread reference. This will ensure that a thread's
> ucred will be the same for an entire syscall which will close many
> races involving multithreaded programs and ucreds. The only place where
> the per-process ucred will be used for access checks is places that
> modify the ucred as we want to ensure there is no race of one thread
> making a credential change it isn't qualified to make due to it performing
> its access checks on a stale ucred before updating the master ucred.
I assume that you say "It won't change" because if the process's cred
is changed, it gets a new one and the thread's pointer
still points to the old one? (ref counted)
>
> I've talked with Robert Watson about these already and they sound good to him.
> Any objections?
>
no, sounds fine!
> --
>
> John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
> PGP Key: http://www.baldwin.cx/~john/pgpkey.asc
> "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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