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/ > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-arch" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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