Date: Tue, 09 Oct 2001 12:25:22 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: Julian Elischer <julian@elischer.org> Cc: arch@FreeBSD.org Subject: Re: ucred API Message-ID: <XFMail.011009122522.jhb@FreeBSD.org> In-Reply-To: <Pine.BSF.4.21.0110091301321.27416-100000@InterJet.elischer.org>
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On 09-Oct-01 Julian Elischer wrote:
>
>
> 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?
Not now, but I think that is on Robert's plans for the future. That should be
suser(p) I suppose. suser() really has nothing to do with threads or
processes but only ucred's anyways.
>> 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)
Right.
--
John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
PGP Key: http://www.baldwin.cx/~john/pgpkey.asc
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