linux-kernel - Re: [PATCH] autofs: fix the wrong usage of the deprecated task_pgrp

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Date:	Mon, 19 Jan 2009 09:32:08 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ian Kent <raven@...maw.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, hpa@...or.com,
	Pavel Emelyanov <xemul@...nvz.org>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, "SergeE.Hallyn" <serue@...ibm.com>
Subject: Re: [PATCH] autofs: fix the wrong usage of the deprecated
	task_pgrp_nr()

On 01/19, Ian Kent wrote:
>
> On Mon, 2009-01-19 at 08:08 +0100, Oleg Nesterov wrote:
> > On 01/19, Ian Kent wrote:
> > >
> > > On Sun, 2009-01-18 at 08:34 +0100, Oleg Nesterov wrote:
> > > > parse_options(&pgid) sets pgid = task_pgrp_nr() which uses the global
> > > > namespace. This is wrong, we use this pgid to find "struct pid" in the
> > > > current's namespace. Change parse_options() to use task_pgrp_vnr().
> > > >
> > > > Also do s/task_pgrp_nr/task_pgrp_vnr/ in the debugging printks.
> > > > checkpatch.pl complains about "line over 80 characters", but it should
> > > > blame the cuurent code, not the patch.
> > >
> > > This changelog entry doesn't really have anything that I can use to work
> > > out if this change might introduce regressions.
> > >
> > > It would be helpful to me if you could include:
> > > 1) A brief statement about what your trying to achieve and why.
> >
> > First of all, I think this patch fixes a bug.
> >
> > What we are doing in autofs_fill_super()->parse_options() path
> > is find_get_pid(task_pgrp_vnr(current)), this is wrong.
>
> So your saying that your patch is wrong?
> I'm not following this at all.

No, I am trying to say that the current code is wrong ;)

> > task_pgrp_vnr() reporst the pid_t in the global namespace, but
> > find_get_pid() searches "struct pid" in the current namespace.
> > We can get the wrong pid. I tried to document this in changelog.
>
> We don't know whether it's the wrong pid because the environments were
> this is used haven't been defined. Depending on expected usage of pid
> namespaces the global pid may or may not be the correct one. This was
> not determined the last time this came up.

Confused. The current code can't be right.

Lets consider the simplest case, there is no "pgrp=" option during mount.
In that case the current code does:

	pid_t pgrp = task_pgrp_nr(current);
	sbi->oz_pgrp = find_get_pid(pgid);

But this means that sbi->oz_pgrp != task_prgp(current), unless of
course we are from the global namespace. ->oz_pgrp is a "random"
pid or NULL.

What I am missed?

Oleg.

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