linux-kernel - Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

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Date:	Wed, 15 Feb 2012 19:10:08 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrey Vagin <avagin@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu,
	Michal Marek <mmarek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

On Wed, Feb 15, 2012 at 03:36:06PM +0100, Oleg Nesterov wrote:
> 
> task->files can be NULL, we can race with exit_files().

So I need to call get_files_struct. Thanks Oleg!

> 
> > +	fdt = files_fdtable(task->files);
> > +	if (idx < fdt->max_fds)
> > +		file = fdt->fd[idx];
> 
> You can probably rely on rcu instead of ->file_lock, but this is minor.
> 

I think so. I'll be updating the patch anyway (on top of current
one) so I'll address this comment too. Thanks!

> > +
> > +	/*
> > +	 * One should have enough rights to inspect task details.
> > +	 */
> > +	if (!ptrace_may_access(task1, PTRACE_MODE_READ) ||
> > +	    !ptrace_may_access(task2, PTRACE_MODE_READ)) {
> > +		ret = -EACCES;
> 
> Well, probably this is fine... but may be you can add a comment.
> The task can change its credentials right after ptrace_may_access()
> succeeds. This _looks_ wrong, perhaps it makes sense to  add the
> "we do not care" note.
> 

Wait, how it's differ from other ptrace_may_access calls all over
the kernel? I suppose I'm missing something obvious?

	Cyrill
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