linux-kernel - Re: [PATCH v2 4/4] proc: avoid ->f_pos overflows in proc_task

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Message-ID: <20130604171435.GA20416@redhat.com>
Date:	Tue, 4 Jun 2013 19:14:35 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Sergey Dyasly <dserrg@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] proc: avoid ->f_pos overflows in
	proc_task_readdir() paths

On 06/03, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> > 1. proc_task_readdir() truncates f_pos to long, this can lead
> >    to wrong result on 32bit.
> >
> This won't compile on some 32bit architectures like x86-32.
>
> switch(unsigned long long) requires helpers that the kernel does not
> included.  Or at least the kernel has not included because such code
> is a problem.  In fact that is the reason Linus put the case to
> unsigned long in there.

Hmm, ee568b25, suprise... I am wondering if the kernel still supports
the compilers which needs __cmpdi2 in this case...

But this doesn't matter. The patch should not blindly revert ee568b25,
thanks!

> There is another bug in here as well that we may return really crazy
> things in the case of seek simultaneous with readdir.

i_mutex? both vfs_readdir() and default_llseek() take it... Anyway, this
is another issue.

> I think we really need to put f_pos
> in a local variable.

Heh. I swear, this is what I did initially. But I was afraid you will
blame this change as "overcomplicated" ;)

OK, I'll redo/resend this one later.

Oleg.

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