linux-kernel - Re: [PATCH v5] Added PR_SET_PROCTITLE

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Date:	Mon, 9 Nov 2009 19:00:17 -0500
From:	Bryan Donlan <bdonlan@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Americo Wang <xiyou.wangcong@...il.com>,
	Timo Sirainen <tss@....fi>,
	Ulrich Drepper <drepper@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org
Subject: Re: [PATCH v5] Added PR_SET_PROCTITLE_AREA option for prctl()

On Mon, Nov 9, 2009 at 5:47 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:

> What happens if userspace unmaps the memory after telling the kernel to
> use it?
>
> Will processes which try to read the command line get an error reading
> /proc?  If so, do all the commandline-reading programs in the world
> handle this in an appropriate fashion?

This case can already occur in the current code; the userspace process
would have to munmap() the top of its stack, but it certainly can do
so if it tries. In any case, access_process_vm() then returns 0
because of the fault, and thus /proc/pid/cmdline is seen to have zero
length. Since a zero-length /proc/pid/cmdline occurs with kernel
threads as well, we know this isn't a problem.
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