linux-kernel - Re: [PATCH] Added PR_SET_PROCTITLE

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Date:	Sun, 4 Oct 2009 23:22:18 -0400
From:	Bryan Donlan <bdonlan@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Timo Sirainen <tss@....fi>, linux-kernel@...r.kernel.org,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [PATCH] Added PR_SET_PROCTITLE_AREA option for prctl()

On Sun, Oct 4, 2009 at 10:48 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:

> +                       } else {
> +                               len = mm->env_end - mm->env_start;
> +                               if (len > PAGE_SIZE - res)
> +                                       len = PAGE_SIZE - res;
> +                               res += access_process_vm(task, mm->env_start,
> +                                                        buffer+res, len, 0);
> +                               res = strnlen(buffer, res);
> +                       }


This bug was in the original code, but since you're touching it
anyway, it should be fixed now; if this access_process_vm fails
(perhaps due to the target unmapping the page in question in between
the two calls), bad things might happen if (error code) + res < 0, as
then strnlen will get a huge value in its length (possibly leading to
OOPS etc). It should be changed to check for an error return here and
fail out properly if there is an error in this second check.
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