linux-kernel - Re: [PATCH] Added PR_SET_PROCTITLE

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Date:	Sun, 4 Oct 2009 23:39:12 -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 11:29 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> 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.
>
> AFAIK, access_process_vm() never return negative value.

Ahh, okay, I had read the if (res > 0 && ...) bit in the original code
as an error test. Nevermind then.
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