From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Bryan Donlan <bdonlan@gmail.com>
Subject: Re: [PATCH] Added PR_SET_PROCTITLE_AREA option for prctl()
Cc: kosaki.motohiro@jp.fujitsu.com,
       KOSAKI Motohiro <kosaki.motohiro@gmail.com>, Timo Sirainen <tss@iki.fi>,
       linux-kernel@vger.kernel.org, Ulrich Drepper <drepper@redhat.com>
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References: <20091005103744.5F83.A69D9226@jp.fujitsu.com> <3e8340490910041844w63720cfq7981c8f5364229de@mail.gmail.com>
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Date: Mon,  5 Oct 2009 10:59:02 +0900 (JST)
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> On Sun, Oct 4, 2009 at 9:38 PM, KOSAKI Motohiro
> <kosaki.motohiro@jp.fujitsu.com> wrote:
> >> The improvement idea is here.
> >>
> >> Changelog
> >> ? - Added task_lock() to prctl(PR_SET_PROCTITLE_AREA)
> >> ?- ?Added small input sanity check to prctl(PR_SET_PROCTITLE_AREA)
> >
> > Doh, task_lock() is obviously wrong. please forget this.
> 
> As another note, in general I think we'd need to hold a lock over the
> entire operation. After all, if userspace changes its PROCTITLE_AREA,
> and then reuses the memory for something else, we have an information
> leak.

if reusing occur, it's obviously userland fault. I don't think we need to care this.
because current kernel also can be information leak by strcpy(argv[0], mypassword).

I think they are userland bug both.

 
> Perhaps a simpler approach would simply be to add a generation
> counter. Read it once at the start, barrier, then grab the title. Then
> at the end, read the generation counter again. If the value changed,
> we need to start over. Also, in this case, an error when reading the
> target process' memory should be ignored and retried, as we may have
> hit a race in which the target process unmapped the proctitle area
> after changing it.


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