linux-kernel - Re: [patch] remove MNT_NOEXEC check for PROT

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Message-ID: <9a8748490610041102n69c5ee15s1c01675aca84625a@mail.gmail.com>
Date:	Wed, 4 Oct 2006 20:02:29 +0200
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Stas Sergeev" <stsp@...et.ru>
Cc:	"Arjan van de Ven" <arjan@...radead.org>,
	"Linux kernel" <linux-kernel@...r.kernel.org>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"Hugh Dickins" <hugh@...itas.com>,
	"Ulrich Drepper" <drepper@...hat.com>, Valdis.Kletnieks@...edu
Subject: Re: [patch] remove MNT_NOEXEC check for PROT_EXEC mmaps

On 03/10/06, Stas Sergeev <stsp@...et.ru> wrote:
> Hello.
>
> Arjan van de Ven wrote:
> > no what bothers me that on the one hand you want no execute from the
> > partition, and AT THE SAME TIME want stuff to execute from there (being
> > libraries or binaries, same thing to me).
> The original problem came from "noexec" on /dev/shm
> mount. There is no library and no binary there, but
> the programs do shm_open(), ftruncate() and
> mmap(MAP_SHARED, PROT_EXEC) to get some shared memory
> with an exec perm. That fails.
>

So first you mount /dev/shm with 'noexec', thereby telling the system
"please make shared memory non executable".
Then an application goes and asks for executable shared memory, gets
denied and thus fails.  And that's a problem? It's exactely what you
asked for.

Either you want non-executable shared memory, so you mount /dev/shm
'noexec' or you want shared memory to be executable, in which case you
don't mount it 'noexec'.

As I see it, that's really all there is to it.

-- 
Jesper Juhl <jesper.juhl@...il.com>
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