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

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Date:	Tue, 3 Oct 2006 17:00:37 -0400
From:	Jakub Jelinek <jakub@...hat.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 Tue, Oct 03, 2006 at 11:07:37PM +0400, Stas Sergeev wrote:
> Arjan van de Ven wrote:
> >then don't put noexec on /dev/shm.
> That's obviously possible, but I'd feel safer having
> "noexec" on *every* user-writable partition. It used
> to work in the past - that way an attacker had no place
> to run his binary from.

Even assuming ld.so would be hacked up so that it parses /proc/mounts
to see if you are trying to run an executable via ld.so from
noexec mount (which isn't going to happen), if mmap with PROT_EXEC
is allowed on noexec mounts, you can always put there a shared
library instead of a binary and put some interesting stuff in its
constructors and then just LD_PRELOAD=/dev/shm/libmyhack.so /bin/true
Really, if noexec is supposed to make any sense at all, it needs
to prevent PROT_EXEC mapping/mprotect, otherwise it is completely
useless.

	Jakub
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