linux-kernel - Re: [patch] honour MNT

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Date:	Sat, 07 Oct 2006 17:30:12 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Stas Sergeev <stsp@...et.ru>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jakub Jelinek <jakub@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Linux kernel <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hugh@...itas.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Jesper Juhl <jesper.juhl@...il.com>
Subject: Re: [patch] honour MNT_NOEXEC for access()

Stas Sergeev wrote:
> Even though the access(X_OK) is mostly not needed
> as the execve() would fail anyway, this is not the
> case for ld.so. I think it would be a good idea for
> ld.so to start using the access(R_OK | X_OK) before
> open().

Not really.  If you want to do something along those lines it would be 
better to add a new open flag called something like O_RDEXONLY which 
would require r-x effective file permissions, and allow 
PROT_READ|PROT_EXEC mmaps (though for that to be really useful, you'd 
need to make an O_RDONLY fd not allow PROT_EXEC mmaps, which would break 
a few things).

access() is just plain racy, and can't be used safely for any kind of 
permission/security check.

    J
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