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

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Message-ID: <451B5096.6020205@aknet.ru>
Date:	Thu, 28 Sep 2006 08:33:26 +0400
From:	Stas Sergeev <stsp@...et.ru>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>, Valdis.Kletnieks@...edu,
	Arjan van de Ven <arjan@...radead.org>,
	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch] remove MNT_NOEXEC check for PROT_EXEC MAP_PRIVATE mmaps

Hello.

Hugh Dickins wrote:
> since executables are typically mapped MAP_PRIVATE, I suspect
> your patch will simply break mmap's intended MNT_NOEXEC check.
The one with ld.so you mean? But its a user-space issue,
I haven't seen anyone claiming the opposite (and you even
explicitly confirmed it is).

> I think you need to face up to the fact that "noexec"
> doesn't suit your mount, and just leave it at that.
But noone have answered this question:
Which configuration is more secure - the one where all
the user-writable fs are mounted with "noexec" (in old
sense of noexec), or the one without "noexec" at all
because I should no longer use it here and there (actually,
everywhere)?

> But I do concede that I'm reluctant to present that patch Alan
> encouraged, adding a matching MNT_NOEXEC check to mprotect: it
> would be consistent, and I do like consistency, but in this case
> fear that change in behaviour may cause new userspace breakage.
I can't think of a single real-life example where it will
break something over whatever is broken already by the mmap
check. But I am not encouraging such a change of course.

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