linux-kernel - Re: [PATCH 1/4] module: add syscall to load module from fd

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Message-ID: <5080C100.2090703@zytor.com>
Date:	Thu, 18 Oct 2012 19:54:56 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	mtk.manpages@...il.com, Kees Cook <keescook@...omium.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Arnd Bergmann <arnd@...db.de>,
	James Morris <james.l.morris@...cle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Paris <eparis@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/4] module: add syscall to load module from fd

On 10/18/2012 07:23 PM, Rusty Russell wrote:
> "H. Peter Anvin" <hpa@...or.com> writes:
>> Given that, I have to say I now seriously question the value of
>> finit_module().  The kernel can trivially discover if the pointed-to
>> memory area is a MAP_SHARED mmap() of a file descriptor and if so which
>> file descriptor... why can't we handle this behind the scenes?
>
> It is a bit more indirect, but also in practice it's a bit trickier than
> that.  We need to ensure the memory doesn't change underneath us and
> stays attached to that fd.  I can easily see that code slipping and
> ending in an exploit.
>
> But that may be my irrational fear of the mm :)

You have to do the same thing with a file/file descriptor, I would think.

However, I keep wondering about the use case for this, as opposed to 
signatures.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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