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

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Date:	Fri, 19 Oct 2012 12:53:14 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"H. Peter Anvin" <hpa@...or.com>, mtk.manpages@...il.com
Cc:	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

"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 :)

Cheers,
Rusty.
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