linux-kernel - Re: + fix-compat-space-msg-size-limit-for-msgsnd-msgrcv.patch added to -mm tree

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Message-Id: <200611140138.19111.arnd@arndb.de>
Date:	Tue, 14 Nov 2006 01:38:18 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	akpm@...l.org
Cc:	suzuki@...ux.vnet.ibm.com, davem@...emloft.net, suzuki@...ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: + fix-compat-space-msg-size-limit-for-msgsnd-msgrcv.patch added to -mm tree

On Tuesday 14 November 2006 00:58, akpm@...l.org wrote:

> Subject: Fix compat space msg size limit for msgsnd/msgrcv
> From: suzuki <suzuki@...ux.vnet.ibm.com>
> 
> Currently we allocate 64k space on the user stack and use it the msgbuf for
> sys_{msgrcv,msgsnd} for compat and the results are later copied in user [by
> copy_in_user].
> 
> This patch introduces helper routines for sys_{msgrcv,msgsnd} which would
> accept the pointer to msgbuf along with the msgp->mtext.  This avoids the
> need to allocate the msgsize on the userspace (thus removing the size
> limit) and the overhead of an extra copy_in_user().
> 
> Signed-off-by: Suzuki K P <suzuki@...ibm.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: "David S. Miller" <davem@...emloft.net>
> Signed-off-by: Andrew Morton <akpm@...l.org>

This patch is definitely a big step in the right direction here, but why 
not go all the way and pass msgp->mtype to do_msgsnd/do_msgrcv as kernel
data instead of a user space pointer? This way you can get rid of the
compat_alloc_userspace entirely and save avoid doing an extra 
put_user/get_user pair in the compat_ function.

	Arnd <><
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