From: Arnd Bergmann <arnd@arndb.de>
To: Mike Frysinger <vapier@gentoo.org>
Subject: Re: [PATCH 1/4] asm-generic: uaccess: do not expand args multiple times
Date: Sun, 14 Jun 2009 22:14:39 +0200
User-Agent: KMail/1.11.90 (Linux/2.6.30-8-generic; KDE/4.2.85; x86_64; ; )
Cc: linux-kernel@vger.kernel.org
References: <1244959204-11269-1-git-send-email-vapier@gentoo.org>
In-Reply-To: <1244959204-11269-1-git-send-email-vapier@gentoo.org>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-15"
Content-Transfer-Encoding: 7bit
Message-Id: <200906142214.40532.arnd@arndb.de>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1159
Lines: 25

On Sunday 14 June 2009, Mike Frysinger wrote:
> While it's debatable whether {get,put}_user() should be called with
> arguments that have side effects, macro's should be written safely in the
> first place.  In this case, a slightly off version of put_user() ended up
> causing random userspace corruption and these things aren't trivial to
> track down.
> 
> While some of these conversions aren't strictly necessary, I think it's
> better to do all of them so as to be proactive in people accidently
> screwing it up in the future.

I've tried this and failed. This change adds an endless number of sparse
warnings in put_user and even gcc warnings in get_user. The problem
is that typeof() carries over the 'const' and '__user' modifiers, both
of which prevent you from assigning data to the new pointer that you
constructed.

I'd love to see a way to do this correctly, but this patch won't cut it.

	Arnd <><
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/