netdev - Re: [PATCH RFC] tun: remove of user-controlled memory allocation

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Message-Id: <20101101.071648.112608839.davem@davemloft.net>
Date:	Mon, 01 Nov 2010 07:16:48 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mst@...hat.com
Cc:	herbert@...dor.hengli.com.au, eric.dumazet@...il.com,
	joe@...ches.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] tun: remove of user-controlled memory allocation

From: "Michael S. Tsirkin" <mst@...hat.com>
Date: Mon, 1 Nov 2010 10:27:49 +0200

> Untested, this is just an RFC.
> 
> tun does a kmalloc where userspace controls the length. This will
> produce warnings in kernel log when the length is too large, or might
> block for a long while. A simple fix is to avoid the allocatiuon
> altogether, and copy from user in a loop.
> 
> However, with this patch an illegal address passed to the ioctl might
> leave the filter disabled.  Is this something we care about?  If
> yes we could recover by creating a copy of the filter.  Thoughts?
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

I think the key issue in situations like this is simply to make
sure that reasonable things that worked before, still do afterwards.

And I think your patch does that, so it's fine as far as I can tell.
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