linux-kernel - Re: [PATCH v2 2/2] virtio-net: Prevent NULL dereference

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Message-ID: <1318063211.7385.1.camel@lappy>
Date:	Sat, 08 Oct 2011 10:40:11 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH v2 2/2] virtio-net: Prevent NULL dereference

On Mon, 2011-10-03 at 21:05 +0200, Michael S. Tsirkin wrote:
> I thought about this some more. If length was too large host is
> right now writing into pages that we have freed.
> That is very bad, and I don't know what do do with it,
> really not worth prettifying that IMO, NULL pointer is the least of our
> worries.
> 
> But, with mergeable buffers at least, and that is the main mode anyway,
> there is always a single page per buf, right?
> So I think we should change the code,
> and for mergeable buffers we shall only verify that
> length <= PAGE_SIZE.

In receive_mergeable() we already verify both 'page' being non-null and
length:

	if (len > PAGE_SIZE)
		len = PAGE_SIZE;

> 
> IOW copy a bit of code from page_to_skb(vi, page, len)
> to receive_mergeable, maybe add a common function
> if we need to avoid duplication.

-- 

Sasha.

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