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

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Date:	Wed, 5 Oct 2011 16:59:42 -0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Sasha Levin <levinsasha928@...il.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 Wed, Oct 05, 2011 at 03:50:14PM +0200, Sasha Levin wrote:
> On Mon, 2011-10-03 at 20:40 +0200, Michael S. Tsirkin wrote:
> > On Wed, Sep 28, 2011 at 05:40:55PM +0300, Sasha Levin wrote:
> > > This patch prevents a NULL dereference when the user has passed a length
> > > longer than an actual buffer to virtio-net.
> > > 
> > > Cc: Rusty Russell <rusty@...tcorp.com.au>
> > > Cc: "Michael S. Tsirkin" <mst@...hat.com>
> > > Cc: virtualization@...ts.linux-foundation.org
> > > Cc: netdev@...r.kernel.org
> > > Cc: kvm@...r.kernel.org
> > > Signed-off-by: Sasha Levin <levinsasha928@...il.com>
> > > ---
> > >  drivers/net/virtio_net.c |   12 +++++++++++-
> > >  1 files changed, 11 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index bde0dec..4a53d2a 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -208,12 +208,22 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> > >  		return NULL;
> > >  	}
> > >  
> > > -	while (len) {
> > > +	while (len && page) {
> > >  		set_skb_frag(skb, page, offset, &len);
> > >  		page = (struct page *)page->private;
> > >  		offset = 0;
> > >  	}
> > >  
> > > +	/*
> > > +	 * This is the case where we ran out of pages in our linked list, but
> > > +	 * supposedly have more data to read.
> > 
> > Again, let's clarify that this only happens with broken devices.
> 
> I think that the code within the if() makes it clear that it isn't the
> regular path.

It doesn't make it clear that this never happens in absence of bugs.

> -- 
> 
> Sasha.
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