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

From: Sasha Levin <[email-masked]>
Date: Wed, 05 Oct 2011 15:50:14 +0200

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 <[email-masked]>
> > Cc: "Michael S. Tsirkin" <[email-masked]>
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Signed-off-by: Sasha Levin <[email-masked]>
> > ---
> >  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.

-- 

Sasha.