Re: [PATCH 5/6] vhost_net: fix use after free of vq->ubufs

[Jason Wang]

On 04/17/2012 06:22 PM, Michael S. Tsirkin wrote:
> On Tue, Apr 17, 2012 at 11:19:42AM +0800, Jason Wang wrote:
> > >  On 04/16/2012 09:28 PM, Michael S. Tsirkin wrote:
> > > >  >On Mon, Apr 16, 2012 at 02:08:25PM +0800, Jason Wang wrote:
> > > > >  >>When zerocopy socket is used, ubufs pointer were used in handle_tx()
> > > > >  >>without any validation. This would cause NULL pointer deference after
> > > > >  >>it has been freed in vhost_net_set_backend(). Fix this by check the
> > > > >  >>pointer before using it.
> > > > >  >>
> > > > >  >>Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx>
> > > >  >
> > > >  >OK so it's NULL dereference and not user after free:)
> > > >  >Also could you clarify how does this happen pls?
> > > >  >Don't we always initialize ubufs when vhost_sock_zcopy is set?
> > >  
> > >  The problem happens when we want to disable backend. At this time
> > >  ubufs were assigned to NULL and it may be dereferenced by
> > >  handle_tx():
> Heh, I see. How about
> - zcopy = vhost_sock_zcopy(sock);
> + zcopy = vq->ubufs;

Yes, It's more is simpler.
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