Re: [QEMU PATCH v4 2/3] virtio-net: introduce a new macaddr control

[Amos Kong <akong@redhat.com>]

On Mon, Jan 21, 2013 at 05:08:26PM +0100, Stefan Hajnoczi wrote:
> On Sat, Jan 19, 2013 at 09:54:27AM +0800, akong@redhat.com wrote:
> > @@ -350,6 +351,18 @@ static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,
> >      struct virtio_net_ctrl_mac mac_data;
> >      size_t s;
> >  
> > +    if (cmd == VIRTIO_NET_CTRL_MAC_ADDR_SET) {
> > +        if (iov_size(iov, iov_cnt) != ETH_ALEN) {
> > +            return VIRTIO_NET_ERR;
> > +        }
> > +        s = iov_to_buf(iov, iov_cnt, 0, &n->mac, sizeof(n->mac));
> > +        if (s != sizeof(n->mac)) {
> > +            return VIRTIO_NET_ERR;
> > +        }

     
> Since iov_size() was checked before iov_to_buf(), we never hit this
> error.  And if we did n->mac would be trashed (i.e. error handling is
> not complete).

You are right.
iov_size() computes the size by accounting iov[].iov_lens, the first
check is enough.
 
> I think assert(s == sizeof(n->mac)) is more appropriate appropriate.
> Also, please change ETH_ALEN to sizeof(n->mac) to make the relationship
> between the check and the copy clear.
> 

Will update this patch.

         if (cmd == VIRTIO_NET_CTRL_MAC_ADDR_SET) {
             if (iov_size(iov, iov_cnt) != sizeof(n->mac)) {
                 return VIRTIO_NET_ERR;
             }
             s = iov_to_buf(iov, iov_cnt, 0, &n->mac, sizeof(n->mac));
             assert(s == sizeof(n->mac));
             qemu_format_nic_info_str(&n->nic->nc, n->mac);
             return VIRTIO_NET_OK;
         }

> Stefan