RE: [PATCH V2] net/colo.c: Fix the pointer issuse reported by Coverity.

[Zhang, Chen]

> -----Original Message-----
> From: Peter Maydell <peter.maydell@linaro.org>
> Sent: Friday, August 5, 2022 5:57 PM
> To: Zhang, Chen <chen.zhang@intel.com>
> Cc: Jason Wang <jasowang@redhat.com>; Li Zhijian <lizhijian@fujitsu.com>;
> qemu-dev <qemu-devel@nongnu.org>
> Subject: Re: [PATCH V2] net/colo.c: Fix the pointer issuse reported by
> Coverity.
> 
> On Fri, 5 Aug 2022 at 10:53, Zhang Chen <chen.zhang@intel.com> wrote:
> >
> > When enable the virtio-net-pci, guest network packet will load the
> > vnet_hdr. In COLO status, the primary VM's network packet maybe
> > redirect to another VM, it need filter-redirect enable the vnet_hdr
> > flag at the same time, COLO-proxy will correctly parse the original
> > network packet. If have any misconfiguration here, the vnet_hdr_len is
> > wrong for parse the packet, the data+offset will point to wrong place.
> >
> > Signed-off-by: Zhang Chen <chen.zhang@intel.com>
> > ---
> >  net/colo.c | 17 +++++++++--------
> >  1 file changed, 9 insertions(+), 8 deletions(-)
> >
> > diff --git a/net/colo.c b/net/colo.c
> > index 6b0ff562ad..524afa3d9b 100644
> > --- a/net/colo.c
> > +++ b/net/colo.c
> > @@ -44,21 +44,22 @@ int parse_packet_early(Packet *pkt)  {
> >      int network_length;
> >      static const uint8_t vlan[] = {0x81, 0x00};
> > -    uint8_t *data = pkt->data + pkt->vnet_hdr_len;
> > +    uint8_t *data = pkt->data;
> >      uint16_t l3_proto;
> >      ssize_t l2hdr_len;
> >
> > -    if (data == NULL) {
> > -        trace_colo_proxy_main_vnet_info("This packet is not parsed 
> > correctly,
> "
> > +    assert(data);
> > +
> > +    /* Check the received vnet_hdr_len then add the offset */
> > +    if (pkt->size < sizeof(struct eth_header) + sizeof(struct vlan_header)
> > +        + pkt->vnet_hdr_len) {
> 
> I think this expression needs more care to avoid overflow with a maliciously
> over-large vnet_hdr_len value.
> 
> Casting pkt->vnet_hdr_len to int64_t would be one way to do that; there
> may be better approaches.

Yes, you are right. And I found better to use this check to avoid overflow:
"pkt->vnet_hdr_len < sizeof(struct virtio_net_hdr)"
I will fix it in next version.

Thanks
Chen


> 
> thanks
> -- PMM