RE: [PATCH V3] net/colo.c: Fix the pointer issue reported by Coverity.

[Zhang, Chen]

> -----Original Message-----
> From: Jason Wang <jasowang@redhat.com>
> Sent: Tuesday, August 9, 2022 4:12 PM
> To: Zhang, Chen <chen.zhang@intel.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>; Li Zhijian
> <lizhijian@fujitsu.com>; qemu-dev <qemu-devel@nongnu.org>
> Subject: Re: [PATCH V3] net/colo.c: Fix the pointer issue reported by 
> Coverity.
> 
> On Tue, Aug 9, 2022 at 11:05 AM 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 | 18 ++++++++++--------
> >  net/colo.h |  1 +
> >  2 files changed, 11 insertions(+), 8 deletions(-)
> >
> > diff --git a/net/colo.c b/net/colo.c
> > index 6b0ff562ad..4f1b4a61f6 100644
> > --- a/net/colo.c
> > +++ b/net/colo.c
> > @@ -44,21 +44,23 @@ 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->vnet_hdr_len > sizeof(struct virtio_net_hdr)) ||
> 
> Virtio-net starts to support RSS so it means the vnet_hdr size could be 
> greater
> than virtio_net_hdr now.
> 
> Or did you actually mean "<" here?

No, I just try to avoid overflow with a maliciously over-large
vnet_hdr_len value as Peter's comments.
If enabled the RSS, how to get the maximum of vnet_hdr size?

Thanks
Chen

> 
> Thanks
> 
> > +        (pkt->size < sizeof(struct eth_header) + sizeof(struct vlan_header)
> > +        + pkt->vnet_hdr_len)) {
> > +        trace_colo_proxy_main_vnet_info("This packet may be load wrong "
> >                                          "pkt->vnet_hdr_len", 
> > pkt->vnet_hdr_len);
> >          return 1;
> >      }
> > -    l2hdr_len = eth_get_l2_hdr_length(data);
> > +    data += pkt->vnet_hdr_len;
> >
> > -    if (pkt->size < ETH_HLEN + pkt->vnet_hdr_len) {
> > -        trace_colo_proxy_main("pkt->size < ETH_HLEN");
> > -        return 1;
> > -    }
> > +    l2hdr_len = eth_get_l2_hdr_length(data);
> >
> >      /*
> >       * TODO: support vlan.
> > diff --git a/net/colo.h b/net/colo.h
> > index 8b3e8d5a83..22fc3031f7 100644
> > --- a/net/colo.h
> > +++ b/net/colo.h
> > @@ -18,6 +18,7 @@
> >  #include "qemu/jhash.h"
> >  #include "qemu/timer.h"
> >  #include "net/eth.h"
> > +#include "standard-headers/linux/virtio_net.h"
> >
> >  #define HASHTABLE_MAX_SIZE 16384
> >
> > --
> > 2.25.1
> >