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

[Peter Maydell]

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.

thanks
-- PMM