Re: [Qemu-devel] [PATCH v4 05/30] virtio-net: out-of-bounds buffer write on load

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Michael S. Tsirkin (mst@redhat.com) wrote:
> CVE-2013-4149 QEMU 1.3.0 out-of-bounds buffer write in
> virtio_net_load()@hw/net/virtio-net.c
> 
> >         } else if (n->mac_table.in_use) {
> >             uint8_t *buf = g_malloc0(n->mac_table.in_use);
> 
> We are allocating buffer of size n->mac_table.in_use
> 
> >             qemu_get_buffer(f, buf, n->mac_table.in_use * ETH_ALEN);
> 
> and read to the n->mac_table.in_use size buffer n->mac_table.in_use *
> ETH_ALEN bytes, corrupting memory.
> 
> If adversary controls state then memory written there is controlled
> by adversary.
> 
> Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  hw/net/virtio-net.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 439477b..8d037b1 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -1363,9 +1363,15 @@ static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
>              qemu_get_buffer(f, n->mac_table.macs,
>                              n->mac_table.in_use * ETH_ALEN);
>          } else if (n->mac_table.in_use) {

You can lose that 'else if' test; 

        if (n->mac_table.in_use <= MAC_TABLE_ENTRIES) {
            qemu_get_buffer(f, n->mac_table.macs,
                            n->mac_table.in_use * ETH_ALEN);
        } else if (n->mac_table.in_use) {

to get to the else  in_use > MAC_TABLE_ENTRIES.

Dave

> -            uint8_t *buf = g_malloc0(n->mac_table.in_use);
> -            qemu_get_buffer(f, buf, n->mac_table.in_use * ETH_ALEN);
> -            g_free(buf);
> +            int i;
> +
> +            /* Overflow detected - can happen if source has a larger MAC table.
> +             * We simply set overflow flag so there's no need to maintain the
> +             * table of addresses, discard them all.
> +             */
> +            for (i = 0; i < n->mac_table.in_use * ETH_ALEN; ++i) {
> +                qemu_get_byte(f);
> +            }
>              n->mac_table.multi_overflow = n->mac_table.uni_overflow = 1;
>              n->mac_table.in_use = 0;
>          }
> -- 
> MST
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK