Re: [Qemu-devel] [PATCH 22/23] virtio-scsi: fix buffer overrun on invalid state load

[Peter Maydell]

On 3 December 2013 16:29, Michael S. Tsirkin <address@hidden> wrote:
> CVE-2013-4542
>
> hw/scsi/scsi-bus.c invokes load_request.
>
>  virtio_scsi_load_request does:
>     qemu_get_buffer(f, (unsigned char *)&req->elem, sizeof(req->elem));
>
> this probably can make elem invalid, for example,
> make in_num or out_num huge, then:
>
>     virtio_scsi_parse_req(s, vs->cmd_vqs[n], req);
>
> will do:
>
>     if (req->elem.out_num > 1) {
>         qemu_sgl_init_external(req, &req->elem.out_sg[1],
>                                &req->elem.out_addr[1],
>                                req->elem.out_num - 1);
>     } else {
>         qemu_sgl_init_external(req, &req->elem.in_sg[1],
>                                &req->elem.in_addr[1],
>                                req->elem.in_num - 1);
>     }
>
> and this will access out of array bounds.
> suggested patch:
>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
>  hw/scsi/virtio-scsi.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 26d95a1..51cc929 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -147,6 +147,8 @@ static void *virtio_scsi_load_request(QEMUFile *f, 
> SCSIRequest *sreq)
>      qemu_get_be32s(f, &n);
>      assert(n < vs->conf.num_queues);
>      qemu_get_buffer(f, (unsigned char *)&req->elem, sizeof(req->elem));
> +    assert(req->elem.in_num <= ARRAY_SIZE(req->elem.in_sg));
> +    assert(req->elem.out_num <= ARRAY_SIZE(req->elem.out_sg));

Wouldn't it be better to fail migration, as other patches in
this series do? "Silent security hole if you compile with
-DNDEBUG" is a little bit unfriendly...

thanks
-- PMM