Re: [Qemu-devel] [PATCH 1/4] libvhost-user: add vmsg_set_reply_u64() helper

[Marc-André Lureau]

On Fri, Jun 21, 2019 at 11:40 AM Stefan Hajnoczi <address@hidden> wrote:
>
> The VhostUserMsg request is reused as the reply by message processing
> functions.  This is risky since request fields may corrupt the reply if
> the vhost-user message handler function forgets to re-initialize them.
>
> Changing this practice would be very invasive but we can introduce a
> helper function to make u64 payload replies safe.  This also eliminates
> code duplication in message processing functions.
>
> Signed-off-by: Stefan Hajnoczi <address@hidden>

Reviewed-by: Marc-André Lureau <address@hidden>


> ---
>  contrib/libvhost-user/libvhost-user.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/contrib/libvhost-user/libvhost-user.c 
> b/contrib/libvhost-user/libvhost-user.c
> index 443b7e08c3..a8657c7af2 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -216,6 +216,15 @@ vmsg_close_fds(VhostUserMsg *vmsg)
>      }
>  }
>
> +/* Set reply payload.u64 and clear request flags and fd_num */
> +static void vmsg_set_reply_u64(VhostUserMsg *vmsg, uint64_t val)
> +{
> +    vmsg->flags = 0; /* defaults will be set by vu_send_reply() */
> +    vmsg->size = sizeof(vmsg->payload.u64);
> +    vmsg->payload.u64 = val;
> +    vmsg->fd_num = 0;
> +}
> +
>  /* A test to see if we have userfault available */
>  static bool
>  have_userfault(void)
> @@ -1168,10 +1177,7 @@ vu_get_protocol_features_exec(VuDev *dev, VhostUserMsg 
> *vmsg)
>          features |= dev->iface->get_protocol_features(dev);
>      }
>
> -    vmsg->payload.u64 = features;
> -    vmsg->size = sizeof(vmsg->payload.u64);
> -    vmsg->fd_num = 0;
> -
> +    vmsg_set_reply_u64(vmsg, features);
>      return true;
>  }
>
> @@ -1307,17 +1313,14 @@ out:
>  static bool
>  vu_set_postcopy_listen(VuDev *dev, VhostUserMsg *vmsg)
>  {
> -    vmsg->payload.u64 = -1;
> -    vmsg->size = sizeof(vmsg->payload.u64);
> -
>      if (dev->nregions) {
>          vu_panic(dev, "Regions already registered at postcopy-listen");
> +        vmsg_set_reply_u64(vmsg, -1);
>          return true;
>      }
>      dev->postcopy_listening = true;
>
> -    vmsg->flags = VHOST_USER_VERSION |  VHOST_USER_REPLY_MASK;
> -    vmsg->payload.u64 = 0; /* Success */
> +    vmsg_set_reply_u64(vmsg, 0);
>      return true;
>  }
>
> @@ -1332,10 +1335,7 @@ vu_set_postcopy_end(VuDev *dev, VhostUserMsg *vmsg)
>          DPRINT("%s: Done close\n", __func__);
>      }
>
> -    vmsg->fd_num = 0;
> -    vmsg->payload.u64 = 0;
> -    vmsg->size = sizeof(vmsg->payload.u64);
> -    vmsg->flags = VHOST_USER_VERSION |  VHOST_USER_REPLY_MASK;
> +    vmsg_set_reply_u64(vmsg, 0);
>      DPRINT("%s: exit\n", __func__);
>      return true;
>  }
> --
> 2.21.0
>