Re: [Qemu-devel] [PATCH v3 2/4] ivshmem: validate incoming_posn value from server

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Sep 15, 2014 at 06:40:06PM +0200, Andreas Färber wrote:
> From: Stefan Hajnoczi <stefanha@redhat.com>
> 
> Check incoming_posn to avoid out-of-bounds array accesses if the ivshmem
> server on the host sends invalid values.
> 
> Cc: Cam Macdonell <cam@cs.ualberta.ca>
> Reported-by: Sebastian Krahmer <krahmer@suse.de>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> [AF: Tighten upper bound check for posn in close_guest_eventfds()]
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Andreas Färber <afaerber@suse.de>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  hw/misc/ivshmem.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> index caeee1e..24f74f6 100644
> --- a/hw/misc/ivshmem.c
> +++ b/hw/misc/ivshmem.c
> @@ -389,6 +389,9 @@ static void close_guest_eventfds(IVShmemState *s, int posn)
>      if (!ivshmem_has_feature(s, IVSHMEM_IOEVENTFD)) {
>          return;
>      }
> +    if (posn < 0 || posn >= s->nb_peers) {
> +        return;
> +    }
>  
>      guest_curr_max = s->peers[posn].nb_eventfds;
>  
> @@ -455,6 +458,11 @@ static void ivshmem_read(void *opaque, const uint8_t *buf, int size)
>          }
>      }
>  
> +    if (incoming_posn < -1) {
> +        IVSHMEM_DPRINTF("invalid incoming_posn %ld\n", incoming_posn);
> +        return;
> +    }
> +
>      /* pick off s->server_chr->msgfd and store it, posn should accompany msg */
>      tmp_fd = qemu_chr_fe_get_msgfd(s->server_chr);
>      IVSHMEM_DPRINTF("posn is %ld, fd is %d\n", incoming_posn, tmp_fd);
> -- 
> 1.8.4.5