Re: KMSAN: uninit-value in _copy_to_iter (2)

Al Viro
2018-06-07T17:44:26Z

On Thu, Jun 07, 2018 at 06:38:48PM +0300, Michael S. Tsirkin wrote:
> #syz test: https://github.com/google/kmsan.git/master d2d741e5d1898dfde1a75ea3d29a9a3e2edf0617
>
> Subject: vhost: fix info leak
>
> Fixes: CVE-2018-1118
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index f0be5f35ab28..9beefa6ed1ce 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2345,6 +2345,9 @@ struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
> struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
> if (!node)
> return NULL;
> +
> + /* Make sure all padding within the structure is initialized. */
> + memset(&node->msg, 0, sizeof node->msg);

Umm... Maybe kzalloc(), then? You have

struct vhost_msg_node {
struct vhost_msg msg;
struct vhost_virtqueue *vq;
struct list_head node;
};

and that's what, 68 bytes in msg, then either 4 bytes pointer or
4 bytes padding + 8 bytes pointer, then two pointers? How much
does explicit partial memset() save you here?

> node->vq = vq;
> node->msg.type = type;
> return node;