Re: [net] vhost: Use kzalloc() to allocate vhost_msg_node

[Guenter Roeck]

On 05/29/2018 08:01 PM, Michael S. Tsirkin wrote:
> On Tue, May 29, 2018 at 03:19:08PM -0700, Guenter Roeck wrote:
> > On Fri, Apr 27, 2018 at 11:45:02AM -0400, Kevin Easton wrote:
> > > The struct vhost_msg within struct vhost_msg_node is copied to userspace,
> > > so it should be allocated with kzalloc() to ensure all structure padding
> > > is zeroed.
> > >
> > > Signed-off-by: Kevin Easton <kevin@xxxxxxxxxxx>
> > > Reported-by: syzbot+87cfa083e727a224754b@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > Is this patch going anywhere ?
> >
> > The patch fixes CVE-2018-1118. It would be useful to understand if and when
> > this problem is going to be fixed.
> >
> > Thanks,
> > Guenter
> > > ---
> > >   drivers/vhost/vhost.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > index f3bd8e9..1b84dcff 100644
> > > --- a/drivers/vhost/vhost.c
> > > +++ b/drivers/vhost/vhost.c
> > > @@ -2339,7 +2339,7 @@ EXPORT_SYMBOL_GPL(vhost_disable_notify);
> > >   /* Create a new message. */
> > >   struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
> > >   {
> > > -	struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
> > > +	struct vhost_msg_node *node = kzalloc(sizeof *node, GFP_KERNEL);
> > >   	if (!node)
> > >   		return NULL;
> > >   	node->vq = vq;
>
> As I pointed out, we don't need to init the whole structure. The proper
> fix is thus (I think) below.
>
> Could you use your testing infrastructure to confirm this fixes the issue?

Sorry, I don't have the means to test the fix.

Guenter

> Thanks!
>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index f3bd8e941224..58d9aec90afb 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2342,6 +2342,9 @@ 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);
>   	node->vq = vq;
>   	node->msg.type = type;
>   	return node;