Re: [PATCH v2] vduse: Validate vq_num in vduse_validate_config()

[Stefano Garzarella]

On Mon, Nov 28, 2022 at 01:58:00PM +0300, Dan Carpenter wrote:
> On Mon, Nov 28, 2022 at 11:53:12AM +0100, Stefano Garzarella wrote:
> > On Mon, Nov 28, 2022 at 12:36:26AM -0800, Harshit Mogalapalli wrote:
> > > Add a limit to 'config->vq_num' which is user controlled data which
> > > comes from an vduse_ioctl to prevent large memory allocations.
> > >
> > > This is found using static analysis with smatch.
> > >
> > > Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > > Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
> > > ---
> > > v1->v2: Change title of the commit and description, add a limit to
> > > 	vq_num.
> > >
> > > Note: I think here 0xffff is the max size of vring =  no: of vqueues.
> > > Only compile and boot tested.
> > > ---
> > > drivers/vdpa/vdpa_user/vduse_dev.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > index 35dceee3ed56..31017ebc4d7c 100644
> > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > @@ -1440,6 +1440,9 @@ static bool vduse_validate_config(struct vduse_dev_config *config)
> > > 	if (config->config_size > PAGE_SIZE)
> > > 		return false;
> > >
> > > +	if (config->vq_num > 0xffff)
> >
> > What about using U16_MAX here?
>
> Where is the ->vq_num stored in a u16?  I looked for this but didn't
> see it.

I thought vq_num referred to the number of elements in the vq (like 
.get_vq_num_max), since this patch wants to limit to 0xffff.

But it actually refers to the number of virtqueue, so @Harshit why do we 
limit it to 0xffff?

Maybe we should explain it in the commit message or in a comment.

Thanks,
Stefano