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

[Harshit Mogalapalli]

On 28/11/22 4:43 pm, Stefano Garzarella wrote:
> 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?

Hi Stefano,

I may be incorrect about the details of this driver, my v1 was purely 
based on static analysis, Micheal suggested me to put a limit of 0xffff 
on vq_num. I really don't know about the driver, while I was searching 
other parts of code, I thought 0xffff is based vring size, I have asked 
the same question on v1 today.

Ref to v1: 
https://lore.kernel.org/all/82e8ce27-0743-59bf-fbe8-a25093167451@xxxxxxxxxx/

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

yeah, we should clarify the limit in commit message, once Micheal shares 
about the limit '0xffff), I will add those details and send a next 
version if that's okay.


Thanks,
Harshit
> Thanks,
> Stefano