Re: [PATCH for 5.10] vdpa_sim: fix param validation in vdpasim_get_config()

[Stefano Garzarella]

On Mon, Feb 15, 2021 at 03:32:19PM +0100, Greg KH wrote:
> On Thu, Feb 11, 2021 at 05:25:19PM +0100, Stefano Garzarella wrote:
> > Commit 65b709586e222fa6ffd4166ac7fdb5d5dad113ee upstream.
>
> No, this really is not that commit, so please do not say it is.

Oops, sorry.

> > Before this patch, if 'offset + len' was equal to
> > sizeof(struct virtio_net_config), the entire buffer wasn't filled,
> > returning incorrect values to the caller.
> >
> > Since 'vdpasim->config' type is 'struct virtio_net_config', we can
> > safely copy its content under this condition.
> >
> > Commit 65b709586e22 ("vdpa_sim: add get_config callback in
> > vdpasim_dev_attr") unintentionally solved it upstream while
> > refactoring vdpa_sim.c to support multiple devices. But we don't want
> > to backport it to stable branches as it contains many changes.
> >
> > Fixes: 2c53d0f64c06 ("vdpasim: vDPA device simulator")
> > Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x
> > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > ---
> >  drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > index 6a90fdb9cbfc..8ca178d7b02f 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > @@ -572,7 +572,7 @@ static void vdpasim_get_config(struct vdpa_device *vdpa, unsigned int offset,
> >  {
> >  	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> >
> > -	if (offset + len < sizeof(struct virtio_net_config))
> > +	if (offset + len <= sizeof(struct virtio_net_config))
> >  		memcpy(buf, (u8 *)&vdpasim->config + offset, len);
> >  }
>
> I'll be glad to take a one-off patch, but why can't we take the real
> upstream patch?  That is always the better long-term solution, right?

Because that patch depends on the following patches merged in v5.11-rc1 
while refactoring vdpa_sim:
  f37cbbc65178 vdpa_sim: make 'config' generic and usable for any device type
  cf1a3b35382c vdpa_sim: store parsed MAC address in a buffer
  a13b5918fdd0 vdpa_sim: add work_fn in vdpasim_dev_attr
  011c35bac5ef vdpa_sim: add supported_features field in vdpasim_dev_attr
  2f8f46188805 vdpa_sim: add device id field in vdpasim_dev_attr
  6c6e28fe4579 vdpa_sim: add struct vdpasim_dev_attr for device attributes
  36a9c3063025 vdpa_sim: rename vdpasim_config_ops variables
  423248d60d2b vdpa_sim: remove hard-coded virtq count

Maybe we can skip some of them, but IMHO should be less risky to apply 
only this change.

If you want I can try to figure out the minimum sub-set of patches 
needed for 65b709586e22 ("vdpa_sim: add get_config callback in 
vdpasim_dev_attr").

Thanks,
Stefano