Messages in this thread | | | Date | Wed, 10 Feb 2021 11:08:21 +0100 | From | Stefano Garzarella <> | Subject | Re: [PATCH] vdpa/mlx5: fix param validation in mlx5_vdpa_get_config() |
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On Tue, Feb 09, 2021 at 04:31:23AM -0500, Michael S. Tsirkin wrote: >On Tue, Feb 09, 2021 at 11:24:03AM +0800, Jason Wang wrote: >> >> On 2021/2/9 上午2:38, Michael S. Tsirkin wrote: >> > On Mon, Feb 08, 2021 at 05:17:41PM +0100, Stefano Garzarella wrote: >> > > It's legal to have 'offset + len' equal to >> > > sizeof(struct virtio_net_config), since 'ndev->config' is a >> > > 'struct virtio_net_config', so we can safely copy its content under >> > > this condition. >> > > >> > > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices") >> > > Cc: stable@vger.kernel.org >> > > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com> >> > > --- >> > > drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +- >> > > 1 file changed, 1 insertion(+), 1 deletion(-) >> > > >> > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c >> > > index dc88559a8d49..10e9b09932eb 100644 >> > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c >> > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c >> > > @@ -1820,7 +1820,7 @@ static void mlx5_vdpa_get_config(struct vdpa_device *vdev, unsigned int offset, >> > > struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev); >> > > struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev); >> > > - if (offset + len < sizeof(struct virtio_net_config)) >> > > + if (offset + len <= sizeof(struct virtio_net_config)) >> > > memcpy(buf, (u8 *)&ndev->config + offset, len); >> > > } >> > Actually first I am not sure we need these checks at all. >> > vhost_vdpa_config_validate already validates the values, right? >> >> >> I think they're working at different levels. There's no guarantee that >> vhost-vdpa is the driver for this vdpa device. > >In fact, get_config returns void, so userspace can easily get >trash if it passes incorrect parameters by mistake, there is >no way for userspace to find out whether that is the case :( > >Any objections to returning the # of bytes copied, or -1 >on error?
Make sense for me, but are we sure we don't break userspace if we return the number of bytes instead of 0 on success?
I had a quick look at QEMU and it looks like we consider success if the return value is >= 0, but I need to check further.
> >> >> > >> > Second, what will happen when we extend the struct and then >> > run new userspace on an old kernel? Looks like it will just >> > fail right? So what is the plan? >> >> >> In this case, get_config() should match the spec behaviour. That is to say >> the size of config space depends on the feature negotiated. >> >> Thanks > >Yes but spec says config space can be bigger than specified by features: > > Drivers MUST NOT limit structure size and device configuration space size. Instead, drivers SHOULD only > check that device configuration space is large enough to contain the fields necessary for device operation. >
So IIUC in the driver we should copy as much as we can.
If you agree, I can send an RFC series and we can continue the discussion on it, but I think we should queue this patch for stable branches.
Thanks, Stefano
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