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SubjectRe: [RFC 1/1] net: introduce OpenVPN Data Channel Offload (ovpn-dco)
On Thu, Jul 28, 2022 at 09:44:18AM +0200, Antonio Quartulli wrote:
> Hi,
>
> On 19/07/2022 17:37, Andrew Lunn wrote:
> > > +static int ovpn_net_change_mtu(struct net_device *dev, int new_mtu)
> > > +{
> > > + if (new_mtu < IPV4_MIN_MTU ||
> > > + new_mtu + dev->hard_header_len > IP_MAX_MTU)
> > > + return -EINVAL;
> >
> > If you set dev->min_mtu and dev->max_mtu, the core will validate this
> > for you, see dev_validate_mtu().
>
> Yeah, thanks for the pointer.
>
> >
> > > +static int ovpn_get_link_ksettings(struct net_device *dev,
> > > + struct ethtool_link_ksettings *cmd)
> > > +{
> > > + ethtool_convert_legacy_u32_to_link_mode(cmd->link_modes.supported, 0);
> > > + ethtool_convert_legacy_u32_to_link_mode(cmd->link_modes.advertising, 0);
> >
> > These two should not be needed. Look at tun, veth etc, they don't set
> > them.
>
> I found this in tun.c:
>
> 3512 ethtool_link_ksettings_zero_link_mode(cmd, supported);
> 3513 ethtool_link_ksettings_zero_link_mode(cmd, advertising);
>
> Which seems a more appropriate version of my code, no?

I would trace is backwards. Where is cmd coming from? In order to
avoid unintentional information leaks, the core should be clearing any
memory which gets passed to a driver which might optionally be filled
in and then returned to user space. So take a look in net/ethtool, and
see if there is a memset() or a kzalloc() etc. If it is already been
zero'ed, you don't need this.

Andrew

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