Re: [PATCH net-next] net: ethtool: Fix out-of-bounds copy to user

[Ding Hui]

On 2023/6/5 1:47, Jakub Kicinski wrote:
> On Sat, 3 Jun 2023 15:11:29 +0800 Ding Hui wrote:
> > Yes.
> >
> > I checked the others ioctl (e.g. ethtool_get_eeprom(), ethtool_get_features()),
> > and searched the git log of ethtool utility, so I think that is an implicit
> > rule and the check is missed in kernel where the patch involves.
> >
> > Without this rule, we cannot guarantee the safety of copy to user.
> >
> > Should we keep to be compatible with that incorrect userspace usage?
>
> If such incorrect user space exists we do, if it doesn't we don't.
> Problem is that we don't know what exists out there.
>
> Maybe we can add a pr_err_once() complaining about bad usage for now
> and see if anyone reports back that they are hitting it?

How about this:

Case 1:
If the user len/n_stats is not zero, we will treat it as correct usage
(although we cannot distinguish between the real correct usage and
uninitialized usage). Return -EINVAL if current length exceed the one
user specified.

Case 2:
If it is zero, we will treat it as incorrect usage, we can add a
pr_err_once() for it and keep to be compatible with it for a period of time.
At a suitable time in the future, this part can be removed by maintainers.

--
Thanks,
- Ding Hui