Re: [PATCH] net: dev_forward_skb(): Scrub packet's per-netns info only when crossing netns

[Liran Alon]

On 20/03/18 18:00, David Miller wrote:
> From: Liran Alon <LIRAN.ALON@xxxxxxxxxx>
> Date: Tue, 20 Mar 2018 17:34:38 +0200
>
> > I personally don't understand why we should maintain
> > backwards-comparability to this behaviour.
>
> The reason is because not breaking things is a cornerstone of Linux
> kernel development.
>
> > This feature is not documented to user-mode and I don't see why it
> > is legit for the user to rely on it.
>
> Whether it is documented or not is irrelevant.  A lot of our
> interfaces and behaviors are not documented or poorly documented
> at best.
>
> > In addition, even if we do want to maintain backwards-comparability to
> > this behaviour, I think it is enough to have an opt-in flag in
> > /proc/sys/net/core/ that when set to 1 will activate the fix in
> > dev_forward_skb() provided by this patch. That would also be a very
> > simple change to the patch provided here.
>
> Making it opt-in makes it more palatable, that's for sure.

1. Do we want to make a flag for every bug that is user-space visible? I 
think there is place for consideration on a per-case basis. I still 
don't see how a user can utilize this behaviour. He is basically loosing 
information (skb->mark) without this patch.

2. Having said that, I don't mind changing patch to maintain backwards 
compatibility here. However, there was also a discussion here on where 
the flag should sit. I think that a global /proc/sys/net/core/ flag 
should be enough. Do you agree it's sufficient for now?

Thanks,
-Liran