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

On 20/03/18 18:00, David Miller wrote:

From: Liran Alon <redacted>
Date: Tue, 20 Mar 2018 17:34:38 +0200

quoted

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.

quoted

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.

quoted

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