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

Roman Mashak
2018-03-15T14:36:00Z

Liran Alon <liran.alon@oracle.com> writes:

[...]

>> Overall I think it might be nice to not need scrubbing skb in such
>> cases,
>> although my concern would be that this has potential to break
>> existing
>> setups when they would expect mark being zero on other veth peer in
>> any
>> case since it's the behavior for a long time already. The safer
>> option
>> would be to have some sort of explicit opt-in e.g. on link creation to
>> let
>> the skb->mark pass through unscrubbed. This would definitely be a
>> useful
>> option e.g. when mark is set in the netns facing veth via
>> clsact/egress
>> on xmit and when the container is unprivileged anyway.
>>
>> Thanks,
>> Daniel
>
> I see your point in regards to backwards comparability.
> However, not scrubbing skb when it cross netns via some kernel functions compared to
> others is basically a bug which could easily break with a little bit of more refactoring.
> Therefore, it seems a bit weird to me to from now on, we will force
> every user on link creation to consider that once there was a bug leading
> to this weird behavior on specific netdevs.
> Thus, I suggest to maybe control this via a global /proc/sys/net file instead.

One valid use case could be preserving a source namespace nsid in
skb->mark when a packet crosses netns.