[Cake] [PATCH net-next 1/5] sch_cake: fix IP protocol handling in the presence of VLAN tags

[David Miller]

From: Toke Høiland-Jørgensen <toke at redhat.com>
Date: Thu, 25 Jun 2020 13:55:03 +0200

> From: Ilya Ponetayev <i.ponetaev at ndmsystems.com>
> 
> CAKE was using the return value of tc_skb_protocol() and expecting it to be
> the IP protocol type. This can fail in the presence of QinQ VLAN tags,
> making CAKE unable to handle ECN marking and diffserv parsing in this case.
> Fix this by implementing our own version of tc_skb_protocol(), which will
> use skb->protocol directly, but also parse and skip over any VLAN tags and
> return the inner protocol number instead.
> 
> Also fix CE marking by implementing a version of INET_ECN_set_ce() that
> uses the same parsing routine.
> 
> Fixes: ea82511518f4 ("sch_cake: Add NAT awareness to packet classifier")
> Fixes: b2100cc56fca ("sch_cake: Use tc_skb_protocol() helper for getting packet protocol")
> Fixes: 046f6fd5daef ("sched: Add Common Applications Kept Enhanced (cake) qdisc")
> Signed-off-by: Ilya Ponetayev <i.ponetaev at ndmsystems.com>
> [ squash original two patches, rewrite commit message ]
> Signed-off-by: Toke Høiland-Jørgensen <toke at redhat.com>

First, this is a bug fix and should probably be steered to 'net'.

Also, other users of tc_skb_protocol() are almost certainly hitting a
similar problem aren't they?  Maybe fix this generically.