netdev - Re: [PATCH v2 net-next 0/2] net/sched: support tunnel options in cls_flower and act_tunnel

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Message-Id: <20170929.055423.108055524887949393.davem@davemloft.net>
Date:   Fri, 29 Sep 2017 05:54:23 +0100 (WEST)
From:   David Miller <davem@...emloft.net>
To:     simon.horman@...ronome.com
Cc:     jiri@...lanox.com, jhs@...atatu.com, xiyou.wangcong@...il.com,
        netdev@...r.kernel.org, oss-drivers@...ronome.com
Subject: Re: [PATCH v2 net-next 0/2] net/sched: support tunnel options in
 cls_flower and act_tunnel_key

From: Simon Horman <simon.horman@...ronome.com>
Date: Wed, 27 Sep 2017 10:16:32 +0200

> Users of options:
> 
> * There are eBPF hooks to allow getting on and setting tunnel metadata:
>   bpf_skb_set_tunnel_opt, bpf_skb_get_tunnel_opt.
> 
> * Open vSwitch is able to match and set Geneve and VXLAN-GBP options.
> 
> Neither of the above appear to assume any structure for the data.

I really worry about this.

These metadata option blobs are internal kernel datastructure which we
could change at any point in time.  They are not exported to
userspace as a UAPI.

It's kinda OK for eBPF programs to access this stuff since they are
expected to cope with changes to internal data-structures.

But for anything user facing, this really doesn't work.