netdev - Re: [PATCH net-next] net: openvswitch: fix uAPI incompatibility with existing user space

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Message-ID: <5d89f306-d3fa-3e96-c4f3-587c9e3c605b@ovn.org>
Date:   Wed, 9 Mar 2022 18:22:42 +0100
From:   Ilya Maximets <i.maximets@....org>
To:     Jakub Kicinski <kuba@...nel.org>, Roi Dayan <roid@...dia.com>
Cc:     i.maximets@....org, "David S. Miller" <davem@...emloft.net>,
        Pravin B Shelar <pshelar@....org>,
        Toms Atteka <cpp.code.lv@...il.com>, netdev@...r.kernel.org,
        dev@...nvswitch.org, linux-kernel@...r.kernel.org,
        Johannes Berg <johannes@...solutions.net>,
        Aaron Conole <aconole@...hat.com>
Subject: Re: [PATCH net-next] net: openvswitch: fix uAPI incompatibility with
 existing user space

On 3/9/22 16:56, Ilya Maximets wrote:
> Few years ago OVS user space made a strange choice in the commit [1]
> to define types only valid for the user space inside the copy of a
> kernel uAPI header.  '#ifndef __KERNEL__' and another attribute was
> added later.
> 
> This leads to the inevitable clash between user space and kernel types
> when the kernel uAPI is extended.  The issue was unveiled with the
> addition of a new type for IPv6 extension header in kernel uAPI.
> 
> When kernel provides the OVS_KEY_ATTR_IPV6_EXTHDRS attribute to the
> older user space application, application tries to parse it as
> OVS_KEY_ATTR_PACKET_TYPE and discards the whole netlink message as
> malformed.  Since OVS_KEY_ATTR_IPV6_EXTHDRS is supplied along with
> every IPv6 packet that goes to the user space, IPv6 support is fully
> broken.
> 
> Fixing that by bringing these user space attributes to the kernel
> uAPI to avoid the clash.  Strictly speaking this is not the problem
> of the kernel uAPI, but changing it is the only way to avoid breakage
> of the older user space applications at this point.
> 
> These 2 types are explicitly rejected now since they should not be
> passed to the kernel.  Additionally, OVS_KEY_ATTR_TUNNEL_INFO moved
> out from the '#ifdef __KERNEL__' as there is no good reason to hide
> it from the userspace.  And it's also explicitly rejected now, because
> it's for in-kernel use only.
> 
> Comments with warnings were added to avoid the problem coming back.
> 
>  [1] beb75a40fdc2 ("userspace: Switching of L3 packets in L2 pipeline")
> 
> Fixes: 28a3f0601727 ("net: openvswitch: IPv6: Add IPv6 extension header support")
> Link: https://lore.kernel.org/netdev/3adf00c7-fe65-3ef4-b6d7-6d8a0cad8a5f@nvidia.com
> Link: https://github.com/openvswitch/ovs/commit/beb75a40fdc295bfd6521b0068b4cd12f6de507c
> Reported-by: Roi Dayan <roid@...dia.com>
> Signed-off-by: Ilya Maximets <i.maximets@....org>
> ---
> 
> Roi, could you please test this change on your setup?
> 
> I didn't run system tests myself yet, setting up environment at the moment.

OK.  I set up my own environment and the patch doesn't seem to work.
Investigating.