linux-kernel - [PATCH net-next v2] net: geneve: accept every ethertype

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Message-Id: <20230319220954.21834-1-josef@miegl.cz>
Date:   Sun, 19 Mar 2023 23:09:54 +0100
From:   Josef Miegl <josef@...gl.cz>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Eyal Birger <eyal.birger@...il.com>,
        Pravin B Shelar <pshelar@....org>,
        Josef Miegl <josef@...gl.cz>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net-next v2] net: geneve: accept every ethertype

The Geneve encapsulation, as defined in RFC 8926, has a Protocol Type
field, which states the Ethertype of the payload appearing after the
Geneve header.

Commit 435fe1c0c1f7 ("net: geneve: support IPv4/IPv6 as inner protocol")
introduced a new IFLA_GENEVE_INNER_PROTO_INHERIT flag that allowed the
use of other Ethertypes than Ethernet. However, it did not get rid of a
restriction that prohibits receiving payloads other than Ethernet,
instead the commit white-listed additional Ethertypes, IPv4 and IPv6.

This patch removes this restriction, making it possible to receive any
Ethertype as a payload, if the IFLA_GENEVE_INNER_PROTO_INHERIT flag is
set.

The restriction was set in place back in commit 0b5e8b8eeae4
("net: Add Geneve tunneling protocol driver"), which implemented a
protocol layer driver for Geneve to be used with Open vSwitch. The
relevant discussion about introducing the Ethertype white-list can be
found here:
https://lore.kernel.org/netdev/CAEP_g=_1q3ACX5NTHxLDnysL+dTMUVzdLpgw1apLKEdDSWPztw@mail.gmail.com/

<quote>
>> +       if (unlikely(geneveh->proto_type != htons(ETH_P_TEB)))
>
> Why? I thought the point of geneve carrying protocol field was to
> allow protocols other than Ethernet... is this temporary maybe?

Yes, it is temporary. Currently OVS only handles Ethernet packets but
this restriction can be lifted once we have a consumer that is capable
of handling other protocols.
</quote>

This white-list was then ported to a generic Geneve netdevice in commit
371bd1061d29 ("geneve: Consolidate Geneve functionality in single
module."). Preserving the Ethertype white-list at this point made sense,
as the Geneve device could send out only Ethernet payloads anyways.

However, now that the Geneve netdevice supports encapsulating other
payloads with IFLA_GENEVE_INNER_PROTO_INHERIT and we have a consumer
capable of other protocols, it seems appropriate to lift the restriction
and allow any Geneve payload to be received.

Signed-off-by: Josef Miegl <josef@...gl.cz>
---
 drivers/net/geneve.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 89ff7f8e8c7e..32684e94eb4f 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -365,13 +365,6 @@ static int geneve_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
 	if (unlikely(geneveh->ver != GENEVE_VER))
 		goto drop;

-	inner_proto = geneveh->proto_type;
-
-	if (unlikely((inner_proto != htons(ETH_P_TEB) &&
-		      inner_proto != htons(ETH_P_IP) &&
-		      inner_proto != htons(ETH_P_IPV6))))
-		goto drop;
-
 	gs = rcu_dereference_sk_user_data(sk);
 	if (!gs)
 		goto drop;
@@ -380,6 +373,8 @@ static int geneve_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
 	if (!geneve)
 		goto drop;

+	inner_proto = geneveh->proto_type;
+
 	if (unlikely((!geneve->cfg.inner_proto_inherit &&
 		      inner_proto != htons(ETH_P_TEB)))) {
 		geneve->dev->stats.rx_dropped++;
-- 
2.37.1