netdev - [PATCH net] ip6_tunnel: fix GRE6 segmentation

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Date:   Mon, 21 Jun 2021 18:52:54 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org,
        dsahern@...nel.org, vfedorenko@...ek.ru,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net] ip6_tunnel: fix GRE6 segmentation

Commit 6c11fbf97e69 ("ip6_tunnel: add MPLS transmit support")
moved assiging inner_ipproto down from ipxip6_tnl_xmit() to
its callee ip6_tnl_xmit(). The latter is also used by GRE.

Since commit 38720352412a ("gre: Use inner_proto to obtain inner
header protocol") GRE had been depending on skb->inner_protocol
during segmentation. It sets it in gre_build_header() and reads
it in gre_gso_segment(). Changes to ip6_tnl_xmit() overwrite
the protocol, resulting in GSO skbs getting dropped.

Note that inner_protocol is a union with inner_ipproto,
GRE uses the former while the change switched it to the latter
(always setting it to just IPPROTO_GRE).

Restore the original location of skb_set_inner_ipproto(),
it is unclear why it was moved in the first place.

Fixes: 6c11fbf97e69 ("ip6_tunnel: add MPLS transmit support")
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
 net/ipv6/ip6_tunnel.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 288bafded998..28ca70af014a 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1239,8 +1239,6 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev, __u8 dsfield,
 	if (max_headroom > dev->needed_headroom)
 		dev->needed_headroom = max_headroom;

-	skb_set_inner_ipproto(skb, proto);
-
 	err = ip6_tnl_encap(skb, t, &proto, fl6);
 	if (err)
 		return err;
@@ -1377,6 +1375,8 @@ ipxip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev,
 	if (iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6))
 		return -1;

+	skb_set_inner_ipproto(skb, protocol);
+
 	err = ip6_tnl_xmit(skb, dev, dsfield, &fl6, encap_limit, &mtu,
 			   protocol);
 	if (err != 0) {
-- 
2.31.1