From: wenxu <we...@ucloud.cn>

ip l add dev tun type gretap key 1000
ip a a dev tun 10.0.0.1/24

Packets with tun-id 1000 can be recived by tun dev. But packet can't
be sent through dev tun for non-tunnel-dst

With this patch: tunnel-dst can be get through lwtunnel like beflow:
ip r a 10.0.0.7 encap ip id 1000 dst 172.168.0.11 key dev tun

Signed-off-by: wenxu <we...@ucloud.cn>
---
 net/ipv4/ip_gre.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index c7a7bd5..d87f92e 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -450,6 +450,24 @@ static void __gre_xmit(struct sk_buff *skb, struct 
net_device *dev,
                         tunnel->parms.o_flags, proto, tunnel->parms.o_key,
                         htonl(tunnel->o_seqno));
 
+       if (!tnl_params->daddr) {
+               struct ip_tunnel_info *tun_info;
+
+               tun_info = skb_tunnel_info(skb);
+               if (tun_info && (tun_info->mode & IP_TUNNEL_INFO_TX) &&
+                   ip_tunnel_info_af(tun_info) == AF_INET &&
+                   tun_info->key.u.ipv4.dst) {
+                       struct iphdr tnl_params_info;
+
+                       memcpy(&tnl_params_info, tnl_params,
+                              sizeof(tnl_params_info));
+                       tnl_params_info.daddr = tun_info->key.u.ipv4.dst;
+
+                       return ip_tunnel_xmit(skb, dev, &tnl_params_info,
+                              tnl_params_info.protocol);
+               }
+       }
+
        ip_tunnel_xmit(skb, dev, tnl_params, tnl_params->protocol);
 }
 
-- 
1.8.3.1

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