ip_tunnels: Set tunnel option flag when tunnel metadata is present

Currently, we may set the tunnel option flag when the size of metadata
is zero.  For example, we set TUNNEL_GENEVE_OPT in the receive function
no matter the geneve option is present or not.  As this may result in
issues on the tunnel flags consumers, this patch fixes the issue.

Related discussion:
* https://lore.kernel.org/netdev/1604448694-19351-1-git-send-email-yihung.wei@gmail.com/T/#u

Fixes: 256c87c17c ("net: check tunnel option type in tunnel flags")
Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
Link: https://lore.kernel.org/r/1605053800-74072-1-git-send-email-yihung.wei@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/geneve.c

@@ -224,8 +224,7 @@ static void geneve_rx(struct geneve_dev *geneve, struct geneve_sock *gs,
 	if (ip_tunnel_collect_metadata() || gs->collect_md) {
 		__be16 flags;
 
-		flags = TUNNEL_KEY | TUNNEL_GENEVE_OPT |
-			(gnvh->oam ? TUNNEL_OAM : 0) |
+		flags = TUNNEL_KEY | (gnvh->oam ? TUNNEL_OAM : 0) |
 			(gnvh->critical ? TUNNEL_CRIT_OPT : 0);
 
 		tun_dst = udp_tun_rx_dst(skb, geneve_get_sk_family(gs), flags,

include/net/ip_tunnels.h

@@ -478,9 +478,11 @@ static inline void ip_tunnel_info_opts_set(struct ip_tunnel_info *info,
 					   const void *from, int len,
 					   __be16 flags)
 {
-	memcpy(ip_tunnel_info_opts(info), from, len);
 	info->options_len = len;
-	info->key.tun_flags |= flags;
+	if (len > 0) {
+		memcpy(ip_tunnel_info_opts(info), from, len);
+		info->key.tun_flags |= flags;
+	}
 }
 
 static inline struct ip_tunnel_info *lwt_tun_info(struct lwtunnel_state *lwtstate)
@@ -526,7 +528,6 @@ static inline void ip_tunnel_info_opts_set(struct ip_tunnel_info *info,
 					   __be16 flags)
 {
 	info->options_len = 0;
-	info->key.tun_flags |= flags;
 }
 
 #endif /* CONFIG_INET */