vxlan: check tun_info options_len properly

BugLink: https://bugs.launchpad.net/bugs/1852110

[ Upstream commit eadf52cf ]

This patch is to improve the tun_info options_len by dropping
the skb when TUNNEL_VXLAN_OPT is set but options_len is less
than vxlan_metadata. This can void a potential out-of-bounds
access on ip_tun_info.

Fixes: ee122c79 ("vxlan: Flow based tunneling")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/net/vxlan.c

@@ -2168,8 +2168,11 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
 		ttl = info->key.ttl;
 		tos = info->key.tos;
 
-		if (info->options_len)
+		if (info->options_len) {
+			if (info->options_len < sizeof(*md))
+				goto drop;
 			md = ip_tunnel_info_opts(info);
+		}
 	} else {
 		md->gbp = skb->mark;
 	}