[PATCH 4.14 47/62] erspan: fix the tun_info options_len check for erspan

[Greg Kroah-Hartman]

From: Xin Long <lucien.xin@xxxxxxxxx>

[ Upstream commit 2eb8d6d2910cfe3dc67dc056f26f3dd9c63d47cd ]

The check for !md doens't really work for ip_tunnel_info_opts(info) which
only does info + 1. Also to avoid out-of-bounds access on info, it should
ensure options_len is not less than erspan_metadata in both erspan_xmit()
and ip6erspan_tunnel_xmit().

Fixes: 1a66a836da ("gre: add collect_md mode to ERSPAN tunnel")
Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/ipv4/ip_gre.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -592,6 +592,9 @@ static void erspan_fb_xmit(struct sk_buf
 		truncate = true;
 	}
 
+	if (tun_info->options_len < sizeof(*md))
+		goto err_free_rt;
+
 	md = ip_tunnel_info_opts(tun_info);
 	if (!md)
 		goto err_free_rt;