erspan: fix the tun_info options_len check for erspan

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@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 4 insertions, 4 deletions

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 52690bb3e40f..10636fb6093e 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -509,9 +509,9 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct net_device *dev)
         key = &tun_info->key;
         if (!(tun_info->key.tun_flags & TUNNEL_ERSPAN_OPT))
                 goto err_free_skb;
-        md = ip_tunnel_info_opts(tun_info);
-        if (!md)
+        if (tun_info->options_len < sizeof(*md))
                 goto err_free_skb;
+        md = ip_tunnel_info_opts(tun_info);
 
         /* ERSPAN has fixed 8 byte GRE header */
         version = md->version;
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 787d9f2a6e99..923034c52ce4 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -980,9 +980,9 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
                 dsfield = key->tos;
                 if (!(tun_info->key.tun_flags & TUNNEL_ERSPAN_OPT))
                         goto tx_err;
-                md = ip_tunnel_info_opts(tun_info);
-                if (!md)
+                if (tun_info->options_len < sizeof(*md))
                         goto tx_err;
+                md = ip_tunnel_info_opts(tun_info);
 
                 tun_id = tunnel_id_to_key32(key->tun_id);
                 if (md->version == 1) {