[PATCH net-next 5/6] erspan: fix the tun_info options_len check

[Xin Long]

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().

Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/ipv4/ip_gre.c  | 4 ++--
 net/ipv6/ip6_gre.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index a53a543..df7149c 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 (sizeof(*md) > tun_info->options_len)
                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 dd2d0b96..4aba9e0 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 (sizeof(*md) > tun_info->options_len)
                        goto tx_err;
+               md = ip_tunnel_info_opts(tun_info);
 
                tun_id = tunnel_id_to_key32(key->tun_id);
                if (md->version == 1) {
-- 
2.1.0