netfilter: xt_TEE: add missing code to get interface index in checkentry.

mainline inclusion
from mainline-4.20
commit 18c0ab87
category: bugfix
bugzilla: 6233
CVE: NA

-------------------------------------------------

checkentry(tee_tg_check) should initialize priv->oif from dev if possible.
But only netdevice notifier handler can set that.
Hence priv->oif is always -1 until notifier handler is called.

Fixes: 9e2f6c5d ("netfilter: Rework xt_TEE netdevice notifier")
Signed-off-by: NTaehee Yoo <ap420073@gmail.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NMao Wenan <maowenan@huawei.com>
Reviewed-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/netfilter/xt_TEE.c

@@ -95,6 +95,8 @@ static int tee_tg_check(const struct xt_tgchk_param *par)
 		return -EINVAL;
 
 	if (info->oif[0]) {
+		struct net_device *dev;
+
 		if (info->oif[sizeof(info->oif)-1] != '\0')
 			return -EINVAL;
 
@@ -106,6 +108,11 @@ static int tee_tg_check(const struct xt_tgchk_param *par)
 		priv->oif     = -1;
 		info->priv    = priv;
 
+		dev = dev_get_by_name(par->net, info->oif);
+		if (dev) {
+			priv->oif = dev->ifindex;
+			dev_put(dev);
+		}
 		mutex_lock(&priv_list_mutex);
 		list_add(&priv->list, &priv_list);
 		mutex_unlock(&priv_list_mutex);