gtp: avoid zero size hashtable

[ Upstream commit 6a902c0f31993ab02e1b6ea7085002b9c9083b6a ]

GTP default hashtable size is 1024 and userspace could set specific
hashtable size with IFLA_GTP_PDP_HASHSIZE. If hashtable size is set to 0
from userspace,  hashtable will not work and panic will occur.

Fixes: 459aa660 ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
Signed-off-by: NTaehee Yoo <ap420073@gmail.com>
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/net/gtp.c

@@ -671,10 +671,13 @@ static int gtp_newlink(struct net *src_net, struct net_device *dev,
 	if (err < 0)
 		return err;
 
-	if (!data[IFLA_GTP_PDP_HASHSIZE])
+	if (!data[IFLA_GTP_PDP_HASHSIZE]) {
 		hashsize = 1024;
-	else
+	} else {
 		hashsize = nla_get_u32(data[IFLA_GTP_PDP_HASHSIZE]);
+		if (!hashsize)
+			hashsize = 1024;
+	}
 
 	err = gtp_hashtable_new(gtp, hashsize);
 	if (err < 0)