xfrm: interface with if_id 0 should return error

xfrm interface if_id = 0 would cause xfrm policy lookup errors since
Commit 9f8550e4.

Now explicitly fail to create an xfrm interface when if_id = 0

With this commit:
 ip link add ipsec0  type xfrm dev lo  if_id 0
 Error: if_id must be non zero.

v1->v2 change:
 - add Fixes: tag

Fixes: 9f8550e4 ("xfrm: fix disable_xfrm sysctl when used on xfrm interfaces")
Signed-off-by: NAntony Antony <antony.antony@secunet.com>
Reviewed-by: NEyal Birger <eyal.birger@gmail.com>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_interface.c

@@ -637,11 +637,16 @@ static int xfrmi_newlink(struct net *src_net, struct net_device *dev,
 			struct netlink_ext_ack *extack)
 {
 	struct net *net = dev_net(dev);
-	struct xfrm_if_parms p;
+	struct xfrm_if_parms p = {};
 	struct xfrm_if *xi;
 	int err;
 
 	xfrmi_netlink_parms(data, &p);
+	if (!p.if_id) {
+		NL_SET_ERR_MSG(extack, "if_id must be non zero");
+		return -EINVAL;
+	}
+
 	xi = xfrmi_locate(net, &p);
 	if (xi)
 		return -EEXIST;
@@ -666,7 +671,12 @@ static int xfrmi_changelink(struct net_device *dev, struct nlattr *tb[],
 {
 	struct xfrm_if *xi = netdev_priv(dev);
 	struct net *net = xi->net;
-	struct xfrm_if_parms p;
+	struct xfrm_if_parms p = {};
+
+	if (!p.if_id) {
+		NL_SET_ERR_MSG(extack, "if_id must be non zero");
+		return -EINVAL;
+	}
 
 	xfrmi_netlink_parms(data, &p);
 	xi = xfrmi_locate(net, &p);