media: dvb_net: avoid speculation from net slot

The risk of especulation is actually almost-non-existing here,
as there are very few users of TCP/IP using the DVB stack,
as, this is mainly used with DVB-S/S2 cards, and only by people
that receives TCP/IP from satellite connections, which limits
a lot the number of users of such feature(*).

(*) In thesis, DVB-C cards could also benefit from it, but I'm
yet to see a hardware that supports it.

Yet, fixing it is trivial.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/dvb-core/dvb_net.c

@@ -45,6 +45,7 @@
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/netdevice.h>
+#include <linux/nospec.h>
 #include <linux/etherdevice.h>
 #include <linux/dvb/net.h>
 #include <linux/uio.h>
@@ -1462,14 +1463,20 @@ static int dvb_net_do_ioctl(struct file *file,
 		struct net_device *netdev;
 		struct dvb_net_priv *priv_data;
 		struct dvb_net_if *dvbnetif = parg;
+		int if_num = dvbnetif->if_num;
 
-		if (dvbnetif->if_num >= DVB_NET_DEVICES_MAX ||
-		    !dvbnet->state[dvbnetif->if_num]) {
+		if (if_num >= DVB_NET_DEVICES_MAX) {
 			ret = -EINVAL;
 			goto ioctl_error;
 		}
+		if_num = array_index_nospec(if_num, DVB_NET_DEVICES_MAX);
 
-		netdev = dvbnet->device[dvbnetif->if_num];
+		if (!dvbnet->state[if_num]) {
+			ret = -EINVAL;
+			goto ioctl_error;
+		}
+
+		netdev = dvbnet->device[if_num];
 
 		priv_data = netdev_priv(netdev);
 		dvbnetif->pid=priv_data->pid;
@@ -1522,14 +1529,20 @@ static int dvb_net_do_ioctl(struct file *file,
 		struct net_device *netdev;
 		struct dvb_net_priv *priv_data;
 		struct __dvb_net_if_old *dvbnetif = parg;
+		int if_num = dvbnetif->if_num;
+
+		if (if_num >= DVB_NET_DEVICES_MAX) {
+			ret = -EINVAL;
+			goto ioctl_error;
+		}
+		if_num = array_index_nospec(if_num, DVB_NET_DEVICES_MAX);
 
-		if (dvbnetif->if_num >= DVB_NET_DEVICES_MAX ||
-		    !dvbnet->state[dvbnetif->if_num]) {
+		if (!dvbnet->state[if_num]) {
 			ret = -EINVAL;
 			goto ioctl_error;
 		}
 
-		netdev = dvbnet->device[dvbnetif->if_num];
+		netdev = dvbnet->device[if_num];
 
 		priv_data = netdev_priv(netdev);
 		dvbnetif->pid=priv_data->pid;