Revert "blackhole_netdev: fix syzkaller reported issue"

This reverts commit b0818f80c8.

Started seeing weird behavior after this patch especially in
the IPv6 code path. Haven't root caused it, but since this was
applied to net branch, taking a precautionary measure to revert
it and look / analyze those failures

Revert this now and I'll send a better fix after analysing / fixing
the weirdness observed.

CC: Eric Dumazet <edumazet@google.com>
CC: Wei Wang <weiwan@google.com>
CC: David S. Miller <davem@davemloft.net>
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -6996,7 +6996,7 @@ static struct rtnl_af_ops inet6_ops __read_mostly = {
 
 int __init addrconf_init(void)
 {
-	struct inet6_dev *idev, *bdev;
+	struct inet6_dev *idev;
 	int i, err;
 
 	err = ipv6_addr_label_init();
@@ -7036,14 +7036,10 @@ int __init addrconf_init(void)
 	 */
 	rtnl_lock();
 	idev = ipv6_add_dev(init_net.loopback_dev);
-	bdev = ipv6_add_dev(blackhole_netdev);
 	rtnl_unlock();
 	if (IS_ERR(idev)) {
 		err = PTR_ERR(idev);
 		goto errlo;
-	} else if (IS_ERR(bdev)) {
-		err = PTR_ERR(bdev);
-		goto errlo;
 	}
 
 	ip6_route_init_special_entries();
@@ -7128,7 +7124,6 @@ void addrconf_cleanup(void)
 		addrconf_ifdown(dev, 1);
 	}
 	addrconf_ifdown(init_net.loopback_dev, 2);
-	addrconf_ifdown(blackhole_netdev, 2);
 
 	/*
 	 *	Check hash table.

net/ipv6/route.c

@@ -155,9 +155,10 @@ void rt6_uncached_list_del(struct rt6_info *rt)
 
 static void rt6_uncached_list_flush_dev(struct net *net, struct net_device *dev)
 {
+	struct net_device *loopback_dev = net->loopback_dev;
 	int cpu;
 
-	if (dev == net->loopback_dev)
+	if (dev == loopback_dev)
 		return;
 
 	for_each_possible_cpu(cpu) {
@@ -170,7 +171,7 @@ static void rt6_uncached_list_flush_dev(struct net *net, struct net_device *dev)
 			struct net_device *rt_dev = rt->dst.dev;
 
 			if (rt_idev->dev == dev) {
-				rt->rt6i_idev = in6_dev_get(blackhole_netdev);
+				rt->rt6i_idev = in6_dev_get(loopback_dev);
 				in6_dev_put(rt_idev);
 			}
 
@@ -385,11 +386,13 @@ static void ip6_dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 {
 	struct rt6_info *rt = (struct rt6_info *)dst;
 	struct inet6_dev *idev = rt->rt6i_idev;
+	struct net_device *loopback_dev =
+		dev_net(dev)->loopback_dev;
 
-	if (idev && idev->dev != dev_net(dev)->loopback_dev) {
-		struct inet6_dev *ibdev = in6_dev_get(blackhole_netdev);
-		if (ibdev) {
-			rt->rt6i_idev = ibdev;
+	if (idev && idev->dev != loopback_dev) {
+		struct inet6_dev *loopback_idev = in6_dev_get(loopback_dev);
+		if (loopback_idev) {
+			rt->rt6i_idev = loopback_idev;
 			in6_dev_put(idev);
 		}
 	}