[PATCH net] Revert "blackhole_netdev: fix syzkaller reported issue"

[Mahesh Bandewar <maheshb@google.com>]

This reverts commit b0818f80c8c1bc215bba276bd61c216014fab23b.

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>
---
 net/ipv6/addrconf.c |  7 +------
 net/ipv6/route.c    | 15 +++++++++------
 2 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 4c87594d1389..34ccef18b40e 100644
--- a/net/ipv6/addrconf.c
+++ b/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.
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 742120728869..a63ff85fe141 100644
--- a/net/ipv6/route.c
+++ b/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);
 		}
 	}
-- 
2.23.0.700.g56cf767bdb-goog