Revert "phonet: no longer hold RTNL in route_dumpit()"

This reverts commit a8e473f which is
commit 58a4ff5 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Iaccabecb3c82b59e8bf01e47e9f2b6e0be8c039b
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: gregkh

net/phonet/pn_netlink.c

@@ -178,7 +178,7 @@ static int fill_route(struct sk_buff *skb, struct net_device *dev, u8 dst,
 	rtm->rtm_type = RTN_UNICAST;
 	rtm->rtm_flags = 0;
 	if (nla_put_u8(skb, RTA_DST, dst) ||
-	    nla_put_u32(skb, RTA_OIF, READ_ONCE(dev->ifindex)))
+	    nla_put_u32(skb, RTA_OIF, dev->ifindex))
 		goto nla_put_failure;
 	nlmsg_end(skb, nlh);
 	return 0;
@@ -263,7 +263,6 @@ static int route_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
 static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct net *net = sock_net(skb->sk);
-	int err = 0;
 	u8 addr;
 
 	rcu_read_lock();
@@ -273,16 +272,16 @@ static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 		if (!dev)
 			continue;
 
-		err = fill_route(skb, dev, addr << 2,
-				 NETLINK_CB(cb->skb).portid,
-				 cb->nlh->nlmsg_seq, RTM_NEWROUTE);
-		if (err < 0)
-			break;
+		if (fill_route(skb, dev, addr << 2, NETLINK_CB(cb->skb).portid,
+			       cb->nlh->nlmsg_seq, RTM_NEWROUTE) < 0)
+			goto out;
 	}
+
+out:
 	rcu_read_unlock();
 	cb->args[0] = addr;
 
-	return err;
+	return skb->len;
 }
 
 int __init phonet_netlink_register(void)
@@ -302,6 +301,6 @@ int __init phonet_netlink_register(void)
 	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_DELROUTE,
 			     route_doit, NULL, 0);
 	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_GETROUTE,
-			     NULL, route_dumpit, RTNL_FLAG_DUMP_UNLOCKED);
+			     NULL, route_dumpit, 0);
 	return 0;
 }