From: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Date: Thu, 29 Nov 2018 14:45:39 +0100
Subject: tun: forbid iface creation with rtnl ops
Git-commit: 35b827b6d06199841a83839e8bb69c0cd13a28be
Patch-mainline: v4.20-rc6
References: networking-stable-18_12_12

It's not supported right now (the goal of the initial patch was to support
'ip link del' only).

Before the patch:
$ ip link add foo type tun
[  239.632660] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
[snip]
[  239.636410] RIP: 0010:register_netdevice+0x8e/0x3a0

This panic occurs because dev->netdev_ops is not set by tun_setup(). But to
have something usable, it will require more than just setting
netdev_ops.

[js] no extack in 4.12 yet

Fixes: f019a7a594d9 ("tun: Implement ip link del tunXXX")
CC: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/net/tun.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1597,9 +1597,7 @@ static void tun_setup(struct net_device
  */
 static int tun_validate(struct nlattr *tb[], struct nlattr *data[])
 {
-	if (!data)
-		return 0;
-	return -EINVAL;
+	return -EOPNOTSUPP;
 }
 
 static struct rtnl_link_ops tun_link_ops __read_mostly = {