Subject: [PATCH 14/15] tun: forbid iface creation with rtnl ops

From: Nicolas Dichtel <[email-masked]>
Date: Thu, 29 Nov 2018 14:45:39 +0100

[ Upstream commit 35b827b6d06199841a83839e8bb69c0cd13a28be ]

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.

Fixes: f019a7a594d9 ("tun: Implement ip link del tunXXX")
CC: Eric W. Biederman <[email-masked]>
Signed-off-by: Nicolas Dichtel <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 drivers/net/tun.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 0a008d136aae..2956bb6cda72 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1818,9 +1818,9 @@ static void tun_setup(struct net_device *dev)
 static int tun_validate(struct nlattr *tb[], struct nlattr *data[],
 			struct netlink_ext_ack *extack)
 {
-	if (!data)
-		return 0;
-	return -EINVAL;
+	NL_SET_ERR_MSG(extack,
+		       "tun/tap creation via rtnetlink is not supported.");
+	return -EOPNOTSUPP;
 }
 
 static struct rtnl_link_ops tun_link_ops __read_mostly = {
-- 
2.19.2