linux-kernel - [PATCH 4.9 09/51] tun: forbid iface creation with rtnl ops

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Message-Id: <20181214115714.132525314@linuxfoundation.org>
Date:   Fri, 14 Dec 2018 13:00:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 09/51] tun: forbid iface creation with rtnl ops

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolas Dichtel <nicolas.dichtel@...nd.com>

[ 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 <ebiederm@...ssion.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/tun.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1570,9 +1570,9 @@ static void tun_setup(struct net_device
  */
 static int tun_validate(struct nlattr *tb[], struct nlattr *data[])
 {
-	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 = {