From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Fri, 13 Oct 2017 11:58:53 -0700
Subject: tun: call dev_get_valid_name() before register_netdevice()
Git-commit: 0ad646c81b2182f7fa67ec0c8c825e0ee165696d
Patch-mainline: v4.14-rc6
References: networking-stable-17_11_14, CVE-2018-7191, bsc#1135603

register_netdevice() could fail early when we have an invalid
dev name, in which case ->ndo_uninit() is not called. For tun
device, this is a problem because a timer etc. are already
initialized and it expects ->ndo_uninit() to clean them up.

We could move these initializations into a ->ndo_init() so
that register_netdevice() knows better, however this is still
complicated due to the logic in tun_detach().

Therefore, I choose to just call dev_get_valid_name() before
register_netdevice(), which is quicker and much easier to audit.
And for this specific case, it is already enough.

Fixes: 96442e42429e ("tuntap: choose the txq based on rxq")
Reported-by: Dmitry Alexeev <avekceeb@gmail.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/net/tun.c         |    3 +++
 include/linux/netdevice.h |    3 +++
 net/core/dev.c            |    6 +++---
 3 files changed, 9 insertions(+), 3 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1810,6 +1810,9 @@ static int tun_set_iff(struct net *net,
 
 		if (!dev)
 			return -ENOMEM;
+		err = dev_get_valid_name(net, dev, name);
+		if (err)
+			goto err_free_dev;
 
 		dev_net_set(dev, net);
 		dev->rtnl_link_ops = &tun_link_ops;
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3692,6 +3692,9 @@ struct net_device *alloc_netdev_mqs(int
 				    unsigned char name_assign_type,
 				    void (*setup)(struct net_device *),
 				    unsigned int txqs, unsigned int rxqs);
+int dev_get_valid_name(struct net *net, struct net_device *dev,
+		       const char *name);
+
 #define alloc_netdev(sizeof_priv, name, name_assign_type, setup) \
 	alloc_netdev_mqs(sizeof_priv, name, name_assign_type, setup, 1, 1)
 
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1146,9 +1146,8 @@ static int dev_alloc_name_ns(struct net
 	return ret;
 }
 
-static int dev_get_valid_name(struct net *net,
-			      struct net_device *dev,
-			      const char *name)
+int dev_get_valid_name(struct net *net, struct net_device *dev,
+		       const char *name)
 {
 	BUG_ON(!net);
 
@@ -1164,6 +1163,7 @@ static int dev_get_valid_name(struct net
 
 	return 0;
 }
+EXPORT_SYMBOL(dev_get_valid_name);
 
 /**
  *	dev_change_name - change name of a device