ipip: potential race in ip_tunnel_init_net()

Eric Dumazet says that my previous fix for an ERR_PTR dereference
(ea857f28ab 'ipip: dereferencing an ERR_PTR in ip_tunnel_init_net()')
could be racy and suggests the following fix instead.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 6 deletions

diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 24549b4aeae2..830de3f4e293 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -854,16 +854,14 @@ int ip_tunnel_init_net(struct net *net, int ip_tnl_net_id,
 
         rtnl_lock();
         itn->fb_tunnel_dev = __ip_tunnel_create(net, ops, &parms);
-        rtnl_unlock();
-
-        if (IS_ERR(itn->fb_tunnel_dev))
-                return PTR_ERR(itn->fb_tunnel_dev);
         /* FB netdevice is special: we have one, and only one per netns.
          * Allowing to move it to another netns is clearly unsafe.
          */
-        itn->fb_tunnel_dev->features |= NETIF_F_NETNS_LOCAL;
+        if (!IS_ERR(itn->fb_tunnel_dev))
+                itn->fb_tunnel_dev->features |= NETIF_F_NETNS_LOCAL;
+        rtnl_unlock();
 
-        return 0;
+        return PTR_RET(itn->fb_tunnel_dev);
 }
 EXPORT_SYMBOL_GPL(ip_tunnel_init_net);