[PATCH net-next] sit: proper dev_{hold|put} in ndo_[un]init methods

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

After adopting CONFIG_PCPU_DEV_REFCNT=n option, syzbot was able to trigger
a warning [1]

Issue here is that:

- all dev_put() should be paired with a corresponding prior dev_hold().

- A driver doing a dev_put() in its ndo_uninit() MUST also
  do a dev_hold() in its ndo_init(), only when ndo_init()
  is returning 0.

Otherwise, register_netdevice() would call ndo_uninit()
in its error path and release a refcount too soon.

Fixes: 919067cc845f ("net: add CONFIG_PCPU_DEV_REFCNT")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: syzbot <syzkal...@googlegroups.com>
---
 net/ipv6/sit.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 
b9bd2723f89a314d15c8c4ea785e84530c8acb95..488d3181aec3a5558dbefb6145400627535df761
 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -218,8 +218,6 @@ static int ipip6_tunnel_create(struct net_device *dev)
 
        ipip6_tunnel_clone_6rd(dev, sitn);
 
-       dev_hold(dev);
-
        ipip6_tunnel_link(sitn, t);
        return 0;
 
@@ -1456,7 +1454,7 @@ static int ipip6_tunnel_init(struct net_device *dev)
                dev->tstats = NULL;
                return err;
        }
-
+       dev_hold(dev);
        return 0;
 }
 
-- 
2.31.0.291.g576ba9dcdaf-goog