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

From: Eric Dumazet <edumazet@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 <edumazet@google.com>
Reported-by: syzbot <redacted>
---
 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

Hello:

This patch was applied to netdev/net-next.git (refs/heads/master):

On Mon, 29 Mar 2021 12:25:22 -0700 you wrote:

From: Eric Dumazet <edumazet@google.com>

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

Issue here is that:

[...]

Here is the summary with links:
  - [net-next] sit: proper dev_{hold|put} in ndo_[un]init methods
    https://git.kernel.org/netdev/net-next/c/6289a98f0817

You are awesome, thank you!
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