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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
        syzbot <syzkaller@googlegroups.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.12 43/45] sit: proper dev_{hold|put} in ndo_[un]init methods
Date:   Thu, 20 May 2021 11:22:31 +0200
Message-Id: <20210520092054.909014767@linuxfoundation.org>
In-Reply-To: <20210520092053.516042993@linuxfoundation.org>
References: <20210520092053.516042993@linuxfoundation.org>
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From: Eric Dumazet <edumazet@google.com>

commit 6289a98f0817a4a457750d6345e754838eae9439 upstream.

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 <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/sit.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -218,8 +218,6 @@ static int ipip6_tunnel_create(struct ne
 
 	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_
 		dev->tstats = NULL;
 		return err;
 	}
-
+	dev_hold(dev);
 	return 0;
 }