linux-kernel - [PATCH 4.4 186/190] sit: proper dev_{hold|put} in ndo

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Date:   Thu, 20 May 2021 11:24:10 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        syzbot <syzkaller@...glegroups.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 186/190] sit: proper dev_{hold|put} in ndo_[un]init methods

From: Eric Dumazet <edumazet@...gle.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@...gle.com>
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv6/sit.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -209,8 +209,6 @@ static int ipip6_tunnel_create(struct ne
 
 	dev->rtnl_link_ops = &sit_link_ops;
 
-	dev_hold(dev);
-
 	ipip6_tunnel_link(sitn, t);
 	return 0;
 
@@ -1399,7 +1397,7 @@ static int ipip6_tunnel_init(struct net_
 		dev->tstats = NULL;
 		return err;
 	}
-
+	dev_hold(dev);
 	return 0;
 }