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Date: Mon, 14 Apr 2025 10:37:27 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: <syzbot+de1c7d68a10e3f123bdd@syzkaller.appspotmail.com>,
 <cratiu@nvidia.com>, <davem@davemloft.net>, <edumazet@google.com>,
 <horms@kernel.org>, <linux-kernel@vger.kernel.org>,
 <netdev@vger.kernel.org>, <pabeni@redhat.com>, <sdf@fomichev.me>,
 <syzkaller-bugs@googlegroups.com>
Subject: Re: [syzbot] [net?] general protection fault in rtnl_create_link
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On Sun, 13 Apr 2025 19:30:46 -0700 Kuniyuki Iwashima wrote:
> diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
> index 5706835a660c..270e157a4a79 100644
> --- a/include/net/netdev_lock.h
> +++ b/include/net/netdev_lock.h
> @@ -30,7 +30,8 @@ static inline bool netdev_need_ops_lock(const struct net_device *dev)
>  	bool ret = dev->request_ops_lock || !!dev->queue_mgmt_ops;
>  
>  #if IS_ENABLED(CONFIG_NET_SHAPER)
> -	ret |= !!dev->netdev_ops->net_shaper_ops;
> +	if (dev->netdev_ops)
> +		ret |= !!dev->netdev_ops->net_shaper_ops;
>  #endif

This is a bit surprising, we pretty much never validate if dev has ops.

I think we're guaranteed that IFF_UP will not be set if we just
allocated the device, so we can remove the locks in rtnl_create_link()
and to double confirm add a netdev_ops_assert_locked_or_invisible() 
in netif_state_change() ?