netdev - Re: [PATCH v4 net 2/3] net: Fix dev_net(dev) race in unregister_netdevice_notifier_dev

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Message-ID: <CANn89iKOYktLb19QvyWgkSeJe7XyS2J+O04MR7U0B=VpTcSu6w@mail.gmail.com>
Date: Wed, 12 Feb 2025 14:54:40 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	Yael Chemla <ychemla@...dia.com>
Subject: Re: [PATCH v4 net 2/3] net: Fix dev_net(dev) race in unregister_netdevice_notifier_dev_net().

On Wed, Feb 12, 2025 at 7:43 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> After the cited commit, dev_net(dev) is fetched before holding RTNL
> and passed to __unregister_netdevice_notifier_net().
>
> However, dev_net(dev) might be different after holding RTNL.
>
> In the reported case [0], while removing a VF device, its netns was
> being dismantled and the VF was moved to init_net.
>
> So the following sequence is basically illegal when dev was fetched
> without lookup:
>
>   net = dev_net(dev);
>   rtnl_net_lock(net);
>
> Let's use a new helper rtnl_net_dev_lock() to fix the race.
>
> It fetches dev_net_rcu(dev), bumps its net->passive, and checks if
> dev_net_rcu(dev) is changed after rtnl_net_lock().
>
>

> Fixes: 7fb1073300a2 ("net: Hold rtnl_net_lock() in (un)?register_netdevice_notifier_dev_net().")
> Reported-by: Yael Chemla <ychemla@...dia.com>
> Closes: https://lore.kernel.org/netdev/146eabfe-123c-4970-901e-e961b4c09bc3@nvidia.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>