netdev - Re: [PATCH v1] hamradio: remove needs_free

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Message-ID: <20211111175500.2f67e18a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 11 Nov 2021 17:55:00 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lin Ma <linma@....edu.cn>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jirislaby@...nel.org,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] hamradio: remove needs_free_netdev to avoid UAF

On Thu, 11 Nov 2021 22:14:02 +0800 Lin Ma wrote:
> The former patch "defer 6pack kfree after unregister_netdev" reorders
> the kfree of two buffer after the unregister_netdev to prevent the race
> condition. It also adds free_netdev() function in sixpack_close(), which
> is a direct copy from the similar code in mkiss_close().
> 
> However, in sixpack driver, the flag needs_free_netdev is set to true in
> sp_setup(), hence the unregister_netdev() will free the netdev
> automatically. Therefore, as the sp is netdev_priv, use-after-free
> occurs.
> 
> This patch removes the needs_free_netdev = true and just let the
> free_netdev to finish this deallocation task.
> 
> Signed-off-by: Lin Ma <linma@....edu.cn>

Fixes: 0b9111922b1f ("hamradio: defer 6pack kfree after unregister_netdev")