netdev - Re: [PATCH] usbnet: Fix use-after-free on disconnect

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Date:   Wed, 13 Apr 2022 20:59:48 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Lukas Wunner <lukas@...ner.de>, Oliver Neukum <oneukum@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Jann Horn <jannh@...gle.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>
CC:     netdev@...r.kernel.org, linux-usb@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Eric Dumazet <edumazet@...gle.com>,
        Jacky Chou <jackychou@...x.com.tw>, Willy Tarreau <w@....eu>,
        Lino Sanfilippo <LinoSanfilippo@....de>,
        Philipp Rosenberger <p.rosenberger@...bus.com>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH] usbnet: Fix use-after-free on disconnect



On 13.04.22 16:16, Lukas Wunner wrote:
> Jann Horn reports a use-after-free on disconnect of a USB Ethernet
> (ax88179_178a.c).  Oleksij Rempel has witnessed the same issue with a
> different driver (ax88172a.c).
I see. Very good catch
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -469,6 +469,9 @@ static enum skb_state defer_bh(struct usbnet *dev, struct sk_buff *skb,
>   */
>  void usbnet_defer_kevent (struct usbnet *dev, int work)
>  {
> +	if (dev->intf->condition == USB_INTERFACE_UNBINDING)
> +		return;
But, no, you cannot do this. This is a very blatant layering violation.
You cannot use states internal to usb core like that in a driver.

I see two options.
1. A dedicated flag in usbnet (then please with the correct smp barriers)
2. You introduce an API to usb core to query this.

    Regards
        Oliver