linux-kernel - Re: [PATCH v2] usb: misc: fix improper handling of refcount in uss720

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Message-ID: <CAD-N9QV27nJW=_goZKB0666Nq1pNphbgoHeYn_FmSkkJh9vyKg@mail.gmail.com>
Date:   Thu, 7 Apr 2022 11:09:41 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Hangyu Hua <hbh25y@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Oliver Neukum <oneukum@...e.com>, linux-usb@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: misc: fix improper handling of refcount in uss720_probe()

On Thu, Apr 7, 2022 at 10:40 AM Hangyu Hua <hbh25y@...il.com> wrote:
>
> usb_put_dev shouldn't be called when uss720_probe succeeds because of
> priv->usbdev. At the same time, priv->usbdev shouldn't be set to NULL
> before destroy_priv in uss720_disconnect because usb_put_dev is in
> destroy_priv.
>
> Fix this by moving priv->usbdev = NULL after usb_put_dev.

Hi Hangyu,

good catch as priv->usbdev is still used after the probe function.

I agree with this patch.

Reviewed-by: Dongliang Mu <mudongliangabcd@...il.com>

>
> Fixes: dcb4b8ad6a44 ("misc/uss720: fix memory leak in uss720_probe")
> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
> ---
>
> v2: fix a stupid UAF in the previous version.
>
>  drivers/usb/misc/uss720.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/usb/misc/uss720.c b/drivers/usb/misc/uss720.c
> index 748139d26263..0be8efcda15d 100644
> --- a/drivers/usb/misc/uss720.c
> +++ b/drivers/usb/misc/uss720.c
> @@ -71,6 +71,7 @@ static void destroy_priv(struct kref *kref)
>
>         dev_dbg(&priv->usbdev->dev, "destroying priv datastructure\n");
>         usb_put_dev(priv->usbdev);
> +       priv->usbdev = NULL;
>         kfree(priv);
>  }
>
> @@ -736,7 +737,6 @@ static int uss720_probe(struct usb_interface *intf,
>         parport_announce_port(pp);
>
>         usb_set_intfdata(intf, pp);
> -       usb_put_dev(usbdev);
>         return 0;
>
>  probe_abort:
> @@ -754,7 +754,6 @@ static void uss720_disconnect(struct usb_interface *intf)
>         usb_set_intfdata(intf, NULL);
>         if (pp) {
>                 priv = pp->private_data;
> -               priv->usbdev = NULL;
>                 priv->pp = NULL;
>                 dev_dbg(&intf->dev, "parport_remove_port\n");
>                 parport_remove_port(pp);
> --
> 2.25.1
>