[PATCH v2] usb: misc: fix improper handling of refcount in uss720_probe()

[PATCH v2] usb: misc: fix improper handling of refcount in uss720_probe()

[Hangyu Hua]

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.

Fixes: dcb4b8ad6a44 ("misc/uss720: fix memory leak in uss720_probe")
Signed-off-by: Hangyu Hua <hbh25y@gmail.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

Re: [PATCH v2] usb: misc: fix improper handling of refcount in uss720_probe()

[Dongliang Mu]

On Thu, Apr 7, 2022 at 10:40 AM Hangyu Hua <hbh25y@gmail.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@gmail.com>

>
> Fixes: dcb4b8ad6a44 ("misc/uss720: fix memory leak in uss720_probe")
> Signed-off-by: Hangyu Hua <hbh25y@gmail.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
>