[PATCH] carl9170: Fix misuse of device driver API

[PATCH] carl9170: Fix misuse of device driver API

[Christian Lamparter]

This patch follows Alan Stern's recent patch:
"p54: Fix race between disconnect and firmware loading"

that overhauled carl9170 buggy firmware loading and driver
unbinding procedures.

Since the carl9170 code was adapted from p54 it uses the
same functions and is likely to have the same problem, but
it's just that the syzbot hasn't reproduce them (yet).

a summary from the changes (copied from the p54 patch):
 * Call usb_driver_release_interface() rather than
   device_release_driver().

 * Lock udev (the interface's parent) before unbinding the
   driver instead of locking udev->parent.

 * During the firmware loading process, take a reference
   to the USB interface instead of the USB device.

 * Don't take an unnecessary reference to the device during
   probe (and then don't drop it during disconnect).

and

 * Make sure to prevent use-after-free bugs by explicitly
   setting the driver context to NULL after signaling the
   completion.

Cc: <stable@vger.kernel.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
---
 drivers/net/wireless/ath/carl9170/usb.c | 26 ++++++++++++-------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/drivers/net/wireless/ath/carl9170/usb.c b/drivers/net/wireless/ath/carl9170/usb.c
index e7c3f3b8457d..297a7b877d31 100644
--- a/drivers/net/wireless/ath/carl9170/usb.c
+++ b/drivers/net/wireless/ath/carl9170/usb.c
@@ -128,6 +128,8 @@ static const struct usb_device_id carl9170_usb_ids[] = {
 };
 MODULE_DEVICE_TABLE(usb, carl9170_usb_ids);
 
+static struct usb_driver carl9170_driver;
+
 static void carl9170_usb_submit_data_urb(struct ar9170 *ar)
 {
 	struct urb *urb;
@@ -966,7 +968,7 @@ static int carl9170_usb_init_device(struct ar9170 *ar)
 
 static void carl9170_usb_firmware_failed(struct ar9170 *ar)
 {
-	struct device *parent = ar->udev->dev.parent;
+	struct usb_interface *intf = ar->intf;
 	struct usb_device *udev;
 
 	/*
@@ -978,16 +980,15 @@ static void carl9170_usb_firmware_failed(struct ar9170 *ar)
 	udev = ar->udev;
 
 	complete(&ar->fw_load_wait);
+	/* at this point 'ar' could be already freed. Don't use it anymore */
+	ar = NULL;
 
 	/* unbind anything failed */
-	if (parent)
-		device_lock(parent);
-
-	device_release_driver(&udev->dev);
-	if (parent)
-		device_unlock(parent);
+	usb_lock_device(udev);
+	usb_driver_release_interface(&carl9170_driver, intf);
+	usb_unlock_device(udev);
 
-	usb_put_dev(udev);
+	usb_put_intf(intf);
 }
 
 static void carl9170_usb_firmware_finish(struct ar9170 *ar)
@@ -1009,7 +1010,7 @@ static void carl9170_usb_firmware_finish(struct ar9170 *ar)
 		goto err_unrx;
 
 	complete(&ar->fw_load_wait);
-	usb_put_dev(ar->udev);
+	usb_put_intf(ar->intf);
 	return;
 
 err_unrx:
@@ -1052,7 +1053,6 @@ static int carl9170_usb_probe(struct usb_interface *intf,
 		return PTR_ERR(ar);
 
 	udev = interface_to_usbdev(intf);
-	usb_get_dev(udev);
 	ar->udev = udev;
 	ar->intf = intf;
 	ar->features = id->driver_info;
@@ -1094,15 +1094,14 @@ static int carl9170_usb_probe(struct usb_interface *intf,
 	atomic_set(&ar->rx_anch_urbs, 0);
 	atomic_set(&ar->rx_pool_urbs, 0);
 
-	usb_get_dev(ar->udev);
+	usb_get_intf(intf);
 
 	carl9170_set_state(ar, CARL9170_STOPPED);
 
 	err = request_firmware_nowait(THIS_MODULE, 1, CARL9170FW_NAME,
 		&ar->udev->dev, GFP_KERNEL, ar, carl9170_usb_firmware_step2);
 	if (err) {
-		usb_put_dev(udev);
-		usb_put_dev(udev);
+		usb_put_intf(intf);
 		carl9170_free(ar);
 	}
 	return err;
@@ -1131,7 +1130,6 @@ static void carl9170_usb_disconnect(struct usb_interface *intf)
 
 	carl9170_release_firmware(ar);
 	carl9170_free(ar);
-	usb_put_dev(udev);
 }
 
 #ifdef CONFIG_PM
-- 
2.20.1

Re: [PATCH] carl9170: Fix misuse of device driver API

[Alan Stern]

On Sun, 2 Jun 2019, Christian Lamparter wrote:

> This patch follows Alan Stern's recent patch:
> "p54: Fix race between disconnect and firmware loading"
> 
> that overhauled carl9170 buggy firmware loading and driver
> unbinding procedures.
> 
> Since the carl9170 code was adapted from p54 it uses the
> same functions and is likely to have the same problem, but
> it's just that the syzbot hasn't reproduce them (yet).
> 
> a summary from the changes (copied from the p54 patch):
>  * Call usb_driver_release_interface() rather than
>    device_release_driver().
> 
>  * Lock udev (the interface's parent) before unbinding the
>    driver instead of locking udev->parent.
> 
>  * During the firmware loading process, take a reference
>    to the USB interface instead of the USB device.
> 
>  * Don't take an unnecessary reference to the device during
>    probe (and then don't drop it during disconnect).
> 
> and
> 
>  * Make sure to prevent use-after-free bugs by explicitly
>    setting the driver context to NULL after signaling the
>    completion.
> 
> Cc: <stable@vger.kernel.org>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

This basically looks right.  However...

> ---
>  drivers/net/wireless/ath/carl9170/usb.c | 26 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/carl9170/usb.c b/drivers/net/wireless/ath/carl9170/usb.c
> index e7c3f3b8457d..297a7b877d31 100644
> --- a/drivers/net/wireless/ath/carl9170/usb.c
> +++ b/drivers/net/wireless/ath/carl9170/usb.c
> @@ -128,6 +128,8 @@ static const struct usb_device_id carl9170_usb_ids[] = {
>  };
>  MODULE_DEVICE_TABLE(usb, carl9170_usb_ids);
>  
> +static struct usb_driver carl9170_driver;
> +
>  static void carl9170_usb_submit_data_urb(struct ar9170 *ar)
>  {
>  	struct urb *urb;
> @@ -966,7 +968,7 @@ static int carl9170_usb_init_device(struct ar9170 *ar)
>  
>  static void carl9170_usb_firmware_failed(struct ar9170 *ar)
>  {
> -	struct device *parent = ar->udev->dev.parent;
> +	struct usb_interface *intf = ar->intf;
>  	struct usb_device *udev;

It looks a little strange to initialize intf in the definition but to 
initialize udev afterward.  Nothing wrong with it, just odd.

>  
>  	/*
> @@ -978,16 +980,15 @@ static void carl9170_usb_firmware_failed(struct ar9170 *ar)
>  	udev = ar->udev;
>  
>  	complete(&ar->fw_load_wait);
> +	/* at this point 'ar' could be already freed. Don't use it anymore */
> +	ar = NULL;
>  
>  	/* unbind anything failed */
> -	if (parent)
> -		device_lock(parent);
> -
> -	device_release_driver(&udev->dev);
> -	if (parent)
> -		device_unlock(parent);
> +	usb_lock_device(udev);
> +	usb_driver_release_interface(&carl9170_driver, intf);
> +	usb_unlock_device(udev);
>  
> -	usb_put_dev(udev);
> +	usb_put_intf(intf);
>  }
>  
>  static void carl9170_usb_firmware_finish(struct ar9170 *ar)
> @@ -1009,7 +1010,7 @@ static void carl9170_usb_firmware_finish(struct ar9170 *ar)
>  		goto err_unrx;
>  
>  	complete(&ar->fw_load_wait);
> -	usb_put_dev(ar->udev);
> +	usb_put_intf(ar->intf);

But this could be a problem.  As soon as the complete() call runs, ar 
might be deallocated.  The code should copy ar->intf before calling 
complete().

Alan Stern

>  	return;
>  
>  err_unrx:
> @@ -1052,7 +1053,6 @@ static int carl9170_usb_probe(struct usb_interface *intf,
>  		return PTR_ERR(ar);
>  
>  	udev = interface_to_usbdev(intf);
> -	usb_get_dev(udev);
>  	ar->udev = udev;
>  	ar->intf = intf;
>  	ar->features = id->driver_info;
> @@ -1094,15 +1094,14 @@ static int carl9170_usb_probe(struct usb_interface *intf,
>  	atomic_set(&ar->rx_anch_urbs, 0);
>  	atomic_set(&ar->rx_pool_urbs, 0);
>  
> -	usb_get_dev(ar->udev);
> +	usb_get_intf(intf);
>  
>  	carl9170_set_state(ar, CARL9170_STOPPED);
>  
>  	err = request_firmware_nowait(THIS_MODULE, 1, CARL9170FW_NAME,
>  		&ar->udev->dev, GFP_KERNEL, ar, carl9170_usb_firmware_step2);
>  	if (err) {
> -		usb_put_dev(udev);
> -		usb_put_dev(udev);
> +		usb_put_intf(intf);
>  		carl9170_free(ar);
>  	}
>  	return err;
> @@ -1131,7 +1130,6 @@ static void carl9170_usb_disconnect(struct usb_interface *intf)
>  
>  	carl9170_release_firmware(ar);
>  	carl9170_free(ar);
> -	usb_put_dev(udev);
>  }
>  
>  #ifdef CONFIG_PM
>