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Date:   Thu, 08 Aug 2019 07:33:25 -0700
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Message-ID: <000000000000bef340058f9bf02b@google.com>
Subject: Re: Re: possible deadlock in open_rio
From:   syzbot <syzbot+7bbcbe9c9ff0cd49592a@syzkaller.appspotmail.com>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     andreyknvl@google.com, gregkh@linuxfoundation.org,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        oliver@neukum.org, stern@rowland.harvard.edu,
        syzkaller-bugs@googlegroups.com
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> On Wed, 7 Aug 2019, Oliver Neukum wrote:

>> Am Mittwoch, den 07.08.2019, 10:07 -0400 schrieb Alan Stern:
>> > On Wed, 7 Aug 2019, Oliver Neukum wrote:

>> > > technically yes. However in practical terms the straight revert I  
>> sent
>> > > out yesterday should fix it.
>> >
>> > I didn't see the revert, and it doesn't appear to have reached the
>> > mailing list archive.  Can you post it again?

>> As soon as our VPN server is back up again.

> The revert may not be necessay; a little fix should get rid of the
> locking violation.  The key is to avoid calling the registration or
> deregistration routines while holding the rio500_mutex, and to
> recognize that the probe and disconnect routines are both protected by
> the device mutex.

> How does this patch look?

> Alan Stern


> #syz test: https://github.com/google/kasan.git 7f7867ff

This crash does not have a reproducer. I cannot test it.


> Index: usb-devel/drivers/usb/misc/rio500.c
> ===================================================================
> --- usb-devel.orig/drivers/usb/misc/rio500.c
> +++ usb-devel/drivers/usb/misc/rio500.c
> @@ -454,52 +454,54 @@ static int probe_rio(struct usb_interfac
>   {
>   	struct usb_device *dev = interface_to_usbdev(intf);
>   	struct rio_usb_data *rio = &rio_instance;
> -	int retval = 0;
> +	int retval;
> +	char *ibuf, *obuf;

> -	mutex_lock(&rio500_mutex);
>   	if (rio->present) {
>   		dev_info(&intf->dev, "Second USB Rio at address %d refused\n",  
> dev->devnum);
> -		retval = -EBUSY;
> -		goto bail_out;
> -	} else {
> -		dev_info(&intf->dev, "USB Rio found at address %d\n", dev->devnum);
> +		return -EBUSY;
>   	}
> +	dev_info(&intf->dev, "USB Rio found at address %d\n", dev->devnum);

>   	retval = usb_register_dev(intf, &usb_rio_class);
>   	if (retval) {
>   		dev_err(&dev->dev,
>   			"Not able to get a minor for this device.\n");
> -		retval = -ENOMEM;
> -		goto bail_out;
> +		goto err_register;
>   	}

> -	rio->rio_dev = dev;
> -
> -	if (!(rio->obuf = kmalloc(OBUF_SIZE, GFP_KERNEL))) {
> +	obuf = kmalloc(OBUF_SIZE, GFP_KERNEL);
> +	if (!obuf) {
>   		dev_err(&dev->dev,
>   			"probe_rio: Not enough memory for the output buffer\n");
> -		usb_deregister_dev(intf, &usb_rio_class);
> -		retval = -ENOMEM;
> -		goto bail_out;
> +		goto err_obuf;
>   	}
> -	dev_dbg(&intf->dev, "obuf address:%p\n", rio->obuf);
> +	dev_dbg(&intf->dev, "obuf address: %p\n", obuf);

> -	if (!(rio->ibuf = kmalloc(IBUF_SIZE, GFP_KERNEL))) {
> +	ibuf = kmalloc(IBUF_SIZE, GFP_KERNEL);
> +	if (!ibuf) {
>   		dev_err(&dev->dev,
>   			"probe_rio: Not enough memory for the input buffer\n");
> -		usb_deregister_dev(intf, &usb_rio_class);
> -		kfree(rio->obuf);
> -		retval = -ENOMEM;
> -		goto bail_out;
> +		goto err_ibuf;
>   	}
> -	dev_dbg(&intf->dev, "ibuf address:%p\n", rio->ibuf);
> +	dev_dbg(&intf->dev, "ibuf address: %p\n", ibuf);

> +	mutex_lock(&rio500_mutex);
> +	rio->rio_dev = dev;
> +	rio->ibuf = ibuf;
> +	rio->obuf = obuf;
>   	usb_set_intfdata (intf, rio);
>   	rio->present = 1;
> -bail_out:
>   	mutex_unlock(&rio500_mutex);

>   	return retval;
> +
> + err_ibuf:
> +	kfree(obuf);
> + err_obuf:
> +	usb_deregister_dev(intf, &usb_rio_class);
> + err_register:
> +	return -ENOMEM;
>   }

>   static void disconnect_rio(struct usb_interface *intf)
> @@ -507,10 +509,10 @@ static void disconnect_rio(struct usb_in
>   	struct rio_usb_data *rio = usb_get_intfdata (intf);

>   	usb_set_intfdata (intf, NULL);
> -	mutex_lock(&rio500_mutex);
>   	if (rio) {
>   		usb_deregister_dev(intf, &usb_rio_class);

> +		mutex_lock(&rio500_mutex);
>   		if (rio->isopen) {
>   			rio->isopen = 0;
>   			/* better let it finish - the release will do whats needed */
> @@ -524,8 +526,8 @@ static void disconnect_rio(struct usb_in
>   		dev_info(&intf->dev, "USB Rio disconnected.\n");

>   		rio->present = 0;
> +		mutex_unlock(&rio500_mutex);
>   	}
> -	mutex_unlock(&rio500_mutex);
>   }

>   static const struct usb_device_id rio_table[] = {