linux-kernel - Re: [Regression, 2.6.33-rc1->current git] NULL pointer in usb_serial_probe() introduced by the recent kfifo changes

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Date:	Tue, 22 Dec 2009 23:06:54 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Greg KH <greg@...ah.com>, <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stefani Seibold <stefani@...bold.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Regression, 2.6.33-rc1->current git] NULL pointer in
 usb_serial_probe() introduced by the recent kfifo changes

On Wed, 23 Dec 2009, Rafael J. Wysocki wrote:

> Hi,
> 
> Something like the patch below is necessary to fix a new NULL pointer deref
> in usb_serial_probe() that appeared after the recent kfifo changes (in short,
> the kfifo changes modified the semantics of kfifo_alloc() that
> usb_serial_probe() reiled on).
> 
> Thanks,
> Rafael
> 
> ---
>  drivers/usb/serial/usb-serial.c |   10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/drivers/usb/serial/usb-serial.c
> ===================================================================
> --- linux-2.6.orig/drivers/usb/serial/usb-serial.c
> +++ linux-2.6/drivers/usb/serial/usb-serial.c
> @@ -595,8 +595,10 @@ static void port_release(struct device *
>  	usb_free_urb(port->write_urb);
>  	usb_free_urb(port->interrupt_in_urb);
>  	usb_free_urb(port->interrupt_out_urb);
> -	if (!IS_ERR(port->write_fifo) && port->write_fifo)
> +	if (port->write_fifo) {
>  		kfifo_free(port->write_fifo);
> +		kfree(port->write_fifo);
> +	}
>  	kfree(port->bulk_in_buffer);
>  	kfree(port->bulk_out_buffer);
>  	kfree(port->interrupt_in_buffer);
> @@ -939,6 +941,12 @@ int usb_serial_probe(struct usb_interfac
>  			dev_err(&interface->dev, "No free urbs available\n");
>  			goto probe_error;
>  		}
> +		port->write_fifo = kzalloc(sizeof(struct kfifo), GFP_KERNEL);
> +		if (!port->write_fifo) {
> +			dev_err(&interface->dev,
> +				"Couldn't allocate write_fifo\n");
> +			goto probe_error;
> +		}
>  		if (kfifo_alloc(port->write_fifo, PAGE_SIZE, GFP_KERNEL))
>  			goto probe_error;
>  		buffer_size = le16_to_cpu(endpoint->wMaxPacketSize);

Although this would mean further changes elsewhere, doesn't it make
more sense to embed the struct kfifo directly in the usb_serial_port
structure instead of allocating it dynamically?

Alan Stern

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