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Date: Mon, 24 Apr 2017 09:27:22 -0400 (EDT)
From: Alan Stern <stern@rowland.harvard.edu>
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To: Florian Fainelli <f.fainelli@gmail.com>
cc: linux-kernel@vger.kernel.org, <arnd@arndb.de>,
        <maksim.salau@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mathias Nyman <mathias.nyman@linux.intel.com>,
        Peter Chen <peter.chen@nxp.com>, Roger Quadros <rogerq@ti.com>,
        Baoyou Xie <baoyou.xie@linaro.org>, Sekhar Nori <nsekhar@ti.com>,
        Chris Bainbridge <chris.bainbridge@gmail.com>,
        Wolfram Sang <wsa-dev@sang-engineering.com>,
        "open list:USB SUBSYSTEM" <linux-usb@vger.kernel.org>
Subject: Re: [PATCH v2] usb: core: Warn if an URB's transfer_buffer is on
 stack
In-Reply-To: <20170424012939.29929-1-f.fainelli@gmail.com>
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On Sun, 23 Apr 2017, Florian Fainelli wrote:

> We see a large number of fixes to several drivers to remove the usage of
> on-stack buffers feeding into USB transfer functions. Make it easier to spot
> the offenders by adding a warning in usb_hcd_map_urb_for_dma() checking that
> urb->transfer_buffer is not a stack object.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
> Changes in v2:
> 
> - moved the check from usb_start_wait_urb() to usb_hcd_map_urb_for_dma()

You probably should add a similar check to the pathway that maps 
urb->setup_packet, for the sake of consistency.

Alan Stern

>  drivers/usb/core/hcd.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 49550790a3cb..ce9063ce906a 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -26,6 +26,7 @@
>  #include <linux/module.h>
>  #include <linux/version.h>
>  #include <linux/kernel.h>
> +#include <linux/sched/task_stack.h>
>  #include <linux/slab.h>
>  #include <linux/completion.h>
>  #include <linux/utsname.h>
> @@ -1587,6 +1588,9 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
>  			} else if (is_vmalloc_addr(urb->transfer_buffer)) {
>  				WARN_ONCE(1, "transfer buffer not dma capable\n");
>  				ret = -EAGAIN;
> +			} else if (object_is_on_stack(urb->transfer_buffer)) {
> +				WARN_ONCE(1, "transfer buffer is on stack\n");
> +				ret = -EAGAIN;
>  			} else {
>  				urb->transfer_dma = dma_map_single(
>  						hcd->self.sysdev,
>