linux-kernel - Re: [PATCH] USB: core: of: Check device_node before parsing in usb_of_get_child

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Date:	Tue, 16 Aug 2016 09:33:36 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
Cc:	linux-usb@...r.kernel.org, gregkh@...uxfoundation.org,
	robh@...nel.org, p.zabel@...gutronix.de, stern@...land.harvard.edu,
	arnd@...db.de, peter.chen@...escale.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: core: of: Check device_node before parsing in
 usb_of_get_child_node()

On Mon, Aug 15, 2016 at 11:31:10AM -0700, Vaibhav Hiremath wrote:
> In case of HUB devices connected to USB ports, we may not have DT
> node representing it inside USB, and when devices connected to hub
> gets enumerated, call to usb_of_get_child_node() leads to NULL pointer
> dereference.
> 
> In the usecase we have, where EHCI port is connected to USB HUB
> device, and downward ports of HUB are connected to further USB
> devices. When those devices gets enumerated, in order,
>  1. USB HUB ->
> 	-> Call to usb_of_get_child_node() is OK, as
> 	parent->dev.of_node is pointing to host node.
>  2. Devices connected to downward port of USB HUB
>  	-> Call to usb_of_get_child_node() leads to NULL
> 	pointer dereference as parent->dev.of_node = NULL,
> 	as USB HUB DTS node may be empty.
> 
> Fix this NULL pointer dereference by adding check for pointer
> device_node inside usb_of_get_child_node() fn.
> 
> Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
> ---
> Testing: I have build tested it against mainline.
> 
>  drivers/usb/core/of.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/usb/core/of.c b/drivers/usb/core/of.c
> index 2289700..dc667a3 100644
> --- a/drivers/usb/core/of.c
> +++ b/drivers/usb/core/of.c
> @@ -34,6 +34,9 @@ struct device_node *usb_of_get_child_node(struct device_node *parent,
>  	struct device_node *node;
>  	u32 port;
>  
> +	if (!parent)
> +		return NULL;
> +
>  	for_each_child_of_node(parent, node) {
>  		if (!of_property_read_u32(node, "reg", &port)) {
>  			if (port == portnum)

I am afraid I can't reproduce it, would you please show me your dump
when null pointer dereference occurs? From what I find the
__of_get_next_child checks null pointer for parent node.

-- 

Best Regards,
Peter Chen