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 14:14:33 -0700
From:	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
To:	Peter Chen <hzpeterchen@...il.com>
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 Monday 15 August 2016 06:33 PM, Peter Chen wrote:
> 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.
>

Peter,
You are right, __of_get_next_child is taking care of this.

When I observed this issue with my setup [1], I only looked at changes in
the mainline for of.c and core/usb.c, did not see the anything.....

Anyways, for the record, we do not need this patch. Instead I need to 
backport
below commit from mainline to my kernel base.

commit 43cb43678705e39b175b325f17938295996aefc7
Author: Florian Fainelli <f.fainelli@...il.com>
Date:   Wed May 28 10:39:02 2014 -0700

     of: handle NULL node in next_child iterators

     Add an early check for the node argument in __of_get_next_child and
     of_get_next_available_child() to avoid dereferencing a NULL node 
pointer
     a few lines after.


[1] Also I missed to mention about my kernel version, I am based on very
ancient kernel version (3.10). Do not ask me why, it is something out of my
control :)

-- 
Thanks,
Vaibhav