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SubjectRe: [PATCH] USB: core: of: Check device_node before parsing in usb_of_get_child_node()
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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@linaro.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@gmail.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

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