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

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Date:	Mon, 15 Aug 2016 11:31:10 -0700
From:	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
To:	linux-usb@...r.kernel.org
Cc:	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,
	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
Subject: [PATCH] USB: core: of: Check device_node before parsing in usb_of_get_child_node()

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)
-- 
2.7.4