[PATCH] misc: hisi_hikey_usb: cancel role switch work on remove

[Hongyan Xu <getshell@seu.edu.cn>]

The hub role switch set callback schedules private work that dereferences
both driver data and the downstream role switch. Unregistering the hub
switch does not drain work already queued, and a callback that fetched
driver data before unregister can queue more work during removal.

Mark the instance as removing under its mutex and serialize removal
with role switch set callbacks by setting the role to USB_ROLE_NONE.
The callback clears the switch driver data when it observes removal and
no longer queues work. Unregister the switch, cancel the work, and only
then drop the downstream role switch reference.

This issue was found by a static analysis tool.

Signed-off-by: Hongyan Xu <getshell@seu.edu.cn>
---
 drivers/misc/hisi_hikey_usb.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/misc/hisi_hikey_usb.c b/drivers/misc/hisi_hikey_usb.c
index 2165ec3..9db6429 100644
--- a/drivers/misc/hisi_hikey_usb.c
+++ b/drivers/misc/hisi_hikey_usb.c
@@ -45,6 +45,7 @@ struct hisi_hikey_usb {
 
 	struct mutex lock;
 	struct work_struct work;
+	bool removing;
 
 	struct notifier_block nb;
 };
@@ -130,17 +131,23 @@ static void relay_set_role_switch(struct work_struct *work)
 static int hub_usb_role_switch_set(struct usb_role_switch *sw, enum usb_role role)
 {
 	struct hisi_hikey_usb *hisi_hikey_usb = usb_role_switch_get_drvdata(sw);
+	int ret = 0;
 
-	if (!hisi_hikey_usb || !hisi_hikey_usb->dev_role_sw)
-		return -EINVAL;
+	if (!hisi_hikey_usb)
+		return -ENODEV;
 
 	mutex_lock(&hisi_hikey_usb->lock);
-	hisi_hikey_usb->role = role;
+	if (hisi_hikey_usb->removing || !hisi_hikey_usb->dev_role_sw) {
+		if (hisi_hikey_usb->removing)
+			usb_role_switch_set_drvdata(sw, NULL);
+		ret = -ENODEV;
+	} else {
+		hisi_hikey_usb->role = role;
+		schedule_work(&hisi_hikey_usb->work);
+	}
 	mutex_unlock(&hisi_hikey_usb->lock);
 
-	schedule_work(&hisi_hikey_usb->work);
-
-	return 0;
+	return ret;
 }
 
 static int hisi_hikey_usb_of_role_switch(struct platform_device *pdev,
@@ -244,7 +251,15 @@ static int  hisi_hikey_usb_remove(struct platform_device *pdev)
 	struct hisi_hikey_usb *hisi_hikey_usb = platform_get_drvdata(pdev);
 
 	if (hisi_hikey_usb->hub_role_sw) {
+		mutex_lock(&hisi_hikey_usb->lock);
+		hisi_hikey_usb->removing = true;
+		mutex_unlock(&hisi_hikey_usb->lock);
+
+		/* Serialize with set callbacks and clear their private data. */
+		usb_role_switch_set_role(hisi_hikey_usb->hub_role_sw,
+					 USB_ROLE_NONE);
 		usb_role_switch_unregister(hisi_hikey_usb->hub_role_sw);
+		cancel_work_sync(&hisi_hikey_usb->work);
 
 		if (hisi_hikey_usb->dev_role_sw)
 			usb_role_switch_put(hisi_hikey_usb->dev_role_sw);
-- 
2.50.1.windows.1