[PATCH v3 1/2] HID: bigben: use spinlock to safely schedule workers

[Pietro Borrello]

Use spinlocks to deal with workers introducing a wrapper
bigben_schedule_work(), and several spinlock checks.
Otherwise, bigben_set_led() may schedule bigben->worker after the
structure has been freed, causing a use-after-free.

Fixes: 4eb1b01de5b9 ("HID: hid-bigbenff: fix race condition for scheduled work during removal")
Signed-off-by: Pietro Borrello <borrello@xxxxxxxxxxxxxxxx>
---
 drivers/hid/hid-bigbenff.c | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/drivers/hid/hid-bigbenff.c b/drivers/hid/hid-bigbenff.c
index e8b16665860d..28769aa7fed6 100644
--- a/drivers/hid/hid-bigbenff.c
+++ b/drivers/hid/hid-bigbenff.c
@@ -174,6 +174,7 @@ static __u8 pid0902_rdesc_fixed[] = {
 struct bigben_device {
 	struct hid_device *hid;
 	struct hid_report *report;
+	spinlock_t lock;
 	bool removed;
 	u8 led_state;         /* LED1 = 1 .. LED4 = 8 */
 	u8 right_motor_on;    /* right motor off/on 0/1 */
@@ -184,15 +185,24 @@ struct bigben_device {
 	struct work_struct worker;
 };
 
+static inline void bigben_schedule_work(struct bigben_device *bigben)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&bigben->lock, flags);
+	if (!bigben->removed)
+		schedule_work(&bigben->worker);
+	spin_unlock_irqrestore(&bigben->lock, flags);
+}
 
 static void bigben_worker(struct work_struct *work)
 {
 	struct bigben_device *bigben = container_of(work,
 		struct bigben_device, worker);
 	struct hid_field *report_field = bigben->report->field[0];
+	unsigned long flags;
 
-	if (bigben->removed || !report_field)
-		return;
+	spin_lock_irqsave(&bigben->lock, flags);
 
 	if (bigben->work_led) {
 		bigben->work_led = false;
@@ -219,6 +229,8 @@ static void bigben_worker(struct work_struct *work)
 		report_field->value[7] = 0x00; /* padding */
 		hid_hw_request(bigben->hid, bigben->report, HID_REQ_SET_REPORT);
 	}
+
+	spin_unlock_irqrestore(&bigben->lock, flags);
 }
 
 static int hid_bigben_play_effect(struct input_dev *dev, void *data,
@@ -228,6 +240,7 @@ static int hid_bigben_play_effect(struct input_dev *dev, void *data,
 	struct bigben_device *bigben = hid_get_drvdata(hid);
 	u8 right_motor_on;
 	u8 left_motor_force;
+	unsigned long flags;
 
 	if (!bigben) {
 		hid_err(hid, "no device data\n");
@@ -242,10 +255,13 @@ static int hid_bigben_play_effect(struct input_dev *dev, void *data,
 
 	if (right_motor_on != bigben->right_motor_on ||
 			left_motor_force != bigben->left_motor_force) {
+		spin_lock_irqsave(&bigben->lock, flags);
 		bigben->right_motor_on   = right_motor_on;
 		bigben->left_motor_force = left_motor_force;
 		bigben->work_ff = true;
-		schedule_work(&bigben->worker);
+		spin_unlock_irqrestore(&bigben->lock, flags);
+
+		bigben_schedule_work(bigben);
 	}
 
 	return 0;
@@ -259,6 +275,7 @@ static void bigben_set_led(struct led_classdev *led,
 	struct bigben_device *bigben = hid_get_drvdata(hid);
 	int n;
 	bool work;
+	unsigned long flags;
 
 	if (!bigben) {
 		hid_err(hid, "no device data\n");
@@ -267,6 +284,7 @@ static void bigben_set_led(struct led_classdev *led,
 
 	for (n = 0; n < NUM_LEDS; n++) {
 		if (led == bigben->leds[n]) {
+			spin_lock_irqsave(&bigben->lock, flags);
 			if (value == LED_OFF) {
 				work = (bigben->led_state & BIT(n));
 				bigben->led_state &= ~BIT(n);
@@ -274,10 +292,11 @@ static void bigben_set_led(struct led_classdev *led,
 				work = !(bigben->led_state & BIT(n));
 				bigben->led_state |= BIT(n);
 			}
+			spin_unlock_irqrestore(&bigben->lock, flags);
 
 			if (work) {
 				bigben->work_led = true;
-				schedule_work(&bigben->worker);
+				bigben_schedule_work(bigben);
 			}
 			return;
 		}
@@ -307,8 +326,12 @@ static enum led_brightness bigben_get_led(struct led_classdev *led)
 static void bigben_remove(struct hid_device *hid)
 {
 	struct bigben_device *bigben = hid_get_drvdata(hid);
+	unsigned long flags;
 
+	spin_lock_irqsave(&bigben->lock, flags);
 	bigben->removed = true;
+	spin_unlock_irqrestore(&bigben->lock, flags);
+
 	cancel_work_sync(&bigben->worker);
 	hid_hw_stop(hid);
 }
@@ -362,6 +385,7 @@ static int bigben_probe(struct hid_device *hid,
 	set_bit(FF_RUMBLE, hidinput->input->ffbit);
 
 	INIT_WORK(&bigben->worker, bigben_worker);
+	spin_lock_init(&bigben->lock);
 
 	error = input_ff_create_memless(hidinput->input, NULL,
 		hid_bigben_play_effect);
@@ -402,7 +426,7 @@ static int bigben_probe(struct hid_device *hid,
 	bigben->left_motor_force = 0;
 	bigben->work_led = true;
 	bigben->work_ff = true;
-	schedule_work(&bigben->worker);
+	bigben_schedule_work(bigben);
 
 	hid_info(hid, "LED and force feedback support for BigBen gamepad\n");
 

-- 
2.25.1