[PATCH v4 3/5] 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 | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/hid/hid-bigbenff.c b/drivers/hid/hid-bigbenff.c
index b98c5f31c184..9d6560db762b 100644
--- a/drivers/hid/hid-bigbenff.c
+++ b/drivers/hid/hid-bigbenff.c
@@ -185,6 +185,15 @@ 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)
 {
@@ -197,9 +206,6 @@ static void bigben_worker(struct work_struct *work)
 	u32 len;
 	unsigned long flags;
 
-	if (bigben->removed)
-		return;
-
 	buf = hid_alloc_report_buf(bigben->report, GFP_KERNEL);
 	if (!buf)
 		return;
@@ -285,7 +291,7 @@ static int hid_bigben_play_effect(struct input_dev *dev, void *data,
 		bigben->work_ff = true;
 		spin_unlock_irqrestore(&bigben->lock, flags);
 
-		schedule_work(&bigben->worker);
+		bigben_schedule_work(bigben);
 	}
 
 	return 0;
@@ -320,7 +326,7 @@ static void bigben_set_led(struct led_classdev *led,
 
 			if (work) {
 				bigben->work_led = true;
-				schedule_work(&bigben->worker);
+				bigben_schedule_work(bigben);
 			}
 			return;
 		}
@@ -450,7 +456,7 @@ 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