linux-kernel - [PATCH 2/2] HID: uhid: Use READ_ONCE()/WRITE

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Date:   Fri, 14 Jan 2022 14:33:31 +0100
From:   Jann Horn <jannh@...gle.com>
To:     David Rheinsberg <david.rheinsberg@...il.com>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input@...r.kernel.org
Cc:     Roderick Colenbrander <roderick.colenbrander@...y.com>,
        linux-kernel@...r.kernel.org, Jann Horn <jannh@...gle.com>
Subject: [PATCH 2/2] HID: uhid: Use READ_ONCE()/WRITE_ONCE() for ->running

The flag uhid->running can be set to false by uhid_device_add_worker()
without holding the uhid->devlock. Mark all reads/writes of the flag
that might race with READ_ONCE()/WRITE_ONCE() for clarity and
correctness.

Signed-off-by: Jann Horn <jannh@...gle.com>
---

Notes:
    This is just some cleanup to make it clearer what's going on and avoid UB.
    If you don't want to take this patch, feel free to just take patch 1/2.

 drivers/hid/uhid.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index fc06d8bb42e0..614adb510dbd 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -84,7 +84,7 @@ static void uhid_device_add_worker(struct work_struct *work)
 		 * However, we do have to clear the ->running flag and do a
 		 * wakeup to make sure userspace knows that the device is gone.
 		 */
-		uhid->running = false;
+		WRITE_ONCE(uhid->running, false);
 		wake_up_interruptible(&uhid->report_wait);
 	}
 }
@@ -194,9 +194,9 @@ static int __uhid_report_queue_and_wait(struct uhid_device *uhid,
 	spin_unlock_irqrestore(&uhid->qlock, flags);
 
 	ret = wait_event_interruptible_timeout(uhid->report_wait,
-				!uhid->report_running || !uhid->running,
+				!uhid->report_running || !READ_ONCE(uhid->running),
 				5 * HZ);
-	if (!ret || !uhid->running || uhid->report_running)
+	if (!ret || !READ_ONCE(uhid->running) || uhid->report_running)
 		ret = -EIO;
 	else if (ret < 0)
 		ret = -ERESTARTSYS;
@@ -237,7 +237,7 @@ static int uhid_hid_get_report(struct hid_device *hid, unsigned char rnum,
 	struct uhid_event *ev;
 	int ret;
 
-	if (!uhid->running)
+	if (!READ_ONCE(uhid->running))
 		return -EIO;
 
 	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
@@ -279,7 +279,7 @@ static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
 	struct uhid_event *ev;
 	int ret;
 
-	if (!uhid->running || count > UHID_DATA_MAX)
+	if (!READ_ONCE(uhid->running) || count > UHID_DATA_MAX)
 		return -EIO;
 
 	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
@@ -579,7 +579,7 @@ static int uhid_dev_destroy(struct uhid_device *uhid)
 	if (!uhid->hid)
 		return -EINVAL;
 
-	uhid->running = false;
+	WRITE_ONCE(uhid->running, false);
 	wake_up_interruptible(&uhid->report_wait);
 
 	cancel_work_sync(&uhid->worker);
@@ -593,7 +593,7 @@ static int uhid_dev_destroy(struct uhid_device *uhid)
 
 static int uhid_dev_input(struct uhid_device *uhid, struct uhid_event *ev)
 {
-	if (!uhid->running)
+	if (!READ_ONCE(uhid->running))
 		return -EINVAL;
 
 	hid_input_report(uhid->hid, HID_INPUT_REPORT, ev->u.input.data,
@@ -604,7 +604,7 @@ static int uhid_dev_input(struct uhid_device *uhid, struct uhid_event *ev)
 
 static int uhid_dev_input2(struct uhid_device *uhid, struct uhid_event *ev)
 {
-	if (!uhid->running)
+	if (!READ_ONCE(uhid->running))
 		return -EINVAL;
 
 	hid_input_report(uhid->hid, HID_INPUT_REPORT, ev->u.input2.data,
@@ -616,7 +616,7 @@ static int uhid_dev_input2(struct uhid_device *uhid, struct uhid_event *ev)
 static int uhid_dev_get_report_reply(struct uhid_device *uhid,
 				     struct uhid_event *ev)
 {
-	if (!uhid->running)
+	if (!READ_ONCE(uhid->running))
 		return -EINVAL;
 
 	uhid_report_wake_up(uhid, ev->u.get_report_reply.id, ev);
@@ -626,7 +626,7 @@ static int uhid_dev_get_report_reply(struct uhid_device *uhid,
 static int uhid_dev_set_report_reply(struct uhid_device *uhid,
 				     struct uhid_event *ev)
 {
-	if (!uhid->running)
+	if (!READ_ONCE(uhid->running))
 		return -EINVAL;
 
 	uhid_report_wake_up(uhid, ev->u.set_report_reply.id, ev);
-- 
2.34.1.703.g22d0c6ccf7-goog