linux-kernel - [PATCH v2] usb: Add a lock when freeing data in usbtmc

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Date:   Tue, 23 Mar 2021 02:28:54 -0700
From:   Lv Yunlong <lyl2019@...l.ustc.edu.cn>
To:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Subject: [PATCH v2] usb: Add a lock when freeing data in usbtmc_disconnect

In usbtmc_disconnect, data is got from intf with the initial reference.
There is no refcount inc operation before usbmc_free_int(data). In
usbmc_free_int(data), the data may be freed.

But later in usbtmc_disconnect, there is another put function of data.
It could cause errors in race.

My patch adds a lock to protect kref from changing in race.

Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
---
 drivers/usb/class/usbtmc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
index 74d5a9c5238a..44f1fcabbb1e 100644
--- a/drivers/usb/class/usbtmc.c
+++ b/drivers/usb/class/usbtmc.c
@@ -2493,8 +2493,13 @@ static void usbtmc_disconnect(struct usb_interface *intf)
 		usb_scuttle_anchored_urbs(&file_data->in_anchor);
 	}
 	mutex_unlock(&data->io_mutex);
+
+	spinlock_t *dev_lock = &data->dev_lock;
+
+	spin_lock_irq(dev_lock);
 	usbtmc_free_int(data);
 	kref_put(&data->kref, usbtmc_delete);
+	spin_unlock_irq(dev_lock);
 }
 
 static void usbtmc_draw_down(struct usbtmc_file_data *file_data)
-- 
2.25.1