linux-kernel - [PATCH v2] usbip: vudc: Fix use after free bug in vudc

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Date:   Fri, 17 Mar 2023 02:09:40 +0800
From:   Zheng Wang <zyytlz.wz@....com>
To:     valentina.manea.m@...il.com
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, hackerzheng666@...il.com,
        1395428693sheep@...il.com, alex000young@...il.com,
        skhan@...uxfoundation.org, Zheng Wang <zyytlz.wz@....com>
Subject: [PATCH v2] usbip: vudc: Fix use after free bug in vudc_remove due to race condition

In vudc_probe, it calls init_vudc_hw, which bound &udc->timer with v_timer.

When it calls usbip_sockfd_store, it will call v_start_timer to start the 
timer work.

When we call vudc_remove to remove the driver, theremay be a sequence as 
follows:

Fix it by shutdown the timer work before cleanup in vudc_remove.

Note that removing a driver is a root-only operation, and should never
happen.

CPU0                  CPU1

                     |v_timer
vudc_remove          |
kfree(udc);          |
//free shost         |
                     |udc->gadget
                     |//use

This bug was found by static analysis.

Fixes: b6a0ca111867 ("usbip: vudc: Add UDC specific ops")
Signed-off-by: Zheng Wang <zyytlz.wz@....com>
---
v2:
- add more details about how the bug was found suggested by Shuah
---
 drivers/usb/usbip/vudc_dev.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/usbip/vudc_dev.c b/drivers/usb/usbip/vudc_dev.c
index 2bc428f2e261..33d0991755bb 100644
--- a/drivers/usb/usbip/vudc_dev.c
+++ b/drivers/usb/usbip/vudc_dev.c
@@ -633,6 +633,7 @@ int vudc_remove(struct platform_device *pdev)
 {
 	struct vudc *udc = platform_get_drvdata(pdev);
 
+	timer_shutdown_sync(&udc->timer);
 	usb_del_gadget_udc(&udc->gadget);
 	cleanup_vudc_hw(udc);
 	kfree(udc);
-- 
2.25.1