linux-kernel - [PATCH v9] usb: gadget: udc: renesas_usb3: Fix use after free bug in renesas_usb3

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Date:   Fri, 17 Mar 2023 17:55:05 +0800
From:   Zheng Wang <zyytlz.wz@....com>
To:     gregkh@...uxfoundation.org
Cc:     skhan@...uxfoundation.org, p.zabel@...gutronix.de,
        biju.das.jz@...renesas.com, phil.edworthy@...esas.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        hackerzheng666@...il.com, 1395428693sheep@...il.com,
        alex000young@...il.com, yoshihiro.shimoda.uh@...esas.com,
        Zheng Wang <zyytlz.wz@....com>
Subject: [PATCH v9] usb: gadget: udc: renesas_usb3: Fix use after free bug in  renesas_usb3_remove due to race condition

In renesas_usb3_probe, role_work is bound with renesas_usb3_role_work.
renesas_usb3_start will be called to start the work.

If we remove the driver which will call usbhs_remove, there may be
an unfinished work. The possible sequence is as follows:

CPU0                  			CPU1

                    			 renesas_usb3_role_work
renesas_usb3_remove
usb_role_switch_unregister
device_unregister
kfree(sw)
//free usb3->role_sw
                    			 usb_role_switch_set_role
                    			 //use usb3->role_sw

The usb3->role_sw could be freed under such circumstance and use in usb_role_switch_set_role.

This bug was found by static analysis. And note that removing a driver is a root-only operation, and should never
happen in normal case. But the attacker can directly remove the device which will also triggering remove function.

Fix it by canceling the work before cleanup in the renesas_usb3_remove.

Fixes: 39facfa01c9f ("usb: gadget: udc: renesas_usb3: Add register of usb role switch")
Signed-off-by: Zheng Wang <zyytlz.wz@....com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
---
v9:
- append with more information suggested by Greg KH
v8:
- replace | with spaces to make line up suggested by Greg KH
v7:
- add more details about how the bug was found suggested by Shuah
v6:
- beautify the format and add note suggested by Greg KH
v5:
- fix typo
v4:
- add Reviewed-by label and resubmit v4 suggested by Greg KH
v3:
- modify the commit message to make it clearer suggested by Yoshihiro Shimoda
v2:
- fix typo, use clearer commit message and only cancel the UAF-related work suggested by Yoshihiro Shimoda
---
 drivers/usb/gadget/udc/renesas_usb3.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/gadget/udc/renesas_usb3.c b/drivers/usb/gadget/udc/renesas_usb3.c
index bee6bceafc4f..a301af66bd91 100644
--- a/drivers/usb/gadget/udc/renesas_usb3.c
+++ b/drivers/usb/gadget/udc/renesas_usb3.c
@@ -2661,6 +2661,7 @@ static int renesas_usb3_remove(struct platform_device *pdev)
 	debugfs_remove_recursive(usb3->dentry);
 	device_remove_file(&pdev->dev, &dev_attr_role);
 
+	cancel_work_sync(&usb3->role_work);
 	usb_role_switch_unregister(usb3->role_sw);
 
 	usb_del_gadget_udc(&usb3->gadget);
-- 
2.25.1