linux-kernel - [RFC PATCH] usb: dwc3: gadget: Fix NULL pointer dereference in dwc3_gadget

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Message-ID: <20240110095532.4776-1-quic_uaggarwa@quicinc.com>
Date: Wed, 10 Jan 2024 15:25:32 +0530
From: Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>
CC: <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        "Uttkarsh
 Aggarwal" <quic_uaggarwa@...cinc.com>
Subject: [RFC PATCH] usb: dwc3: gadget: Fix NULL pointer dereference in dwc3_gadget_suspend

In current scenario if Plug-out and Plug-In performed continuously
there could be a chance while checking for dwc->gadget_driver in
dwc3_gadget_suspend, a NULL pointer dereference may occur.

Call Stack:

	CPU1:                           CPU2:
	gadget_unbind_driver            dwc3_suspend_common
	dw3_gadget_stop                 dwc3_gadget_suspend
                                        dwc3_disconnect_gadget

CPU1 basically clears the variable and CPU2 checks the variable.
Consider CPU1 is running and right before gadget_driver is cleared
and in parallel CPU2 executes dwc3_gadget_suspend where it finds
dwc->gadget_driver which is not NULL and resumes execution and then
CPU1 completes execution. CPU2 executes dwc3_disconnect_gadget where
it checks dwc->gadget_driver is already NULL because of which the
NULL pointer deference occur.

To prevent this, moving NULL pointer check inside of spin_lock.

Signed-off-by: Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>
---
 drivers/usb/dwc3/gadget.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 019368f8e9c4..564976b3e2b9 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -4709,15 +4709,13 @@ int dwc3_gadget_suspend(struct dwc3 *dwc)
 	unsigned long flags;
 	int ret;

-	if (!dwc->gadget_driver)
-		return 0;
-
 	ret = dwc3_gadget_soft_disconnect(dwc);
 	if (ret)
 		goto err;

 	spin_lock_irqsave(&dwc->lock, flags);
-	dwc3_disconnect_gadget(dwc);
+	if (dwc->gadget_driver)
+		dwc3_disconnect_gadget(dwc);
 	spin_unlock_irqrestore(&dwc->lock, flags);

 	return 0;
-- 
2.17.1