[PATCH v2 4/9] usb: dwc3: qcom: fix use-after-free on runtime-PM wakeup

[Johan Hovold <johan+linaro@kernel.org>]

The Qualcomm dwc3 runtime-PM implementation checks the xhci
platform-device pointer in the wakeup-interrupt handler to determine
whether the controller is in host mode and if so triggers a resume.

After a role switch in OTG mode the xhci platform-device would have been
freed and the next wakeup from runtime suspend would access the freed
memory.

Note that role switching is executed from a freezable workqueue, which
guarantees that the pointer is stable during suspend.

Also note that runtime PM has been broken since commit 2664deb09306
("usb: dwc3: qcom: Honor wakeup enabled/disabled state"), which
incidentally also prevents this issue from being triggered.

Fixes: a4333c3a6ba9 ("usb: dwc3: Add Qualcomm DWC3 glue driver")
Cc: stable@vger.kernel.org      # 4.18
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---

Changes in v2
 - new patch

 drivers/usb/dwc3/dwc3-qcom.c | 14 +++++++++++++-
 drivers/usb/dwc3/host.c      |  1 +
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
index e9364141661b..6884026b9fad 100644
--- a/drivers/usb/dwc3/dwc3-qcom.c
+++ b/drivers/usb/dwc3/dwc3-qcom.c
@@ -298,6 +298,14 @@ static void dwc3_qcom_interconnect_exit(struct dwc3_qcom *qcom)
 	icc_put(qcom->icc_path_apps);
 }
 
+/* Only usable in contexts where the role can not change. */
+static bool dwc3_qcom_is_host(struct dwc3_qcom *qcom)
+{
+	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
+
+	return dwc->xhci;
+}
+
 static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom)
 {
 	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
@@ -460,7 +468,11 @@ static irqreturn_t qcom_dwc3_resume_irq(int irq, void *data)
 	if (qcom->pm_suspended)
 		return IRQ_HANDLED;
 
-	if (dwc->xhci)
+	/*
+	 * This is safe as role switching is done from a freezable workqueue
+	 * and the wakeup interrupts are disabled as part of resume.
+	 */
+	if (dwc3_qcom_is_host(qcom))
 		pm_runtime_resume(&dwc->xhci->dev);
 
 	return IRQ_HANDLED;
diff --git a/drivers/usb/dwc3/host.c b/drivers/usb/dwc3/host.c
index f56c30cf151e..f6f13e7f1ba1 100644
--- a/drivers/usb/dwc3/host.c
+++ b/drivers/usb/dwc3/host.c
@@ -135,4 +135,5 @@ int dwc3_host_init(struct dwc3 *dwc)
 void dwc3_host_exit(struct dwc3 *dwc)
 {
 	platform_device_unregister(dwc->xhci);
+	dwc->xhci = NULL;
 }
-- 
2.35.1