[PATCH v5 05/21] usb: dwc2: host: Avoid use of chan->qh after qh freed

[Douglas Anderson <dianders@chromium.org>]

When poking around with USB devices with slub_debug enabled, I found
another obvious use after free.  Turns out that in dwc2_hc_n_intr() I
was in a state when the contents of chan->qh was filled with 0x6b,
indicating that chan->qh was freed but chan still had a reference to
it.

Let's make sure that whenever we free qh we also make sure we remove a
reference from its channel.

The bug fixed here doesn't appear to be new--I believe I just got lucky
and happened to see it while stress testing.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
Changes in v5: None
Changes in v4:
- Avoid use of chan->qh after qh freed new for v4.

Changes in v3: None
Changes in v2: None

 drivers/usb/dwc2/hcd.c      |  8 ++++++++
 drivers/usb/dwc2/hcd_intr.c | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
index bc4bdbc1534e..7783c8ba0173 100644
--- a/drivers/usb/dwc2/hcd.c
+++ b/drivers/usb/dwc2/hcd.c
@@ -164,6 +164,9 @@ static void dwc2_qh_list_free(struct dwc2_hsotg *hsotg,
 					 qtd_list_entry)
 			dwc2_hcd_qtd_unlink_and_free(hsotg, qtd, qh);
 
+		if (qh->channel && qh->channel->qh == qh)
+			qh->channel->qh = NULL;
+
 		spin_unlock_irqrestore(&hsotg->lock, flags);
 		dwc2_hcd_qh_free(hsotg, qh);
 		spin_lock_irqsave(&hsotg->lock, flags);
@@ -554,7 +557,12 @@ static int dwc2_hcd_endpoint_disable(struct dwc2_hsotg *hsotg,
 		dwc2_hcd_qtd_unlink_and_free(hsotg, qtd, qh);
 
 	ep->hcpriv = NULL;
+
+	if (qh->channel && qh->channel->qh == qh)
+		qh->channel->qh = NULL;
+
 	spin_unlock_irqrestore(&hsotg->lock, flags);
+
 	dwc2_hcd_qh_free(hsotg, qh);
 
 	return 0;
diff --git a/drivers/usb/dwc2/hcd_intr.c b/drivers/usb/dwc2/hcd_intr.c
index 352c98364317..99efc2bd1617 100644
--- a/drivers/usb/dwc2/hcd_intr.c
+++ b/drivers/usb/dwc2/hcd_intr.c
@@ -1935,6 +1935,16 @@ static void dwc2_hc_n_intr(struct dwc2_hsotg *hsotg, int chnum)
 	}
 
 	dwc2_writel(hcint, hsotg->regs + HCINT(chnum));
+
+	/*
+	 * If we got an interrupt after someone called
+	 * dwc2_hcd_endpoint_disable() we don't want to crash below
+	 */
+	if (!chan->qh) {
+		dev_warn(hsotg->dev, "Interrupt on disabled channel\n");
+		return;
+	}
+
 	chan->hcint = hcint;
 	hcint &= hcintmsk;
 
-- 
2.7.0.rc3.207.g0ac5344