[PATCH v4 05/21] usb: dwc2: host: Avoid use of chan->qh after qh freed

[Douglas Anderson]

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 <diand...@chromium.org>
---
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

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