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    SubjectRe: [PATCH] usb: dwc3: dwc3-qcom: Avoid use-after-free when USB defers or unbinds
    On Mon 06 Dec 15:28 PST 2021, Douglas Anderson wrote:

    > On sc7180-trogdor class devices with 'fw_devlink=permissive' and KASAN
    > enabled, you'll see a Use-After-Free reported at bootup.
    >
    > The root of the problem is that dwc3_qcom_of_register_core() is adding
    > a devm-allocated "tx-fifo-resize" property to its device tree node
    > using of_add_property().
    >
    > The issue is that of_add_property() makes a _permanent_ addition to
    > the device tree that lasts until reboot. That means allocating memory
    > for the property using "devm" managed memory is a terrible idea since
    > that memory will be freed upon probe deferral or device
    > unbinding. Let's change to just allocate memory once and never free
    > it. This sorta looks like a leak but isn't truly one, since only one
    > property will be allocated per device tree node per boot.
    >
    > NOTE: one would think that perhaps it would be better to use
    > of_remove_property() and then be able to free the property on device
    > remove. That sounds good until you read the comments for
    > of_remove_property(), which says that properties are never really
    > removed and they're just moved to the side.
    >

    Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

    Regards,
    Bjorn

    > Fixes: cefdd52fa045 ("usb: dwc3: dwc3-qcom: Enable tx-fifo-resize property by default")
    > Signed-off-by: Douglas Anderson <dianders@chromium.org>
    > ---
    >
    > drivers/usb/dwc3/dwc3-qcom.c | 32 +++++++++++++++++++++-----------
    > 1 file changed, 21 insertions(+), 11 deletions(-)
    >
    > diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
    > index 9abbd01028c5..34b054033116 100644
    > --- a/drivers/usb/dwc3/dwc3-qcom.c
    > +++ b/drivers/usb/dwc3/dwc3-qcom.c
    > @@ -658,18 +658,28 @@ static int dwc3_qcom_of_register_core(struct platform_device *pdev)
    > return -ENODEV;
    > }
    >
    > - prop = devm_kzalloc(dev, sizeof(*prop), GFP_KERNEL);
    > - if (!prop) {
    > - ret = -ENOMEM;
    > - dev_err(dev, "unable to allocate memory for property\n");
    > - goto node_put;
    > - }
    > + /*
    > + * Permanently add the "tx-fifo-resize" to the device tree. Even if
    > + * our device is unregistered this property will still be part
    > + * of the device tree until reboot. Because this is a "permanent"
    > + * change, we allocate memory _without_ devm. For some context, see
    > + * the fact that of_remove_property() doesn't actually remove things.
    > + */
    > + if (!of_find_property(dwc3_np, "tx-fifo-resize", NULL)) {
    > + prop = kzalloc(sizeof(*prop), GFP_KERNEL);
    > + if (!prop) {
    > + ret = -ENOMEM;
    > + dev_err(dev, "unable to allocate memory for property\n");
    > + goto node_put;
    > + }
    >
    > - prop->name = "tx-fifo-resize";
    > - ret = of_add_property(dwc3_np, prop);
    > - if (ret) {
    > - dev_err(dev, "unable to add property\n");
    > - goto node_put;
    > + prop->name = "tx-fifo-resize";
    > + ret = of_add_property(dwc3_np, prop);
    > + if (ret) {
    > + dev_err(dev, "unable to add property\n");
    > + kfree(prop);
    > + goto node_put;
    > + }
    > }
    >
    > ret = of_platform_populate(np, NULL, NULL, dev);
    > --
    > 2.34.1.400.ga245620fadb-goog
    >

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