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@xxxxxxxxxx> Regards, Bjorn > Fixes: cefdd52fa045 ("usb: dwc3: dwc3-qcom: Enable tx-fifo-resize property by default") > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > --- > > 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 >