linux-kernel - Re: [PATCH] usb: dwc3: dwc3-qcom: Avoid use-after-free when USB defers or unbinds

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Date:   Mon, 6 Dec 2021 16:29:53 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sandeep Maheswaram <quic_c_sanm@...cinc.com>,
        swboyd@...omium.org, Wesley Cheng <quic_wcheng@...cinc.com>,
        robdclark@...omium.org, linux-arm-msm@...r.kernel.org,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Wesley Cheng <wcheng@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH] usb: dwc3: dwc3-qcom: Avoid use-after-free when USB
 defers or unbinds

On Mon, Dec 06, 2021 at 03:28:47PM -0800, 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.
> 
> Fixes: cefdd52fa045 ("usb: dwc3: dwc3-qcom: Enable tx-fifo-resize property by default")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>