Re: [PATCH] usb: dwc3: qcom: fix NULL pointer dereference on dwc3_qcom_read_usb2_speed

[Faisal Hassan <quic_faisalh@quicinc.com>]

On 8/22/2024 4:55 PM, Johan Hovold wrote:
> On Tue, Aug 13, 2024 at 04:48:47PM +0530, Faisal Hassan wrote:
>> Null pointer dereference occurs when accessing 'hcd' to detect speed
>> from dwc3_qcom_suspend after the xhci-hcd is unbound.
> 
> Why are you unbinding the xhci driver?
> 

On our automotive platforms, when preparing for suspend, a script
unbinds the xhci driver to remove all devices, ensuring the platform
reaches the lowest power state.

>> To avoid this issue, ensure to check for NULL in dwc3_qcom_read_usb2_speed.
>>
>> echo xhci-hcd.0.auto > /sys/bus/platform/drivers/xhci-hcd/unbind
>>   xhci_plat_remove() -> usb_put_hcd() -> hcd_release() -> kfree(hcd)
>>
>>   Unable to handle kernel NULL pointer dereference at virtual address
>>   0000000000000060
>>   Call trace:
>>    dwc3_qcom_suspend.part.0+0x17c/0x2d0 [dwc3_qcom]
>>    dwc3_qcom_runtime_suspend+0x2c/0x40 [dwc3_qcom]
>>    pm_generic_runtime_suspend+0x30/0x44
>>    __rpm_callback+0x4c/0x190
>>    rpm_callback+0x6c/0x80
>>    rpm_suspend+0x10c/0x620
>>    pm_runtime_work+0xc8/0xe0
>>    process_one_work+0x1e4/0x4f4
>>    worker_thread+0x64/0x43c
>>    kthread+0xec/0x100
>>    ret_from_fork+0x10/0x20
>>
>> Fixes: c5f14abeb52b ("usb: dwc3: qcom: fix peripheral and OTG suspend")
> 
> This is clearly not the commit that introduced this issue, please be
> more careful.
> 

My mistake, I should have verified that. I appreciate your feedback.
I’ll make sure to be more careful in the future.

> Also make sure to CC the author of any patch introducing a bug so that
> they may help with review.
> 

Understood. I’ll ensure to CC the author from next time.

>> Cc: stable@vger.kernel.org
>> Signed-off-by: Faisal Hassan <quic_faisalh@quicinc.com>
>> ---
>>  drivers/usb/dwc3/dwc3-qcom.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
>> index 88fb6706a18d..0c7846478655 100644
>> --- a/drivers/usb/dwc3/dwc3-qcom.c
>> +++ b/drivers/usb/dwc3/dwc3-qcom.c
>> @@ -319,13 +319,15 @@ static bool dwc3_qcom_is_host(struct dwc3_qcom *qcom)
>>  static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom, int port_index)
>>  {
>>  	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
>> -	struct usb_device *udev;
>> +	struct usb_device __maybe_unused *udev;
>>  	struct usb_hcd __maybe_unused *hcd;
>>  
>>  	/*
>>  	 * FIXME: Fix this layering violation.
>>  	 */
>>  	hcd = platform_get_drvdata(dwc->xhci);
>> +	if (!hcd)
>> +		return USB_SPEED_UNKNOWN;
> 
> This is just papering over the real issue here which is the layering
> violation of having drivers accessing driver data of their children. 
> 
> Nothing is preventing the driver data from being deallocated after you
> check for NULL here.
> 
> I suggest leaving this as is until Bjorn's patches that should address
> this properly lands.
> 

I agree that this part needs to be cleaned up. Currently, this is 100%
reproducible on our platform, and adding this NULL check is very
helpful, but I agree that the vulnerability is still not completely
eliminated.

Until this part is cleaned up, can this check be added to reduce the risk?

>>  
>>  #ifdef CONFIG_USB
>>  	udev = usb_hub_find_child(hcd->self.root_hub, port_index + 1);
> 
> Johan

Thanks,
Faisal