2023-09-25 11:57:21

by Greg Kroah-Hartman

Subject: Re: [PATCH] usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

On Mon, Sep 25, 2023 at 05:17:41PM +0800, Jia-Ju Bai wrote:
> In _dwc2_hcd_urb_enqueue(), "urb->hcpriv = NULL" is executed without
> holding the lock "hsotg->lock". In _dwc2_hcd_urb_dequeue():
>
> spin_lock_irqsave(&hsotg->lock, flags);
> ...
> if (!urb->hcpriv) {
> dev_dbg(hsotg->dev, "## urb->hcpriv is NULL ##\n");
> goto out;
> }
> rc = dwc2_hcd_urb_dequeue(hsotg, urb->hcpriv); // Use urb->hcpriv
> ...
> out:
> spin_unlock_irqrestore(&hsotg->lock, flags);
>
> When _dwc2_hcd_urb_enqueue() and _dwc2_hcd_urb_dequeue() are
> concurrently executed, the NULL check of "urb->hcpriv" can be executed
> before "urb->hcpriv = NULL". After urb->hcpriv is NULL, it can be used
> in the function call to dwc2_hcd_urb_dequeue(), which can cause a NULL
> pointer dereference.

Odd trailing spaces in your changelog text, is that intentional?

>
> To fix this possible bug, "urb->hcpriv = NULL" should be executed with
> holding the lock "hsotg->lock".
>
> Signed-off-by: Jia-Ju Bai <[email protected]>
> ---
> drivers/usb/dwc2/hcd.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
> index 657f1f659ffa..35c7a4df8e71 100644
> --- a/drivers/usb/dwc2/hcd.c
> +++ b/drivers/usb/dwc2/hcd.c
> @@ -4769,8 +4769,8 @@ static int _dwc2_hcd_urb_enqueue(struct usb_hcd *hcd, struct urb *urb,
> if (qh_allocated && qh->channel && qh->channel->qh == qh)
> qh->channel->qh = NULL;
> fail2:
> - spin_unlock_irqrestore(&hsotg->lock, flags);
> urb->hcpriv = NULL;
> + spin_unlock_irqrestore(&hsotg->lock, flags);
> kfree(qtd);
> fail1:
> if (qh_allocated) {
> --
> 2.34.1
>

What commit id does this fix?

And how did you test this to verify it works properly?

And how was it found?

thanks,

greg k-h

2023-09-25 23:06:28

by Jia-Ju Bai

Subject: Re: [PATCH] usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

Thanks for the reply :)

On 2023/9/25 17:38, Greg KH wrote:
> On Mon, Sep 25, 2023 at 05:17:41PM +0800, Jia-Ju Bai wrote:
>> In _dwc2_hcd_urb_enqueue(), "urb->hcpriv = NULL" is executed without
>> holding the lock "hsotg->lock". In _dwc2_hcd_urb_dequeue():
>>
>> spin_lock_irqsave(&hsotg->lock, flags);
>> ...
>> if (!urb->hcpriv) {
>> dev_dbg(hsotg->dev, "## urb->hcpriv is NULL ##\n");
>> goto out;
>> }
>> rc = dwc2_hcd_urb_dequeue(hsotg, urb->hcpriv); // Use urb->hcpriv
>> ...
>> out:
>> spin_unlock_irqrestore(&hsotg->lock, flags);
>>
>> When _dwc2_hcd_urb_enqueue() and _dwc2_hcd_urb_dequeue() are
>> concurrently executed, the NULL check of "urb->hcpriv" can be executed
>> before "urb->hcpriv = NULL". After urb->hcpriv is NULL, it can be used
>> in the function call to dwc2_hcd_urb_dequeue(), which can cause a NULL
>> pointer dereference.
> Odd trailing spaces in your changelog text, is that intentional?

They are caused by the configuration of my file editor, and I changed it
just now.

>
>> To fix this possible bug, "urb->hcpriv = NULL" should be executed with
>> holding the lock "hsotg->lock".
>>
>> Signed-off-by: Jia-Ju Bai <[email protected]>
>> ---
>> drivers/usb/dwc2/hcd.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
>> index 657f1f659ffa..35c7a4df8e71 100644
>> --- a/drivers/usb/dwc2/hcd.c
>> +++ b/drivers/usb/dwc2/hcd.c
>> @@ -4769,8 +4769,8 @@ static int _dwc2_hcd_urb_enqueue(struct usb_hcd *hcd, struct urb *urb,
>> if (qh_allocated && qh->channel && qh->channel->qh == qh)
>> qh->channel->qh = NULL;
>> fail2:
>> - spin_unlock_irqrestore(&hsotg->lock, flags);
>> urb->hcpriv = NULL;
>> + spin_unlock_irqrestore(&hsotg->lock, flags);
>> kfree(qtd);
>> fail1:
>> if (qh_allocated) {
>> --
>> 2.34.1
>>
> What commit id does this fix?
>
> And how did you test this to verify it works properly?
>
> And how was it found?

I sent a v2 patch to add these details and fix the mistakes about
trailing spaces.


Thanks,
Jia-Ju Bai