[PATCH v2] usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

[PATCH v2] usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

[Jia-Ju Bai]

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. 

This possible bug is found by a static tool developed by myself.

To fix this possible bug, "urb->hcpriv = NULL" should be executed with
holding the lock "hsotg->lock". Because I have no associated hardware,
I cannot test the patch in real execution, and just verify it according
to the code logic.

Fixes: 33ad261aa62b ("usb: dwc2: host: spinlock urb_enqueue")
Signed-off-by: Jia-Ju Bai <baijiaju@buaa.edu.cn>
---
v2:
* Add more details in the description.
---
 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

Re: [PATCH v2] usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

[Greg KH]

On Mon, Sep 25, 2023 at 06:07:41PM +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. 
> 
> This possible bug is found by a static tool developed by myself.

Because of this please follow the rules for such things as documented in
Documentation/process/researcher-guidelines.rst

> To fix this possible bug, "urb->hcpriv = NULL" should be executed with
> holding the lock "hsotg->lock". Because I have no associated hardware,
> I cannot test the patch in real execution, and just verify it according
> to the code logic.
> 
> Fixes: 33ad261aa62b ("usb: dwc2: host: spinlock urb_enqueue")
> Signed-off-by: Jia-Ju Bai <baijiaju@buaa.edu.cn>

My bot says:

-----------

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- You have marked a patch with a "Fixes:" tag for a commit that is in an
  older released kernel, yet you do not have a cc: stable line in the
  signed-off-by area at all, which means that the patch will not be
  applied to any older kernel releases.  To properly fix this, please
  follow the documented rules in the
  Documetnation/process/stable-kernel-rules.rst file for how to resolve
  this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot

Re: [PATCH v2] usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

[Jia-Ju Bai]

Thanks for the reply!

I will follow the rules and revise the patch.


Best wishes,
Jia-Ju Bai

On 2023/9/25 20:08, Greg KH wrote:
> On Mon, Sep 25, 2023 at 06:07:41PM +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.
>>
>> This possible bug is found by a static tool developed by myself.
> Because of this please follow the rules for such things as documented in
> Documentation/process/researcher-guidelines.rst
>
>> To fix this possible bug, "urb->hcpriv = NULL" should be executed with
>> holding the lock "hsotg->lock". Because I have no associated hardware,
>> I cannot test the patch in real execution, and just verify it according
>> to the code logic.
>>
>> Fixes: 33ad261aa62b ("usb: dwc2: host: spinlock urb_enqueue")
>> Signed-off-by: Jia-Ju Bai <baijiaju@buaa.edu.cn>
> My bot says:
>
> -----------
>
> Hi,
>
> This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
> a patch that has triggered this response.  He used to manually respond
> to these common problems, but in order to save his sanity (he kept
> writing the same thing over and over, yet to different people), I was
> created.  Hopefully you will not take offence and will fix the problem
> in your patch and resubmit it so that it can be accepted into the Linux
> kernel tree.
>
> You are receiving this message because of the following common error(s)
> as indicated below:
>
> - You have marked a patch with a "Fixes:" tag for a commit that is in an
>    older released kernel, yet you do not have a cc: stable line in the
>    signed-off-by area at all, which means that the patch will not be
>    applied to any older kernel releases.  To properly fix this, please
>    follow the documented rules in the
>    Documetnation/process/stable-kernel-rules.rst file for how to resolve
>    this.
>
> If you wish to discuss this problem further, or you have questions about
> how to resolve this issue, please feel free to respond to this email and
> Greg will reply once he has dug out from the pending patches received
> from other developers.
>
> thanks,
>
> greg k-h's patch email bot