linux-kernel - Re: [PATCH v2] usb: dwc3: Fix race condition between concurrent dwc3_remove

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Message-ID: <20251120013446.n5ibpgxghmvhfo2c@synopsys.com>
Date: Thu, 20 Nov 2025 01:34:52 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Manish Nagar <manish.nagar@....qualcomm.com>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: Fix race condition between concurrent
 dwc3_remove_requests() call paths

On Wed, Nov 19, 2025, Manish Nagar wrote:
> Addresses race condition caused by unsynchronized
> execution of multiple call paths invoking `dwc3_remove_requests()`,
> leading to premature freeing of USB requests and subsequent crashes.
> 
> Three distinct execution paths interact with `dwc3_remove_requests()`:
> Path 1:
> Triggered via `dwc3_gadget_reset_interrupt()` during USB reset
> handling. The call stack includes:
> - `dwc3_ep0_reset_state()`
> - `dwc3_ep0_stall_and_restart()`
> - `dwc3_ep0_out_start()`
> - `dwc3_remove_requests()`
> - `dwc3_gadget_del_and_unmap_request()`
> 
> Path 2:
> Also initiated from `dwc3_gadget_reset_interrupt()`, but through
> `dwc3_stop_active_transfers()`. The call stack includes:
> - `dwc3_stop_active_transfers()`
> - `dwc3_remove_requests()`
> - `dwc3_gadget_del_and_unmap_request()`
> 
> Path 3:
> Occurs independently during `adb root` execution, which triggers
> USB function unbind and bind operations. The sequence includes:
> - `gserial_disconnect()`
> - `usb_ep_disable()`
> - `dwc3_gadget_ep_disable()`
> - `dwc3_remove_requests()` with `-ESHUTDOWN` status
> 
> Path 3 operates asynchronously and lacks synchronization with Paths
> 1 and 2. When Path 3 completes, it disables endpoints and frees 'out'
> requests. If Paths 1 or 2 are still processing these requests,
> accessing freed memory leads to a crash due to use-after-free conditions.
> 
> Add check for request completion for eps,  and skip processing giveback
> for eps if already completed and add the request status for ep0 while
> queue via_dwc3_gadget_ep0_queue.
> 
> Suggested-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
> Signed-off-by: Manish Nagar <manish.nagar@....qualcomm.com>


Add Fixes tag targeting the below:

72246da40f37 ("usb: Introduce DesignWare USB3 DRD Driver")

And also include Cc stable

> ---
> v2:
>  - Add a check for request completion, in v1 I am avoiding this
>     by wait for completion for ep0 then process the other eps.
> 
>  drivers/usb/dwc3/ep0.c    | 1 +
>  drivers/usb/dwc3/gadget.c | 7 +++++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c
> index b4229aa13f37..e0bad5708664 100644
> --- a/drivers/usb/dwc3/ep0.c
> +++ b/drivers/usb/dwc3/ep0.c
> @@ -94,6 +94,7 @@ static int __dwc3_gadget_ep0_queue(struct dwc3_ep *dep,
>  	req->request.actual	= 0;
>  	req->request.status	= -EINPROGRESS;
>  	req->epnum		= dep->number;
> +	req->status		= DWC3_REQUEST_STATUS_QUEUED;
>  
>  	list_add_tail(&req->list, &dep->pending_list);
>  
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 6f18b4840a25..5e4997f974dd 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -228,6 +228,13 @@ void dwc3_gadget_giveback(struct dwc3_ep *dep, struct dwc3_request *req,
>  {
>  	struct dwc3			*dwc = dep->dwc;
>  
> +	/*
> +	 * The request might have been processed and completed while the
> +	 * spinlock was released. Skip processing if already completed.
> +	 */
> +	if (req->status == DWC3_REQUEST_STATUS_COMPLETED)
> +		return;
> +
>  	dwc3_gadget_del_and_unmap_request(dep, req, status);
>  	req->status = DWC3_REQUEST_STATUS_COMPLETED;
>  
> -- 
> 2.25.1
> 

After adding the Fixes tag and Cc stable:

Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>

Thanks,
Thinh