Re: [PATCH] usb: dwc3: Fix race condition between concurrent dwc3_remove_requests() call paths

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Oct 28, 2025 at 01:35:53PM +0530, Manish Nagar wrote:
> This patch addresses a 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.
> 
> To prevent this race condition, `usb_ep_disable()` should be made
> synchronous. Specifically:
> - Issue an `ENDXFER` command to stop the endpoint.
> - Ensure all pending USB requests are returned to the function driver
>   via `dwc3_gadget_giveback()` before freeing.
> 
> Since `gserial_disconnect` calls `usb_ep_disable()` first, modifying
> `ep_disable()` to invoke the `complete()` callback for gser USB
> requests ensures safe deallocation.
> 
> Additionally, the driver already includes the `dwc->ep0_in_setup`
> completion mechanism, which is triggered upon returning to the
> SETUP stage. This can be leveraged to coordinate and synchronize
> the cleanup process effectively.
> 
> Signed-off-by: Manish Nagar <manish.nagar@oss.qualcomm.com>
> ---
>  drivers/usb/dwc3/gadget.c | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)

What commit id does this fix?