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

[Manish Nagar <manish.nagar@oss.qualcomm.com>]

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(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 6f18b4840a25..93c20d5edea1 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1064,7 +1064,7 @@ static int __dwc3_gadget_ep_disable(struct dwc3_ep *dep)
 {
 	struct dwc3		*dwc = dep->dwc;
 	u32			reg;
-	u32			mask;
+	int			ret;
 
 	trace_dwc3_gadget_ep_disable(dep);
 
@@ -1077,18 +1077,23 @@ static int __dwc3_gadget_ep_disable(struct dwc3_ep *dep)
 	dwc3_writel(dwc->regs, DWC3_DALEPENA, reg);
 
 	dwc3_remove_requests(dwc, dep, -ESHUTDOWN);
+	/*
+	 * Stop the endpoint by issuing ENDXFER and synchronously complete
+	 * all pending USB requests before returning from ep disable.
+	 */
+	if (dep->flags & DWC3_EP_DELAY_STOP) {
+		spin_unlock(&dwc->lock);
+		reinit_completion(&dwc->ep0_in_setup);
+		ret = wait_for_completion_timeout(&dwc->ep0_in_setup,
+						  msecs_to_jiffies(DWC3_PULL_UP_TIMEOUT));
+		spin_lock(&dwc->lock);
+		if (ret == 0)
+			dwc3_ep0_reset_state(dwc);
+	}
 
 	dep->stream_capable = false;
 	dep->type = 0;
-	mask = DWC3_EP_TXFIFO_RESIZED | DWC3_EP_RESOURCE_ALLOCATED;
-	/*
-	 * dwc3_remove_requests() can exit early if DWC3 EP delayed stop is
-	 * set.  Do not clear DEP flags, so that the end transfer command will
-	 * be reattempted during the next SETUP stage.
-	 */
-	if (dep->flags & DWC3_EP_DELAY_STOP)
-		mask |= (DWC3_EP_DELAY_STOP | DWC3_EP_TRANSFER_STARTED);
-	dep->flags &= mask;
+	dep->flags &= DWC3_EP_TXFIFO_RESIZED;
 
 	/* Clear out the ep descriptors for non-ep0 */
 	if (dep->number > 1) {
-- 
2.25.1