fix(dcd): Fixed race condition on device disconnect

TinyUSB does not provide any locking means to protect the DCD variables.
This can lead to race conditions when the user is trying to submit
a transfer while the device is being disconnected. This can cause
the device to be in an inconsistent state, leading to a crash or
undefined behavior.

This commit adds a spin-lock to protect the DCD variables during
device disconnect.

Closes espressif/esp-idf#9691
Also reported in espressif/esp-usb#131

Author: tore-espressif

src/portable/synopsys/dwc2/dcd_dwc2.c

@@ -40,6 +40,7 @@
 
 #include "device/dcd.h"
 #include "dwc2_common.h"
+#include "dwc2_critical.h"
 
 #if TU_CHECK_MCU(OPT_MCU_GD32VF103)
   #define DWC2_EP_COUNT(_dwc2)   DWC2_EP_MAX
@@ -58,6 +59,9 @@ typedef struct {
   uint8_t interval;
 } xfer_ctl_t;
 
+/*
+This variable is modified from ISR context, so it must be protected by critical section
+*/
 static xfer_ctl_t xfer_status[DWC2_EP_MAX][2];
 #define XFER_CTL_BASE(_ep, _dir) (&xfer_status[_ep][_dir])
 
@@ -321,6 +325,9 @@ static void edpt_disable(uint8_t rhport, uint8_t ep_addr, bool stall) {
   }
 }
 
+// Since this function returns void, it is not possible to return a boolean success message
+// We must make sure that this function is not called when the EP is disabled
+// Must be called from critical section
 static void edpt_schedule_packets(uint8_t rhport, const uint8_t epnum, const uint8_t dir) {
   dwc2_regs_t* dwc2 = DWC2_REG(rhport);
   xfer_ctl_t* const xfer = XFER_CTL_BASE(epnum, dir);
@@ -540,6 +547,7 @@ void dcd_edpt_close_all(uint8_t rhport) {
   dwc2_regs_t* dwc2 = DWC2_REG(rhport);
   uint8_t const ep_count = _dwc2_controller[rhport].ep_count;
 
+  DCD_ENTER_CRITICAL();
   _dcd_data.allocated_epin_count = 0;
 
   // Disable non-control interrupt
@@ -559,6 +567,7 @@ void dcd_edpt_close_all(uint8_t rhport) {
   dfifo_flush_rx(dwc2);
 
   dfifo_device_init(rhport); // re-init dfifo
+  DCD_EXIT_CRITICAL();
 }
 
 bool dcd_edpt_iso_alloc(uint8_t rhport, uint8_t ep_addr, uint16_t largest_packet_size) {
@@ -577,7 +586,12 @@ bool dcd_edpt_xfer(uint8_t rhport, uint8_t ep_addr, uint8_t* buffer, uint16_t to
   uint8_t const epnum = tu_edpt_number(ep_addr);
   uint8_t const dir = tu_edpt_dir(ep_addr);
 
+  DCD_ENTER_CRITICAL();
   xfer_ctl_t* xfer = XFER_CTL_BASE(epnum, dir);
+  if (xfer->max_size == 0) {
+    DCD_EXIT_CRITICAL();
+    return false; // Endpoint is closed
+  }
   xfer->buffer = buffer;
   xfer->ff = NULL;
   xfer->total_len = total_bytes;
@@ -589,6 +603,7 @@ bool dcd_edpt_xfer(uint8_t rhport, uint8_t ep_addr, uint8_t* buffer, uint16_t to
 
   // Schedule packets to be sent within interrupt
   edpt_schedule_packets(rhport, epnum, dir);
+  DCD_EXIT_CRITICAL();
 
   return true;
 }
@@ -604,14 +619,20 @@ bool dcd_edpt_xfer_fifo(uint8_t rhport, uint8_t ep_addr, tu_fifo_t* ff, uint16_t
   uint8_t const epnum = tu_edpt_number(ep_addr);
   uint8_t const dir = tu_edpt_dir(ep_addr);
 
+  DCD_ENTER_CRITICAL();
   xfer_ctl_t* xfer = XFER_CTL_BASE(epnum, dir);
+  if (xfer->max_size == 0) {
+    DCD_EXIT_CRITICAL();
+    return false; // Endpoint is closed
+  }
   xfer->buffer = NULL;
   xfer->ff = ff;
   xfer->total_len = total_bytes;
 
   // Schedule packets to be sent within interrupt
   // TODO xfer fifo may only available for slave mode
   edpt_schedule_packets(rhport, epnum, dir);
+  DCD_EXIT_CRITICAL();
 
   return true;
 }
@@ -640,6 +661,7 @@ void dcd_edpt_clear_stall(uint8_t rhport, uint8_t ep_addr) {
 //--------------------------------------------------------------------
 
 // 7.4.1 Initialization on USB Reset
+// Must be called from critical section
 static void handle_bus_reset(uint8_t rhport) {
   dwc2_regs_t *dwc2 = DWC2_REG(rhport);
   const uint8_t ep_count =  DWC2_EP_COUNT(dwc2);
@@ -990,8 +1012,10 @@ void dcd_int_handler(uint8_t rhport) {
 
   if (gintsts & GINTSTS_USBRST) {
     // USBRST is start of reset.
+    DCD_ENTER_CRITICAL();
     dwc2->gintsts = GINTSTS_USBRST;
     handle_bus_reset(rhport);
+    DCD_EXIT_CRITICAL();
   }
 
   if (gintsts & GINTSTS_ENUMDNE) {

src/portable/synopsys/dwc2/dwc2_critical.h

@@ -0,0 +1,25 @@
+/*
+ * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef TUSB_DWC2_CRITICAL_H_
+#define TUSB_DWC2_CRITICAL_H_
+
+#include "common/tusb_mcu.h"
+
+#if defined(TUP_USBIP_DWC2_ESP32)
+  #include "freertos/FreeRTOS.h"
+  static portMUX_TYPE dcd_lock = portMUX_INITIALIZER_UNLOCKED;
+  #define DCD_ENTER_CRITICAL()    portENTER_CRITICAL(&dcd_lock)
+  #define DCD_EXIT_CRITICAL()     portEXIT_CRITICAL(&dcd_lock)
+
+#else
+  // Define critical section macros for DWC2 as no-op if not defined
+  // This is to avoid breaking existing code that does not use critical section
+  #define DCD_ENTER_CRITICAL()    // no-op
+  #define DCD_EXIT_CRITICAL()     // no-op
+#endif
+
+#endif // TUSB_DWC2_CRITICAL_H_