gate acm_open descriptor bounds behind CFG_TUH_VALIDATION_LEVEL

add a three-level TUSB_VALIDATION_NONE/BASIC/STRICT knob and default
CFG_TUH_VALIDATION_LEVEL to BASIC, then make acm_open the first user so
the enumeration bounds checks compile out at NONE for trusted-device
setups and stay on by default.

2 files changed, 33 insertions, 8 deletions

diff --git a/src/class/cdc/cdc_host.c b/src/class/cdc/cdc_host.c
index 6045350a8..d1cbc2924 100644
--- a/src/class/cdc/cdc_host.c
+++ b/src/class/cdc/cdc_host.c
@@ -714,11 +714,21 @@ bool cdch_xfer_cb(uint8_t daddr, uint8_t ep_addr, xfer_result_t event, uint32_t
 //--------------------------------------------------------------------+
 // Enumeration
 //--------------------------------------------------------------------+
+
+  // Descriptor-walk hardening gated by CFG_TUH_VALIDATION_LEVEL: at NONE the guards collapse to a pass so
+  // trusted-device setups pay no code size; at BASIC (default) the walk stays inside the enumeration buffer.
+  #if CFG_TUH_VALIDATION_LEVEL >= TUSB_VALIDATION_BASIC
+    #define TU_DESC_VALIDATE(_cond) (_cond)
+  #else
+    #define TU_DESC_VALIDATE(_cond) (true)
+  #endif
+
 static bool open_ep_stream_pair(cdch_interface_t *p_cdc, tusb_desc_endpoint_t const *desc_ep) {
   for (size_t i = 0; i < 2; i++) {
     // pin bLength so tu_desc_next() below cannot walk the second endpoint past a caller-checked bound
-    TU_ASSERT(sizeof(tusb_desc_endpoint_t) == desc_ep->bLength &&
-              TUSB_DESC_ENDPOINT == desc_ep->bDescriptorType && TUSB_XFER_BULK == desc_ep->bmAttributes.xfer, 0);
+    TU_ASSERT(TU_DESC_VALIDATE(sizeof(tusb_desc_endpoint_t) == desc_ep->bLength) &&
+                TUSB_DESC_ENDPOINT == desc_ep->bDescriptorType && TUSB_XFER_BULK == desc_ep->bmAttributes.xfer,
+              0);
     TU_ASSERT(tuh_edpt_open(p_cdc->daddr, desc_ep));
     const uint8_t     ep_dir = tu_edpt_dir(desc_ep->bEndpointAddress);
     tu_edpt_stream_t *stream = (ep_dir == TUSB_DIR_IN) ? &p_cdc->stream.rx : &p_cdc->stream.tx;
@@ -1024,9 +1034,10 @@ static uint16_t acm_open(uint8_t daddr, const tusb_desc_interface_t *itf_desc, u
   // Communication Functional Descriptors
   // need the 3-byte header (bLength/bDescriptorType/bDescriptorSubType) in bounds before reading it, and a
   // bLength >= 3 both keeps those reads valid and stops a zero-length descriptor from spinning the walk
-  while (p_desc + 3 <= desc_end && TUSB_DESC_CS_INTERFACE == tu_desc_type(p_desc) && tu_desc_len(p_desc) >= 3) {
+  while ((p_desc < desc_end) && TU_DESC_VALIDATE(p_desc + 3 <= desc_end) &&
+         TUSB_DESC_CS_INTERFACE == tu_desc_type(p_desc) && TU_DESC_VALIDATE(tu_desc_len(p_desc) >= 3)) {
     if (CDC_FUNC_DESC_ABSTRACT_CONTROL_MANAGEMENT == cdc_functional_desc_typeof(p_desc) &&
-        p_desc + sizeof(cdc_desc_func_acm_t) <= desc_end) {
+        TU_DESC_VALIDATE(p_desc + sizeof(cdc_desc_func_acm_t) <= desc_end)) {
       // save ACM bmCapabilities
       p_cdc->acm.capability = ((cdc_desc_func_acm_t const *) p_desc)->bmCapabilities;
     }
@@ -1037,7 +1048,7 @@ static uint16_t acm_open(uint8_t daddr, const tusb_desc_interface_t *itf_desc, u
   // Open notification endpoint of control interface if any
   if (itf_desc->bNumEndpoints == 1) {
     // whole endpoint descriptor must fit: tuh_edpt_open reads the full struct regardless of bLength
-    TU_ASSERT(p_desc + sizeof(tusb_desc_endpoint_t) <= desc_end, 0);
+    TU_ASSERT(TU_DESC_VALIDATE(p_desc + sizeof(tusb_desc_endpoint_t) <= desc_end), 0);
     TU_ASSERT(TUSB_DESC_ENDPOINT == tu_desc_type(p_desc), 0);
     const tusb_desc_endpoint_t *desc_ep = (const tusb_desc_endpoint_t *)p_desc;
     TU_ASSERT(tuh_edpt_open(daddr, desc_ep), 0);
@@ -1048,14 +1059,15 @@ static uint16_t acm_open(uint8_t daddr, const tusb_desc_interface_t *itf_desc, u
   }
 
   //------------- Data Interface (if any) -------------//
-  if (p_desc + sizeof(tusb_desc_interface_t) <= desc_end && TUSB_DESC_INTERFACE == tu_desc_type(p_desc)) {
+  if (TU_DESC_VALIDATE(p_desc + sizeof(tusb_desc_interface_t) <= desc_end) &&
+      TUSB_DESC_INTERFACE == tu_desc_type(p_desc)) {
     const tusb_desc_interface_t *data_itf = (const tusb_desc_interface_t *)p_desc;
     if (data_itf->bInterfaceClass == TUSB_CLASS_CDC_DATA) {
       p_desc += sizeof(tusb_desc_interface_t); // fixed struct size to endpoint descriptor, not device bLength
 
       // open_ep_stream_pair consumes exactly two endpoints; require that count and that both fit before reading them
-      TU_ASSERT(data_itf->bNumEndpoints == 2, 0);
-      TU_ASSERT(p_desc + 2 * sizeof(tusb_desc_endpoint_t) <= desc_end, 0);
+      TU_ASSERT(TU_DESC_VALIDATE(data_itf->bNumEndpoints == 2), 0);
+      TU_ASSERT(TU_DESC_VALIDATE(p_desc + 2 * sizeof(tusb_desc_endpoint_t) <= desc_end), 0);
       TU_ASSERT(open_ep_stream_pair(p_cdc, (const tusb_desc_endpoint_t *)p_desc), 0);
       p_desc += 2 * sizeof(tusb_desc_endpoint_t);
     }
diff --git a/src/tusb_option.h b/src/tusb_option.h
index e19ee1629..de8439cfb 100644
--- a/src/tusb_option.h
+++ b/src/tusb_option.h
@@ -240,6 +240,15 @@
 #define OPT_MODE_SPEED_MASK     0xff00u
 
 //--------------------------------------------------------------------+
+// Descriptor Validation Level
+// How much the stack hardens itself against mal-configured or hostile devices, traded against code size.
+// Higher levels add more checks; set CFG_TUD_VALIDATION_LEVEL / CFG_TUH_VALIDATION_LEVEL to pick one.
+//--------------------------------------------------------------------+
+#define TUSB_VALIDATION_NONE   0 ///< trusted devices only, minimal code size
+#define TUSB_VALIDATION_BASIC  1 ///< default: mal-configured devices, no OOB reads / zero-length loops
+#define TUSB_VALIDATION_STRICT 2 ///< reject malformed/hostile descriptors, stricter class validation
+
+//--------------------------------------------------------------------+
 // Include tusb_config.h
 //--------------------------------------------------------------------+
 
@@ -694,6 +703,10 @@
   #ifndef CFG_TUH_ENUMERATION_BUFSIZE
     #define CFG_TUH_ENUMERATION_BUFSIZE 256
   #endif
+
+  #ifndef CFG_TUH_VALIDATION_LEVEL
+    #define CFG_TUH_VALIDATION_LEVEL TUSB_VALIDATION_BASIC
+  #endif
 #endif // CFG_TUH_ENABLED
 
 // Attribute to place data in accessible RAM for host controller (default: CFG_TUSB_MEM_SECTION)