improve pointer arithmetic, check funmctional descriptor bLength

Signed-off-by: HiFiPhile <[email protected]>

1 files changed, 10 insertions, 7 deletions

diff --git a/src/class/cdc/cdc_host.c b/src/class/cdc/cdc_host.c
index d1cbc2924..f697c0e73 100644
--- a/src/class/cdc/cdc_host.c
+++ b/src/class/cdc/cdc_host.c
@@ -1024,6 +1024,8 @@ static uint16_t acm_open(uint8_t daddr, const tusb_desc_interface_t *itf_desc, u
   const uint8_t *p_desc   = (const uint8_t *)itf_desc;
   const uint8_t *desc_end = p_desc + max_len;
 
+  TU_ASSERT(TU_DESC_VALIDATE(tu_desc_len(p_desc) <= max_len), 0);
+
   cdch_interface_t *p_cdc = make_new_itf(daddr, itf_desc);
   TU_VERIFY(p_cdc, 0);
   p_cdc->serial_drid = SERIAL_DRIVER_ACM;
@@ -1033,11 +1035,12 @@ 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 < 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)) {
+  // fully contained bLength >= 3 both keeps those reads valid and stops a zero-length descriptor from spinning
+  while ((p_desc < desc_end) && TU_DESC_VALIDATE((size_t)(desc_end - p_desc) >= 3) &&
+    TUSB_DESC_CS_INTERFACE == tu_desc_type(p_desc) && TU_DESC_VALIDATE(tu_desc_len(p_desc) >= 3) &&
+         TU_DESC_VALIDATE(tu_desc_len(p_desc) <= (size_t)(desc_end - p_desc))) {
     if (CDC_FUNC_DESC_ABSTRACT_CONTROL_MANAGEMENT == cdc_functional_desc_typeof(p_desc) &&
-        TU_DESC_VALIDATE(p_desc + sizeof(cdc_desc_func_acm_t) <= desc_end)) {
+        TU_DESC_VALIDATE(tu_desc_len(p_desc) >= sizeof(cdc_desc_func_acm_t))) {
       // save ACM bmCapabilities
       p_cdc->acm.capability = ((cdc_desc_func_acm_t const *) p_desc)->bmCapabilities;
     }
@@ -1048,7 +1051,7 @@ 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(TU_DESC_VALIDATE(p_desc + sizeof(tusb_desc_endpoint_t) <= desc_end), 0);
+    TU_ASSERT(TU_DESC_VALIDATE((size_t)(desc_end - p_desc) >= sizeof(tusb_desc_endpoint_t)), 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);
@@ -1059,7 +1062,7 @@ static uint16_t acm_open(uint8_t daddr, const tusb_desc_interface_t *itf_desc, u
   }
 
   //------------- Data Interface (if any) -------------//
-  if (TU_DESC_VALIDATE(p_desc + sizeof(tusb_desc_interface_t) <= desc_end) &&
+  if (TU_DESC_VALIDATE((size_t)(desc_end - p_desc) >= sizeof(tusb_desc_interface_t)) &&
       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) {
@@ -1067,7 +1070,7 @@ static uint16_t acm_open(uint8_t daddr, const tusb_desc_interface_t *itf_desc, u
 
       // open_ep_stream_pair consumes exactly two endpoints; require that count and that both fit before reading them
       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(TU_DESC_VALIDATE((size_t)(desc_end - p_desc) >= 2 * sizeof(tusb_desc_endpoint_t)), 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);
     }