Update sdu_lenP to uint32_t in get_mac_len

Add check in lcid_crnti_lookahead to ensure subtraction to pdu_len doesn't cause an underflow

openair2/LAYER2/NR_MAC_COMMON/nr_mac.h

@@ -107,12 +107,13 @@ typedef struct {
   uint8_t R: 2;       // octet 1 [7:6]
 } __attribute__ ((__packed__)) NR_MAC_SUBHEADER_FIXED;
 
-static inline int get_mac_len(uint8_t* pdu, int pdu_len, uint16_t *mac_ce_len, uint16_t *mac_subheader_len) {
-  if ( pdu_len < (int)sizeof(NR_MAC_SUBHEADER_SHORT))
+static inline int get_mac_len(uint8_t *pdu, uint32_t pdu_len, uint16_t *mac_ce_len, uint16_t *mac_subheader_len)
+{
+  if (pdu_len < sizeof(NR_MAC_SUBHEADER_SHORT))
     return false;
-  NR_MAC_SUBHEADER_SHORT *s = (NR_MAC_SUBHEADER_SHORT*) pdu;
-  NR_MAC_SUBHEADER_LONG *l = (NR_MAC_SUBHEADER_LONG*) pdu;
-  if (s->F && pdu_len < (int)sizeof(NR_MAC_SUBHEADER_LONG))
+  NR_MAC_SUBHEADER_SHORT *s = (NR_MAC_SUBHEADER_SHORT *)pdu;
+  NR_MAC_SUBHEADER_LONG *l = (NR_MAC_SUBHEADER_LONG *)pdu;
+  if (s->F && pdu_len < sizeof(NR_MAC_SUBHEADER_LONG))
     return false;
   if (s->F) {
     *mac_subheader_len = sizeof(*l);
@@ -123,7 +124,7 @@ static inline int get_mac_len(uint8_t* pdu, int pdu_len, uint16_t *mac_ce_len, u
   }
   return true;
 }
-    
+
 // BSR MAC CEs
 // TS 38.321 ch. 6.1.3.1
 // Short BSR for a specific logical channel group ID

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_ulsch.c

@@ -55,7 +55,13 @@ static rnti_t lcid_crnti_lookahead(uint8_t *pdu, uint32_t pdu_len)
       break;
     }
     pdu += mac_len + mac_subheader_len;
-    pdu_len -= mac_len + mac_subheader_len;
+    // if pdu_len can have the value subtracted without underflow, we can subtract
+    if (pdu_len >= mac_len + mac_subheader_len) {
+      pdu_len -= mac_len + mac_subheader_len;
+    } else {
+      // if not, set to 0 to prevent underflow
+      pdu_len = 0;
+    }
   }
   return 0;
 }