sched/clock Add special handling for TCB null pointer cases

Adding a judgment in the code that null return values are not referenced for dereference

Signed-off-by: zhuanglin <zhuanglin@xiaomi.com>

sched/clock/clock_gettime.c

@@ -153,8 +153,15 @@ int clock_gettime(clockid_t clock_id, struct timespec *tp)
           tcb = nxsched_get_tcb(pid);
         }
 
+      if (tcb != NULL)
+        {
           up_perf_convert(tcb->run_time, tp);
         }
+      else
+        {
+          ret = -EFAULT;
+        }
+    }
   else if (clock_type == CLOCK_PROCESS_CPUTIME_ID)
     {
       FAR struct task_group_s *group;
@@ -174,6 +181,8 @@ int clock_gettime(clockid_t clock_id, struct timespec *tp)
           tcb = nxsched_get_tcb(pid);
         }
 
+      if (tcb != NULL)
+        {
           group = tcb->group;
           runtime = 0;
 
@@ -181,12 +190,20 @@ int clock_gettime(clockid_t clock_id, struct timespec *tp)
           for (i = group->tg_nmembers - 1; i >= 0; i--)
             {
               tcb = nxsched_get_tcb(group->tg_members[i]);
+              if (tcb != NULL)
+                {
                   runtime += tcb->run_time;
                 }
+            }
 
           leave_critical_section(flags);
           up_perf_convert(runtime, tp);
         }
+      else
+        {
+          ret = -EFAULT;
+        }
+    }
 #endif
   else
     {