system: resmonitor: check CPU load reads

Keep the default zero CPU value when the procfs load file cannot be read, and trim only the newline that was actually present. This avoids parsing uninitialized stack data in fillcpu and avoids writing before the showinfo CPU buffer when fgets returns no data.

Signed-off-by: Old-Ding <35417409+Old-Ding@users.noreply.github.com>

system/resmonitor/fillcpu.c

@@ -97,8 +97,11 @@ static float get_cpu(int pid)
     }
 
   char buf[8];
-  fgets(buf, 8, fp);
-  sscanf(buf, "%f", &cpu);
+  if (fgets(buf, 8, fp) != NULL)
+    {
+      sscanf(buf, "%f", &cpu);
+    }
+
   fclose(fp);
   return cpu;
 }

system/resmonitor/showinfo.c

@@ -131,11 +131,16 @@ static void get_cpu(int pid, char *buf)
       return;
     }
 
-  fgets(buf, 8, fp);
+  if (fgets(buf, 8, fp) == NULL)
+    {
+      snprintf(buf, 8, "%.1f%%", 0.0);
+      fclose(fp);
+      return;
+    }
 
   /* sscanf(buf, "%f", &cpu); */
 
-  buf[strlen(buf) - 1] = '\0';
+  buf[strcspn(buf, "\n")] = '\0';
   fclose(fp);
 }