create_surface_from_thumbnail_data (guchar *data,
				    gint    width,
				    gint    height,
 				    gint    rowstride)
 {
   guchar *cairo_pixels;
   cairo_surface_t *surface;
  static cairo_user_data_key_t key;
   int j;
 
  cairo_pixels = (guchar *)g_malloc (4 * width * height);
  surface = cairo_image_surface_create_for_data ((unsigned char *)cairo_pixels,
						 CAIRO_FORMAT_RGB24,
						 width, height, 4 * width);
  cairo_surface_set_user_data (surface, &key,
			       cairo_pixels, (cairo_destroy_func_t)g_free);
 
   for (j = height; j; j--) {
     guchar *p = data;
     guchar *q = cairo_pixels;
     guchar *end = p + 3 * width;
     while (p < end) {
 #if G_BYTE_ORDER == G_LITTLE_ENDIAN
       q[0] = p[2];
       q[1] = p[1];
       q[2] = p[0];
#else	  
       q[1] = p[0];
       q[2] = p[1];
       q[3] = p[2];
#endif
      p += 3;
      q += 4;
     }
 
     data += rowstride;
    cairo_pixels += 4 * width;
   }
 
   return surface;
}

This weakness involves numeric computation errors, such as integer overflows, underflows, or precision losses, which can lead to miscalculations and exploitable behaviors in software.