png_do_read_filler(png_row_infop row_info, png_bytep row,
   png_uint_32 filler, png_uint_32 flags)
{
   png_uint_32 i;
   png_uint_32 row_width = row_info->width;

   png_byte hi_filler = (png_byte)((filler>>8) & 0xff);
   png_byte lo_filler = (png_byte)(filler & 0xff);

   png_debug(1, "in png_do_read_filler");

   if (
#ifdef PNG_USELESS_TESTS_SUPPORTED
       row != NULL  && row_info != NULL &&
#endif
       row_info->color_type == PNG_COLOR_TYPE_GRAY)
   {
      if (row_info->bit_depth == 8)
      {
         /* This changes the data from G to GX */
         if (flags & PNG_FLAG_FILLER_AFTER)
         {
            png_bytep sp = row + (png_size_t)row_width;
            png_bytep dp =  sp + (png_size_t)row_width;
            for (i = 1; i < row_width; i++)
            {
               *(--dp) = lo_filler;
               *(--dp) = *(--sp);
            }
            *(--dp) = lo_filler;
            row_info->channels = 2;
            row_info->pixel_depth = 16;
            row_info->rowbytes = row_width * 2;
         }
      /* This changes the data from G to XG */
         else
         {
            png_bytep sp = row + (png_size_t)row_width;
            png_bytep dp = sp  + (png_size_t)row_width;
            for (i = 0; i < row_width; i++)
            {
               *(--dp) = *(--sp);
               *(--dp) = lo_filler;
            }
            row_info->channels = 2;
            row_info->pixel_depth = 16;
            row_info->rowbytes = row_width * 2;
         }
      }
      else if (row_info->bit_depth == 16)
      {
         /* This changes the data from GG to GGXX */
         if (flags & PNG_FLAG_FILLER_AFTER)
         {
            png_bytep sp = row + (png_size_t)row_width * 2;
            png_bytep dp = sp  + (png_size_t)row_width * 2;
            for (i = 1; i < row_width; i++)
            {
               *(--dp) = hi_filler;
               *(--dp) = lo_filler;
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
            }
            *(--dp) = hi_filler;
            *(--dp) = lo_filler;
            row_info->channels = 2;
            row_info->pixel_depth = 32;
            row_info->rowbytes = row_width * 4;
         }
         /* This changes the data from GG to XXGG */
         else
         {
            png_bytep sp = row + (png_size_t)row_width * 2;
            png_bytep dp = sp  + (png_size_t)row_width * 2;
            for (i = 0; i < row_width; i++)
            {
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = hi_filler;
               *(--dp) = lo_filler;
            }
            row_info->channels = 2;
            row_info->pixel_depth = 32;
            row_info->rowbytes = row_width * 4;
         }
      }
   } /* COLOR_TYPE == GRAY */
   else if (row_info->color_type == PNG_COLOR_TYPE_RGB)
   {
      if (row_info->bit_depth == 8)
      {
         /* This changes the data from RGB to RGBX */
         if (flags & PNG_FLAG_FILLER_AFTER)
         {
            png_bytep sp = row + (png_size_t)row_width * 3;
            png_bytep dp = sp  + (png_size_t)row_width;
            for (i = 1; i < row_width; i++)
            {
               *(--dp) = lo_filler;
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
            }
            *(--dp) = lo_filler;
            row_info->channels = 4;
            row_info->pixel_depth = 32;
            row_info->rowbytes = row_width * 4;
         }
      /* This changes the data from RGB to XRGB */
         else
         {
            png_bytep sp = row + (png_size_t)row_width * 3;
            png_bytep dp = sp + (png_size_t)row_width;
            for (i = 0; i < row_width; i++)
            {
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = lo_filler;
            }
            row_info->channels = 4;
            row_info->pixel_depth = 32;
            row_info->rowbytes = row_width * 4;
         }
      }
      else if (row_info->bit_depth == 16)
      {
         /* This changes the data from RRGGBB to RRGGBBXX */
         if (flags & PNG_FLAG_FILLER_AFTER)
         {
            png_bytep sp = row + (png_size_t)row_width * 6;
            png_bytep dp = sp  + (png_size_t)row_width * 2;
            for (i = 1; i < row_width; i++)
            {
               *(--dp) = hi_filler;
               *(--dp) = lo_filler;
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
            }
            *(--dp) = hi_filler;
            *(--dp) = lo_filler;
            row_info->channels = 4;
            row_info->pixel_depth = 64;
            row_info->rowbytes = row_width * 8;
         }
         /* This changes the data from RRGGBB to XXRRGGBB */
         else
         {
            png_bytep sp = row + (png_size_t)row_width * 6;
            png_bytep dp = sp  + (png_size_t)row_width * 2;
            for (i = 0; i < row_width; i++)
            {
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = hi_filler;
               *(--dp) = lo_filler;
            }
            row_info->channels = 4;
            row_info->pixel_depth = 64;
            row_info->rowbytes = row_width * 8;
         }
      }
   } /* COLOR_TYPE == RGB */
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.