grub_ext2_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
{
  struct grub_ext2_data *data = node->data;
  struct grub_ext2_inode *inode = &node->inode;
  int blknr = -1;
  unsigned int blksz = EXT2_BLOCK_SIZE (data);
  int log2_blksz = LOG2_EXT2_BLOCK_SIZE (data);
 
   if (grub_le_to_cpu32(inode->flags) & EXT4_EXTENTS_FLAG)
     {
#ifndef _MSC_VER
	  char buf[EXT2_BLOCK_SIZE (data)];
#else
	  char * buf = grub_malloc (EXT2_BLOCK_SIZE(data));
#endif
       struct grub_ext4_extent_header *leaf;
       struct grub_ext4_extent *ext;
       int i;

      leaf = grub_ext4_find_leaf (data, buf,
		  (struct grub_ext4_extent_header *) inode->blocks.dir_blocks,
		  fileblock);
       if (! leaf)
         {
           grub_error (GRUB_ERR_BAD_FS, "invalid extent");
           return -1;
         }
 
      ext = (struct grub_ext4_extent *) (leaf + 1);
      for (i = 0; i < grub_le_to_cpu16 (leaf->entries); i++)
        {
          if (fileblock < grub_le_to_cpu32 (ext[i].block))
            break;
        }

       if (--i >= 0)
         {
           fileblock -= grub_le_to_cpu32 (ext[i].block);
          if (fileblock >= grub_le_to_cpu16 (ext[i].len))
             return 0;
          else
             {
               grub_disk_addr_t start;
 
               start = grub_le_to_cpu16 (ext[i].start_hi);
               start = (start << 32) + grub_le_to_cpu32 (ext[i].start);
 
               return fileblock + start;
             }
         }
       else
         {
           grub_error (GRUB_ERR_BAD_FS, "something wrong with extent");
           return -1;
         }
     }
   /* Direct blocks.  */
   if (fileblock < INDIRECT_BLOCKS) {
    blknr = grub_le_to_cpu32 (inode->blocks.dir_blocks[fileblock]);
  /* Indirect.  */
  } else if (fileblock < INDIRECT_BLOCKS + blksz / 4)
    {
       grub_uint32_t *indir;
 
       indir = grub_malloc (blksz);
      if (! indir)
 	return grub_errno;
 
       if (grub_disk_read (data->disk,
 			  ((grub_disk_addr_t)
 			   grub_le_to_cpu32 (inode->blocks.indir_block))
 			  << log2_blksz,
			  0, blksz, indir))
 	return grub_errno;
 
       blknr = grub_le_to_cpu32 (indir[fileblock - INDIRECT_BLOCKS]);
       grub_free (indir);
    }
  /* Double indirect.  */
  else if (fileblock < (grub_disk_addr_t)(INDIRECT_BLOCKS + blksz / 4) \
		  * (grub_disk_addr_t)(blksz / 4 + 1))
    {
      unsigned int perblock = blksz / 4;
      unsigned int rblock = fileblock - (INDIRECT_BLOCKS
					 + blksz / 4);
       grub_uint32_t *indir;
 
       indir = grub_malloc (blksz);
      if (! indir)
 	return grub_errno;
 
       if (grub_disk_read (data->disk,
 			  ((grub_disk_addr_t)
 			   grub_le_to_cpu32 (inode->blocks.double_indir_block))
 			  << log2_blksz,
			  0, blksz, indir))
 	return grub_errno;
 
       if (grub_disk_read (data->disk,
 			  ((grub_disk_addr_t)
 			   grub_le_to_cpu32 (indir[rblock / perblock]))
 			  << log2_blksz,
			  0, blksz, indir))
 	return grub_errno;
 
       blknr = grub_le_to_cpu32 (indir[rblock % perblock]);
             grub_free (indir);
    }
  /* triple indirect.  */
  else
    {
      grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
		  "ext2fs doesn't support triple indirect blocks");
    }

  return blknr;
}

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.