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Filename : badname.stp
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#!/usr/bin/stap
# badname.stp
# Prevent the creation of files with undesirable names.
# Source: http://blog.cuviper.com/2009/04/08/hacking-linux-filenames/

# return non-zero if the filename should be blocked
function filter:long (name:string)
{
  return isinstr(name, "XXXbadnameXXX")
}

global squash_inode_permission

# We really want to probe may_create(). But, may_create() is now
# always inlined, and stap can't find its arguments. So, we have to
# probe may_create()'s callers.

probe kernel.{function("vfs_create"), function("vfs_mknod"),
              function("vfs_mkdir"), function("vfs_symlink"),
              function("vfs_link"), function("vfs_rename")}
{
  # screen out the conditions which may_create will fail anyway
  if (@choose_defined($dentry->d_inode, $new_dentry->d_inode)
      || @choose_defined($dir->i_flags, $new_dir->i_flags) & %{ S_DEAD %}) next

  # check that the new file meets our naming rules
  if (filter(kernel_string(@choose_defined($dentry->d_name->name,
					   $new_dentry->d_name->name))))
    squash_inode_permission[tid()] = 1
}

probe kernel.function("inode_permission@fs/namei.c").return !,
      kernel.function("permission@fs/namei.c").return
{
  if (!$return && squash_inode_permission[tid()])
    $return = -13 # -EACCES (Permission denied)
  delete squash_inode_permission[tid()]
}