zexec - decompress and execute a compressed binary

     zexec decompressor executable [arg...]

     Zexec decompresses and executes a compressed binary.   It  does  this  by
     calling  decompressor  to  uncompress executable to a file in /tmp and by
     calling the  result  with  the  other  arguments  given  to  zexec.   The
     temporary file is removed immediately after startup.

     Zexec checks if the first two bytes of the compressed file are the  magic
     characters  #!.   If so then the first line of the file is skipped before
     it is decompressed.  This allows a utility like install(1)  to  create  a
     compressed executable with a first line that looks like this:

          #!/usr/bin/zexec /usr/bin/zcat

     The kernel recognizes this as a  request  to  run  /usr/bin/zexec  as  an
     interpreter for the file, just like it runs shell scripts that start with
     #!/bin/sh.  The compressed executable can  thus  be  used  transparently,
     without  the  user  knowing  that it is compressed.  The only clue is the
     slower startup time.


     A setuid compressed executable works as required, but setuid  #!  scripts
     are inheritely insecure.  It is trivial to misuse such a script to make a
     setuid shell.

     Kees J. Bot (kjb@cs.vu.nl)