NAME

       Taint::Runtime - Runtime enable taint checking

SYNOPSIS

         ### sample "enable" usage

         #!/usr/bin/perl -w
         use Taint::Runtime qw(enable taint_env);
         taint_env();
         # having the keyword enable in the import list starts taint

         ### sample $TAINT usage

         #!/usr/bin/perl -w
         use Taint::Runtime qw($TAINT taint_env);
         $TAINT = 1;
         taint_env();

         # taint is now enabled

         if (1) {
           local $TAINT = 0;

           # do something we trust
         }

         # back to an untrustwory area

         ### sample functional usage

         #!/usr/bin/perl -w
         use strict;
         use Taint::Runtime qw(taint_start is_tainted taint_env
                               taint untaint
                               taint_enabled);

         ### other operations here

         taint_start(); # taint should become active
         taint_env(); # %ENV was previously untainted

         print taint_enabled() ? "enabled\n" : "not enabled\n";

         my $var = taint("some string");

         print is_tainted($var) ? "tainted\n" : "not tainted\n";

         $var = untaint($var);
         # OR
         untaint \$var;

         print is_tainted($var) ? "tainted\n" : "not tainted\n";

DESCRIPTION

       First - you probably shouldn't use this module to control taint.  You should probably use the -T switch
       on the commandline instead.  There are a somewhat limited number of legitimate use cases where you should
       use this module instead of the -T switch.  Unless you have a specific and good reason for not using the
       -T option, you should use the -T option.

       Taint is a good thing.  However, few people (that I work with or talk to or discuss items with) use taint
       even though they should.  The goal of this module isn't to use taint less, but to actually encourage its
       use more.  This module aims to make using taint as painless as possible (This can be an argument against
       it - often implementation of security implies pain - so taking away pain might lessen security - sort
       of).

       In general - the more secure your script needs to be - the earlier on in your program that tainting
       should be enabled.  For most setuid scripts, you should enable taint by using the -T switch.  Without
       doing so you allow for a non-root user to override @INC which allows for them to put their own module in
       the place of trusted modules.  This is bad.  This is very bad.  Use the -T switch.

       There are some common places where this module may be useful, and where most people don't use it.  One
       such place is in a web server.  The -T switch removes PERL5LIB and PERLLIB and '.' from @INC (or remove
       them before they can be added).  This makes sense under setuid.  The use of the -T switch in a CGI
       environment may cause a bit of a headache.  For new development, CGI scripts it may be possible to use
       the -T switch and for mod_perl environments there is the PerlTaint variable.  Both of these methods will
       enable taint and from that point on development should be done with taint.

       However, many (possibly most) perl web server implentations add their own paths to the PERL5LIB.  All
       CGI's and mod_perl scripts can then have access.  Using the -T switch throws a wrench into the works as
       suddenly PERL5LIB disappears (mod_perl can easily have the extra directories added again using <perl>push
       @INC, '/our/lib/dir';</perl>).  The company I work for has 200 plus user visible scripts mixed with some
       mod_perl.  Currently none of the scripts use taint.  We would like for them all to, but it is not
       feasible to make the change all at once.  Taint::Runtime allows for moving legacy scripts over one at a
       time.

       Again, if you are using setuid - don't use this script.

       If you are not using setuid and have reasons not to use the -T and are using this module, make sure that
       taint is enabled before processing any user data.  Also remember that BECAUSE THE -T SWITCH WAS NOT USED
       %ENV IS INITIALLY NOT MARKED AS TAINTED.  Call taint_env() to mark it as tainted (especially important in
       CGI scripts which all read from $ENV{'QUERY_STRING'}).

       If you are not using the -T switch, you most likely should use the following at the very top of your
       script:

         #!/usr/bin/perl -w

         use strict;
         use Taint::Runtime qw(enable taint_env);
         taint_env();

       Though this module allows for you to turn taint off - you probably shouldn't.  This module is more for
       you to turn taint on - and once it is on it probably ought to stay on.

NON-EXPORTABLE XS FUNCTIONS

       The following very basic functions provide the base functionality.

       _taint_start()
           Sets PL_tainting

       _taint_stop()
           Sets PL_tainting

       _taint_enabled()
           View of PL_tainting

       _tainted()
           Returns a zero length tainted string.

$TAINT VARIABLE

       The variable $TAINT is tied to the current state of taint.  If $TAINT is set to 0 taint mode is off.
       When it is set to 1 taint mode is enabled.

         if (1) {
           local $TAINT = 1;

           # taint is enabled
         }

EXPORT FUNCTIONS

       enable/disable
           Not really functions.  If these keywords are in the import list, taint will be either enabled or
           disabled.

       taint_start
           Start taint mode.  $TAINT will equal 1.

       taint_stop
           Stop taint mode.  $TAINT will equal 0.

       taint_env
           Convenience function that taints the keys and values of %ENV.  If the -T switch was not used - you
           most likely should call this as soon as taint mode is enabled.

       taint
           Taints the passed in variable.  Only works on writeable scalar values.  If a scalar ref is passed in
           - it is modified.  If a scalar is passed in (non ref) it is copied, modified and returned.  If a
           value was undefined, it becomes a zero length defined and tainted string.

             taint(\$var_to_be_tainted);

             my $tainted_copy = taint($some_var);

           For a stronger taint, see the Taint module by Dan Sulgalski which is capable of tainting most types
           of data.

       untaint
           Untaints the passed in variable.  Only works on writeable scalar values.  If a scalar ref is passed
           in - it is modified.  If a scalar is passed in (non ref) it is copied, modified and returned.  If a
           value was undefined it becomes an untainted undefined value.

           Note:  Just because the variable is untainted, doesn't mean that it is safe.  You really should use
           CGI::Ex::Validate, or Data::FormValidator or any of the Untaint:: modules.  If you are doing your own
           validation, and once you have put the user data through very strict checks, then you can use untaint.

             if ($var_to_be_untainted =~ /^[\w\.\-]{0,100}$/) {
               untaint(\$var_to_be_untainted);
             }

             my $untainted_copy = untaint($some_var);

       taint_enabled
           Boolean - Is taint on.

       tainted
           Returns a zero length tainted string.

       is_tainted
           Boolean - True if the passed value is tainted.

       taint_deeply
           Convenience function that attempts to deply recurse a structure and mark it as tainted.  Takes a
           hashref, arrayref, scalar ref, or scalar and recursively untaints the structure.

           For a stronger taint, see the Taint module by Dan Sulgalski which is capable of tainting most types
           of data.

TURNING TAINT ON

       (Be sure to call taint_env() after turning taint on the first time)

         #!/usr/bin/perl -T

         use Taint::Runtime qw(enable);
         # this does not create a function called enable - just starts taint

         use Taint::Runtime qw($TAINT);
         $TAINT = 1;

         use Taint::Runtime qw(taint_start);
         taint_start;

TURNING TAINT OFF

         use Taint::Runtime qw(disable);
         # this does not create a function called disable - just stops taint

         use Taint::Runtime qw($TAINT);
         $TAINT = 0;

         use Taint::Runtime qw(taint_stop);
         taint_stop;

CREDITS

       C code was provided by "hv" on perlmonks.  This module wouldn't really be possible without insight into
       the internals that "hv" provided.  His post with the code was shown in this node on perlmonks:

         http://perlmonks.org/?node_id=434086

       The basic premise in that node was the following code:

         use Inline C => 'void _start_taint() { PL_tainting = 1; }';
         use Inline C => 'SV* _tainted() { PL_tainted = 1; return newSVpvn("", 0); }';

       In this module, these two lines have instead been turned into XS for runtime speed (and so you won't need
       Inline and Parse::RecDescent).

       Note: even though "hv" provided the base code example, that doesn't mean that he necessarily endorses the
       idea.  If there are disagreements, quirks, annoyances or any other negative side effects with this module
       - blame me - not "hv."

THANKS

       Thanks to Alexey A. Kiritchun for pointing out untaint failure on multiline strings.

AUTHOR

       Paul Seamons (2005)

       C stub functions by "hv" on perlmonks.org

LICENSE

       This module may be used and distributed under the same terms as Perl itself.