Perl is designed to make it easy to program securely even when running
with extra privileges, like setuid or setgid programs. Unlike most
-command-line shells, which are based on multiple substitution passes on
+command line shells, which are based on multiple substitution passes on
each line of the script, Perl uses a more conventional evaluation scheme
with fewer hidden snags. Additionally, because the language has more
-built-in functionality, it can rely less upon external (and possibly
+builtin functionality, it can rely less upon external (and possibly
untrustworthy) programs to accomplish its purposes.
Perl automatically enables a set of special security checks, called I<taint
program more secure than the corresponding C program.
You may not use data derived from outside your program to affect something
-else outside your program--at least, not by accident. All command-line
+else outside your program--at least, not by accident. All command line
arguments, environment variables, locale information (see L<perllocale>),
and file input are marked as "tainted". Tainted data may not be used
directly or indirectly in any command that invokes a sub-shell, nor in any
$path = $ENV{'PATH'}; # $path now tainted
- $ENV{'PATH'} = '/bin:/usr/bin';
+ $ENV{'PATH'} = '/bin:/usr/bin';
$ENV{'IFS'} = '' if $ENV{'IFS'} ne '';
$path = $ENV{'PATH'}; # $path now NOT tainted
If you try to do something insecure, you will get a fatal error saying
something like "Insecure dependency" or "Insecure PATH". Note that you
can still write an insecure B<system> or B<exec>, but only by explicitly
-doing something like the last example above.
+doing something like the last example above.
=head2 Laundering and Detecting Tainted Data
I<is_tainted()> function.
sub is_tainted {
- return ! eval {
- join('',@_), kill 0;
- 1;
+ return ! eval {
+ join('',@_), kill 0;
+ 1;
};
}
But testing for taintedness gets you only so far. Sometimes you have just
to clear your data's taintedness. The only way to bypass the tainting
-mechanism is by referencing sub-patterns from a regular expression match.
+mechanism is by referencing subpatterns from a regular expression match.
Perl presumes that if you reference a substring using $1, $2, etc., that
you knew what you were doing when you wrote the pattern. That means using
a bit of thought--don't just blindly untaint anything, or you defeat the
characters (alphabetics, numerics, and underscores), a hyphen, an at sign,
or a dot.
- if ($data =~ /^([-\@\w.]+)$/) {
+ if ($data =~ /^([-\@\w.]+)$/) {
$data = $1; # $data now untainted
} else {
die "Bad data in $data"; # log this somewhere
When you make a script executable, in order to make it usable as a
command, the system will pass switches to perl from the script's #!
-line. Perl checks that any command-line switches given to a setuid
+line. Perl checks that any command line switches given to a setuid
(or setgid) script actually match the ones set on the #! line. Some
-UNIX and UNIX-like environments impose a one-switch limit on the #!
+Unix and Unix-like environments impose a one-switch limit on the #!
line, so you may need to use something like C<-wU> instead of C<-w -U>
-under such systems. (This issue should arise only in UNIX or
-UNIX-like environments that support #! and setuid or setgid scripts.)
+under such systems. (This issue should arise only in Unix or
+Unix-like environments that support #! and setuid or setgid scripts.)
=head2 Cleaning Up Your Path
you didn't set it to something that was safe. Because Perl can't
guarantee that the executable in question isn't itself going to turn
around and execute some other program that is dependent on your PATH, it
-makes sure you set the PATH.
+makes sure you set the PATH.
It's also possible to get into trouble with other operations that don't
care whether they use tainted values. Make judicious use of the file
Perl does not call the shell to expand wild cards when you pass B<system>
and B<exec> explicit parameter lists instead of strings with possible shell
wildcards in them. Unfortunately, the B<open>, B<glob>, and
-back-tick functions provide no such alternate calling convention, so more
-subterfuge will be required.
+backtick functions provide no such alternate calling convention, so more
+subterfuge will be required.
Perl provides a reasonably safe way to open a file or pipe from a setuid
or setgid program: just create a child process with reduced privilege who
under less privilege than the parent, it's not apt to be tricked into
doing something it shouldn't.
-Here's a way to do back-ticks reasonably safely. Notice how the B<exec> is
+Here's a way to do backticks reasonably safely. Notice how the B<exec> is
not called with a string that the shell could expand. This is by far the
best way to call something that might be subjected to shell escapes: just
never call the shell at all. By the time we get to the B<exec>, tainting
is turned off, however, so be careful what you call and what you pass it.
- use English;
+ use English;
die unless defined $pid = open(KID, "-|");
if ($pid) { # parent
while (<KID>) {
latter is true, Perl can emulate the setuid and setgid mechanism when it
notices the otherwise useless setuid/gid bits on Perl scripts. It does
this via a special executable called B<suidperl> that is automatically
-invoked for you if it's needed.
+invoked for you if it's needed.
However, if the kernel setuid script feature isn't disabled, Perl will
complain loudly that your setuid script is insecure. You'll need to
in C:
#define REAL_PATH "/path/to/script"
- main(ac, av)
+ main(ac, av)
char **av;
{
execv(REAL_PATH, av);
- }
+ }
-Compile this wrapper into a binary executable and then make I<it> rather
-than your script setuid or setgid.
+Compile this wrapper into a binary executable and then make I<it> rather
+than your script setuid or setgid.
See the program B<wrapsuid> in the F<eg> directory of your Perl
distribution for a convenient way to do this automatically for all your
You can try using encryption via source filters (Filter::* from CPAN).
But crackers might be able to decrypt it. You can try using the
-byte-code compiler and interpreter described below, but crackers might
+byte code compiler and interpreter described below, but crackers might
be able to de-compile it. You can try using the native-code compiler
described below, but crackers might be able to disassemble it. These
pose varying degrees of difficulty to people wanting to get at your
projects / p5sagit/p5-mst-13.2.git / blobdiff