X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlsec.pod;h=1c2dbd266d47e819b6cf12e262647a92e6596126;hb=890ed176d1ab1cf305ce9634210857cfed305fff;hp=87d1f7b3402ad15b99ccf135da4dbb6a00699fb9;hpb=ee556d553a6eff7ecdc9231bcb7bcb56f26130e7;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/pod/perlsec.pod b/pod/perlsec.pod
index 87d1f7b..1c2dbd2 100644
--- a/pod/perlsec.pod
+++ b/pod/perlsec.pod
@@ -44,12 +44,24 @@ directories, or processes, B<with the following exceptions>:
 
 =item *
 
-If you pass more than one argument to either C<system> or C<exec>,
-the arguments are B<not> checked for taintedness.
+Arguments to C<print> and C<syswrite> are B<not> checked for taintedness.
 
 =item *
 
-Arguments to C<print> and C<syswrite> are B<not> checked for taintedness.
+Symbolic methods
+
+    $obj->$method(@args);
+
+and symbolic sub references
+
+    &{$foo}(@args);
+    $foo->(@args);
+
+are not checked for taintedness.  This requires extra carefulness
+unless you want external data to affect your control flow.  Unless
+you carefully limit what these symbolic values are, people are able
+to call functions B<outside> your Perl code, such as POSIX::system,
+in which case they are able to run arbitrary external code.
 
 =back
 
@@ -72,7 +84,8 @@ For example:
     $data = 'abc';		# Not tainted
 
     system "echo $arg";		# Insecure
-    system "/bin/echo", $arg;	# Secure (doesn't use sh)
+    system "/bin/echo", $arg;	# Considered insecure
+				# (Perl doesn't know about /bin/echo)
     system "echo $hid";		# Insecure
     system "echo $data";	# Insecure until PATH set
 
@@ -87,18 +100,18 @@ For example:
     open(FOO, "< $arg");	# OK - read-only file
     open(FOO, "> $arg"); 	# Not OK - trying to write
 
-    open(FOO,"echo $arg|");	# Not OK, but...
+    open(FOO,"echo $arg|");	# Not OK
     open(FOO,"-|")
-	or exec 'echo', $arg;	# OK
+	or exec 'echo', $arg;	# Also not OK
 
     $shout = `echo $arg`;	# Insecure, $shout now tainted
 
     unlink $data, $arg;		# Insecure
     umask $arg;			# Insecure
 
-    exec "echo $arg";		# Insecure (uses the shell)
-    exec "echo", $arg;		# Secure (doesn't use the shell)
-    exec "sh", '-c', $arg;	# Considered secure, alas!
+    exec "echo $arg";		# Insecure
+    exec "echo", $arg;		# Insecure
+    exec "sh", '-c', $arg;	# Very insecure!
 
     @files = <*.c>;		# insecure (uses readdir() or similar)
     @files = glob('*.c');	# insecure (uses readdir() or similar)
@@ -112,9 +125,7 @@ For example:
     $arg, `true`;		# Insecure (although it isn't really)
 
 If you try to do something insecure, you will get a fatal error saying
-something like "Insecure dependency" or "Insecure $ENV{PATH}".  Note that you
-can still write an insecure B<system> or B<exec>, but only by explicitly
-doing something like the "considered secure" example above.
+something like "Insecure dependency" or "Insecure $ENV{PATH}".
 
 =head2 Laundering and Detecting Tainted Data
 
@@ -125,10 +136,7 @@ nearby CPAN mirror, and included in Perl starting from the release 5.8.0.
 Or you may be able to use the following I<is_tainted()> function.
 
     sub is_tainted {
-	return ! eval {
-	    join('',@_), kill 0;
-	    1;
-	};
+        return ! eval { eval("#" . substr(join("", @_), 0, 0)); 1 };
     }
 
 This function makes use of the fact that the presence of tainted data
@@ -156,7 +164,7 @@ or a dot.
     if ($data =~ /^([-\@\w.]+)$/) {
 	$data = $1; 			# $data now untainted
     } else {
-	die "Bad data in $data"; 	# log this somewhere
+	die "Bad data in '$data'"; 	# log this somewhere
     }
 
 This is fairly secure because C</\w+/> doesn't normally match shell
@@ -240,7 +248,7 @@ 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.  
 
-        use English;
+        use English '-no_match_vars';
         die "Can't fork: $!" unless defined($pid = open(KID, "-|"));
         if ($pid) {           # parent
             while (<KID>) {
@@ -371,6 +379,13 @@ Your access to it does not give you permission to use it blah blah
 blah."  You should see a lawyer to be sure your licence's wording will
 stand up in court.
 
+=head2 Unicode
+
+Unicode is a new and complex technology and one may easily overlook
+certain security pitfalls.  See L<perluniintro> for an overview and
+L<perlunicode> for details, and L<perlunicode/"Security Implications
+of Unicode"> for security implications in particular.
+
 =head1 SEE ALSO
 
 L<perlrun> for its description of cleaning up environment variables.