1Util(3) User Contributed Perl Documentation Util(3)
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6 Taint::Util - Test for and flip the taint flag without regex matches or
7 "eval"
8
10 #!/usr/bin/env perl -T
11 use Taint::Util;
12 # eek!
14 untaint $ENV{PATH};
15 # $sv now tainted under taint mode (-T)
17 taint(my $sv = "hlagh");
18 # Untaint $sv again
20 untaint $sv if tainted $sv;
21
23 Wraps perl's internal routines for checking and setting the taint flag
24 and thus does not rely on regular expressions for untainting or odd
25 tricks involving "eval" and "kill" for checking whether data is
26 tainted, instead it checks and flips a flag on the scalar in-place.
27
29 tainted
30 Returns a boolean indicating whether a scalar is tainted. Always false
31 when not under taint mode.
32 taint & untaint
34 Taints or untaints given values, arrays will be flattened and their
35 elements tainted, likewise with the values of hashes (keys can't be
36 tainted, see perlsec). Returns no value (which evaluates to false).
37 untaint(%ENV); # Untaints the environment
39 taint(my @hlagh = qw(a o e u)); # elements of @hlagh now tainted
40 References (being scalars) can also be tainted, a stringified reference
42 reference raises an error where a tainted scalar would:
43 taint(my $ar = \@hlagh);
45 system echo => $ar; # err: Insecure dependency in system
46 This feature is used by perl internally to taint the blessed object
48 "qr//" stringifies to.
49 taint(my $str = "oh noes");
51 my $re = qr/$str/;
52 system echo => $re; # err: Insecure dependency in system
53 This does not mean that tainted blessed objects with overloaded
55 stringification via overload need return a tainted object since those
56 objects may return a non-tainted scalar when stringified (see t/usage.t
57 for an example). The internal handling of "qr//" however ensures that
58 this holds true.
59 File handles can also be tainted, but this is pretty useless as the
61 handle itself and not lines retrieved from it will be tainted, see the
62 next section for details.
63 taint(*DATA); # *DATA tainted
65 my $ln = <DATA>; # $ln not tainted
66
68 Since this module is a low level interface that directly exposes the
69 internal "SvTAINTED*" functions it also presents new and exciting ways
70 for shooting yourself in the foot.
71 Tainting in Perl was always meant to be used for potentially hostile
73 external data passed to the program. Perl is passed a soup of strings
74 from the outside; it never receives any complex datatypes directly.
75 For instance, you might get tainted hash keys in %ENV or tainted
77 strings from *STDIN, but you'll never get a tainted Hash reference or a
78 tainted subroutine. Internally, the perl compiler sets the taint flag
79 on external data in a select few functions mainly having to do with IO
80 and string operations. For example, the "ucfirst" function will
81 manually set a tainted flag on its newly created string depending on
82 whether the original was tainted or not.
83 However, since Taint::Util is exposing some of perl's guts, things get
85 more complex. Internally, tainting is implemented via perl's MAGIC
86 facility, which allows you to attach attach magic to any scalar, but
87 since perl doesn't liberally taint scalars it's there to back you up if
88 you do.
89 You can "taint(*DATA)" and "tainted(*DATA)" will subsequently be true
91 but if you read from the filehandle via "<DATA>" you'll get untainted
92 data back. As you might have guessed this is completely useless.
93 The test file t/usage.t highlights some of these edge cases.
95 Back in the real world, the only reason tainting makes sense is because
97 perl will back you up when you use it, e.g. it will slap your hand if
98 you try to pass a tainted value to system().
99 If you taint references, perl doesn't offer that protection, because it
101 doesn't know anything about tainted references since it would never
102 create one. The things that do work like the stringification of
103 "taint($t = [])" (i.e. "ARRAY(0x11a5d48)") being tainted only work
104 incidentally.
105 But I'm not going to stop you. By all means, have at it! Just don't
107 expect it to do anything more useful than warming up your computer.
108 See RT #53988 <https://rt.cpan.org/Ticket/Display.html?id=53988> for
110 the bug that inspired this section.
111
113 Exports "tainted", "taint" and "untaint" by default. Individual
114 functions can be exported by specifying them in the "use" list, to
115 export none use "()".
116
118 I wrote this when implementing re::engine::Plugin so that someone
119 writing a custom regex engine with it wouldn't have to rely on perl
120 regexps for untainting capture variables, which would be a bit odd.
121
123 perlsec
124
126 Ævar Arnfjörð Bjarmason <avar@cpan.org>
127
129 Copyright 2007-2010 Ævar Arnfjörð Bjarmason.
130 This program is free software; you can redistribute it and/or modify it
132 under the same terms as Perl itself.
133perl v5.34.0 2022-01-21 Util(3)