Laundering and Detecting Tainted Data To test whether a variable contains tainted data, and whose use would +thus trigger an "Insecure dependency" message, you can use the tainte +d() function of the Scalar::Util module, available in your nearby CPA +N mirror, and included in Perl starting from the release 5.8.0. Or yo +u may be able to use the following is_tainted() function. sub is_tainted { return ! eval { eval("#" . substr(join("", @_), 0, 0)); 1 }; } This function makes use of the fact that the presence of tainted data +anywhere within an expression renders the entire expression tainted. +It would be inefficient for every operator to test every argument for + taintedness. Instead, the slightly more efficient and conservative a +pproach is used that if any tainted value has been accessed within th +e same expression, the whole expression is considered tainted. But testing for taintedness gets you only so far. Sometimes you have j +ust to clear your data's taintedness. Values may be untainted by usin +g them as keys in a hash; otherwise the only way to bypass the tainti +ng 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. T +hat means using a bit of thought--don't just blindly untaint anything +, or you defeat the entire mechanism. It's better to verify that the +variable has only good characters (for certain values of "good") rath +er than checking whether it has any bad characters. That's because it +'s far too easy to miss bad characters that you never thought of.
In reply to Re: is_tainted function
by Anonymous Monk
in thread is_tainted function
by perlknight
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