Taint mode and concatenation

Pirax has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks,

Im trying to get my script working with taint mode on, but...

$GET{mode}

is tainted - ok, all clear.

Result of

($GET{mode} ? 'str1' : 'str2')

is untainted - ok, correct.

But can anyone tell me why the result of something like this:

($GET{mode} ? 'str1' : 'str2').'str3'
[download]

is tainted? :/ I have no idea, really... Two untainted strings in result gave a tainted one...

What I know after my research is that any tainted data in condition of ternary operator after concatenation taints whole concatenated string.

Comment on Taint mode and concatenation Select or Download Code

Replies are listed 'Best First'.
Re: Taint mode and concatenation by Anonymous Monk on Nov 16, 2009 at 10:18 UTC
perldoc perlsec says The presence of tainted data anywhere within an expression renders the entire expression tainted.	[reply]
Re^2: Taint mode and concatenation by Pirax (Initiate) on Nov 16, 2009 at 10:45 UTC
Yes, I know, but acording to the "exception to the principle" the ternary conditional operator does not taint the result... So... Shouldn't this be true everywhere?	[reply]