ikiwiki/doc/bugs/taint_issue_with_regular_expressions.mdwn

Built from 2.1.17 source, works fine on commandline, but not working from CGI wrapper.  Traced problem to regular expressions failing to match, specifically in contexts like the following in Render.pm:

    my ($f)=/$config{wiki_file_regexp}/; # untaint

It works if I replace it with:

    my ($f)=/(^[-[:alnum:]_.:\/+]+$)/; # untaint

which is exactly the same regular expression drawn out as a constant.  It appears that %config gets some tainted data and is itself being marked entirely tainted, which may prevent using regular expressions contained in it for untainting other data.  I'm using Perl 5.8.8.

> How could `%config` possible get tainted? That would be a major security
> hole. It seems more likely that perl containes to have taint flag bugs
> even in 5.8. See also: [[prune_causing_taint_mode_failures]],
> [[Insecure_dependency_in_mkdir]],
> [[Insecure_dependency_in_eval_while_running_with_-T_switch.mdwn]],
> and especially [[debbug 411786]]
>
> The last of those was the last straw for me, and I disabled taint
> checking in the debian package. You can do the same by building ikiwiki
> with NOTAINT=1. :-( --[[Joey]]

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