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Re^2: One true regexp for untainting windows filenames?

by jaldhar (Vicar)
on Jan 08, 2009 at 22:13 UTC ( #735034=note: print w/ replies, xml ) Need Help??


in reply to Re: One true regexp for untainting windows filenames?
in thread One true regexp for untainting windows filenames?

It seems that despite the length of my post I still managed to leave out some pertinent information. Sorry! I use untaint_path() to check several filenames not just $^X. It just happens that this is the first test that encountered a weird path. So the question still stands even if $^X is safe.

On that topic, I am using the value of $^X in a qx// call. On Linux at least, if I don't untaint it, I get a nastygram about "insecure dependency." Should perl be a little smarter here?

As for the regexps themselves, I am embarrassed to say I just copied them from existing code. Now I will use the ones from File::Basename as cdarke suggested.

Thank you for your help.

--
જલધર


Comment on Re^2: One true regexp for untainting windows filenames?
Re^3: One true regexp for untainting windows filenames?
by ikegami (Pope) on Jan 09, 2009 at 05:14 UTC

    I use untaint_path() to check several filenames not just $^X.

    To make them safe for what? Most most applications, untaint_path might remove the taint flag, but it doesn't make sure they're safe first.

    On that topic, I am using the value of $^X in a qx// call. On Linux at least, if I don't untaint it, I get a nastygram about "insecure dependency." Should perl be a little smarter here?

    In unix systems, it's possible to execute a binary at one path while making it think it's at a different path.

    $ cat > a.c #include <stdio.h> int main(int argc, char** argv) { printf("%s\n", argv[0]); return 0; } $ gcc -o a a.c $ perl -e'exec { "a" } "evil"' evil

    Based on a comment in $^X, it looks like there's a way for processes to find out which binary is actually being executed on some systems, and Perl uses it.

    If the following doesn't print "evil" on your system, $^X can probably be trusted on your system.

    $ perl -e'system { "perl" } "evil", "-le", "print \$^X"' /usr/bin/perl

      To make them safe for what? Most most applications, untaint_path might remove the taint flag, but it doesn't make sure they're safe first.

      Safe to use in qx//; in taint mode Earlier, I set $ENV{PATH} to q{}. This means I need to use complete paths to every file or command I use and they need to be untainted to prevent the 'insecure dependency' error.

      I had forgotten about argv[0]. Now you have led me to realize that running under -T will not really buying me anything here without additional checking.

      Hopefully this conversation will remind others to not complacently assume untainted eq secure if nothing else.

      --
      જલધર

        Safe to use in qx//; in taint mode

        In such general terms, it's impossible. You can make it so qx// doesn't croak, but you can't make it safe. Need more info.

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