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

[jaldhar]

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.

[ikegami]

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

[jaldhar]

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.

[ikegami]

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.