Hi monks

I'm looking at the Locale::Maketext code and came across this in the _compile method (line 435 onwards in Maketext.pm): 

  if(length $c[-1]) {
    # Now actually processing the preceding literal
    $big_pile .= $c[-1];
    if($USE_LITERALS and (
      (ord('A') == 65)
      ? $c[-1] !~ m<[^\x20-\x7E]>s
      # ASCII very safe chars
      : $c[-1] !~ m/[^ !"\#\$%&'()*+,\-.\/0-9:;<=>?\@A-Z[\\\]^_`a-z{|}
+~\x07]/s
      # EBCDIC very safe chars
    )) {
      # normal case -- all very safe chars
      $c[-1] =~ s/'/\\'/g;
      push @code, q{ '} . $c[-1] . "',\n";
      $c[-1] = ''; # reuse this slot
    } else {
      push @code, ' $c[' . $#c . "],\n";
      push @c, ''; # new chunk
    }

[download]
I'm wondering why potentially unsafe characters are handled differently in the above code?

Since this is extracting string literals from an external source for a later eval, would the following generalized code be safe: 


  my $literal = <DATA>;

  $literal =~ s/\\*'/\\'/g;

  # later on...

  # There may be a number of literals in reality - 
  # each would be single quoted to prevent interpolation

  my $string = eval "'$literal'";

__DATA__
this could be \'; system("ls -la");\'

[download]
IE, the above code could look something like this instead: 
  if(length $c[-1]) {
    # Now actually processing the preceding literal
    $big_pile .= $c[-1];

    $c[-1] =~ s/\\*'/\\'/g;
    push @code, " '$c[-1]',\n";
    $c[-1] = ''; # reuse this slot
  }

[download]
This isn't a criticism of L::Maketext, rather I'm just curious to know if there are situations where evaling a single quoted literal with all single quotes escaped might still cause accidental interpolation.

Can anyone suggest security problems with this - if you can give a simple example to illustrate, even better. BTW, I appreciate that the noddy example code I've provided doesn't need eval - its just there as a simple example.

Thanks

In reply to Safe eval of string literals? by Anonymous Monk

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