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--- lib/RT/Util.pm.orig 2016-07-18 20:20:17 UTC
+++ lib/RT/Util.pm
@@ -54,6 +54,8 @@ use warnings;
use base 'Exporter';
our @EXPORT = qw/safe_run_child mime_recommended_filename/;
+use Encode qw/encode/;
+
sub safe_run_child (&) {
my $our_pid = $$;
@@ -150,6 +152,58 @@ sub assert_bytes {
}
+=head2 C<constant_time_eq($a, $b)>
+
+Compares two strings for equality in constant-time. Replacement for the C<eq>
+operator designed to avoid timing side-channel vulnerabilities. Returns zero
+or one.
+
+This is intended for use in cryptographic subsystems for comparing well-formed
+data such as hashes - not for direct use with user input or as a general
+replacement for the C<eq> operator.
+
+The two string arguments B<MUST> be of equal length. If the lengths differ,
+this function will call C<die()>, as proceeding with execution would create
+a timing vulnerability. Length is defined by characters, not bytes.
+
+This code has been tested to do what it claims. Do not change it without
+thorough statistical timing analysis to validate the changes.
+
+Added to resolve CVE-2017-5361
+
+For more on timing attacks, see this Wikipedia article:
+B<https://en.wikipedia.org/wiki/Timing_attack>
+
+=cut
+
+sub constant_time_eq {
+ my ($a, $b) = @_;
+
+ my $result = 0;
+
+ # generic error message avoids potential information leaks
+ my $generic_error = "Cannot compare values";
+ die $generic_error unless defined $a and defined $b;
+ die $generic_error unless length $a == length $b;
+ die $generic_error if ref($a) or ref($b);
+
+ for (my $i = 0; $i < length($a); $i++) {
+ my $a_char = substr($a, $i, 1);
+ my $b_char = substr($b, $i, 1);
+
+ # encode() is set to die on malformed
+ my @a_octets = unpack("C*", encode('UTF-8', $a_char, Encode::FB_CROAK));
+ my @b_octets = unpack("C*", encode('UTF-8', $b_char, Encode::FB_CROAK));
+ die $generic_error if (scalar @a_octets) != (scalar @b_octets);
+
+ for (my $j = 0; $j < scalar @a_octets; $j++) {
+ $result |= $a_octets[$j] ^ $b_octets[$j];
+ }
+ }
+ return 0 + not $result;
+}
+
+
RT::Base->_ImportOverlays();
1;
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