1395833 - Logically dead code in Curve25519

Status: RESOLVED FIXED

(NSS :: Libraries, defect, P5)

Description

[Sylvestre Ledru [:Sylvestre]]

Coverity considers that this line is useless        
if (ctr > (uint32_t)0)
            Hacl_Bignum_Fmul_shift_reduce(input);
https://hg.mozilla.org/projects/nss/file/7fcf7848095c/lib/freebl/verified/hacl_curve25519_64.c#l222
because ctr is always > 0:
uint32_t ctr = (uint32_t)5 - (uint32_t)3 - (uint32_t)1;

Comment 1

[Franziskus Kiefer [:franziskus]]

It probably is. But we won't change this code manually. It's auto-generated and proven to be correct. Dead code gets compiled out.
We'll work with the INRIA folks to improve the code generation to get rid of this. But that might take a while.

Comment 2

[Sylvestre Ledru [:Sylvestre]]

I will just ignore it in coverity then :) Do you want to leave it open?

I used to be an Inria engineer, make me happy to see that name here ;)

Comment 3

[Franziskus Kiefer [:franziskus]]

Let's leave it open so we can track it.

Comment 4

[Benjamin Beurdouche (do not use this account)]

Fixed by https://bugzilla.mozilla.org/show_bug.cgi?id=1419173

Comment 5

[Franziskus Kiefer [:franziskus]]

Coverity didn't pick up the change yet but the offending code is gone.