Commit 3681a455 authored by Matt Caswell's avatar Matt Caswell
Browse files

More fix DSA, preserve BN_FLG_CONSTTIME 



The previous "fix" still left "k" exposed to constant time problems in
the later BN_mod_inverse() call. Ensure both k and kq have the
BN_FLG_CONSTTIME flag set at the earliest opportunity after creation.

CVE-2016-2178

Reviewed-by: default avatarRich Salz <rsalz@openssl.org>
(cherry picked from commit b7d0f283)
parent d168705e

crypto/dsa/dsa_ossl.c

+8 −3
Original line number Diff line number Diff line
@@ -249,6 +249,11 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 
            goto err;

    while (BN_is_zero(&k));



    if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {

        BN_set_flags(&k, BN_FLG_CONSTTIME);

    }





    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {

        if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,

                                    CRYPTO_LOCK_DSA, dsa->p, ctx))
@@ -261,6 +266,8 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 
        if (!BN_copy(&kq, &k))

            goto err;



        BN_set_flags(&kq, BN_FLG_CONSTTIME);



        /*

         * We do not want timing information to leak the length of k, so we

         * compute g^k using an equivalent exponent of fixed length. (This
@@ -276,8 +283,6 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 
        }



        K = &kq;



        BN_set_flags(K, BN_FLG_CONSTTIME);

    } else {

        K = &k;

    }