RSA key generation: ensure BN_mod_inverse and BN_mod_exp_mont both get called with BN_FLG_CONSTTIME flag set.

CVE-2018-0737

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>

Author: bbbrumley

crypto/rsa/rsa_gen.c

@@ -89,6 +89,8 @@ static int rsa_builtin_keygen(RSA *rsa, int bits, BIGNUM *e_value,
     if (BN_copy(rsa->e, e_value) == NULL)
         goto err;
 
+    BN_set_flags(rsa->p, BN_FLG_CONSTTIME);
+    BN_set_flags(rsa->q, BN_FLG_CONSTTIME);
     BN_set_flags(r2, BN_FLG_CONSTTIME);
     /* generate p and q */
     for (;;) {