add missing check for BN_mod_inverse
Fixes
@@ -128,6 +128,8 @@ int RSA_X931_derive_ex(RSA *rsa, BIGNUM *p1, BIGNUM *p2, BIGNUM *q1,
/* calculate inverse of q mod p */
rsa->iqmp = BN_mod_inverse(NULL, rsa->q, rsa->p, ctx2);
+ if (rsa->iqmp == NULL)
+ goto err;
ret = 1;
err:
