Fix BN_is_prime* calls.

This function returns a tri-state -1 on error. See BoringSSL's
53409ee3d7595ed37da472bc73b010cd2c8a5ffd.
Signed-off-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NRich Salz <rsalz@openssl.org>

GH: #1251

apps/s_client.c

@@ -249,10 +249,10 @@ static int srp_Verify_N_and_g(const BIGNUM *N, const BIGNUM *g)
     BIGNUM *r = BN_new();
     int ret =
         g != NULL && N != NULL && bn_ctx != NULL && BN_is_odd(N) &&
-        BN_is_prime_ex(N, SRP_NUMBER_ITERATIONS_FOR_PRIME, bn_ctx, NULL) &&
+        BN_is_prime_ex(N, SRP_NUMBER_ITERATIONS_FOR_PRIME, bn_ctx, NULL) == 1 &&
         p != NULL && BN_rshift1(p, N) &&
         /* p = (N-1)/2 */
-        BN_is_prime_ex(p, SRP_NUMBER_ITERATIONS_FOR_PRIME, bn_ctx, NULL) &&
+        BN_is_prime_ex(p, SRP_NUMBER_ITERATIONS_FOR_PRIME, bn_ctx, NULL) == 1 &&
         r != NULL &&
         /* verify g^((N-1)/2) == -1 (mod N) */
         BN_mod_exp(r, g, p, N, bn_ctx) &&

crypto/bn/bn_x931p.c

@@ -21,7 +21,7 @@
 static int bn_x931_derive_pi(BIGNUM *pi, const BIGNUM *Xpi, BN_CTX *ctx,
                              BN_GENCB *cb)
 {
-    int i = 0;
+    int i = 0, is_prime;
     if (!BN_copy(pi, Xpi))
         return 0;
     if (!BN_is_odd(pi) && !BN_add_word(pi, 1))
@@ -30,7 +30,10 @@ static int bn_x931_derive_pi(BIGNUM *pi, const BIGNUM *Xpi, BN_CTX *ctx,
         i++;
         BN_GENCB_call(cb, 0, i);
         /* NB 27 MR is specified in X9.31 */
-        if (BN_is_prime_fasttest_ex(pi, 27, ctx, 1, cb))
+        is_prime = BN_is_prime_fasttest_ex(pi, 27, ctx, 1, cb);
+        if (is_prime < 0)
+            return 0;
+        if (is_prime)
             break;
         if (!BN_add_word(pi, 2))
             return 0;
@@ -119,14 +122,18 @@ int BN_X931_derive_prime_ex(BIGNUM *p, BIGNUM *p1, BIGNUM *p2,
             goto err;
         if (!BN_gcd(t, pm1, e, ctx))
             goto err;
-        if (BN_is_one(t)
+        if (BN_is_one(t)) {
             /*
              * X9.31 specifies 8 MR and 1 Lucas test or any prime test
              * offering similar or better guarantees 50 MR is considerably
              * better.
              */
-            && BN_is_prime_fasttest_ex(p, 50, ctx, 1, cb))
-            break;
+            int r = BN_is_prime_fasttest_ex(p, 50, ctx, 1, cb);
+            if (r < 0)
+                goto err;
+            if (r)
+                break;
+        }
         if (!BN_add(p, p, p1p2))
             goto err;
     }

crypto/dh/dh_check.c

@@ -24,7 +24,7 @@
 
 int DH_check(const DH *dh, int *ret)
 {
-    int ok = 0;
+    int ok = 0, r;
     BN_CTX *ctx = NULL;
     BN_ULONG l;
     BIGNUM *t1 = NULL, *t2 = NULL;
@@ -53,7 +53,10 @@ int DH_check(const DH *dh, int *ret)
             if (!BN_is_one(t1))
                 *ret |= DH_NOT_SUITABLE_GENERATOR;
         }
-        if (!BN_is_prime_ex(dh->q, BN_prime_checks, ctx, NULL))
+        r = BN_is_prime_ex(dh->q, BN_prime_checks, ctx, NULL);
+        if (r < 0)
+            goto err;
+        if (!r)
             *ret |= DH_CHECK_Q_NOT_PRIME;
         /* Check p == 1 mod q  i.e. q divides p - 1 */
         if (!BN_div(t1, t2, dh->p, dh->q, ctx))
@@ -74,12 +77,18 @@ int DH_check(const DH *dh, int *ret)
     } else
         *ret |= DH_UNABLE_TO_CHECK_GENERATOR;
 
-    if (!BN_is_prime_ex(dh->p, BN_prime_checks, ctx, NULL))
+    r = BN_is_prime_ex(dh->p, BN_prime_checks, ctx, NULL);
+    if (r < 0)
+        goto err;
+    if (!r)
         *ret |= DH_CHECK_P_NOT_PRIME;
     else if (!dh->q) {
         if (!BN_rshift1(t1, dh->p))
             goto err;
-        if (!BN_is_prime_ex(t1, BN_prime_checks, ctx, NULL))
+        r = BN_is_prime_ex(t1, BN_prime_checks, ctx, NULL);
+        if (r < 0)
+            goto err;
+	if (!r)
             *ret |= DH_CHECK_P_NOT_SAFE_PRIME;
     }
     ok = 1;