EAP-pwd: Verify BN_rand_range return code

This makes the EAP-pwd server and peer implementations more robust
should OpenSSL fail to derive random number for some reason. While this
is unlikely to happen in practice, the implementation better be prepared
for this should something unexpected ever happen. See
http://jbp.io/2014/01/16/openssl-rand-api/#review-of-randbytes-callers
for more details.

Signed-off-by: Florent Daigniere <nextgens@freenetproject.org>

src/eap_peer/eap_pwd.c

@@ -317,11 +317,15 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
 		goto fin;
 	}
 
-	BN_rand_range(data->private_value, data->grp->order);
-	BN_rand_range(mask, data->grp->order);
-	BN_add(data->my_scalar, data->private_value, mask);
-	BN_mod(data->my_scalar, data->my_scalar, data->grp->order,
-	       data->bnctx);
+	if (BN_rand_range(data->private_value, data->grp->order) != 1 ||
+	    BN_rand_range(mask, data->grp->order) != 1 ||
+	    BN_add(data->my_scalar, data->private_value, mask) != 1 ||
+	    BN_mod(data->my_scalar, data->my_scalar, data->grp->order,
+		   data->bnctx) != 1) {
+		wpa_printf(MSG_INFO,
+			   "EAP-pwd (peer): unable to get randomness");
+		goto fin;
+	}
 
 	if (!EC_POINT_mul(data->grp->group, data->my_element, NULL,
 			  data->grp->pwe, mask, data->bnctx)) {

src/eap_server/eap_server_pwd.c

@@ -210,11 +210,15 @@ static void eap_pwd_build_commit_req(struct eap_sm *sm,
 		goto fin;
 	}
 
-	BN_rand_range(data->private_value, data->grp->order);
-	BN_rand_range(mask, data->grp->order);
-	BN_add(data->my_scalar, data->private_value, mask);
-	BN_mod(data->my_scalar, data->my_scalar, data->grp->order,
-	       data->bnctx);
+	if (BN_rand_range(data->private_value, data->grp->order) != 1 ||
+	    BN_rand_range(mask, data->grp->order) != 1 ||
+	    BN_add(data->my_scalar, data->private_value, mask) != 1 ||
+	    BN_mod(data->my_scalar, data->my_scalar, data->grp->order,
+		   data->bnctx) != 1) {
+		wpa_printf(MSG_INFO,
+			   "EAP-pwd (server): unable to get randomness");
+		goto fin;
+	}
 
 	if (!EC_POINT_mul(data->grp->group, data->my_element, NULL,
 			  data->grp->pwe, mask, data->bnctx)) {