Add option to disable Extended Master Secret
authorTodd Short <tshort@akamai.com>
Mon, 10 Jul 2017 17:28:35 +0000 (13:28 -0400)
committerMatt Caswell <matt@openssl.org>
Fri, 15 Feb 2019 10:11:18 +0000 (10:11 +0000)
Add SSL_OP64_NO_EXTENDED_MASTER_SECRET, that can be set on either
an SSL or an SSL_CTX. When processing a ClientHello, if this flag
is set, do not indicate that the EMS TLS extension was received in
either the ssl3 object or the SSL_SESSION.  Retain most of the
sanity checks between the previous and current session during
session resumption, but weaken the check when the current SSL
object is configured to not use EMS.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3910)

12 files changed:
doc/man3/SSL_CONF_cmd.pod
doc/man3/SSL_CTX_set_options.pod
include/openssl/ssl.h
ssl/ssl_conf.c
ssl/statem/extensions.c
ssl/statem/extensions_clnt.c
ssl/statem/extensions_srvr.c
test/recipes/80-test_ssl_new.t
test/ssl-tests/16-certstatus.conf [deleted file]
test/ssl-tests/30-extended-master-secret.conf [new file with mode: 0644]
test/ssl-tests/30-extended-master-secret.conf.in [new file with mode: 0644]
test/sslapitest.c

index 0a51e9ed89d82c72a69b05940386940237405aef..b8c2a357e819dfeac8655ae30900886a710d4984 100644 (file)
@@ -486,6 +486,10 @@ specification. Some applications may be able to mitigate the replay risks in
 other ways and in such cases the built-in OpenSSL functionality is not required.
 Disabling anti-replay is equivalent to setting B<SSL_OP_NO_ANTI_REPLAY>.
 
+B<ExtendedMasterSecret>: use extended master secret extension, enabled by
+default. Inverse of B<SSL_OP_NO_EXTENDED_MASTER_SECRET>: that is,
+B<-ExtendedMasterSecret> is the same as setting B<SSL_OP_NO_EXTENDED_MASTER_SECRET>.
+
 =item B<VerifyMode>
 
 The B<value> argument is a comma separated list of flags to set.
index 63d3aae97a52433b356251872ff7374c8e114acb..7626bd338b6363b22272165c1fe837d2fda60b24 100644 (file)
@@ -198,6 +198,14 @@ RFC7366 Encrypt-then-MAC option on TLS and DTLS connection.
 If this option is set, Encrypt-then-MAC is disabled. Clients will not
 propose, and servers will not accept the extension.
 
+=item SSL_OP_NO_EXTENDED_MASTER_SECRET
+
+Normally clients and servers will transparently attempt to negotiate the
+RFC7627 Extended Master Secret option on TLS and DTLS connection.
+
+If this option is set, Extended Master Secret is disabled. Clients will
+not propose, and servers will not accept the extension.
+
 =item SSL_OP_NO_RENEGOTIATION
 
 Disable all renegotiation in TLSv1.2 and earlier. Do not send HelloRequest
@@ -366,9 +374,11 @@ OpenSSL 0.9.8m.
 The B<SSL_OP_PRIORITIZE_CHACHA> and B<SSL_OP_NO_RENEGOTIATION> options
 were added in OpenSSL 1.1.1.
 
+The B<SSL_OP_NO_EXTENDED_MASTER_SECRET> option was added in OpenSSL 3.0.0.
+
 =head1 COPYRIGHT
 
-Copyright 2001-2018 The OpenSSL Project Authors. All Rights Reserved.
+Copyright 2001-2019 The OpenSSL Project Authors. All Rights Reserved.
 
 Licensed under the Apache License 2.0 (the "License").  You may not use
 this file except in compliance with the License.  You can obtain a copy
index 35311acaf4322e880cf29cf169d9b4223f8643de..9d6e1c502473b62138c6d56c2a7e4a3965e674aa 100644 (file)
@@ -297,23 +297,26 @@ typedef int (*SSL_verify_cb)(int preverify_ok, X509_STORE_CTX *x509_ctx);
 typedef int (*SSL_async_callback_fn)(SSL *s, void *arg);
 
 /*
- * Some values are reserved until OpenSSL 1.2.0 because they were previously
+ * Some values are reserved until OpenSSL 3.0.0 because they were previously
  * included in SSL_OP_ALL in a 1.1.x release.
- *
- * Reserved value (until OpenSSL 1.2.0)                  0x00000001U
- * Reserved value (until OpenSSL 1.2.0)                  0x00000002U
  */
+
+/* Disable Extended master secret */
+# define SSL_OP_NO_EXTENDED_MASTER_SECRET                0x00000001U
+
+/* Reserved value (until OpenSSL 3.0.0)                  0x00000002U */
+
 /* Allow initial connection to servers that don't support RI */
 # define SSL_OP_LEGACY_SERVER_CONNECT                    0x00000004U
 
-/* Reserved value (until OpenSSL 1.2.0)                  0x00000008U */
+/* Reserved value (until OpenSSL 3.0.0)                  0x00000008U */
 # define SSL_OP_TLSEXT_PADDING                           0x00000010U
-/* Reserved value (until OpenSSL 1.2.0)                  0x00000020U */
+/* Reserved value (until OpenSSL 3.0.0)                  0x00000020U */
 # define SSL_OP_SAFARI_ECDHE_ECDSA_BUG                   0x00000040U
 /*
- * Reserved value (until OpenSSL 1.2.0)                  0x00000080U
- * Reserved value (until OpenSSL 1.2.0)                  0x00000100U
- * Reserved value (until OpenSSL 1.2.0)                  0x00000200U
+ * Reserved value (until OpenSSL 3.0.0)                  0x00000080U
+ * Reserved value (until OpenSSL 3.0.0)                  0x00000100U
+ * Reserved value (until OpenSSL 3.0.0)                  0x00000200U
  */
 
 /* In TLSv1.3 allow a non-(ec)dhe based kex_mode */
index 6d4c69df014e411ab9a5539e44e976181620af5a..f0bec364bb320f2f928bd3138588bb3a0a6d6efa 100644 (file)
@@ -380,7 +380,8 @@ static int cmd_Options(SSL_CONF_CTX *cctx, const char *value)
         SSL_FLAG_TBL("AllowNoDHEKEX", SSL_OP_ALLOW_NO_DHE_KEX),
         SSL_FLAG_TBL("PrioritizeChaCha", SSL_OP_PRIORITIZE_CHACHA),
         SSL_FLAG_TBL("MiddleboxCompat", SSL_OP_ENABLE_MIDDLEBOX_COMPAT),
-        SSL_FLAG_TBL_INV("AntiReplay", SSL_OP_NO_ANTI_REPLAY)
+        SSL_FLAG_TBL_INV("AntiReplay", SSL_OP_NO_ANTI_REPLAY),
+        SSL_FLAG_TBL_INV("ExtendedMasterSecret", SSL_OP_NO_EXTENDED_MASTER_SECRET)
     };
     if (value == NULL)
         return -3;
index 773309a13cf0d10682aba82f1c10cfa6d6a33c4c..60d4da044230f924ef33e1de14ab04903fd60eb4 100644 (file)
@@ -1169,8 +1169,7 @@ static int init_etm(SSL *s, unsigned int context)
 
 static int init_ems(SSL *s, unsigned int context)
 {
-    if (!s->server)
-        s->s3->flags &= ~TLS1_FLAGS_RECEIVED_EXTMS;
+    s->s3->flags &= ~TLS1_FLAGS_RECEIVED_EXTMS;
 
     return 1;
 }
index 6e133e026e6061b5574e8311d9b7ec6df0682129..f01e9eef64d9e11d4385de467626dcb0c1b43e2b 100644 (file)
@@ -494,6 +494,9 @@ EXT_RETURN tls_construct_ctos_sct(SSL *s, WPACKET *pkt, unsigned int context,
 EXT_RETURN tls_construct_ctos_ems(SSL *s, WPACKET *pkt, unsigned int context,
                                   X509 *x, size_t chainidx)
 {
+    if (s->options & SSL_OP_NO_EXTENDED_MASTER_SECRET)
+        return EXT_RETURN_NOT_SENT;
+
     if (!WPACKET_put_bytes_u16(pkt, TLSEXT_TYPE_extended_master_secret)
             || !WPACKET_put_bytes_u16(pkt, 0)) {
         SSLfatal(s, SSL_AD_INTERNAL_ERROR, SSL_F_TLS_CONSTRUCT_CTOS_EMS,
@@ -1743,6 +1746,8 @@ int tls_parse_stoc_etm(SSL *s, PACKET *pkt, unsigned int context, X509 *x,
 int tls_parse_stoc_ems(SSL *s, PACKET *pkt, unsigned int context, X509 *x,
                        size_t chainidx)
 {
+    if (s->options & SSL_OP_NO_EXTENDED_MASTER_SECRET)
+        return 1;
     s->s3->flags |= TLS1_FLAGS_RECEIVED_EXTMS;
     if (!s->hit)
         s->session->flags |= SSL_SESS_FLAG_EXTMS;
index 6545f5727debeeda5daf8d3eb3314d75082a20e6..73ceadc34a9388d2e492e123a522fc5173aa5981 100644 (file)
@@ -989,6 +989,9 @@ int tls_parse_ctos_ems(SSL *s, PACKET *pkt, unsigned int context, X509 *x,
         return 0;
     }
 
+    if (s->options & SSL_OP_NO_EXTENDED_MASTER_SECRET)
+        return 1;
+
     s->s3->flags |= TLS1_FLAGS_RECEIVED_EXTMS;
 
     return 1;
index fa98f24b57f5c3fe7d7663650cd80c2a2944803a..31c4399dc3f51594b06ba438fa38a1b9f5fde4c7 100644 (file)
@@ -28,7 +28,7 @@ map { s/\^// } @conf_files if $^O eq "VMS";
 
 # We hard-code the number of tests to double-check that the globbing above
 # finds all files as expected.
-plan tests => 29;  # = scalar @conf_srcs
+plan tests => 30;  # = scalar @conf_srcs
 
 # Some test results depend on the configuration of enabled protocols. We only
 # verify generated sources in the default configuration.
@@ -70,6 +70,7 @@ my %conf_dependent_tests = (
   "25-cipher.conf" => disabled("poly1305") || disabled("chacha"),
   "27-ticket-appdata.conf" => !$is_default_tls,
   "28-seclevel.conf" => disabled("tls1_2") || $no_ec,
+  "30-extended-master-secret.conf" => disabled("tls1_2"),
 );
 
 # Add your test here if it should be skipped for some compile-time
diff --git a/test/ssl-tests/16-certstatus.conf b/test/ssl-tests/16-certstatus.conf
deleted file mode 100644 (file)
index e69de29..0000000
diff --git a/test/ssl-tests/30-extended-master-secret.conf b/test/ssl-tests/30-extended-master-secret.conf
new file mode 100644 (file)
index 0000000..9dae431
--- /dev/null
@@ -0,0 +1,203 @@
+# Generated with generate_ssl_tests.pl
+
+num_tests = 7
+
+test-0 = 0-disable-extended-master-secret-server-sha
+test-1 = 1-disable-extended-master-secret-client-sha
+test-2 = 2-disable-extended-master-secret-both-sha
+test-3 = 3-disable-extended-master-secret-both-resume
+test-4 = 4-disable-extended-master-secret-server-sha2
+test-5 = 5-disable-extended-master-secret-client-sha2
+test-6 = 6-disable-extended-master-secret-both-sha2
+# ===========================================================
+
+[0-disable-extended-master-secret-server-sha]
+ssl_conf = 0-disable-extended-master-secret-server-sha-ssl
+
+[0-disable-extended-master-secret-server-sha-ssl]
+server = 0-disable-extended-master-secret-server-sha-server
+client = 0-disable-extended-master-secret-server-sha-client
+
+[0-disable-extended-master-secret-server-sha-server]
+Certificate = ${ENV::TEST_CERTS_DIR}/servercert.pem
+CipherString = DEFAULT
+Options = -ExtendedMasterSecret
+PrivateKey = ${ENV::TEST_CERTS_DIR}/serverkey.pem
+
+[0-disable-extended-master-secret-server-sha-client]
+CipherString = AES128-SHA
+MaxProtocol = TLSv1.2
+VerifyCAFile = ${ENV::TEST_CERTS_DIR}/rootcert.pem
+VerifyMode = Peer
+
+[test-0]
+ExpectedResult = Success
+
+
+# ===========================================================
+
+[1-disable-extended-master-secret-client-sha]
+ssl_conf = 1-disable-extended-master-secret-client-sha-ssl
+
+[1-disable-extended-master-secret-client-sha-ssl]
+server = 1-disable-extended-master-secret-client-sha-server
+client = 1-disable-extended-master-secret-client-sha-client
+
+[1-disable-extended-master-secret-client-sha-server]
+Certificate = ${ENV::TEST_CERTS_DIR}/servercert.pem
+CipherString = DEFAULT
+PrivateKey = ${ENV::TEST_CERTS_DIR}/serverkey.pem
+
+[1-disable-extended-master-secret-client-sha-client]
+CipherString = AES128-SHA
+MaxProtocol = TLSv1.2
+Options = -ExtendedMasterSecret
+VerifyCAFile = ${ENV::TEST_CERTS_DIR}/rootcert.pem
+VerifyMode = Peer
+
+[test-1]
+ExpectedResult = Success
+
+
+# ===========================================================
+
+[2-disable-extended-master-secret-both-sha]
+ssl_conf = 2-disable-extended-master-secret-both-sha-ssl
+
+[2-disable-extended-master-secret-both-sha-ssl]
+server = 2-disable-extended-master-secret-both-sha-server
+client = 2-disable-extended-master-secret-both-sha-client
+
+[2-disable-extended-master-secret-both-sha-server]
+Certificate = ${ENV::TEST_CERTS_DIR}/servercert.pem
+CipherString = DEFAULT
+Options = -ExtendedMasterSecret
+PrivateKey = ${ENV::TEST_CERTS_DIR}/serverkey.pem
+
+[2-disable-extended-master-secret-both-sha-client]
+CipherString = AES128-SHA
+MaxProtocol = TLSv1.2
+Options = -ExtendedMasterSecret
+VerifyCAFile = ${ENV::TEST_CERTS_DIR}/rootcert.pem
+VerifyMode = Peer
+
+[test-2]
+ExpectedResult = Success
+
+
+# ===========================================================
+
+[3-disable-extended-master-secret-both-resume]
+ssl_conf = 3-disable-extended-master-secret-both-resume-ssl
+
+[3-disable-extended-master-secret-both-resume-ssl]
+server = 3-disable-extended-master-secret-both-resume-server
+client = 3-disable-extended-master-secret-both-resume-client
+resume-server = 3-disable-extended-master-secret-both-resume-resume-server
+resume-client = 3-disable-extended-master-secret-both-resume-resume-client
+
+[3-disable-extended-master-secret-both-resume-server]
+Certificate = ${ENV::TEST_CERTS_DIR}/servercert.pem
+CipherString = DEFAULT
+Options = -ExtendedMasterSecret
+PrivateKey = ${ENV::TEST_CERTS_DIR}/serverkey.pem
+
+[3-disable-extended-master-secret-both-resume-resume-server]
+Certificate = ${ENV::TEST_CERTS_DIR}/servercert.pem
+CipherString = DEFAULT
+PrivateKey = ${ENV::TEST_CERTS_DIR}/serverkey.pem
+
+[3-disable-extended-master-secret-both-resume-client]
+CipherString = AES128-SHA
+MaxProtocol = TLSv1.2
+Options = -ExtendedMasterSecret
+VerifyCAFile = ${ENV::TEST_CERTS_DIR}/rootcert.pem
+VerifyMode = Peer
+
+[3-disable-extended-master-secret-both-resume-resume-client]
+CipherString = AES128-SHA
+MaxProtocol = TLSv1.2
+VerifyCAFile = ${ENV::TEST_CERTS_DIR}/rootcert.pem
+VerifyMode = Peer
+
+[test-3]
+ExpectedResult = Success
+HandshakeMode = Resume
+
+
+# ===========================================================
+
+[4-disable-extended-master-secret-server-sha2]
+ssl_conf = 4-disable-extended-master-secret-server-sha2-ssl
+
+[4-disable-extended-master-secret-server-sha2-ssl]
+server = 4-disable-extended-master-secret-server-sha2-server
+client = 4-disable-extended-master-secret-server-sha2-client
+
+[4-disable-extended-master-secret-server-sha2-server]
+Certificate = ${ENV::TEST_CERTS_DIR}/servercert.pem
+CipherString = DEFAULT
+Options = -ExtendedMasterSecret
+PrivateKey = ${ENV::TEST_CERTS_DIR}/serverkey.pem
+
+[4-disable-extended-master-secret-server-sha2-client]
+CipherString = AES128-SHA256
+MaxProtocol = TLSv1.2
+VerifyCAFile = ${ENV::TEST_CERTS_DIR}/rootcert.pem
+VerifyMode = Peer
+
+[test-4]
+ExpectedResult = Success
+
+
+# ===========================================================
+
+[5-disable-extended-master-secret-client-sha2]
+ssl_conf = 5-disable-extended-master-secret-client-sha2-ssl
+
+[5-disable-extended-master-secret-client-sha2-ssl]
+server = 5-disable-extended-master-secret-client-sha2-server
+client = 5-disable-extended-master-secret-client-sha2-client
+
+[5-disable-extended-master-secret-client-sha2-server]
+Certificate = ${ENV::TEST_CERTS_DIR}/servercert.pem
+CipherString = DEFAULT
+PrivateKey = ${ENV::TEST_CERTS_DIR}/serverkey.pem
+
+[5-disable-extended-master-secret-client-sha2-client]
+CipherString = AES128-SHA256
+MaxProtocol = TLSv1.2
+Options = -ExtendedMasterSecret
+VerifyCAFile = ${ENV::TEST_CERTS_DIR}/rootcert.pem
+VerifyMode = Peer
+
+[test-5]
+ExpectedResult = Success
+
+
+# ===========================================================
+
+[6-disable-extended-master-secret-both-sha2]
+ssl_conf = 6-disable-extended-master-secret-both-sha2-ssl
+
+[6-disable-extended-master-secret-both-sha2-ssl]
+server = 6-disable-extended-master-secret-both-sha2-server
+client = 6-disable-extended-master-secret-both-sha2-client
+
+[6-disable-extended-master-secret-both-sha2-server]
+Certificate = ${ENV::TEST_CERTS_DIR}/servercert.pem
+CipherString = DEFAULT
+Options = -ExtendedMasterSecret
+PrivateKey = ${ENV::TEST_CERTS_DIR}/serverkey.pem
+
+[6-disable-extended-master-secret-both-sha2-client]
+CipherString = AES128-SHA256
+MaxProtocol = TLSv1.2
+Options = -ExtendedMasterSecret
+VerifyCAFile = ${ENV::TEST_CERTS_DIR}/rootcert.pem
+VerifyMode = Peer
+
+[test-6]
+ExpectedResult = Success
+
+
diff --git a/test/ssl-tests/30-extended-master-secret.conf.in b/test/ssl-tests/30-extended-master-secret.conf.in
new file mode 100644 (file)
index 0000000..2386c98
--- /dev/null
@@ -0,0 +1,122 @@
+# -*- mode: perl; -*-
+# Copyright 2016-2016 The OpenSSL Project Authors. All Rights Reserved.
+#
+# Licensed under the OpenSSL license (the "License").  You may not use
+# this file except in compliance with the License.  You can obtain a copy
+# in the file LICENSE in the source distribution or at
+# https://www.openssl.org/source/license.html
+
+
+## SSL test configurations
+
+package ssltests;
+
+use OpenSSL::Test::Utils;
+
+our @tests = ();
+
+my @tests_tls1_2 = (
+    {
+        name => "disable-extended-master-secret-server-sha",
+        server => {
+          "Options" => "-ExtendedMasterSecret",
+        },
+        client => {
+          "CipherString" => "AES128-SHA",
+          "MaxProtocol" => "TLSv1.2"
+        },
+        test   => {
+          "ExpectedResult" => "Success",
+        },
+    },
+    {
+        name => "disable-extended-master-secret-client-sha",
+        server => {
+        },
+        client => {
+          "CipherString" => "AES128-SHA",
+          "Options" => "-ExtendedMasterSecret",
+          "MaxProtocol" => "TLSv1.2"
+        },
+        test   => {
+          "ExpectedResult" => "Success",
+        },
+    },
+    {
+        name => "disable-extended-master-secret-both-sha",
+        server => {
+          "Options" => "-ExtendedMasterSecret",
+        },
+        client => {
+          "CipherString" => "AES128-SHA",
+          "Options" => "-ExtendedMasterSecret",
+          "MaxProtocol" => "TLSv1.2"
+        },
+        test   => {
+          "ExpectedResult" => "Success",
+        },
+    },
+    {
+        name => "disable-extended-master-secret-both-resume",
+        server => {
+          "Options" => "-ExtendedMasterSecret",
+        },
+        resume_server => {
+        },
+        client => {
+          "CipherString" => "AES128-SHA",
+          "Options" => "-ExtendedMasterSecret",
+          "MaxProtocol" => "TLSv1.2"
+        },
+        resume_client => {
+          "CipherString" => "AES128-SHA",
+          "MaxProtocol" => "TLSv1.2"
+        },
+        test   => {
+         "HandshakeMode" => "Resume",
+          "ExpectedResult" => "Success",
+        },
+    },
+    {
+        name => "disable-extended-master-secret-server-sha2",
+        server => {
+          "Options" => "-ExtendedMasterSecret",
+        },
+        client => {
+          "CipherString" => "AES128-SHA256",
+          "MaxProtocol" => "TLSv1.2"
+        },
+        test   => {
+          "ExpectedResult" => "Success",
+        },
+    },
+    {
+        name => "disable-extended-master-secret-client-sha2",
+        server => {
+        },
+        client => {
+          "CipherString" => "AES128-SHA256",
+          "Options" => "-ExtendedMasterSecret",
+          "MaxProtocol" => "TLSv1.2"
+        },
+        test   => {
+          "ExpectedResult" => "Success",
+        },
+    },
+    {
+        name => "disable-extended-master-secret-both-sha2",
+        server => {
+          "Options" => "-ExtendedMasterSecret",
+        },
+        client => {
+          "CipherString" => "AES128-SHA256",
+          "Options" => "-ExtendedMasterSecret",
+          "MaxProtocol" => "TLSv1.2"
+        },
+        test   => {
+          "ExpectedResult" => "Success",
+        },
+    },
+);
+
+push @tests, @tests_tls1_2 unless disabled("tls1_2");
index 02eb1fef7e8f05dac05c8099fdfcfa76c4d19c54..788ac4609ef7d7d40f421872f062a011e393ccb9 100644 (file)
@@ -571,6 +571,51 @@ static int test_client_hello_cb(void)
 
     testresult = 1;
 
+end:
+    SSL_free(serverssl);
+    SSL_free(clientssl);
+    SSL_CTX_free(sctx);
+    SSL_CTX_free(cctx);
+
+    return testresult;
+}
+
+static int test_no_ems(void)
+{
+    SSL_CTX *cctx = NULL, *sctx = NULL;
+    SSL *clientssl = NULL, *serverssl = NULL;
+    int testresult = 0;
+
+    if (!create_ssl_ctx_pair(TLS_server_method(), TLS_client_method(),
+                             TLS1_VERSION, TLS1_2_VERSION,
+                             &sctx, &cctx, cert, privkey)) {
+        printf("Unable to create SSL_CTX pair\n");
+        goto end;
+    }
+
+    SSL_CTX_set_options(sctx, SSL_OP_NO_EXTENDED_MASTER_SECRET);
+
+    if (!create_ssl_objects(sctx, cctx, &serverssl, &clientssl, NULL, NULL)) {
+        printf("Unable to create SSL objects\n");
+        goto end;
+    }
+
+    if (!create_ssl_connection(serverssl, clientssl, SSL_ERROR_NONE)) {
+        printf("Creating SSL connection failed\n");
+        goto end;
+    }
+
+    if (SSL_get_extms_support(serverssl)) {
+        printf("Server reports Extended Master Secret support\n");
+        goto end;
+    }
+
+    if (SSL_get_extms_support(clientssl)) {
+        printf("Client reports Extended Master Secret support\n");
+        goto end;
+    }
+    testresult = 1;
+
 end:
     SSL_free(serverssl);
     SSL_free(clientssl);
@@ -6087,6 +6132,7 @@ int setup_tests(void)
 #endif
 #ifndef OPENSSL_NO_TLS1_2
     ADD_TEST(test_client_hello_cb);
+    ADD_TEST(test_no_ems);
 #endif
 #ifndef OPENSSL_NO_TLS1_3
     ADD_ALL_TESTS(test_early_data_read_write, 3);