Support configuring multiple ECDH curves

The ssl_ecdh_curve GUC only accepts a single value, but the TLS
handshake can list multiple curves in the groups extension (the
extension has been renamed to contain more than elliptic curves).
This changes the GUC to accept a colon-separated list of curves.
This commit also renames the GUC to ssl_groups to match the new
nomenclature for the TLS extension.

Original patch by Erica Zhang with additional hacking by me.

Author: Erica Zhang <ericazhangy2021@qq.com>
Author: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/tencent_063F89FA72CCF2E48A0DF5338841988E9809@qq.com

doc/src/sgml/config.sgml

@@ -1452,20 +1452,20 @@ include_dir 'conf.d'
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-ssl-ecdh-curve" xreflabel="ssl_ecdh_curve">
-      <term><varname>ssl_ecdh_curve</varname> (<type>string</type>)
+     <varlistentry id="guc-ssl-groups" xreflabel="ssl_groups">
+      <term><varname>ssl_groups</varname> (<type>string</type>)
       <indexterm>
-       <primary><varname>ssl_ecdh_curve</varname> configuration parameter</primary>
+       <primary><varname>ssl_groups</varname> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
         Specifies the name of the curve to use in <acronym>ECDH</acronym> key
         exchange.  It needs to be supported by all clients that connect.
+        Multiple curves can be specified by using a colon-separated list.
         It does not need to be the same curve used by the server's Elliptic
-        Curve key.
-        This parameter can only be set in the <filename>postgresql.conf</filename>
-        file or on the server command line.
+        Curve key.  This parameter can only be set in the
+        <filename>postgresql.conf</filename> file or on the server command line.
         The default is <literal>prime256v1</literal>.
        </para>
 
@@ -1475,9 +1475,16 @@ include_dir 'conf.d'
         <literal>prime256v1</literal> (NIST P-256),
         <literal>secp384r1</literal> (NIST P-384),
         <literal>secp521r1</literal> (NIST P-521).
-        The full list of available curves can be shown with the command
-        <command>openssl ecparam -list_curves</command>.  Not all of them
-        are usable in <acronym>TLS</acronym> though.
+        An incomplete list of available groups can be shown with the command
+        <command>openssl ecparam -list_curves</command>.  Not all of them are
+        usable with <acronym>TLS</acronym> though, and many supported group
+        names and aliases are omitted.
+       </para>
+
+       <para>
+        In <productname>PostgreSQL</productname> versions before 18.0 this
+        setting was named <literal>ssl_ecdh_curve</literal> and only accepted
+        a single value.
        </para>
       </listitem>
      </varlistentry>

src/backend/libpq/be-secure-openssl.c

@@ -76,6 +76,7 @@ static int	alpn_cb(SSL *ssl,
 					void *userdata);
 static bool initialize_dh(SSL_CTX *context, bool isServerStart);
 static bool initialize_ecdh(SSL_CTX *context, bool isServerStart);
+static const char *SSLerrmessageExt(unsigned long ecode, const char *replacement);
 static const char *SSLerrmessage(unsigned long ecode);
 
 static char *X509_NAME_to_cstring(X509_NAME *name);
@@ -1409,35 +1410,50 @@ static bool
 initialize_ecdh(SSL_CTX *context, bool isServerStart)
 {
 #ifndef OPENSSL_NO_ECDH
-	EC_KEY	   *ecdh;
-	int			nid;
-
-	nid = OBJ_sn2nid(SSLECDHCurve);
-	if (!nid)
+	if (SSL_CTX_set1_groups_list(context, SSLECDHCurve) != 1)
 	{
+		/*
+		 * OpenSSL 3.3.0 introduced proper error messages for group parsing
+		 * errors, earlier versions returns "no SSL error reported" which is
+		 * far from helpful. For older versions, we replace with a better
+		 * error message. Injecting the error into the OpenSSL error queue
+		 * need APIs from OpenSSL 3.0.
+		 */
 		ereport(isServerStart ? FATAL : LOG,
-				(errcode(ERRCODE_CONFIG_FILE_ERROR),
-				 errmsg("ECDH: unrecognized curve name: %s", SSLECDHCurve)));
+				errcode(ERRCODE_CONFIG_FILE_ERROR),
+				errmsg("failed to set group names specified in ssl_groups: %s",
+					   SSLerrmessageExt(ERR_get_error(),
+										_("No valid groups found"))),
+				errhint("Ensure that each group name is spelled correctly and supported by the installed version of OpenSSL"));
 		return false;
 	}
-
-	ecdh = EC_KEY_new_by_curve_name(nid);
-	if (!ecdh)
-	{
-		ereport(isServerStart ? FATAL : LOG,
-				(errcode(ERRCODE_CONFIG_FILE_ERROR),
-				 errmsg("ECDH: could not create key")));
-		return false;
-	}
-
-	SSL_CTX_set_options(context, SSL_OP_SINGLE_ECDH_USE);
-	SSL_CTX_set_tmp_ecdh(context, ecdh);
-	EC_KEY_free(ecdh);
 #endif
 
 	return true;
 }
 
+/*
+ * Obtain reason string for passed SSL errcode with replacement
+ *
+ * The error message supplied in replacement will be used in case the error
+ * code from OpenSSL is 0, else the error message from SSLerrmessage() will
+ * be returned.
+ *
+ * Not all versions of OpenSSL place an error on the queue even for failing
+ * operations, which will yield "no SSL error reported" by SSLerrmessage. This
+ * function can be used to ensure that a proper error message is displayed for
+ * versions reporting no error, while using the OpenSSL error via SSLerrmessage
+ * for versions where there is one.
+ */
+static const char *
+SSLerrmessageExt(unsigned long ecode, const char *replacement)
+{
+	if (ecode == 0)
+		return replacement;
+	else
+		return SSLerrmessage(ecode);
+}
+
 /*
  * Obtain reason string for passed SSL errcode
  *

src/backend/utils/misc/guc.c

@@ -190,6 +190,7 @@ static const unit_conversion time_unit_conversion_table[] =
 static const char *const map_old_guc_names[] = {
 	"sort_mem", "work_mem",
 	"vacuum_mem", "maintenance_work_mem",
+	"ssl_ecdh_curve", "ssl_groups",
 	NULL
 };
 

src/backend/utils/misc/guc_tables.c

@@ -4656,9 +4656,9 @@ struct config_string ConfigureNamesString[] =
 	},
 
 	{
-		{"ssl_ecdh_curve", PGC_SIGHUP, CONN_AUTH_SSL,
-			gettext_noop("Sets the curve to use for ECDH."),
-			NULL,
+		{"ssl_groups", PGC_SIGHUP, CONN_AUTH_SSL,
+			gettext_noop("Sets the group(s) to use for Diffie-Hellman key exchange."),
+			gettext_noop("Multiple groups can be specified using colon-separated list."),
 			GUC_SUPERUSER_ONLY
 		},
 		&SSLECDHCurve,

src/backend/utils/misc/postgresql.conf.sample

@@ -112,7 +112,7 @@
 #ssl_key_file = 'server.key'
 #ssl_ciphers = 'HIGH:MEDIUM:+3DES:!aNULL'	# allowed SSL ciphers
 #ssl_prefer_server_ciphers = on
-#ssl_ecdh_curve = 'prime256v1'
+#ssl_groups = 'prime256v1'
 #ssl_min_protocol_version = 'TLSv1.2'
 #ssl_max_protocol_version = ''
 #ssl_dh_params_file = ''

src/test/ssl/t/001_ssltests.pl

@@ -116,6 +116,18 @@ ssl_max_protocol_version=''});
 $result = $node->restart(fail_ok => 1);
 is($result, 1, 'restart succeeds with correct SSL protocol bounds');
 
+# Test parsing colon-separated groups. Resetting to a default value to clear
+# the error is fine since the call to switch_server_cert in the client side
+# tests will overwrite ssl_groups with a known set of groups.
+$node->append_conf('sslconfig.conf', qq{ssl_groups='bad:value'});
+my $log_size = -s $node->logfile;
+$result = $node->restart(fail_ok => 1);
+is($result, 0, 'restart fails with incorrect groups');
+ok($node->log_contains(qr/no SSL error reported/) == 0,
+	'error message translated');
+$node->append_conf('ssl_config.conf', qq{ssl_groups='prime256v1'});
+$result = $node->restart(fail_ok => 1);
+
 ### Run client-side tests.
 ###
 ### Test that libpq accepts/rejects the connection correctly, depending

src/test/ssl/t/SSL/Server.pm

@@ -300,6 +300,9 @@ sub switch_server_cert
 	ok(unlink($node->data_dir . '/sslconfig.conf'));
 	$node->append_conf('sslconfig.conf', "ssl=on");
 	$node->append_conf('sslconfig.conf', $backend->set_server_cert(\%params));
+	# use lists of ECDH curves for syntax testing
+	$node->append_conf('sslconfig.conf', 'ssl_groups=prime256v1:secp521r1');
+
 	$node->append_conf('sslconfig.conf',
 		"ssl_passphrase_command='" . $params{passphrase_cmd} . "'")
 	  if defined $params{passphrase_cmd};