MEDIUM: ssl: add the possibility to use a global DH parameters file

This patch adds the ssl-dh-param-file global setting. It sets the
default DH parameters that will be used during the SSL/TLS handshake when
ephemeral Diffie-Hellman (DHE) key exchange is used, for all "bind" lines
which do not explicitely define theirs.

doc/configuration.txt

@@ -766,6 +766,20 @@ ssl-default-server-options [<option>]...
   default ssl-options to force on all "server" lines. Please check the "server"
   keyword to see available options.
 
+ssl-dh-param-file <file>
+  This setting is only available when support for OpenSSL was built in. It sets
+  the default DH parameters that are used during the SSL/TLS handshake when
+  ephemeral Diffie-Hellman (DHE) key exchange is used, for all "bind" lines
+  which do not explicitely define theirs. It will be overridden by custom DH
+  parameters found in a bind certificate file if any. If custom DH parameters
+  are not specified either by using ssl-dh-param-file or by setting them directly
+  in the certificate file, pre-generated DH parameters of the size specified
+  by tune.ssl.default-dh-param will be used. Custom parameters are known to be
+  more secure and therefore their use is recommended.
+  Custom DH parameters may be generated by using the OpenSSL command
+  "openssl dhparam <size>", where size should be at least 2048, as 1024-bit DH
+  parameters should not be considered secure anymore.
+
 ssl-server-verify [none|required]
   The default behavior for SSL verify on servers side. If specified to 'none',
   servers certificates are not verified. The default is 'required' except if
@@ -1224,7 +1238,8 @@ tune.ssl.default-dh-param <number>
   this maximum value. Default value if 1024. Only 1024 or higher values are
   allowed. Higher values will increase the CPU load, and values greater than
   1024 bits are not supported by Java 7 and earlier clients. This value is not
-  used if static Diffie-Hellman parameters are supplied via the certificate file.
+  used if static Diffie-Hellman parameters are supplied either directly
+  in the certificate file or by using the ssl-dh-param-file parameter.
 
 tune.zlib.memlevel <number>
   Sets the memLevel parameter in zlib initialization for each session. It

include/proto/ssl_sock.h

@@ -64,6 +64,9 @@ struct tls_keys_ref *tlskeys_ref_lookup(const char *filename);
 struct tls_keys_ref *tlskeys_ref_lookupid(int unique_id);
 void tlskeys_finalize_config(void);
 #endif
+#ifndef OPENSSL_NO_DH
+int ssl_sock_load_global_dh_param_from_file(const char *filename);
+#endif
 
 #endif /* _PROTO_SSL_SOCK_H */
 

src/cfgparse.c

@@ -753,6 +753,7 @@ int cfg_parse_global(const char *file, int linenum, char **args, int kwm)
 		}
 		global.tune.ssl_max_record = atol(args[1]);
 	}
+#ifndef OPENSSL_NO_DH
 	else if (!strcmp(args[0], "tune.ssl.default-dh-param")) {
 		if (alertif_too_many_args(1, file, linenum, args, &err_code))
 			goto out;
@@ -768,6 +769,7 @@ int cfg_parse_global(const char *file, int linenum, char **args, int kwm)
 			goto out;
 		}
 	}
+#endif
 #endif
 	else if (!strcmp(args[0], "tune.buffers.limit")) {
 		if (alertif_too_many_args(1, file, linenum, args, &err_code))
@@ -1187,6 +1189,22 @@ int cfg_parse_global(const char *file, int linenum, char **args, int kwm)
 		goto out;
 #endif
 	}
+#ifdef USE_OPENSSL
+#ifndef OPENSSL_NO_DH
+	else if (!strcmp(args[0], "ssl-dh-param-file")) {
+		if (*(args[1]) == 0) {
+			Alert("parsing [%s:%d] : '%s' expects a file path as an argument.\n", file, linenum, args[0]);
+			err_code |= ERR_ALERT | ERR_FATAL;
+			goto out;
+		}
+		if (ssl_sock_load_global_dh_param_from_file(args[1])) {
+			Alert("parsing [%s:%d] : '%s': unable to load DH parameters from file <%s>.\n", file, linenum, args[0], args[1]);
+			err_code |= ERR_ALERT | ERR_FATAL;
+			goto out;
+		}
+	}
+#endif
+#endif
 	else if (!strcmp(args[0], "ssl-server-verify")) {
 		if (alertif_too_many_args(1, file, linenum, args, &err_code))
 			goto out;

src/ssl_sock.c

@@ -124,6 +124,7 @@ struct list tlskeys_reference = LIST_HEAD_INIT(tlskeys_reference);
 
 #ifndef OPENSSL_NO_DH
 static int ssl_dh_ptr_index = -1;
+static DH *global_dh = NULL;
 static DH *local_dh_1024 = NULL;
 static DH *local_dh_2048 = NULL;
 static DH *local_dh_4096 = NULL;
@@ -1332,22 +1333,44 @@ static DH *ssl_get_tmp_dh(SSL *ssl, int export, int keylen)
 	return dh;
 }
 
+static DH * ssl_sock_get_dh_from_file(const char *filename)
+{
+	DH *dh = NULL;
+	BIO *in = BIO_new(BIO_s_file());
+
+	if (in == NULL)
+		goto end;
+
+	if (BIO_read_filename(in, filename) <= 0)
+		goto end;
+
+	dh = PEM_read_bio_DHparams(in, NULL, NULL, NULL);
+
+end:
+        if (in)
+                BIO_free(in);
+
+	return dh;
+}
+
+int ssl_sock_load_global_dh_param_from_file(const char *filename)
+{
+	global_dh = ssl_sock_get_dh_from_file(filename);
+
+	if (global_dh) {
+		return 0;
+	}
+
+	return -1;
+}
+
 /* Loads Diffie-Hellman parameter from a file. Returns 1 if loaded, else -1
    if an error occured, and 0 if parameter not found. */
 int ssl_sock_load_dh_params(SSL_CTX *ctx, const char *file)
 {
 	int ret = -1;
-	BIO *in;
-	DH *dh = NULL;
+	DH *dh = ssl_sock_get_dh_from_file(file);
 
-	in = BIO_new(BIO_s_file());
-	if (in == NULL)
-		goto end;
-
-	if (BIO_read_filename(in, file) <= 0)
-		goto end;
-
-	dh = PEM_read_bio_DHparams(in, NULL, ctx->default_passwd_callback, ctx->default_passwd_callback_userdata);
 	if (dh) {
 		ret = 1;
 		SSL_CTX_set_tmp_dh(ctx, dh);
@@ -1358,6 +1381,10 @@ int ssl_sock_load_dh_params(SSL_CTX *ctx, const char *file)
 			SSL_CTX_set_ex_data(ctx, ssl_dh_ptr_index, dh);
 		}
 	}
+	else if (global_dh) {
+		SSL_CTX_set_tmp_dh(ctx, global_dh);
+		ret = 0; /* DH params not found */
+	}
 	else {
 		/* Clear openssl global errors stack */
 		ERR_clear_error();
@@ -1381,9 +1408,6 @@ end:
 	if (dh)
 		DH_free(dh);
 
-	if (in)
-		BIO_free(in);
-
 	return ret;
 }
 #endif
@@ -1901,9 +1925,11 @@ int ssl_sock_prepare_ctx(struct bind_conf *bind_conf, SSL_CTX *ctx, struct proxy
 		cfgerr++;
 	}
 
-	/* If tune.ssl.default-dh-param has not been set and
-	   no static DH params were in the certificate file. */
+	/* If tune.ssl.default-dh-param has not been set,
+	   neither has ssl-default-dh-file and no static DH
+	   params were in the certificate file. */
 	if (global.tune.ssl_default_dh_param == 0 &&
+	    global_dh == NULL &&
 	    (ssl_dh_ptr_index == -1 ||
 	     SSL_CTX_get_ex_data(ctx, ssl_dh_ptr_index) == NULL)) {
 
@@ -5083,6 +5109,11 @@ static void __ssl_sock_deinit(void)
                 DH_free(local_dh_8192);
                 local_dh_8192 = NULL;
         }
+
+	if (global_dh) {
+		DH_free(global_dh);
+		global_dh = NULL;
+	}
 #endif
 
         ERR_remove_state(0);