plugin: Export base64 encode and decode functions

This patch builds on the "Export secure_memzero() to plug-ins" patch and
adds export of openvpn_base64_encode() and openvpn_base64_decode()

This also ships with a very simple plug-in which demonstrates how to use
the new exported functions.

Signed-off-by: David Sommerseth <davids@openvpn.net>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <20170505214624.11675-1-davids@openvpn.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14558.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

include/openvpn-plugin.h.in

@@ -219,6 +219,8 @@ struct openvpn_plugin_string_list
  *           OpenVPN to plug-ins.
  *
  *    4      Exported secure_memzero() as plugin_secure_memzero()
+ *           Exported openvpn_base64_encode() as plugin_base64_encode()
+ *           Exported openvpn_base64_decode() as plugin_base64_decode()
  */
 #define OPENVPN_PLUGINv3_STRUCTVER 4
 
@@ -267,6 +269,33 @@ typedef void (*plugin_vlog_t)(openvpn_plugin_log_flags_t flags,
  */
 typedef void (*plugin_secure_memzero_t)(void *data, size_t len);
 
+/**
+ *  Export of openvpn_base64_encode() to be used inside plug-ins
+ *
+ *  @param data   Pointer to data to BASE64 encode
+ *  @param size   Length of data, in bytes
+ *  @param *str   Pointer to the return buffer.  This needed memory is
+ *                allocated by openvpn_base64_encode() and needs to be free()d
+ *                after use.
+ *
+ *  @return int   Returns the length of the buffer created, or -1 on error.
+ *
+ */
+typedef int (*plugin_base64_encode_t)(const void *data, int size, char **str);
+
+/**
+ *  Export of openvpn_base64_decode() to be used inside plug-ins
+ *
+ *  @param str    Pointer to the BASE64 encoded data
+ *  @param data   Pointer to the buffer where save the decoded data
+ *  @param size   Size of the destination buffer
+ *
+ *  @return int   Returns the length of the decoded data, or -1 on error or
+ *                if the destination buffer is too small.
+ *
+ */
+typedef int (*plugin_base64_decode_t)(const char *str, void *data, int size);
+
 
 /**
  * Used by the openvpn_plugin_open_v3() function to pass callback
@@ -289,6 +318,8 @@ struct openvpn_plugin_callbacks
     plugin_log_t plugin_log;
     plugin_vlog_t plugin_vlog;
     plugin_secure_memzero_t plugin_secure_memzero;
+    plugin_base64_encode_t plugin_base64_encode;
+    plugin_base64_decode_t plugin_base64_decode;
 };
 
 /**

sample/sample-plugins/simple/base64.c

@@ -0,0 +1,203 @@
+/*
+ *  OpenVPN -- An application to securely tunnel IP networks
+ *             over a single TCP/UDP port, with support for SSL/TLS-based
+ *             session authentication and key exchange,
+ *             packet encryption, packet authentication, and
+ *             packet compression.
+ *
+ *  Copyright (C) 2017  David Sommerseth <davids@openvpn.net>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2
+ *  as published by the Free Software Foundation.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program (see the file COPYING included with this
+ *  distribution); if not, write to the Free Software Foundation, Inc.,
+ *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "openvpn-plugin.h"
+
+#define PLUGIN_NAME "base64.c"
+
+/* Exported plug-in v3 API functions */
+plugin_log_t ovpn_log = NULL;                      /**< Pointer to the OpenVPN log function.  See plugin_log() */
+plugin_vlog_t ovpn_vlog = NULL;                    /**< Pointer to the OpenVPN vlog function. See plugin_vlog() */
+plugin_base64_encode_t ovpn_base64_encode = NULL;  /**< Pointer to the openvpn_base64_encode () function */
+plugin_base64_decode_t ovpn_base64_decode = NULL;  /**< Pointer to the openvpn_base64_decode () function */
+
+/**
+ * Search the environment pointer for a specific env var name
+ *
+ * PLEASE NOTE! The result is not valid outside the local
+ * scope of the calling function.  Once the calling function
+ * returns, any returned pointers are invalid.
+ *
+ * @param name  String containing the env.var name to search for
+ * @param envp  String array pointer to the environment variable
+ *
+ * @return Returns a pointer to the value in the environment variable
+ *         table on successful match.  Otherwise NULL is returned
+ *
+ */
+static const char *
+get_env(const char *name, const char *envp[])
+{
+    if (envp)
+    {
+        int i;
+        const int namelen = strlen(name);
+        for (i = 0; envp[i]; ++i)
+        {
+            if (!strncmp(envp[i], name, namelen))
+            {
+                const char *cp = envp[i] + namelen;
+                if (*cp == '=')
+                {
+                    return cp + 1;
+                }
+            }
+        }
+    }
+    return NULL;
+}
+
+
+/**
+ * This function is called when OpenVPN loads the plug-in.
+ * The purpose is to initialize the plug-in and tell OpenVPN
+ * which plug-in hooks this plug-in wants to be involved in
+ *
+ * For the arguments, see the include/openvpn-plugin.h file
+ * for details on the function parameters
+ *
+ * @param v3structver  An integer containing the API version of
+ *                     the plug-in structs OpenVPN uses
+ * @param args         A pointer to the argument struct for
+ *                     information and features provided by
+ *                     OpenVPN to the plug-in
+ * @param ret          A pointer to the struct OpenVPN uses to
+ *                     receive information back from the plug-in
+ *
+ * @return Must return OPENVPN_PLUGIN_FUNC_SUCCESS when everything
+ *         completed successfully.  Otherwise it must be returned
+ *         OPENVPN_PLUGIN_FUNC_ERROR, which will stop OpenVPN
+ *         from running
+ *
+ */
+OPENVPN_EXPORT int
+openvpn_plugin_open_v3(const int v3structver,
+                       struct openvpn_plugin_args_open_in const *args,
+                       struct openvpn_plugin_args_open_return *ret)
+{
+    /* Check that we are API compatible */
+    if (v3structver != OPENVPN_PLUGINv3_STRUCTVER)
+    {
+        printf("base64.c: ** ERROR ** Incompatible plug-in interface between this plug-in and OpenVPN\n");
+        return OPENVPN_PLUGIN_FUNC_ERROR;
+    }
+
+    /*  Which callbacks to intercept.  */
+    ret->type_mask =
+        OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_TLS_VERIFY)
+        |OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_CLIENT_CONNECT_V2);
+
+    /* we don't need a plug-in context in this example, but OpenVPN expects "something" */
+    ret->handle = calloc(1, 1);
+
+    /* Hook into the exported functions from OpenVPN */
+    ovpn_log = args->callbacks->plugin_log;
+    ovpn_vlog = args->callbacks->plugin_vlog;
+    ovpn_base64_encode = args->callbacks->plugin_base64_encode;
+    ovpn_base64_decode = args->callbacks->plugin_base64_decode;
+
+    /* Print some version information about the OpenVPN process using this plug-in */
+    ovpn_log(PLOG_NOTE, PLUGIN_NAME, "OpenVPN %s  (Major: %i, Minor: %i, Patch: %s)\n",
+             args->ovpn_version, args->ovpn_version_major,
+             args->ovpn_version_minor, args->ovpn_version_patch);
+
+    return OPENVPN_PLUGIN_FUNC_SUCCESS;
+}
+
+
+/**
+ * This function is called by OpenVPN each time the OpenVPN reaches
+ * a point where plug-in calls should happen.  It only happens for those
+ * plug-in hooks enabled in openvpn_plugin_open_v3().
+ *
+ * For the arguments, see the include/openvpn-plugin.h file
+ * for details on the function parameters
+ *
+ * @param args        Pointer to a struct with details about the plug-in
+ *                    call from the main OpenVPN process.
+ * @param returndata  Pointer to a struct where the plug-in can provide
+ *                    information back to OpenVPN to be processed
+ *
+ * @return  Must return OPENVPN_PLUGIN_FUNC_SUCCESS or
+ *          OPENVPN_PLUGIN_FUNC_DEFERRED on success.  Otherwise it
+ *          should return OPENVPN_FUNC_ERROR, which will stop and reject
+ *          the client session from progressing.
+ *
+ */
+
+OPENVPN_EXPORT int
+openvpn_plugin_func_v1(openvpn_plugin_handle_t handle, const int type, const char *argv[], const char *envp[])
+{
+    if (type != OPENVPN_PLUGIN_TLS_VERIFY
+        && type != OPENVPN_PLUGIN_CLIENT_CONNECT_V2)
+    {
+        ovpn_log(PLOG_ERR, PLUGIN_NAME, "Unsupported plug-in hook call attempted");
+        return OPENVPN_PLUGIN_FUNC_ERROR;
+    }
+
+    /* get username/password from envp string array */
+    const char *clcert_cn = get_env("X509_0_CN", envp);
+    if (!clcert_cn)
+    {
+        /* Ignore certificate checks not being a client certificate */
+        return OPENVPN_PLUGIN_FUNC_SUCCESS;
+    }
+
+    /* test the BASE64 encode function */
+    char *buf = NULL;
+    int r = ovpn_base64_encode(clcert_cn, strlen(clcert_cn), &buf);
+    ovpn_log(PLOG_NOTE, PLUGIN_NAME, "BASE64 encoded '%s' (return value %i):  '%s'",
+             clcert_cn, r, buf);
+
+    /* test the BASE64 decode function */
+    char buf2[256] = {0};
+    r = ovpn_base64_decode(buf, &buf2, 255);
+    ovpn_log(PLOG_NOTE, PLUGIN_NAME, "BASE64 decoded '%s' (return value %i):  '%s'",
+             buf, r, buf2);
+
+    /* Verify the result, and free the buffer allocated by ovpn_base64_encode() */
+    r = strcmp(clcert_cn, buf2);
+    free(buf);
+
+    return (r == 0) ? OPENVPN_PLUGIN_FUNC_SUCCESS : OPENVPN_PLUGIN_FUNC_ERROR;
+}
+
+
+/**
+ * This cleans up the last part of the plug-in, allows it to
+ * shut down cleanly and release the plug-in global context buffer
+ *
+ * @param handle   Pointer to the plug-in global context buffer, which
+ *                 need to be released by this function
+ */
+OPENVPN_EXPORT void
+openvpn_plugin_close_v1(openvpn_plugin_handle_t handle)
+{
+    struct plugin_context *context = (struct plugin_context *) handle;
+    free(context);
+}

src/openvpn/plugin.c

@@ -43,6 +43,7 @@
 #include "misc.h"
 #include "plugin.h"
 #include "ssl_backend.h"
+#include "base64.h"
 #include "win32.h"
 #include "memdbg.h"
 
@@ -410,7 +411,9 @@ plugin_log(openvpn_plugin_log_flags_t flags, const char *name, const char *forma
 static struct openvpn_plugin_callbacks callbacks = {
     plugin_log,
     plugin_vlog,
-    secure_memzero   /* plugin_secure_memzero */
+    secure_memzero,         /* plugin_secure_memzero */
+    openvpn_base64_encode,  /* plugin_base64_encode */
+    openvpn_base64_decode,  /* plugin_base64_decode */
 };