plugin: Extend the plug-in v3 API to identify the SSL implementation used

OpenVPN would segfault unexpectedly if it would be compiled against
PolarSSL
and the plug-in would expect OpenSSL, or vice-versa.  This segfault would
not appear before the plug-in would try to access functions which would
be available if the plug-in and OpenVPN uses the same SSL implementation.

This patch adds a member to the plug-in initialisation function, which
identifies the SSL implementation.

The log_v3 plug-in is updated accordingly + a simple fix to make it
buildable again using the ./build script.

A minor documentation error in the openvpn-plugin.h was also
corrected, where it mentioned OPENVPN_PLUGIN_VERSION instead of
OPENVPN_PLUGINv3_STRUCTVER.

 v2 - add const ovpnSSLAPI ssl_api at the end of
      struct openvpn_plugin_args_open_in and not in the "middle"

 v3 - fix bug in plug-in init, as the SSLAPI was located wrong in the
      args struct sent to the openvpn_plugin_open_v3() function.

 v4 - Ensure SSLAPI got a sane/known value if SSL is disabled or unknown

Signed-off-by: David Sommerseth <davids@redhat.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1372879030-10576-1-git-send-email-dazo@users.sourceforge.net>
URL: http://article.gmane.org/gmane.network.openvpn.devel/7754
Signed-off-by: Gert Doering <gert@greenie.muc.de>

include/openvpn-plugin.h

@@ -201,10 +201,15 @@ struct openvpn_plugin_string_list
  *
  * Version   Comment
  *    1      Initial plugin v3 structures providing the same API as
- *           the v2 plugin interface + X509 certificate information.
+ *           the v2 plugin interface, X509 certificate information +
+ *           a logging API for plug-ins.
+ *
+ *    2      Added ssl_api member in struct openvpn_plugin_args_open_in
+ *           which identifies the SSL implementation OpenVPN is compiled
+ *           against.
  *
  */
-#define OPENVPN_PLUGINv3_STRUCTVER 1
+#define OPENVPN_PLUGINv3_STRUCTVER 2
 
 /**
  * Definitions needed for the plug-in callback functions.
@@ -259,6 +264,18 @@ struct openvpn_plugin_callbacks
   plugin_vlog_t   plugin_vlog;
 };
 
+/**
+ * Used by the openvpn_plugin_open_v3() function to indicate to the
+ * plug-in what kind of SSL implementation OpenVPN uses.  This is
+ * to avoid SEGV issues when OpenVPN is complied against PolarSSL
+ * and the plug-in against OpenSSL.
+ */
+typedef enum {
+  SSLAPI_NONE,
+  SSLAPI_OPENSSL,
+  SSLAPI_POLARSSL
+} ovpnSSLAPI;
+
 /**
  * Arguments used to transport variables to the plug-in.
  * The struct openvpn_plugin_args_open_in is only used
@@ -286,6 +303,7 @@ struct openvpn_plugin_args_open_in
   const char ** const argv;
   const char ** const envp;
   struct openvpn_plugin_callbacks *callbacks;
+  const ovpnSSLAPI ssl_api;
 };
 
 
@@ -557,7 +575,8 @@ OPENVPN_PLUGIN_DEF int OPENVPN_PLUGIN_FUNC(openvpn_plugin_func_v2)
  * ARGUMENTS
  *
  * version : fixed value, defines the API version of the OpenVPN plug-in API.  The plug-in
- *	     should validate that this value is matching the OPENVPN_PLUGIN_VERSION value.
+ *	     should validate that this value is matching the OPENVPN_PLUGINv3_STRUCTVER
+ *	     value.
  *
  * arguments : Structure with all arguments available to the plug-in.
  *

sample/sample-plugins/log/build

@@ -6,7 +6,7 @@
 #
 
 # This directory is where we will look for openvpn-plugin.h
-CPPFLAGS="${CPPFLAGS:--I../../..}"
+CPPFLAGS="${CPPFLAGS:--I../../../include}"
 
 CC="${CC:-gcc}"
 CFLAGS="${CFLAGS:--O2 -Wall -g}"

sample/sample-plugins/log/log_v3.c

@@ -85,6 +85,11 @@ openvpn_plugin_open_v3 (const int v3structver,
     return OPENVPN_PLUGIN_FUNC_ERROR;
   }
 
+  if( args->ssl_api != SSLAPI_OPENSSL ) {
+    printf("This plug-in can only be used against OpenVPN with OpenSSL\n");
+    return OPENVPN_PLUGIN_FUNC_ERROR;
+  }
+
   /*  Which callbacks to intercept.  */
   ret->type_mask =
     OPENVPN_PLUGIN_MASK (OPENVPN_PLUGIN_UP) |

src/openvpn/plugin.c

@@ -40,8 +40,8 @@
 #include "error.h"
 #include "misc.h"
 #include "plugin.h"
+#include "ssl_backend.h"
 #include "win32.h"
-
 #include "memdbg.h"
 
 #define PLUGIN_SYMBOL_REQUIRED (1<<0)
@@ -374,7 +374,8 @@ plugin_open_item (struct plugin *p,
         struct openvpn_plugin_args_open_in args = { p->plugin_type_mask,
                                                     (const char ** const) o->argv,
                                                     (const char ** const) envp,
-                                                    &callbacks };
+                                                    &callbacks,
+                                                    SSLAPI };
         struct openvpn_plugin_args_open_return retargs;
 
         CLEAR(retargs);

src/openvpn/ssl_backend.h

@@ -36,10 +36,17 @@
 #ifdef ENABLE_CRYPTO_OPENSSL
 #include "ssl_openssl.h"
 #include "ssl_verify_openssl.h"
+#define SSLAPI SSLAPI_OPENSSL
 #endif
 #ifdef ENABLE_CRYPTO_POLARSSL
 #include "ssl_polarssl.h"
 #include "ssl_verify_polarssl.h"
+#define SSLAPI SSLAPI_POLARSSL
+#endif
+
+/* Ensure that SSLAPI got a sane value if SSL is disabled or unknown */
+#ifndef SSLAPI
+#define SSLAPI SSLAPI_NONE
 #endif
 
 /**