extensions.c

/*
  Copyright 2021 Northern.tech AS

  This file is part of CFEngine 3 - written and maintained by Northern.tech AS.

  This program is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by the
  Free Software Foundation; version 3.

  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; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA

  To the extent this program is licensed as part of the Enterprise
  versions of CFEngine, the applicable Commercial Open Source License
  (COSL) may apply to this file if you as a licensee so wish it. See
  included file COSL.txt.
*/

#include <enterprise_extension.h>

#include <known_dirs.h>
#include <misc_lib.h>

#include <pthread.h>

/*
 * A note regarding the loading of the extension plugins:
 *
 * The extension plugin was originally statically linked into each agent,
 * but was then refactored into plugins.
 * Therefore, since it hasn't been written according to plugin guidelines,
 * it is not safe to assume that we can unload it once we have
 * loaded it, since it may allocate resources that are not freed. It is also
 * not safe to assume that we can load it after initialization is complete
 * (for example if the plugin is dropped into the directory after cf-serverd
 * has already been running for some time), because some data structures may
 * not have been initialized.
 *
 * Therefore, the load strategy is as follows:
 *
 * - If we find the plugin immediately, load it, and keep it loaded.
 *
 * - If we don't find the plugin, NEVER attempt to load it again afterwards.
 *
 * - Never unload the plugin.
 *
 * - Any installation/upgrade/removal of the plugin requires daemon restarts.
 *
 * - The exception is for testing (see getenv below).
 */

#ifndef BUILTIN_EXTENSIONS

static bool enable_extension_libraries = true; /* GLOBAL_X */
static bool attempted_loading = false; /* GLOBAL_X */

void extension_libraries_disable()
{
    if (attempted_loading)
    {
        ProgrammingError("extension_libraries_disable() MUST be called before any call to extension functions");
    }
    enable_extension_libraries = false;
}

void *extension_library_open(const char *name)
{
    if (!enable_extension_libraries)
    {
        return NULL;
    }

    if (getenv("CFENGINE_TEST_OVERRIDE_EXTENSION_LIBRARY_DO_CLOSE") == NULL)
    {
        // Only do loading checks if we are not doing tests.
        attempted_loading = true;
    }

    const char *dirs_to_try[3] = { NULL };
    const char *dir = getenv("CFENGINE_TEST_OVERRIDE_EXTENSION_LIBRARY_DIR");
    char lib[] = "/lib";
    if (dir)
    {
        lib[0] = '\0';
        dirs_to_try[0] = dir;
    }
    else
    {
        dirs_to_try[0] = GetWorkDir();
        if (strcmp(WORKDIR, dirs_to_try[0]) != 0)
        {
            // try to load from the real WORKDIR in case GetWorkDir returned the local workdir to the user
            // We try this because enterprise "make install" is in WORKDIR, not per user
            dirs_to_try[1] = WORKDIR;
        }
    }

    void *handle = NULL;
    for (int i = 0; dirs_to_try[i]; i++)
    {
        char path[strlen(dirs_to_try[i]) + strlen(lib) + strlen(name) + 2];
        xsnprintf(path, sizeof(path), "%s%s/%s", dirs_to_try[i], lib, name);

        Log(LOG_LEVEL_DEBUG, "Trying to shlib_open extension plugin '%s' from '%s'", name, path);

        handle = shlib_open(path);
        if (handle)
        {
            Log(LOG_LEVEL_VERBOSE, "Successfully opened extension plugin '%s' from '%s'", name, path);
            break;
        }
        else
        {
            const char *error;
            if (errno == ENOENT)
            {
                error = "(not installed)";
            }
            else
            {
                error = GetErrorStr();
            }
            Log(LOG_LEVEL_VERBOSE, "Could not open extension plugin '%s' from '%s': %s", name, path, error);
        }
    }

    if (!handle)
    {
        return handle;
    }

    // Version check, to avoid binary incompatible plugins.
    const char * (*GetExtensionLibraryVersion)() = shlib_load(handle, "GetExtensionLibraryVersion");
    if (!GetExtensionLibraryVersion)
    {
        Log(LOG_LEVEL_ERR, "Could not retrieve version from extension plugin (%s). Not loading the plugin.", name);
        goto close_and_fail;
    }

    const char *plugin_version = GetExtensionLibraryVersion();
    unsigned int bin_major, bin_minor, bin_patch;
    unsigned int plug_major, plug_minor, plug_patch;
    if (sscanf(VERSION, "%u.%u.%u", &bin_major, &bin_minor, &bin_patch) != 3)
    {
        Log(LOG_LEVEL_ERR, "Not able to extract version number from binary (%s). Not loading extension plugin.", name);
        goto close_and_fail;
    }
    if (sscanf(plugin_version, "%u.%u.%u", &plug_major, &plug_minor, &plug_patch) != 3)
    {
        Log(LOG_LEVEL_ERR, "Not able to extract version number from plugin (%s). Not loading extension plugin.", name);
        goto close_and_fail;
    }

    if (bin_major != plug_major || bin_minor != plug_minor || bin_patch != plug_patch)
    {
        Log(LOG_LEVEL_ERR, "Extension plugin version does not match CFEngine Community version "
            "(CFEngine Community v%u.%u.%u, Extension (%s) v%u.%u.%u). Refusing to load it.",
            bin_major, bin_minor, bin_patch, name, plug_major, plug_minor, plug_patch);
        goto close_and_fail;
    }

    Log(LOG_LEVEL_VERBOSE, "Successfully loaded extension plugin '%s'", name);

    return handle;

close_and_fail:
    shlib_close(handle);
    return NULL;
}

void extension_library_close(void *handle)
{
    shlib_close(handle);
}

#endif // !BUILTIN_EXTENSIONS