Extending MySQL using the Component Infrastructure – part 9: adding a new function

This post is the nine one of a series of articles on extending MySQL with the Component Infrastructure, the list above will be updated as new articles are published:

If you have use the Component we created during part 8, you may have noticed that on the error log (not the one in performance_schema), there was the following message if your virus database was not up to date:

Once the Component and the ClamAV engine are loaded, even if the virus database is updated (freshclam), the virus database used will still be the previous one. We then need to call again reload_engine().

We will create now a new user function that we can use to reload the ClamAV engine after having upgraded the virus database. We could also detect this automatically using cl_statchkdir() every time we scan data, but I find such method too expansive.

I prefer that the System Engineer in charge of upgrading the Virus Database will also reload the engine in MySQL.

So let start by creating a new user function called virus_reload_engine() on line 335:

/* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is also distributed with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have included with MySQL.
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, version 2.0, 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
#define LOG_COMPONENT_TAG "viruscan"
#define NO_SIGNATURE_CHANGE 0
#define SIGNATURE_CHANGE 1
#include <components/viruscan/scan.h>
REQUIRES_SERVICE_PLACEHOLDER(log_builtins);
REQUIRES_SERVICE_PLACEHOLDER(log_builtins_string);
REQUIRES_SERVICE_PLACEHOLDER(dynamic_privilege_register);
REQUIRES_SERVICE_PLACEHOLDER(udf_registration);
REQUIRES_SERVICE_PLACEHOLDER(mysql_udf_metadata);
REQUIRES_SERVICE_PLACEHOLDER(mysql_thd_security_context);
REQUIRES_SERVICE_PLACEHOLDER(global_grants_check);
REQUIRES_SERVICE_PLACEHOLDER(mysql_current_thread_reader);
REQUIRES_SERVICE_PLACEHOLDER(mysql_runtime_error);
SERVICE_TYPE(log_builtins) * log_bi;
SERVICE_TYPE(log_builtins_string) * log_bs;
static const char *SCAN_PRIVILEGE_NAME = "VIRUS_SCAN";
struct scan_result scan_data(const char *data, size_t data_size);
/*
* Holds the data of a virus scan
*/
struct scan_result
{
int return_code;
const char *virus_name;
long unsigned int scanned;
};
/*
* Global variable to access the ClamAV engine
*/
struct cl_engine *engine = NULL;
char *signatureDir;
struct cl_stat signatureStat;
class udf_list {
typedef std::list<std::string> udf_list_t;
public:
~udf_list() { unregister(); }
bool add_scalar(const char *func_name, enum Item_result return_type,
Udf_func_any func, Udf_func_init init_func = NULL,
Udf_func_deinit deinit_func = NULL) {
if (!mysql_service_udf_registration->udf_register(
func_name, return_type, func, init_func, deinit_func)) {
set.push_back(func_name);
return false;
}
return true;
}
bool unregister() {
udf_list_t delete_set;
/* try to unregister all of the udfs */
for (auto udf : set) {
int was_present = 0;
if (!mysql_service_udf_registration->udf_unregister(udf.c_str(),
&was_present) ||
!was_present)
delete_set.push_back(udf);
}
/* remove the unregistered ones from the list */
for (auto udf : delete_set) set.remove(udf);
/* success: empty set */
if (set.empty()) return false;
/* failure: entries still in the set */
return true;
}
private:
udf_list_t set;
} * list;
unsigned int reload_engine()
{
unsigned int signatureNum = 0;
int rv;
if (engine != NULL)
{
cl_engine_free(engine);
}
engine = cl_engine_new();
memset(&signatureStat, 0, sizeof(struct cl_stat));
signatureDir = const_cast<char*>(cl_retdbdir());
cl_statinidir(signatureDir, &signatureStat);
/*
* Load the signatures from signatureDir, we use only the default dir
*/
rv = cl_load(signatureDir, engine, &signatureNum, CL_DB_STDOPT);
char buf[1024];
if (CL_SUCCESS != rv)
{
sprintf(buf, "failure loading clamav databases: %s", cl_strerror(rv));
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, buf);
}
rv = cl_engine_compile(engine);
if (CL_SUCCESS != rv)
{
sprintf(buf, "cannot create clamav engine: %s", cl_strerror(rv));
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, buf);
cl_engine_free(engine);
}
sprintf(buf, "clamav engine loaded with signatureNum %d from %s", signatureNum, signatureDir);
LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, buf);
return signatureNum;
}
namespace udf_impl {
struct scan_result scan_data(const char *data, size_t data_size)
{
struct scan_result result = {0, "", 0};
cl_fmap_t *map;
map = cl_fmap_open_memory(data, data_size);
/* scan file descriptor */
static struct cl_scan_options cl_scan_options;
memset(&cl_scan_options, 0, sizeof(struct cl_scan_options));
cl_scan_options.parse |= ~0; /* enable all parsers */
cl_scan_options.general |= CL_SCAN_GENERAL_ALLMATCHES;
result.return_code = cl_scanmap_callback(map,
NULL,
&result.virus_name,
&result.scanned,
engine,
&cl_scan_options,
NULL);
cl_fmap_close(map);
return result;
}
bool have_virus_scan_privilege(void *opaque_thd) {
// get the security context of the thread
Security_context_handle ctx = nullptr;
if (mysql_service_mysql_thd_security_context->get(opaque_thd, &ctx) || !ctx) {
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG,
"problem trying to get security context");
return false;
}
if (mysql_service_global_grants_check->has_global_grant(
ctx, SCAN_PRIVILEGE_NAME, strlen(SCAN_PRIVILEGE_NAME)))
return true;
return false;
}
const char *udf_init = "udf_init", *my_udf = "my_udf",
*my_udf_clear = "my_clear", *my_udf_add = "my_udf_add";
static bool viruscan_udf_init(UDF_INIT *initid, UDF_ARGS *, char *) {
const char* name = "utf8mb4";
char *value = const_cast<char*>(name);
initid->ptr = const_cast<char *>(udf_init);
if (mysql_service_mysql_udf_metadata->result_set(
initid, "charset",
const_cast<char *>(value))) {
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, "failed to set result charset");
return false;
}
return 0;
}
static void viruscan_udf_deinit(__attribute__((unused)) UDF_INIT *initid) {
assert(initid->ptr == udf_init || initid->ptr == my_udf);
}
const char *viruscan_udf(UDF_INIT *, UDF_ARGS *args, char *outp,
unsigned long *length, char *is_null, char *error) {
MYSQL_THD thd;
mysql_service_mysql_current_thread_reader->get(&thd);
struct scan_result result;
char buf[1024];
if(!have_virus_scan_privilege(thd)) {
mysql_error_service_printf(
ER_SPECIFIC_ACCESS_DENIED_ERROR, 0,
SCAN_PRIVILEGE_NAME);
*error = 1;
*is_null = 1;
return 0;
}
result = scan_data(args->args[0], args->lengths[0]);
if (result.return_code == 0) {
strcpy(outp, "clean: no virus found");
} else {
strcpy(outp, result.virus_name);
sprintf(buf, "Virus found: %s !!", result.virus_name);
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, buf);
}
*length = strlen(outp);
return const_cast<char *>(outp);
}
static bool virusreload_udf_init(UDF_INIT *initid, UDF_ARGS *, char *) {
const char* name = "utf8mb4";
char *value = const_cast<char*>(name);
initid->ptr = const_cast<char *>(udf_init);
if (mysql_service_mysql_udf_metadata->result_set(
initid, "charset",
const_cast<char *>(value))) {
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, "failed to set result charset");
return false;
}
return 0;
}
static void virusreload_udf_deinit(__attribute__((unused)) UDF_INIT *initid) {
assert(initid->ptr == udf_init || initid->ptr == my_udf);
}
const char *virusreload_udf(UDF_INIT *, UDF_ARGS *args, char *outp,
unsigned long *length, char *is_null, char *error) {
MYSQL_THD thd;
mysql_service_mysql_current_thread_reader->get(&thd);
unsigned int signatureNum = 0;
if(!have_virus_scan_privilege(thd)) {
mysql_error_service_printf(
ER_SPECIFIC_ACCESS_DENIED_ERROR, 0,
SCAN_PRIVILEGE_NAME);
*error = 1;
*is_null = 1;
return 0;
}
if (args->arg_count > 0) {
sprintf(outp, "ERROR: this function doesn't require any parameter !");
*length = strlen(outp);
return const_cast<char *>(outp);
}
sprintf(outp, "No need to reload ClamAV engine");
if(cl_statchkdir(&signatureStat) == SIGNATURE_CHANGE) {
signatureNum = reload_engine();
cl_statfree(&signatureStat);
cl_statinidir(cl_retdbdir(), &signatureStat);
sprintf(outp, "ClamAV engine reloaded with new virus database: %d signatures", signatureNum);
}
*length = strlen(outp);
return const_cast<char *>(outp);
}
} /* namespace udf_impl */
static mysql_service_status_t viruscan_service_init() {
mysql_service_status_t result = 0;
log_bi = mysql_service_log_builtins;
log_bs = mysql_service_log_builtins_string;
LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, "initializing…");
int rv;
rv = cl_init(CL_INIT_DEFAULT);
char buf[1024];
if (CL_SUCCESS != rv) {
sprintf(buf, "can't initialize libclamav: %s", cl_strerror(rv));
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, buf);
} else {
// Print the version of ClamAV engine
sprintf(buf, "ClamAV %s intialized", cl_retver());
LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, buf);
}
struct cl_engine *cl_engine_new(void);
reload_engine();
// Registration of the privilege
if (mysql_service_dynamic_privilege_register->register_privilege(SCAN_PRIVILEGE_NAME, strlen(SCAN_PRIVILEGE_NAME))) {
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG,
"could not register privilege 'VIRUS_SCAN'.");
result = 1;
} else {
LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG,
"new privilege 'VIRUS_SCAN' has been registered successfully.");
}
list = new udf_list();
if (list->add_scalar("virus_scan", Item_result::STRING_RESULT,
(Udf_func_any)udf_impl::viruscan_udf,
udf_impl::viruscan_udf_init,
udf_impl::viruscan_udf_deinit)) {
delete list;
return 1; /* failure: one of the UDF registrations failed */
}
if (list->add_scalar("virus_reload_engine", Item_result::STRING_RESULT,
(Udf_func_any)udf_impl::virusreload_udf,
udf_impl::virusreload_udf_init,
udf_impl::virusreload_udf_deinit)) {
delete list;
return 1; /* failure: one of the UDF registrations failed */
}
return result;
}
static mysql_service_status_t viruscan_service_deinit() {
mysql_service_status_t result = 0;
cl_engine_free(engine);
if (mysql_service_dynamic_privilege_register->unregister_privilege(SCAN_PRIVILEGE_NAME, strlen(SCAN_PRIVILEGE_NAME))) {
LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG,
"could not unregister privilege 'VIRUS_SCAN'.");
result = 1;
} else {
LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG,
"privilege 'VIRUS_SCAN' has been unregistered successfully.");
}
if (list->unregister()) return 1; /* failure: some UDFs still in use */
delete list;
LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, "uninstalled.");
return result;
}
BEGIN_COMPONENT_PROVIDES(viruscan_service)
END_COMPONENT_PROVIDES();
BEGIN_COMPONENT_REQUIRES(viruscan_service)
REQUIRES_SERVICE(log_builtins),
REQUIRES_SERVICE(log_builtins_string),
REQUIRES_SERVICE(dynamic_privilege_register),
REQUIRES_SERVICE(mysql_udf_metadata),
REQUIRES_SERVICE(udf_registration),
REQUIRES_SERVICE(mysql_thd_security_context),
REQUIRES_SERVICE(global_grants_check),
REQUIRES_SERVICE(mysql_current_thread_reader),
REQUIRES_SERVICE(mysql_runtime_error),
END_COMPONENT_REQUIRES();
/* A list of metadata to describe the Component. */
BEGIN_COMPONENT_METADATA(viruscan_service)
METADATA("mysql.author", "Oracle Corporation"),
METADATA("mysql.license", "GPL"), METADATA("mysql.dev", "lefred"),
END_COMPONENT_METADATA();
/* Declaration of the Component. */
DECLARE_COMPONENT(viruscan_service,
"mysql:viruscan_service")
viruscan_service_init,
viruscan_service_deinit END_DECLARE_COMPONENT();
/* Defines list of Components contained in this library. Note that for now
we assume that library will have exactly one Component. */
DECLARE_LIBRARY_COMPONENTS &COMPONENT_REF(viruscan_service)
END_DECLARE_LIBRARY_COMPONENTS
view raw scan.cc hosted with ❤ by GitHub

This new function calls udf_impl::virusreload_udf defined on line 253 (the init and deinit are also defined on lines 236 and 249). We already the details about this in part 6.

Let’s try our new feature after having compiled our new component and run mtr:

Perfect, the engine is indeed reloaded only if new signatures are present on the system.

We can also see the messages we created in error log:

Our component is improving and is already perfectly usable. On the next article we will learn how to add status variables.

Stay tuned and as usual enjoy MySQL and enjoy coding !

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