rpluem at apache
Jul 1, 2009, 12:31 PM
Post #1 of 11
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Re: svn commit: r790205 - /httpd/httpd/trunk/modules/experimental/mod_noloris.c
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tOn 01.07.2009 17:01, niq [at] apache wrote:
> Author: niq
> Date: Wed Jul 1 15:01:55 2009
> New Revision: 790205
>
> URL: http://svn.apache.org/viewvc?rev=790205&view=rev
> Log:
> mod_noloris just moved from discussion to attracting its first patch
> on dev@. That means it wants to be in svn. Adding to modules/experimental
> pending anything more definite.
>
> Added:
> httpd/httpd/trunk/modules/experimental/mod_noloris.c
>
> Added: httpd/httpd/trunk/modules/experimental/mod_noloris.c
> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/modules/experimental/mod_noloris.c?rev=790205&view=auto
> ==============================================================================
> --- httpd/httpd/trunk/modules/experimental/mod_noloris.c (added)
> +++ httpd/httpd/trunk/modules/experimental/mod_noloris.c Wed Jul 1 15:01:55 2009
> @@ -0,0 +1,245 @@
> +/* Licensed to the Apache Software Foundation (ASF) under one or more
> + * contributor license agreements. See the NOTICE file distributed with
> + * this work for additional information regarding copyright ownership.
> + * The ASF licenses this file to You under the Apache License, Version 2.0
> + * (the "License"); you may not use this file except in compliance with
> + * the License. You may obtain a copy of the License at
> + *
> + * http://www.apache.org/licenses/LICENSE-2.0
> + *
> + * Unless required by applicable law or agreed to in writing, software
> + * distributed under the License is distributed on an "AS IS" BASIS,
> + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
> + * See the License for the specific language governing permissions and
> + * limitations under the License.
> + */
> +
> +
> +/* The use of the scoreboard in this module is based on a similar
> + * but simpler module, mod_antiloris by Kees Monshouwer, from
> + * ftp://ftp.monshouwer.eu/pub/linux/mod_antiloris/
> + * Note the FIXME that affects both modules.
> + *
> + * The major difference is that mod_antiloris checks the scoreboard
> + * on every request. This implies a per-request overhead that grows
> + * with the scoreboard, and gets very expensive on a big server.
> + * On the other hand, this module (mod_noloris) may be slower to
> + * react to a DoS attack, and in the case of a very small server
> + * it might be too late.
I am not sure if doing this for each connection (not each *request*)
is really that much of a performace hit. I used a modified version of
mod_limitipcon and do just that. So far I haven't noticed any performance
issues with this approach. But maybe with a maximum of 1040 clients
I am just having a small server :-).
> + *
> + * Author's untested instinct: mod_antiloris will suit servers with
> + * Prefork MPM and low traffic. A server with a threaded MPM
> + * (or possibly a big prefork server with lots of memory) should
> + * raise MaxClients and use mod_noloris.
> + */
> +
> +#include "httpd.h"
> +#include "http_config.h"
> +#include "http_connection.h"
> +#include "http_log.h"
> +#include "mpm_common.h"
> +#include "ap_mpm.h"
> +#include "apr_hash.h"
> +
> +module AP_MODULE_DECLARE_DATA noloris_module;
> +module AP_MODULE_DECLARE_DATA core_module;
> +
> +static unsigned int default_max_connections;
> +static apr_hash_t *trusted;
> +static apr_interval_time_t recheck_time;
> +static apr_shm_t *shm;
> +static apr_size_t shm_size;
> +static int server_limit;
> +static int thread_limit;
> +
> +static int noloris_conn(conn_rec *conn)
> +{
> + /*** FIXME
> + * This is evil: we're assuming info that's private to the scoreboard
> + * We need to do that because there's no API to update the scoreboard
> + * on a connection, only with a request (or NULL to say not processing
> + * any request). We need a version of ap_update_child_status that
> + * accepts a conn_rec.
> + */
> + struct { int child_num; int thread_num; } *sbh = conn->sbh;
> +
> + char *shm_rec;
> + worker_score *ws;
> + if (shm == NULL) {
> + return DECLINED; /* we're disabled */
> + }
> +
> + /* check the IP is not banned */
> + shm_rec = apr_shm_baseaddr_get(shm);
> + if (strstr(shm_rec, conn->remote_ip)) {
> + apr_socket_t *csd = ap_get_module_config(conn->conn_config, &core_module);
> + ap_log_cerror(APLOG_MARK, APLOG_ERR, 0, conn,
> + "Dropping connection from banned IP %s", conn->remote_ip);
> + //ap_flush_conn(conn); /* just close it */
> + apr_socket_close(csd);
This looks like an ugly thing to do for an module. Why not running the whole
thing in the pre_connection hook and return something different then OK or DONE.
This lets the core perform this dirty work in the predefined way.
> +
> + return DONE;
> + }
> +
> + /* store this client IP for the monitor to pick up */
> + /* under traditional scoreboard, none of this happens until
> + * there's a request_rec. This is where we use the illegally-
> + * obtained private info from the scoreboard.
> + */
> +
> + ws = &ap_scoreboard_image->servers[sbh->child_num][sbh->thread_num];
Shouldn't we use ap_get_scoreboard_worker here instead?
> + strcpy(ws->client, conn->remote_ip);
> +
> + return DECLINED;
> +}
> +static int noloris_monitor(apr_pool_t *pool)
> +{
> + static apr_hash_t *connections = NULL;
> + static apr_time_t last_check = 0;
> + static int *totals;
> +
> + int i, j;
> + int *n;
> + int index = 0;
> + apr_hash_index_t *hi;
> + char *ip;
> + apr_time_t time_now;
> + char *shm_rec;
> + worker_score *ws;
> +
> + /* do nothing if disabled */
> + if (shm == NULL) {
> + return 0;
> + }
> +
> + /* skip check if it's not due yet */
> + time_now = apr_time_now();
> + if (time_now - last_check < recheck_time) {
> + return 0;
> + }
> + last_check = time_now;
> +
> + /* alloc lots of stuff at start, so we don't leak memory per-call */
> + if (connections == NULL) {
> + connections = apr_hash_make(pool);
> + totals = apr_palloc(pool, server_limit*thread_limit);
> + ip = apr_palloc(pool, 18);
Harcoded values are IMHO ugly. Why 18 at all?
> + }
> +
> + /* Get a per-client count of connections in READ state */
> + for (i = 0; i < server_limit; ++i) {
> + for (j = 0; j < thread_limit; ++j) {
> + ws = ap_get_scoreboard_worker(i, j);
> + if (ws->status == SERVER_BUSY_READ) {
> + n = apr_hash_get(connections, ws->client, APR_HASH_KEY_STRING);
> + if (n == NULL) {
> + n = totals + index++ ;
> + *n = 0;
> + }
> + ++*n;
> + apr_hash_set(connections, ws->client, APR_HASH_KEY_STRING, n);
> + }
> + }
> + }
> +
> + /* reset shm before writing to it.
> + * We're only dealing with approx. counts, so we ignore the race condition
> + * with our prospective readers
> + */
> + shm_rec = apr_shm_baseaddr_get(shm);
> + memset(shm_rec, NULL, shm_size);
Why NULL and not 0?
> +
> + /* Now check the hash for clients with too many connections in READ state */
> + for (hi = apr_hash_first(NULL, connections); hi; hi = apr_hash_next(hi)) {
> + apr_hash_this(hi, (const void**) &ip, NULL, (void**)&n);
> + if (*n >= default_max_connections) {
> + /* if this isn't a trusted proxy, we mark it as bad */
> + if (!apr_hash_get(trusted, ip, APR_HASH_KEY_STRING)) {
> + ap_log_error(APLOG_MARK, APLOG_WARNING, 0, 0,
> + "noloris: banning %s with %d connections in READ state",
> + ip, *n);
> + strcpy(shm_rec++, " "); /* space == separator */
> + strcpy(shm_rec, ip);
> + shm_rec += strlen(ip);
> + }
> + }
> + }
> + apr_hash_clear(connections);
> + return 0;
> +}
> +static int noloris_post(apr_pool_t *pconf, apr_pool_t *ptmp, apr_pool_t *plog,
> + server_rec *s)
> +{
> + apr_status_t rv;
> + int max_bans = thread_limit * server_limit / default_max_connections;
> + shm_size = 18 * max_bans;
Hardcoded values always look ugly. Why 18 at all?
> +
> + rv = apr_shm_create(&shm, shm_size, NULL, pconf);
> + if (rv != APR_SUCCESS) {
> + ap_log_error(APLOG_MARK, APLOG_CRIT, rv, s,
> + "Failed to create shm segment; mod_noloris disabled");
> + apr_hash_clear(trusted);
> + shm = NULL;
> + }
> + return 0;
> +}
> +static int noloris_pre(apr_pool_t *pconf, apr_pool_t *ptmp, apr_pool_t *plog)
> +{
> + ap_mpm_query(AP_MPMQ_HARD_LIMIT_THREADS, &thread_limit);
> + ap_mpm_query(AP_MPMQ_HARD_LIMIT_DAEMONS, &server_limit);
> +
> + /* set up default config stuff here */
> + trusted = apr_hash_make(pconf);
> + default_max_connections = 50;
> + recheck_time = apr_time_from_sec(10);
> + return 0;
> +}
> +static void noloris_hooks(apr_pool_t *p)
> +{
> + ap_hook_process_connection(noloris_conn, NULL, NULL, APR_HOOK_FIRST);
> + ap_hook_pre_config(noloris_pre, NULL, NULL, APR_HOOK_MIDDLE);
> + ap_hook_post_config(noloris_post, NULL, NULL, APR_HOOK_MIDDLE);
> + ap_hook_monitor(noloris_monitor, NULL, NULL, APR_HOOK_MIDDLE);
> +}
> +static const char *noloris_trusted(cmd_parms *cmd, void *cfg, const char *val)
> +{
> + const char* err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
> + if (!err) {
> + apr_hash_set(trusted, val, APR_HASH_KEY_STRING, &noloris_module);
> + }
> + return err;
> +}
> +static const char *noloris_recheck(cmd_parms *cmd, void *cfg, const char *val)
> +{
> + const char* err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
> + if (!err) {
> + recheck_time = apr_time_from_sec(atoi(val));
> + }
> + return err;
> +}
> +static const char *noloris_max_conn(cmd_parms *cmd, void *cfg, const char *val)
> +{
> + const char* err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
> + if (!err) {
> + default_max_connections = atoi(val);
> + }
> + return err;
> +}
Storing the configuration in global variables looks kind of ugly.
But I get the point that it is hard to get them in the monitor hook.
But at least a struct for them and a global pointer to the struct would
make them look a little nicer :-).
> +static const command_rec noloris_cmds[] = {
> + AP_INIT_ITERATE("TrustedProxy", noloris_trusted, NULL, RSRC_CONF,
> + "IP addresses from which to allow unlimited connections"),
> + AP_INIT_TAKE1("ClientRecheckTime", noloris_recheck, NULL, RSRC_CONF,
> + "Time interval for rechecking client connection tables"),
> + AP_INIT_TAKE1("MaxClientConnections", noloris_max_conn, NULL, RSRC_CONF,
> + "Max connections in READ state to permit from an untrusted client"),
> + {NULL}
> +};
> +module AP_MODULE_DECLARE_DATA noloris_module = {
> + STANDARD20_MODULE_STUFF,
> + NULL,
> + NULL,
> + NULL,
> + NULL,
> + noloris_cmds,
> + noloris_hooks
> +};
>
Regards
Rüdiger
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