/*
  * Anti mixed UTF8 - a filter written by Bram Matthys ("Syzop").
  * Reported by Mr_Smoke in https://bugs.unrealircd.org/view.php?id=5163
  * Tested by PeGaSuS (The_Myth) with some of the most used spam lines.
  * Help with testing and fixing Cyrillic from 'i' <info@servx.org>
  *
  * ==[ ABOUT ]==
  * This module will detect and stop spam containing of characters of
  * mixed "scripts", where some characters are in Latin script and other
  * characters are in Cyrillic.
  * This unusual behavior can be detected easily and action can be taken.
  *
  * ==[ MODULE LOADING AND CONFIGURATION ]==
  * loadmodule "antimixedutf8";
  * set {
  *         antimixedutf8 {
  *                 score 10;
  *                 ban-action block;
  *                 ban-reason "Possible mixed character spam";
  *                 ban-time 4h; // For other types
  *                 except {
  *                 }
  *         };
  * };
  *
  * ==[ LICENSE AND PORTING ]==
  * Feel free to copy/move the idea or code to other IRCds.
  * The license is GPLv1 (or later, at your option):
  *
  * 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; either version 1, or (at your option)
  * any later version.
  *
  * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
 #include "unrealircd.h"
 
 ModuleHeader MOD_HEADER
 = {
 	"antimixedutf8",
 	"1.0",
 	"Mixed UTF8 character filter (look-alike character spam) - by Syzop",
 	"UnrealIRCd Team",
 	"unrealircd-6",
 };
 
 struct {
 	int score;
 	BanAction ban_action;
 	char *ban_reason;
 	long ban_time;
 	SecurityGroup *except;
 } cfg;
 
 static void free_config(void);
 static void init_config(void);
 int antimixedutf8_config_test(ConfigFile *, ConfigEntry *, int, int *);
 int antimixedutf8_config_run(ConfigFile *, ConfigEntry *, int);
 
 #define SCRIPT_UNDEFINED	0
 #define SCRIPT_LATIN		1
 #define SCRIPT_CYRILLIC		2
 #define SCRIPT_CJK		3
 #define SCRIPT_HANGUL		4
 #define SCRIPT_CANADIAN		5
 #define SCRIPT_TELUGU		6
 
 /**** the detection algorithm follows first, the module/config code is at the end ****/
 
 /** Detect which script the current character is,
  * such as latin script or cyrillic script.
  * @retval See SCRIPT_*
  */
 int detect_script(const char *t)
 {
 	/* Safety: as long as *t is never \0 then at worst
 	 * the character after this will be \0 and since we
 	 * only look at 2 characters (at most) at a time
 	 * this will be safe.
 	 */
 
 	/* Currently we only detect cyrillic and call all the
 	 * rest latin (which is not true). This can always
 	 * be enhanced later.
 	 */
 
 	if ((t[0] == 0xd0) && (t[1] >= 0x80) && (t[1] <= 0xbf))
 		return SCRIPT_CYRILLIC;
 	else if ((t[0] == 0xd1) && (t[1] >= 0x80) && (t[1] <= 0xbf))
 		return SCRIPT_CYRILLIC;
 	else if ((t[0] == 0xd2) && (t[1] >= 0x80) && (t[1] <= 0xbf))
 		return SCRIPT_CYRILLIC;
 	else if ((t[0] == 0xd3) && (t[1] >= 0x80) && (t[1] <= 0xbf))
 		return SCRIPT_CYRILLIC;
 
 	if ((t[0] == 0xe4) && (t[1] >= 0xb8) && (t[1] <= 0xbf))
 		return SCRIPT_CJK;
 	else if ((t[0] >= 0xe5) && (t[0] <= 0xe9) && (t[1] >= 0x80) && (t[1] <= 0xbf))
 		return SCRIPT_CJK;
 
 	if ((t[0] == 0xea) && (t[1] >= 0xb0) && (t[1] <= 0xbf))
 		return SCRIPT_HANGUL;
 	else if ((t[0] >= 0xeb) && (t[0] <= 0xec) && (t[1] >= 0x80) && (t[1] <= 0xbf))
 		return SCRIPT_HANGUL;
 	else if ((t[0] == 0xed) && (t[1] >= 0x80) && (t[1] <= 0x9f))
 		return SCRIPT_HANGUL;
 
 	if ((t[0] == 0xe1) && (t[1] >= 0x90) && (t[1] <= 0x99))
 		return SCRIPT_CANADIAN;
 
 	if ((t[0] == 0xe0) && (t[1] >= 0xb0) && (t[1] <= 0xb1))
 		return SCRIPT_TELUGU;
 
 	if ((t[0] >= 'a') && (t[0] <= 'z'))
 		return SCRIPT_LATIN;
 	if ((t[0] >= 'A') && (t[0] <= 'Z'))
 		return SCRIPT_LATIN;
 
 	return SCRIPT_UNDEFINED;
 }
 
 /** Returns length of an (UTF8) character. May return <1 for error conditions.
  * Made by i <info@servx.org>
  */
 static int utf8_charlen(const char *str)
 {
 	struct { char mask; char val; } t[4] =
 	{ { 0x80, 0x00 }, { 0xE0, 0xC0 }, { 0xF0, 0xE0 }, { 0xF8, 0xF0 } };
 	unsigned k, j;
 
 	for (k = 0; k < 4; k++)
 	{
 		if ((*str & t[k].mask) == t[k].val)
 		{
 			for (j = 0; j < k; j++)
 			{
 				if ((*(++str) & 0xC0) != 0x80)
 					return -1;
 			}
 			return k + 1;
 		}
 	}
 	return 1;
 }
 
 int lookalikespam_score(const char *text)
 {
 	const char *p;
 	int last_script = SCRIPT_UNDEFINED;
 	int current_script;
 	int points = 0;
 	int last_character_was_word_separator = 0;
 	int skip = 0;
 
 	for (p = text; *p; p++)
 	{
 		current_script = detect_script(p);
 
 		if (current_script != SCRIPT_UNDEFINED)
 		{
 			if ((current_script != last_script) && (last_script != SCRIPT_UNDEFINED))
 			{
 				/* A script change = 1 point */
 				points++;
 
 				/* Give an additional point if the script change happened
 				 * within the same word, as that would be rather unusual
 				 * in normal cases.
 				 */
 				if (!last_character_was_word_separator)
 					points++;
 			}
 			last_script = current_script;
 		}
 
 		if (strchr("., ", *p))
 			last_character_was_word_separator = 1;
 		else
 			last_character_was_word_separator = 0;
 
 		skip = utf8_charlen(p);
 		if (skip > 1)
 			p += skip - 1;
 	}
 
 	return points;
 }
 
 CMD_OVERRIDE_FUNC(override_msg)
 {
 	int score, ret;
 	
 	if (!MyUser(client) || (parc < 3) || BadPtr(parv[2]) ||
 	    user_allowed_by_security_group(client, cfg.except))
 	{
 		/* Short circuit for: remote clients, insufficient parameters,
 		 * antimixedutf8::except.
 		 */
 		CALL_NEXT_COMMAND_OVERRIDE();
 		return;
 	}
 
 	score = lookalikespam_score(StripControlCodes(parv[2]));
 	if ((score >= cfg.score) && !find_tkl_exception(TKL_ANTIMIXEDUTF8, client))
 	{
 		unreal_log(ULOG_INFO, "antimixedutf8", "ANTIMIXEDUTF8_HIT", client,
 		           "[antimixedutf8] Client $client.details hit score $score -- taking action",
 		           log_data_integer("score", score));
 		if ((cfg.ban_action == BAN_ACT_BLOCK) ||
 		    ((cfg.ban_action == BAN_ACT_SOFT_BLOCK) && !IsLoggedIn(client)))
 		{
 			sendnotice(client, "%s", cfg.ban_reason);
 			return;
 		} else {
 			if (place_host_ban(client, cfg.ban_action, cfg.ban_reason, cfg.ban_time))
 				return;
 			/* a return value of 0 means the user is exempted, so fallthrough.. */
 		}
 	}
 
 	CALL_NEXT_COMMAND_OVERRIDE();
 }
 
 /*** rest is module and config stuff ****/
 
 MOD_TEST()
 {
 	HookAdd(modinfo->handle, HOOKTYPE_CONFIGTEST, 0, antimixedutf8_config_test);
 	return MOD_SUCCESS;
 }
 
 MOD_INIT()
 {
 	MARK_AS_OFFICIAL_MODULE(modinfo);
 	
 	init_config();
 	HookAdd(modinfo->handle, HOOKTYPE_CONFIGRUN, 0, antimixedutf8_config_run);
 	return MOD_SUCCESS;
 }
 
 MOD_LOAD()
 {
 	if (!CommandOverrideAdd(modinfo->handle, "PRIVMSG", 0, override_msg))
 		return MOD_FAILED;
 
 	if (!CommandOverrideAdd(modinfo->handle, "NOTICE", 0, override_msg))
 		return MOD_FAILED;
 
 	return MOD_SUCCESS;
 }
 
 MOD_UNLOAD()
 {
 	free_config();
 	return MOD_SUCCESS;
 }
 
 static void init_config(void)
 {
 	memset(&cfg, 0, sizeof(cfg));
 	/* Default values */
 	cfg.score = 10;
 	safe_strdup(cfg.ban_reason, "Possible mixed character spam");
 	cfg.ban_action = BAN_ACT_BLOCK;
 	cfg.ban_time = 60 * 60 * 4; /* irrelevant for block, but some default for others */
 }
 
 static void free_config(void)
 {
 	safe_free(cfg.ban_reason);
 	free_security_group(cfg.except);
 	memset(&cfg, 0, sizeof(cfg)); /* needed! */
 }
 
 int antimixedutf8_config_test(ConfigFile *cf, ConfigEntry *ce, int type, int *errs)
 {
 	int errors = 0;
 	ConfigEntry *cep;
 
 	if (type != CONFIG_SET)
 		return 0;
 	
 	/* We are only interrested in set::antimixedutf8... */
 	if (!ce || !ce->name || strcmp(ce->name, "antimixedutf8"))
 		return 0;
 	
 	for (cep = ce->items; cep; cep = cep->next)
 	{
 		if (!cep->value)
 		{
 			config_error("%s:%i: set::antimixedutf8::%s with no value",
 				cep->file->filename, cep->line_number, cep->name);
 			errors++;
 		} else
 		if (!strcmp(cep->name, "score"))
 		{
 			int v = atoi(cep->value);
 			if ((v < 1) || (v > 99))
 			{
 				config_error("%s:%i: set::antimixedutf8::score: must be between 1 - 99 (got: %d)",
 					cep->file->filename, cep->line_number, v);
 				errors++;
 			}
 		} else
 		if (!strcmp(cep->name, "ban-action"))
 		{
 			if (!banact_stringtoval(cep->value))
 			{
 				config_error("%s:%i: set::antimixedutf8::ban-action: unknown action '%s'",
 					cep->file->filename, cep->line_number, cep->value);
 				errors++;
 			}
 		} else
 		if (!strcmp(cep->name, "ban-reason"))
 		{
 		} else
 		if (!strcmp(cep->name, "ban-time"))
 		{
 		} else
 		if (!strcmp(cep->name, "except"))
 		{
 			test_match_block(cf, cep, &errors);
 		} else
 		{
 			config_error("%s:%i: unknown directive set::antimixedutf8::%s",
 				cep->file->filename, cep->line_number, cep->name);
 			errors++;
 		}
 	}
 	*errs = errors;
 	return errors ? -1 : 1;
 }
 
 int antimixedutf8_config_run(ConfigFile *cf, ConfigEntry *ce, int type)
 {
 	ConfigEntry *cep;
 
 	if (type != CONFIG_SET)
 		return 0;
 	
 	/* We are only interrested in set::antimixedutf8... */
 	if (!ce || !ce->name || strcmp(ce->name, "antimixedutf8"))
 		return 0;
 	
 	for (cep = ce->items; cep; cep = cep->next)
 	{
 		if (!strcmp(cep->name, "score"))
 		{
 			cfg.score = atoi(cep->value);
 		} else
 		if (!strcmp(cep->name, "ban-action"))
 		{
 			cfg.ban_action = banact_stringtoval(cep->value);
 		} else
 		if (!strcmp(cep->name, "ban-reason"))
 		{
 			safe_strdup(cfg.ban_reason, cep->value);
 		} else
 		if (!strcmp(cep->name, "ban-time"))
 		{
 			cfg.ban_time = config_checkval(cep->value, CFG_TIME);
 		} else
 		if (!strcmp(cep->name, "except"))
 		{
 			conf_match_block(cf, cep, &cfg.except);
 		}
 	}
 	return 1;
 }

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