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/*
* Copyright (c) 2007,2008 Mij <mij@bitchx.it>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* SSHGuard. See http://www.sshguard.net
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <pthread.h>
#include <signal.h>
#include <assert.h>
#include <simclist.h>
/* subsystem for parsing log entries, notably parse_line() */
#include "parser.h"
/* logging subsystem, sshguard_log() */
#include "sshguard_log.h"
/* functions for getting user's preferences */
#include "sshguard_options.h"
/* constant definitions for address types */
#include "sshguard_addresskind.h"
/* functions for managing whitelist (addresses not to block): whitelist_*() */
#include "sshguard_whitelist.h"
/* functions for reading and updating the blacklist (addresses to block and never release): blacklist_*() */
#include "sshguard_blacklist.h"
/* functions for log messages verification: procauth_*() */
#include "sshguard_procauth.h"
/* functions for controlling the underlying firewall: fw_*() */
#include "sshguard_fw.h"
/* seeker functions for lists */
#include "seekers.h"
/* data types for tracking attacks (attack_t, attacker_t etc) */
#include "sshguard_attack.h"
#include "sshguard.h"
#define MAX_LOGLINE_LEN 1000
/* switch from 0 (normal) to 1 (suspended) with SIGTSTP and SIGCONT respectively */
int suspended;
/* FUNDAMENTAL DATA STRUCTURES */
/* These lists are all lists of attacker_t structures.
* limbo and hell maintain "temporary" entries: in limbo, entries are deleted
* when the address is detected to have abused a service (right after it is
* blocked); in hell, it is deleted when the address is released.
*
* The list offenders maintains a permanent history of the abuses of
* attackers, their first and last attempt, the number of abuses etc. These
* are maintained for entire runtime. When the number of abuses exceeds a
* limit, an address might be blacklisted (if blacklisting is enabled with
* -b). After blacklisting, the block of an attacker is released, because it
* has already been blocked permanently.
*
* The invariant of "offenders" is: it is sorted in decreasing order of the
* "whenlast" field.
*/
/* list of addresses that failed some times, but not enough to get blocked */
list_t limbo;
/* list of addresses currently blocked (offenders) */
list_t hell;
/* list of offenders (addresses already blocked in the past) */
list_t offenders;
/* global debugging flag */
int sshg_debugging = 0;
/* fill an attacker_t structure for usage */
static inline void attackerinit(attacker_t *restrict ipe, const attack_t *restrict attack);
/* comparison operator for sorting offenders list */
static int attackt_whenlast_comparator(const void *a, const void *b);
#ifdef EINTR
/* get line unaffected by interrupts */
char *safe_fgets(char *restrict s, int size, FILE *restrict stream);
#endif
/* handler for termination-related signals */
void sigfin_handler(int signo);
/* handler for suspension/resume signals */
void sigstpcont_handler(int signo);
/* called at exit(): flush blocked addresses and finalize subsystems */
void finishup(void);
/* handle an attack: addr is the author, addrkind its address kind, service the attacked service code */
void report_address(attack_t attack);
/* cleanup false-alarm attackers from limbo list (ones with too few attacks in too much time) */
void purge_limbo_stale(void);
/* release blocked attackers after their penalty expired */
void *pardonBlocked(void *par);
int main(int argc, char *argv[]) {
pthread_t tid;
int retv;
char buf[MAX_LOGLINE_LEN];
/* list of addresses that have been blacklisted */
list_t *blacklist = NULL;
/* initializations */
srand(time(NULL));
suspended = 0;
sshg_debugging = (getenv("SSHGUARD_DEBUG") != NULL);
/* pending, blocked, and offender address lists */
list_init(&limbo);
list_attributes_seeker(& limbo, seeker_addr);
list_init(&hell);
list_attributes_seeker(& hell, seeker_addr);
list_init(&offenders);
list_attributes_seeker(& offenders, seeker_addr);
list_attributes_comparator(& offenders, attackt_whenlast_comparator);
/* logging system */
sshguard_log_init(sshg_debugging);
/* whitelisting system */
if (whitelist_init() != 0 || whitelist_conf_init() != 0) {
fprintf(stderr, "Could not nitialize the whitelist engine.\n");
exit(1);
}
/* process authorization system */
if (procauth_init() != 0) {
fprintf(stderr, "Could not initialize the process authorization subsystem.");
exit(1);
}
/* parsing the command line */
if (get_options_cmdline(argc, argv) != 0) {
exit(1);
}
/* whitelist localhost */
if (whitelist_add("127.0.0.1") != 0) {
fprintf(stderr, "Could not whitelist localhost. terminating...\n");
exit(1);
}
whitelist_conf_fin();
/* address blocking system */
if (fw_init() != FWALL_OK) {
sshguard_log(LOG_CRIT, "Could not init firewall. Terminating.\n");
fprintf(stderr, "Could not init firewall. Terminating.\n");
exit(1);
}
/* set finalization routine */
atexit(finishup);
/* suspension signals */
signal(SIGTSTP, sigstpcont_handler);
signal(SIGCONT, sigstpcont_handler);
/* termination signals */
signal(SIGTERM, sigfin_handler);
signal(SIGHUP, sigfin_handler);
signal(SIGINT, sigfin_handler);
/* if blacklist enabled, block blacklisted addresses */
if (opts.blacklist_filename != NULL) {
blacklist = blacklist_load(opts.blacklist_filename);
if (blacklist == NULL) {
sshguard_log(LOG_NOTICE, "Blacklist file '%s' doesn't exist, I'll create it for you.\n", opts.blacklist_filename);
if (blacklist_create(opts.blacklist_filename) != 0) {
/* write to both destinations to make sure the user notice it */
fprintf(stderr, "Unable to create a blacklist file at '%s'! Terminating.\n", opts.blacklist_filename);
sshguard_log(LOG_CRIT, "Unable to create a blacklist file at '%s'! Terminating.\n", opts.blacklist_filename);
exit(1);
}
blacklist = blacklist_load(opts.blacklist_filename);
}
/* blacklist enabled */
assert(blacklist != NULL);
sshguard_log(LOG_INFO, "Blacklist loaded, %d addresses.", list_size(blacklist));
for (retv = 0; retv < list_size(blacklist); retv++) {
attacker_t *bl_attacker = list_get_at(blacklist, retv);
assert(bl_attacker != NULL);
sshguard_log(LOG_DEBUG, "Loaded from blacklist (%d): '%s:%d', service %d, last seen %s.", retv,
bl_attacker->attack.address.value, bl_attacker->attack.address.kind, bl_attacker->attack.service,
ctime(& bl_attacker->whenlast));
if (fw_block(bl_attacker->attack.address.value, bl_attacker->attack.address.kind, bl_attacker->attack.service) != FWALL_OK) {
fprintf(stderr, "Unable to block addresses in firewall. Terminating.\n");
exit(1);
}
}
list_destroy(blacklist);
free(blacklist);
blacklist = NULL;
blacklist = blacklist_load(opts.blacklist_filename);
}
/* set debugging value for parser/scanner ... */
yydebug = sshg_debugging;
yy_flex_debug = sshg_debugging;
/* start thread for purging stale blocked addresses */
if (pthread_create(&tid, NULL, pardonBlocked, NULL) != 0) {
perror("pthread_create()");
exit(2);
}
/* initialization successful */
sshguard_log(LOG_INFO, "Started successfully [(a,p,s)=(%u, %u, %u)], now ready to scan.", \
opts.abuse_threshold, (unsigned int)opts.pardon_threshold, (unsigned int)opts.stale_threshold);
#ifdef EINTR
while (safe_fgets(buf, MAX_LOGLINE_LEN, stdin) != NULL) {
#else
while (fgets(buf, MAX_LOGLINE_LEN, stdin) != NULL) {
#endif
if (suspended) continue;
retv = parse_line(buf);
if (retv != 0) {
/* sshguard_log(LOG_DEBUG, "Skip line '%s'", buf); */
continue;
}
/* extract the IP address */
sshguard_log(LOG_DEBUG, "Matched address %s:%d attacking service %d", parsed_attack.address.value, parsed_attack.address.kind, parsed_attack.service);
/* report IP */
report_address(parsed_attack);
}
/* let exit() call finishup() */
exit(0);
}
#ifdef EINTR
char *safe_fgets(char *restrict s, int size, FILE *restrict stream) {
char *restrict ret;
do {
clearerr(stream);
ret = fgets(s, size, stream);
if (ret != NULL)
return s;
if (errno != EINTR)
return NULL;
} while (ret == NULL && errno == EINTR);
/* pretend we arrive here to make compiler happy */
return NULL;
}
#endif
/*
* This function is called every time an attack pattern is matched.
* It does the following:
* 1) update the attacker infos (counter, timestamps etc)
* --OR-- create them if first sight.
* 2) block the attacker, if attacks > threshold (abuse)
* 3) blacklist the address, if the number of abuses is excessive
*/
void report_address(attack_t attack) {
attacker_t *tmpent = NULL;
attacker_t *offenderent;
int ret;
assert(attack.address.value != NULL);
/* clean list from stale entries */
purge_limbo_stale();
/* protected address? */
if (whitelist_match(attack.address.value, attack.address.kind)) {
sshguard_log(LOG_INFO, "Pass over address %s because it's been whitelisted.", attack.address.value);
return;
}
/* search entry in list */
tmpent = list_seek(& limbo, attack.address.value);
if (tmpent == NULL) { /* entry not already in list, add it */
/* otherwise: insert the new item */
tmpent = malloc(sizeof(attacker_t));
attackerinit(tmpent, & attack);
list_append(&limbo, tmpent);
}
/* otherwise, the entry was already existing */
/* update last hit */
tmpent->whenlast = time(NULL);
tmpent->numhits++;
if (tmpent->numhits < opts.abuse_threshold) {
/* do nothing now, just keep an eye on this guy */
return;
}
/* otherwise, we have to block it */
/* find out if this is a recidivous offender to determine the
* duration of blocking */
tmpent->pardontime = opts.pardon_threshold;
offenderent = list_seek(& offenders, & attack.address);
if (offenderent == NULL) {
/* first time we block this guy */
sshguard_log(LOG_DEBUG, "First sight of offender '%s:%d', adding to offenders list.", tmpent->attack.address.value, tmpent->attack.address.kind);
offenderent = (attacker_t *)malloc(sizeof(attacker_t));
memcpy(offenderent, tmpent, sizeof(attacker_t));
offenderent->numhits = 1;
list_prepend(& offenders, offenderent);
assert(! list_empty(& offenders));
#if 0
/* we assume that the list is already sorted by decreasing last-attack time */
/* prune list */
if (list_size(& offenders) > MAX_OFFENDER_ITEMS) {
list_delete_range(& offenders, MAX_OFFENDER_ITEMS, list_size(& offenders)-1);
}
#endif
} else {
/* this is a previous offender */
offenderent->numhits++;
offenderent->whenlast = tmpent->whenlast;
if (offenderent->numhits >= opts.blacklist_threshold) {
/* this host must be blacklisted -- blocked and never unblocked */
tmpent->pardontime = 0;
/* insert in the blacklisted db iff enabled */
if (opts.blacklist_filename != NULL) {
switch (blacklist_lookup_address(opts.blacklist_filename, & offenderent->attack.address)) {
case 1: /* in blacklist */
/* do nothing */
break;
case 0: /* not in blacklist */
/* add it */
sshguard_log(LOG_NOTICE, "Offender '%s:%d' seen %d times (threshold %d) -> blacklisted.",
tmpent->attack.address.value, tmpent->attack.address.kind, offenderent->numhits,
opts.blacklist_threshold);
if (blacklist_add(opts.blacklist_filename, offenderent) != 0) {
sshguard_log(LOG_ERR, "Could not blacklist address: %s", strerror(errno));
}
break;
default: /* error while looking up */
sshguard_log(LOG_ERR, "Error while looking up '%s:%d' in blacklist '%s'.", attack.address.value, attack.address.kind, opts.blacklist_filename);
}
}
} else {
sshguard_log(LOG_INFO, "Offender '%s:%d' seen %d times.", tmpent->attack.address.value, tmpent->attack.address.kind, offenderent->numhits);
/* compute blocking time wrt the "offensiveness" */
for (ret = 0; ret < offenderent->numhits; ret++) {
tmpent->pardontime *= 2;
}
}
}
list_sort(& offenders, -1);
sshguard_log(LOG_NOTICE, "Blocking %s:%d for >%dsecs: %u failures over %u seconds.\n", tmpent->attack.address.value,
tmpent->attack.address.kind, tmpent->pardontime, tmpent->numhits, tmpent->whenlast - tmpent->whenfirst);
ret = fw_block(attack.address.value, attack.address.kind, attack.service);
if (ret != FWALL_OK) sshguard_log(LOG_ERR, "Blocking command failed. Exited: %d", ret);
/* append blocked attacker to the blocked list, and remove it from the pending list */
list_append(&hell, tmpent);
assert(list_locate(& limbo, tmpent) >= 0);
list_delete_at(& limbo, list_locate(& limbo, tmpent));
}
static inline void attackerinit(attacker_t *restrict ipe, const attack_t *restrict attack) {
assert(ipe != NULL && attack != NULL);
strcpy(ipe->attack.address.value, attack->address.value);
ipe->attack.address.kind = attack->address.kind;
ipe->attack.service = attack->service;
ipe->whenfirst = ipe->whenlast = time(NULL);
ipe->numhits = 0;
}
void purge_limbo_stale(void) {
attacker_t *tmpent;
time_t now;
unsigned int pos = 0;
now = time(NULL);
for (pos = 0; pos < list_size(&limbo); pos++) {
tmpent = list_get_at(&limbo, pos);
if (now - tmpent->whenfirst > opts.stale_threshold)
list_delete_at(&limbo, pos);
}
}
void *pardonBlocked(void *par) {
time_t now;
attacker_t *tmpel;
int ret, pos;
while (1) {
/* wait some time, at most opts.pardon_threshold/3 + 1 sec */
sleep(1 + (rand() % (1+opts.pardon_threshold/2)));
now = time(NULL);
tmpel = list_get_at(&hell, 0);
pthread_testcancel();
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &ret);
for (pos = 0; pos < list_size(& hell); pos++) {
tmpel = list_get_at(&hell, pos);
/* skip blacklisted hosts (pardontime = infinite/0) */
if (tmpel->pardontime == 0) continue;
/* process hosts with finite pardon time */
if (now - tmpel->whenlast > tmpel->pardontime) {
/* pardon time passed, release block */
sshguard_log(LOG_INFO, "Releasing %s after %u seconds.\n", tmpel->attack.address.value, now - tmpel->whenlast);
ret = fw_release(tmpel->attack.address.value, tmpel->attack.address.kind, tmpel->attack.service);
if (ret != FWALL_OK) sshguard_log(LOG_ERR, "Release command failed. Exited: %d", ret);
list_delete_at(&hell, 0);
free(tmpel);
/* element removed, next element is at current index (don't step pos) */
pos--;
}
}
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &ret);
pthread_testcancel();
}
pthread_exit(NULL);
return NULL;
}
/* finalization routine */
void finishup(void) {
/* flush blocking rules */
sshguard_log(LOG_INFO, "Got exit signal, flushing blocked addresses and exiting...");
fw_flush();
if (fw_fin() != FWALL_OK) sshguard_log(LOG_ERR, "Cound not finalize firewall.");
if (whitelist_fin() != 0) sshguard_log(LOG_ERR, "Could not finalize the whitelisting system.");
if (procauth_fin() != 0) sshguard_log(LOG_ERR, "Could not finalize the process authorization subsystem.");
sshguard_log_fin();
}
void sigfin_handler(int signo) {
/* let exit() call finishup() */
exit(0);
}
void sigstpcont_handler(int signo) {
/* update "suspended" status */
switch (signo) {
case SIGTSTP:
suspended = 1;
sshguard_log(LOG_NOTICE, "Got STOP signal, suspending activity.");
break;
case SIGCONT:
suspended = 0;
sshguard_log(LOG_NOTICE, "Got CONTINUE signal, resuming activity.");
break;
}
}
static int attackt_whenlast_comparator(const void *a, const void *b) {
const attacker_t *aa = (const attacker_t *)a;
const attacker_t *bb = (const attacker_t *)b;
return ((aa->whenlast > bb->whenlast) - (aa->whenlast < bb->whenlast));
}
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