/*
 * ProFTPD: mod_dovecot_anvil -- slows down bruteforce attacks with the use
 *                               of dovecot's anvil/penalty backend
 *
 * Copyright (c) 2016 Manuel Mausz
 *
 * 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 2 of the License, 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307, USA.
 */

#define MOD_DOVECOT_ANVIL_VERSION "mod_dovecot_anvil/0.3.0"

#define ANVIL_DEFAULT_URI            "/var/run/dovecot/anvil-auth-penalty"
#define ANVIL_HANDSHAKE              "VERSION\tanvil\t1\t0\n"
#define ANVIL_PENALTY_INIT_SECS      2
#define ANVIL_PENALTY_MAX_SECS       60
#define ANVIL_PENALTY_IPV6_MASK_BITS 48

#include "conf.h"
#include "privs.h"

static const char *trace_channel = "dovecot_anvil";

static struct {
  int fd;
  const char *ident;
  int penalty;
  uint32_t checksum;
} anvil = { .fd = -1, .checksum = 0 };

module dovecot_anvil_module;

static int dovecot_anvil_sess_init(void);
static uint32_t crc32_str(const char *str);
static uint32_t crc32_str_more(uint32_t crc, const char *str);

static const char *anvil_get_ident(pool *p)
{
  const char *addr = pr_table_get(session.notes, "mod_xclient.addr", NULL);
  const pr_netaddr_t *remote_addr = (addr)
    ? pr_netaddr_get_addr2(session.pool, addr, NULL, PR_NETADDR_GET_ADDR_FL_EXCL_DNS)
    : pr_netaddr_get_sess_remote_addr();
  pr_trace_msg(trace_channel, 5, "fetching ident for %s",
    pr_netaddr_get_ipstr(remote_addr));

#ifdef PR_USE_IPV6
  if (pr_netaddr_use_ipv6() && pr_netaddr_get_family(remote_addr) == AF_INET6) {
    pr_netaddr_t *remote_addr4 = pr_netaddr_v6tov4(p, remote_addr);
    if (remote_addr4 != NULL)
      return pr_netaddr_get_ipstr(remote_addr4);

    struct in6_addr ip = *(struct in6_addr *)pr_netaddr_get_inaddr(remote_addr);
    memset(ip.s6_addr + ANVIL_PENALTY_IPV6_MASK_BITS/CHAR_BIT, 0,
      sizeof(ip.s6_addr) - ANVIL_PENALTY_IPV6_MASK_BITS/CHAR_BIT);
    char remote_ip6[INET6_ADDRSTRLEN];
    pr_inet_ntop(AF_INET6, &ip, remote_ip6, INET6_ADDRSTRLEN);
    return pstrdup(p, remote_ip6);
  }
#endif
  return pr_netaddr_get_ipstr(remote_addr);
}

static int net_connect_inet(const char *host, const char *port)
{
  struct addrinfo hints = {
    .ai_family = AF_UNSPEC,
    .ai_socktype = SOCK_STREAM
  };
  struct addrinfo *result;

  pr_trace_msg(trace_channel, 5, "connecting to tcp://%s:%s", host, port);
  int s = getaddrinfo(host, port, &hints, &result);
  if (s != 0) {
    pr_log_pri(PR_LOG_ERR, MOD_DOVECOT_ANVIL_VERSION ": getaddrinfo: %s",
      gai_strerror(s));
    return -1;
  }

  //FIXME: connect might hang
  int sockfd = -1;
  struct addrinfo *r;
  for (r = result; r != NULL; r=r->ai_next) {
    sockfd = socket(r->ai_family, r->ai_socktype | SOCK_CLOEXEC,
      r->ai_protocol);
    if (sockfd == -1)
      continue;
    if (connect(sockfd, r->ai_addr, r->ai_addrlen) != -1)
      break; /* success */
    close(sockfd);
    sockfd = -1;
    break; /* we only try the first record */
  }

  freeaddrinfo(result);
  return sockfd;
}

static int net_connect_unix(const char *path)
{
  pr_trace_msg(trace_channel, 5, "connecting to unix://%s", path);
  int sockfd = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
  if (sockfd < 0)
    return -1;

  struct sockaddr_un saddr;
  saddr.sun_family = AF_UNIX;
  strcpy(saddr.sun_path, path);
  PRIVS_ROOT
  int conn = connect(sockfd, (struct sockaddr *)&saddr, sizeof(saddr));
  PRIVS_RELINQUISH
  if (conn != -1)
    return sockfd;
  close(sockfd);
  return -1;
}

static int anvil_connect(config_rec *c)
{
  int sockfd = (c->argc == 2) ? net_connect_inet(c->argv[0], c->argv[1]) :
    net_connect_unix(c->argv[0]);
  if (sockfd < 0) {
    pr_log_pri(PR_LOG_ERR, MOD_DOVECOT_ANVIL_VERSION
      ": Unable to connect to socket: %s", strerror(errno));
    return -1;
  }
  if (send(sockfd, ANVIL_HANDSHAKE, strlen(ANVIL_HANDSHAKE), 0)
      != strlen(ANVIL_HANDSHAKE)) {
    pr_log_pri(PR_LOG_ERR, MOD_DOVECOT_ANVIL_VERSION
      ": Error while sending handshake: %s", strerror(errno));
    close(sockfd);
    return -1;
  }
  return sockfd;
}

typedef int anvil_penalty_callback_t(uint16_t penalty,
  unsigned long last_penalty);
static int anvil_penalty_get(int sockfd, const char *ident,
  anvil_penalty_callback_t *callback)
{
  char buf[100];
  int len = sprintf(buf, "PENALTY-GET\t%s\n", ident);
  if (send(sockfd, buf, len, 0) != len)
    return -1;

  if ((len = recv(sockfd, &buf, sizeof(buf), 0)) < 0)
    return -1;
  buf[len] = '\0';

  uint16_t penalty = 0;
  unsigned long last_penalty = 0;
  if (sscanf(buf, "%" SCNu16 " %lu", &penalty, &last_penalty) != 2) {
    pr_log_pri(PR_LOG_ERR, MOD_DOVECOT_ANVIL_VERSION
      "Invalid PENALTY-GET reply: %s", buf);
    return -1;
  }

  pr_trace_msg(trace_channel, 5, "penalty for '%s' is %u", ident, penalty);
  return callback(penalty, last_penalty);
}

static void anvil_penalty_inc(int sockfd, const char *ident, uint32_t checksum)
{
  char buf[100];
  pr_trace_msg(trace_channel, 5, "incrementing penalty for '%s'", ident);
  int len = sprintf(buf, "PENALTY-INC\t%s\t%u\n", ident, checksum);
  (void)send(sockfd, buf, len, 0);
}

static void anvil_penalty_set(int sockfd, const char *ident, uint16_t value)
{
  char buf[100];
  pr_trace_msg(trace_channel, 5, "setting penalty for '%s' to %" PRIu16,
    ident, value);
  int len = sprintf(buf, "PENALTY-SET\t%s\t%u\n", ident, value);
  (void)send(sockfd, buf, len, 0);
}

static unsigned int anvil_penalty_to_secs(uint16_t penalty)
{
  unsigned int i, secs = ANVIL_PENALTY_INIT_SECS;

  for (i = 0; i < penalty; i++)
    secs *= 2;
  return secs < ANVIL_PENALTY_MAX_SECS ? secs : ANVIL_PENALTY_MAX_SECS;
}

static void mask_sigalarm(unsigned char block)
{
  static sigset_t mask_sigset;

  if (block) {
    sigemptyset(&mask_sigset);
    sigaddset(&mask_sigset, SIGALRM);

    if (sigprocmask(SIG_BLOCK, &mask_sigset, NULL) < 0)
      pr_log_pri(PR_LOG_NOTICE, "unable to block signal set: %s",
        strerror(errno));
  }
  else {
    if (sigprocmask(SIG_UNBLOCK, &mask_sigset, NULL) < 0)
      pr_log_pri(PR_LOG_NOTICE, "unable to unblock signal set: %s",
        strerror(errno));
  }
}

static int anvil_penalty_callback_sleep(uint16_t penalty,
  unsigned long last_penalty)
{
  if (penalty > 0) {
    unsigned int secs = anvil_penalty_to_secs(penalty);
    pr_trace_msg(trace_channel, 5, "sleeping %u secs", secs);

    mask_sigalarm(TRUE);
    struct timeval tv = { .tv_sec = secs, .tv_usec = 0 };
    (void)select(0, NULL, NULL, NULL, &tv);
    mask_sigalarm(FALSE);

    pr_timer_reset(PR_TIMER_LOGIN, ANY_MODULE);
  }
  return penalty;
}

/* command handlers */
MODRET dovecot_anvil_pre_pass(cmd_rec *cmd)
{
  const char *user = pr_table_get(session.notes, "mod_auth.orig-user", NULL);
  if (user == NULL)
    return PR_DECLINED(cmd);

  config_rec *c;
  c = find_config(main_server->conf, CONF_PARAM, "DovecotAnvil", FALSE);
  if (!c)
  {
    pr_trace_msg(trace_channel, 5, "directive DovecotAnvil not enabled."
      " mod_dovecot_anvil not enabled.");
    return PR_DECLINED(cmd);
  }

  // our auth handler will be called in the middle of command handling, so
  // lifetime of cmd->pool is ok
  if ((anvil.ident = anvil_get_ident(cmd->pool)) == NULL)
  {
    pr_log_pri(PR_LOG_ERR, MOD_DOVECOT_ANVIL_VERSION ": Unable to get ident");
    return PR_DECLINED(cmd);
  }

  if ((anvil.fd = anvil_connect(c)) == -1)
    return PR_DECLINED(cmd);

  anvil.penalty = anvil_penalty_get(anvil.fd, anvil.ident,
    anvil_penalty_callback_sleep);
  if (anvil.penalty == -1) {
    pr_log_pri(PR_LOG_ERR, MOD_DOVECOT_ANVIL_VERSION
      "Error while fetching penalty: %s", strerror(errno));
    close(anvil.fd);
    anvil.fd = -1;
    return PR_DECLINED(cmd);
  }

  return PR_DECLINED(cmd);
}

MODRET dovecot_anvil_post_pass(cmd_rec *cmd)
{
  if (anvil.fd != -1) {
    (void)anvil_penalty_set(anvil.fd, anvil.ident, 0);
    close(anvil.fd);
    anvil.fd = -1;
  }
  return PR_DECLINED(cmd);
}

MODRET dovecot_anvil_post_pass_err(cmd_rec *cmd)
{
  if (anvil.fd != -1) {
    int do_increment = TRUE;
    if ((cmd->cmd_class & CL_SFTP) || (cmd->cmd_class & CL_SSH)) {
      const char *sftp_method = pr_env_get(cmd->pool, "SFTP_USER_AUTH_METHOD");
      do_increment = (sftp_method != NULL && strncmp(sftp_method, "password", 9) == 0)
        ? TRUE : FALSE;
    }
    if (do_increment)
      (void)anvil_penalty_inc(anvil.fd, anvil.ident, anvil.checksum);
    close(anvil.fd);
    anvil.fd = -1;
  }
  return PR_DECLINED(cmd);
}

/* configuration handlers */
MODRET set_dovecot_anvil(cmd_rec *cmd)
{
  CHECK_ARGS(cmd, 1);
  CHECK_CONF(cmd, CONF_ROOT|CONF_VIRTUAL|CONF_GLOBAL);

  int val = get_boolean(cmd, 1);
  if (val == TRUE)
    add_config_param_str(cmd->argv[0], 1, ANVIL_DEFAULT_URI);
  else if (val == -1) {
    if (strncmp(cmd->argv[1], "tcp://", strlen("tcp://")) == 0) {
      config_rec *c = add_config_param(cmd->argv[0], 2, NULL, NULL);
      char *path = pstrdup(c->pool, cmd->argv[1] + strlen("tcp://"));

      char *portptr = rindex(path, ':');
      if (portptr == NULL)
        CONF_ERROR(cmd, "Invalid uri: port missing?");
      *portptr = '\0';

      char *host = path;
      if (host[0] == '[' && *(portptr - 1) == ']') {
        host++;
        *(portptr - 1) = '\0';
      }

      c->argv[0] = host;
      c->argv[1] = portptr + 1;
    }
    else if (strncmp(cmd->argv[1], "unix://", strlen("unix://")) == 0)
      add_config_param_str(cmd->argv[0], 1, cmd->argv[1] + strlen("unix://"));
    else
      CONF_ERROR(cmd, "has invalid uri syntax");
  }

  return PR_HANDLED(cmd);
}

/* authentication handlers */
MODRET dovecot_anvil_auth(cmd_rec *cmd)
{
  if (cmd->argc != 2)
    return PR_DECLINED(cmd);
  if (anvil.fd != -1)
    anvil.checksum = crc32_str_more(crc32_str(cmd->argv[1]), cmd->argv[0]);
  return PR_DECLINED(cmd);
}

/* event handlers */
#if defined(PR_SHARED_MODULE)
static void dovecot_anvil_mod_unload_ev(const void *event_data, void *user_data)
{
  if (strcmp("mod_dovecot_anvil.c", (const char *)event_data) == 0)
    pr_event_unregister(&dovecot_anvil_module, NULL, NULL);
}
#endif

static void dovecot_anvil_sess_reinit_ev(const void *event_data, void *user_data)
{
  /* A HOST command changed the main_server pointer, reinitialize ourselves. */
  pr_event_unregister(&dovecot_anvil_module, "core.session-reinit",
      dovecot_anvil_sess_reinit_ev);
  pr_auth_remove_auth_only_module("mod_dovecot_anvil.c");

  if (dovecot_anvil_sess_init() < 0)
    pr_session_disconnect(&dovecot_anvil_module,
        PR_SESS_DISCONNECT_SESSION_INIT_FAILED, NULL);
}

/* initialization routines */
static int dovecot_anvil_sess_init(void)
{
  pr_event_register(&dovecot_anvil_module, "core.session-reinit",
      dovecot_anvil_sess_reinit_ev, NULL);

  config_rec *c;
  c = find_config(main_server->conf, CONF_PARAM, "DovecotAnvil", FALSE);
  if (!c)
  {
    pr_trace_msg(trace_channel, 5, "directive DovecotAnvil not enabled."
      " mod_dovecot_anvil not enabled.");
    return 0;
  }

  if (pr_auth_add_auth_only_module("mod_dovecot_anvil.c") < 0) {
    int xerrno = errno;

    pr_log_pri(PR_LOG_NOTICE, MOD_DOVECOT_ANVIL_VERSION
      ": unable to add 'mod_dovecot_anvil.c' as an auth-only module: %s",
      strerror(xerrno));

    errno = xerrno;
    return -1;
  }
  return 0;
}

static int dovecot_anvil_init(void)
{
#if defined(PR_SHARED_MODULE)
  pr_event_register(&dovecot_anvil_module, "core.module-unload",
      dovecot_anvil_mod_unload_ev, NULL);
#endif
  return 0;
}

/* module api tables */
static conftable dovecot_anvil_conftab[] =
{
  { "DovecotAnvil", set_dovecot_anvil, NULL },
  { NULL }
};

static cmdtable dovecot_anvil_cmdtab[] =
{
  { PRE_CMD,      C_PASS, G_NONE, dovecot_anvil_pre_pass,
    FALSE,  FALSE, CL_AUTH },
  { POST_CMD,     C_PASS, G_NONE, dovecot_anvil_post_pass,
    FALSE,  FALSE, CL_AUTH },
  { POST_CMD_ERR, C_PASS, G_NONE, dovecot_anvil_post_pass_err,
    FALSE,  FALSE, CL_AUTH },
  { 0, NULL }
};

static authtable dovecot_anvil_authtab[] = {
  { 0, "auth", dovecot_anvil_auth },
  { 0, NULL, NULL }
};

module dovecot_anvil_module =
{
  /* always NULL */
  NULL, NULL,

  /* module api version 2.0 */
  0x20,

  /* module name */
  "dovecot_anvil",

  /* module configuration handler table */
  dovecot_anvil_conftab,

  /* module command handler table */
  dovecot_anvil_cmdtab,

  /* module authentication handler table */
  dovecot_anvil_authtab,

  /* module initialization function */
  dovecot_anvil_init,

  /* module session initialization function */
  dovecot_anvil_sess_init,

  /* module version */
  MOD_DOVECOT_ANVIL_VERSION
};

/* copied from dovecot/lib/crc32.c, MIT licence */
static uint32_t crc32tab[256] = {
    0x00000000,
    0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F,
    0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E,
    0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
    0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE, 0x1ADAD47D,
    0x6DDDE4EB, 0xF4D4B551, 0x83D385C7, 0x136C9856, 0x646BA8C0,
    0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9, 0xFA0F3D63,
    0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
    0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B, 0x35B5A8FA,
    0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75,
    0xDCD60DCF, 0xABD13D59, 0x26D930AC, 0x51DE003A, 0xC8D75180,
    0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
    0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, 0x2F6F7C87,
    0x58684C11, 0xC1611DAB, 0xB6662D3D, 0x76DC4190, 0x01DB7106,
    0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5,
    0xE8B8D433, 0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818,
    0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01, 0x6B6B51F4,
    0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED, 0x1B01A57B,
    0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA,
    0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
    0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541,
    0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A, 0x346ED9FC,
    0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5, 0xAA0A4C5F,
    0xDD0D7CC9, 0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086,
    0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F, 0x5EDEF90E,
    0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81,
    0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C,
    0x74B1D29A, 0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
    0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B,
    0x9309FF9D, 0x0A00AE27, 0x7D079EB1, 0xF00F9344, 0x8708A3D2,
    0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB, 0x196C3671,
    0x6E6B06E7, 0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
    0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5, 0xD6D6A3E8,
    0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767,
    0x3FB506DD, 0x48B2364B, 0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6,
    0x41047A60, 0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
    0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, 0xCC0C7795,
    0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE, 0xB2BD0B28,
    0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B,
    0x5BDEAE1D, 0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A,
    0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713, 0x95BF4A82,
    0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B, 0xE5D5BE0D,
    0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8,
    0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
    0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF,
    0xF862AE69, 0x616BFFD3, 0x166CCF45, 0xA00AE278, 0xD70DD2EE,
    0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7, 0x4969474D,
    0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0,
    0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9, 0xBDBDF21C,
    0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693,
    0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8, 0x5D681B02,
    0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
};

static uint32_t crc32_str(const char *str)
{
    return crc32_str_more(0, str);
}

static uint32_t crc32_str_more(uint32_t crc, const char *str)
{
    const uint8_t *p = (const uint8_t *)str;

    crc ^= 0xffffffff;
    for (; *p != '\0'; p++)
        crc = (crc >> 8) ^ crc32tab[((crc ^ *p) & 0xff)];
    crc ^= 0xffffffff;
    return crc;
}