/*

 * Dropbear - a SSH2 server

 * 

 * Copyright (c) 2002,2003 Matt Johnston

 * All rights reserved.

 * 

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 * 

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 * 

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

 * SOFTWARE. */

/* This file (auth.c) handles authentication requests, passing it to the

 * particular type (auth-passwd, auth-pubkey). */

#include "includes.h"

#include "dbutil.h"

#include "session.h"

#include "buffer.h"

#include "ssh.h"

#include "packet.h"

#include "auth.h"

#include "runopts.h"

#include "dbrandom.h"

static int checkusername(const char *username, unsigned int userlen);

/* initialise the first time for a session, resetting all parameters */

void svr_authinitialise() {

  memset(&ses.authstate, 0, sizeof(ses.authstate));

#if DROPBEAR_SVR_PUBKEY_AUTH

  ses.authstate.authtypes |= AUTH_TYPE_PUBKEY;

#endif

#if DROPBEAR_SVR_PASSWORD_AUTH || DROPBEAR_SVR_PAM_AUTH

  if (!svr_opts.noauthpass) {

    ses.authstate.authtypes |= AUTH_TYPE_PASSWORD;

  }

#endif

}

/* Send a banner message if specified to the client. The client might

 * ignore this, but possibly serves as a legal "no trespassing" sign */

void send_msg_userauth_banner(const buffer *banner) {

  TRACE(("enter send_msg_userauth_banner"))

  CHECKCLEARTOWRITE();

  buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_BANNER);

  buf_putbufstring(ses.writepayload, banner);

  buf_putstring(ses.writepayload, "en", 2);

  encrypt_packet();

  TRACE(("leave send_msg_userauth_banner"))

}

/* handle a userauth request, check validity, pass to password or pubkey

 * checking, and handle success or failure */

void recv_msg_userauth_request() {

  char *username = NULL, *servicename = NULL, *methodname = NULL;

  unsigned int userlen, servicelen, methodlen;

  int valid_user = 0;

  TRACE(("enter recv_msg_userauth_request"))

  /* for compensating failure delay */

  gettime_wrapper(&ses.authstate.auth_starttime);

  /* ignore packets if auth is already done */

  if (ses.authstate.authdone == 1) {

    TRACE(("leave recv_msg_userauth_request: authdone already"))

    return;

  }

  /* send the banner if it exists, it will only exist once */

  if (svr_opts.banner) {

    send_msg_userauth_banner(svr_opts.banner);

    buf_free(svr_opts.banner);

    svr_opts.banner = NULL;

  }

  username = buf_getstring(ses.payload, &userlen);

  servicename = buf_getstring(ses.payload, &servicelen);

  methodname = buf_getstring(ses.payload, &methodlen);

  /* only handle 'ssh-connection' currently */

  if (!(servicelen == SSH_SERVICE_CONNECTION_LEN

      && (strncmp(servicename, SSH_SERVICE_CONNECTION,

          SSH_SERVICE_CONNECTION_LEN) == 0))) {

    m_free(username);

    m_free(servicename);

    m_free(methodname);

    dropbear_exit("unknown service in auth");

  }

  /* check username is good before continuing. 

   * the 'incrfail' varies depending on the auth method to

   * avoid giving away which users exist on the system through

   * the time delay. */

  if (checkusername(username, userlen) == DROPBEAR_SUCCESS) {

    valid_user = 1;

  }

  /* user wants to know what methods are supported */

  if (methodlen == AUTH_METHOD_NONE_LEN &&

      strncmp(methodname, AUTH_METHOD_NONE,

        AUTH_METHOD_NONE_LEN) == 0) {

    TRACE(("recv_msg_userauth_request: 'none' request"))

    if (valid_user

        && svr_opts.allowblankpass

        && !svr_opts.noauthpass

        && !(svr_opts.norootpass && ses.authstate.pw_uid == 0) 

        && ses.authstate.pw_passwd[0] == '\0') 

    {

      dropbear_log(LOG_NOTICE, 

          "Auth succeeded with blank password for '%s' from %s",

          ses.authstate.pw_name,

          svr_ses.addrstring);

      send_msg_userauth_success();

      goto out;

    }

    else

    {

      /* 'none' has no failure delay */

      send_msg_userauth_failure(0, 0);

      goto out;

    }

  }

#if DROPBEAR_SVR_PASSWORD_AUTH

  if (!svr_opts.noauthpass &&

      !(svr_opts.norootpass && ses.authstate.pw_uid == 0) ) {

    /* user wants to try password auth */

    if (methodlen == AUTH_METHOD_PASSWORD_LEN &&

        strncmp(methodname, AUTH_METHOD_PASSWORD,

          AUTH_METHOD_PASSWORD_LEN) == 0) {

      svr_auth_password(valid_user);

      goto out;

    }

  }

#endif

#if DROPBEAR_SVR_PAM_AUTH

  if (!svr_opts.noauthpass &&

      !(svr_opts.norootpass && ses.authstate.pw_uid == 0) ) {

    /* user wants to try password auth */

    if (methodlen == AUTH_METHOD_PASSWORD_LEN &&

        strncmp(methodname, AUTH_METHOD_PASSWORD,

          AUTH_METHOD_PASSWORD_LEN) == 0) {

      svr_auth_pam(valid_user);

      goto out;

    }

  }

#endif

#if DROPBEAR_SVR_PUBKEY_AUTH

  /* user wants to try pubkey auth */

  if (methodlen == AUTH_METHOD_PUBKEY_LEN &&

      strncmp(methodname, AUTH_METHOD_PUBKEY,

        AUTH_METHOD_PUBKEY_LEN) == 0) {

    svr_auth_pubkey(valid_user);

    goto out;

  }

#endif

  /* nothing matched, we just fail with a delay */

  send_msg_userauth_failure(0, 1);

out:

  m_free(username);

  m_free(servicename);

  m_free(methodname);

}

#ifdef HAVE_GETGROUPLIST

/* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */

static int check_group_membership(gid_t check_gid, const char* username, gid_t user_gid) {

  int ngroups, i, ret;

  gid_t *grouplist = NULL;

  int match = DROPBEAR_FAILURE;

  for (ngroups = 32; ngroups <= DROPBEAR_NGROUP_MAX; ngroups *= 2) {

    grouplist = m_malloc(sizeof(gid_t) * ngroups);

    /* BSD returns ret==0 on success. Linux returns ret==ngroups on success */

    ret = getgrouplist(username, user_gid, grouplist, &ngroups);

    if (ret >= 0) {

      break;

    }

    m_free(grouplist);

    grouplist = NULL;

  }

  if (!grouplist) {

    dropbear_log(LOG_ERR, "Too many groups for user '%s'", username);

    return DROPBEAR_FAILURE;

  }

  for (i = 0; i < ngroups; i++) {

    if (grouplist[i] == check_gid) {

      match = DROPBEAR_SUCCESS;

      break;

    }

  }

  m_free(grouplist);

  return match;

}

#endif

/* Check that the username exists and isn't disallowed (root), and has a valid shell.

 * returns DROPBEAR_SUCCESS on valid username, DROPBEAR_FAILURE on failure */

static int checkusername(const char *username, unsigned int userlen) {

  char* listshell = NULL;

  char* usershell = NULL;

  uid_t uid;

  TRACE(("enter checkusername"))

  if (userlen > MAX_USERNAME_LEN) {

    return DROPBEAR_FAILURE;

  }

  if (strlen(username) != userlen) {

    dropbear_exit("Attempted username with a null byte");

  }

  if (ses.authstate.username == NULL) {

    /* first request */

    fill_passwd(username);

    ses.authstate.username = m_strdup(username);

  } else {

    /* check username hasn't changed */

    if (strcmp(username, ses.authstate.username) != 0) {

      dropbear_exit("Client trying multiple usernames");

    }

  }

  /* avoids cluttering logs with repeated failure messages from

  consecutive authentication requests in a sesssion */

  if (ses.authstate.checkusername_failed) {

    TRACE(("checkusername: returning cached failure"))

    return DROPBEAR_FAILURE;

  }

  /* check that user exists */

  if (!ses.authstate.pw_name) {

    TRACE(("leave checkusername: user '%s' doesn't exist", username))

    dropbear_log(LOG_WARNING,

        "Login attempt for nonexistent user from %s",

        svr_ses.addrstring);

    ses.authstate.checkusername_failed = 1;

    return DROPBEAR_FAILURE;

  }

  /* check if we are running as non-root, and login user is different from the server */

  uid = geteuid();

  if (!(DROPBEAR_SVR_MULTIUSER && uid == 0) && uid != ses.authstate.pw_uid) {

    TRACE(("running as nonroot, only server uid is allowed"))

    dropbear_log(LOG_WARNING,

        "Login attempt with wrong user %s from %s",

        ses.authstate.pw_name,

        svr_ses.addrstring);

    ses.authstate.checkusername_failed = 1;

    return DROPBEAR_FAILURE;

  }

  /* check for non-root if desired */

  if (svr_opts.norootlogin && ses.authstate.pw_uid == 0) {

    TRACE(("leave checkusername: root login disabled"))

    dropbear_log(LOG_WARNING, "root login rejected");

    ses.authstate.checkusername_failed = 1;

    return DROPBEAR_FAILURE;

  }

  /* check for login restricted to certain group if desired */

#ifdef HAVE_GETGROUPLIST

  if (svr_opts.restrict_group) {

    if (check_group_membership(svr_opts.restrict_group_gid,

        ses.authstate.pw_name, ses.authstate.pw_gid) == DROPBEAR_FAILURE) {

      dropbear_log(LOG_WARNING,

        "Logins are restricted to the group %s but user '%s' is not a member",

        svr_opts.restrict_group, ses.authstate.pw_name);

      ses.authstate.checkusername_failed = 1;

      return DROPBEAR_FAILURE;

    }

  }

#endif /* HAVE_GETGROUPLIST */

  TRACE(("shell is %s", ses.authstate.pw_shell))

  /* check that the shell is set */

  usershell = ses.authstate.pw_shell;

  if (usershell[0] == '\0') {

    /* empty shell in /etc/passwd means /bin/sh according to passwd(5) */

    usershell = "/bin/sh";

  }

  /* check the shell is valid. If /etc/shells doesn't exist, getusershell()

   * should return some standard shells like "/bin/sh" and "/bin/csh" (this

   * is platform-specific) */

  setusershell();

  while ((listshell = getusershell()) != NULL) {

    TRACE(("test shell is '%s'", listshell))

    if (strcmp(listshell, usershell) == 0) {

      /* have a match */

      goto goodshell;

    }

  }

  /* no matching shell */

  endusershell();

  TRACE(("no matching shell"))

  ses.authstate.checkusername_failed = 1;

  dropbear_log(LOG_WARNING, "User '%s' has invalid shell, rejected",

        ses.authstate.pw_name);

  return DROPBEAR_FAILURE;

goodshell:

  endusershell();

  TRACE(("matching shell"))

  TRACE(("uid = %d", ses.authstate.pw_uid))

  TRACE(("leave checkusername"))

  return DROPBEAR_SUCCESS;

}

/* Send a failure message to the client, in responds to a userauth_request.

 * Partial indicates whether to set the "partial success" flag,

 * incrfail is whether to count this failure in the failure count (which

 * is limited. This function also handles disconnection after too many

 * failures */

void send_msg_userauth_failure(int partial, int incrfail) {

  buffer *typebuf = NULL;

  TRACE(("enter send_msg_userauth_failure"))

  CHECKCLEARTOWRITE();

  buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_FAILURE);

  /* put a list of allowed types */

  typebuf = buf_new(30); /* long enough for PUBKEY and PASSWORD */

  if (ses.authstate.authtypes & AUTH_TYPE_PUBKEY) {

    buf_putbytes(typebuf, (const unsigned char *)AUTH_METHOD_PUBKEY, AUTH_METHOD_PUBKEY_LEN);

    if (ses.authstate.authtypes & AUTH_TYPE_PASSWORD) {

      buf_putbyte(typebuf, ',');

    }

  }

  if (ses.authstate.authtypes & AUTH_TYPE_PASSWORD) {

    buf_putbytes(typebuf, (const unsigned char *)AUTH_METHOD_PASSWORD, AUTH_METHOD_PASSWORD_LEN);

  }

  buf_putbufstring(ses.writepayload, typebuf);

  TRACE(("auth fail: methods %d, '%.*s'", ses.authstate.authtypes,

        typebuf->len, typebuf->data))

  buf_free(typebuf);

  buf_putbyte(ses.writepayload, partial ? 1 : 0);

  encrypt_packet();

  if (incrfail) {

    /* The SSH_MSG_AUTH_FAILURE response is delayed to attempt to

    avoid user enumeration and slow brute force attempts.

    The delay is adjusted by the time already spent in processing

    authentication (ses.authstate.auth_starttime timestamp). */

    /* Desired total delay 300ms +-50ms (in nanoseconds).

    Beware of integer overflow if increasing these values */

    const uint32_t mindelay = 250000000;

    const uint32_t vardelay = 100000000;

    uint32_t rand_delay;

    struct timespec delay;

    gettime_wrapper(&delay);

    delay.tv_sec -= ses.authstate.auth_starttime.tv_sec;

    delay.tv_nsec -= ses.authstate.auth_starttime.tv_nsec;

    /* carry */

    if (delay.tv_nsec < 0) {

      delay.tv_nsec += 1000000000;

      delay.tv_sec -= 1;

    }

    genrandom((unsigned char*)&rand_delay, sizeof(rand_delay));

    rand_delay = mindelay + (rand_delay % vardelay);

    if (delay.tv_sec == 0 && delay.tv_nsec <= rand_delay) {

      /* Compensate for elapsed time */

      delay.tv_nsec = rand_delay - delay.tv_nsec;

    } else {

      /* No time left or time went backwards, just delay anyway */

      delay.tv_sec = 0;

      delay.tv_nsec = rand_delay;

    }

#if DROPBEAR_FUZZ

    if (!fuzz.fuzzing)

#endif

    {

      while (nanosleep(&delay, &delay) == -1 && errno == EINTR) { /* Go back to sleep */ }

    }

    ses.authstate.failcount++;

  }

  if (ses.authstate.failcount > svr_opts.maxauthtries) {

    char * userstr;

    /* XXX - send disconnect ? */

    TRACE(("Max auth tries reached, exiting"))

    if (ses.authstate.pw_name == NULL) {

      userstr = "is invalid";

    } else {

      userstr = ses.authstate.pw_name;

    }

    dropbear_exit("Max auth tries reached - user '%s'",

        userstr);

  }

  TRACE(("leave send_msg_userauth_failure"))

}

/* Send a success message to the user, and set the "authdone" flag */

void send_msg_userauth_success() {

  TRACE(("enter send_msg_userauth_success"))

  CHECKCLEARTOWRITE();

  buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_SUCCESS);

  encrypt_packet();

  /* authdone must be set after encrypt_packet() for 

   * delayed-zlib mode */

  ses.authstate.authdone = 1;

#if DROPBEAR_SVR_DROP_PRIVS

  /* Drop privileges as soon as authentication has happened. */

  svr_switch_user();

  /* If running as the user, we can rely on the OS

   * to limit allowed ports */

  ses.allowprivport = 1;

#else

  if (ses.authstate.pw_uid == 0) {

    ses.allowprivport = 1;

  }

#endif

  /* Remove from the list of pre-auth sockets. Should be m_close(), since if

   * we fail, we might end up leaking connection slots, and disallow new

   * logins - a nasty situation. */              

  m_close(svr_ses.childpipe);

  TRACE(("leave send_msg_userauth_success"))

}

#if DROPBEAR_SVR_DROP_PRIVS

/* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */

static int utmp_gid(gid_t *ret_gid) {

  struct group *utmp_gr = getgrnam("utmp");

  if (!utmp_gr) {

    TRACE(("No utmp group"));

    return DROPBEAR_FAILURE;

  }

  *ret_gid = utmp_gr->gr_gid;

  return DROPBEAR_SUCCESS;

}

#endif

/* Switch to the ses.authstate user.

 * Fails if not running as root and the user differs.

 *

 * This may be called either after authentication, or 

 * after shell/command fork if DROPBEAR_SVR_DROP_PRIVS is unset.

 */

void svr_switch_user(void) {

  assert(ses.authstate.authdone);

  /* We can only change uid/gid as root ... */

  if (getuid() == 0) {

    if ((setgid(ses.authstate.pw_gid) < 0) ||

      (initgroups(ses.authstate.pw_name, 

            ses.authstate.pw_gid) < 0)) {

      dropbear_exit("Error changing user group");

    }

#if DROPBEAR_SVR_DROP_PRIVS

    /* Retain utmp saved group so that wtmp/utmp can be written */

    int ret = utmp_gid(&svr_ses.utmp_gid);

    if (ret == DROPBEAR_SUCCESS) {

      /* Set saved gid to utmp so that it can be

       * restored for login_logout() etc. This saved

       * group is cleared by the OS on execve() */

      int rc = setresgid(-1, -1, svr_ses.utmp_gid);

      if (rc == 0) {

        svr_ses.have_utmp_gid = 1;

      } else {

        /* Will not attempt to switch to utmp gid.

         * login() etc may fail. */

        TRACE(("utmp setresgid failed"));

      }

    }

#endif

    if (setuid(ses.authstate.pw_uid) < 0) {

      dropbear_exit("Error changing user");

    }

  } else {

    /* ... but if the daemon is the same uid as the requested uid, we don't

     * need to */

    /* XXX - there is a minor issue here, in that if there are multiple

     * usernames with the same uid, but differing groups, then the

     * differing groups won't be set (as with initgroups()). The solution

     * is for the sysadmin not to give out the UID twice */

    if (getuid() != ses.authstate.pw_uid) {

      dropbear_exit("Couldn't change user as non-root");

    }

  }

}

void svr_raise_gid_utmp(void) {

#if DROPBEAR_SVR_DROP_PRIVS

  if (!svr_ses.have_utmp_gid) {

    return;

  }

  if (setegid(svr_ses.utmp_gid) != 0) {

    dropbear_log(LOG_WARNING, "failed setegid");

  }

#endif

}

void svr_restore_gid(void) {

#if DROPBEAR_SVR_DROP_PRIVS

  if (!svr_ses.have_utmp_gid) {

    return;

  }

  if (setegid(getgid()) != 0) {

    dropbear_log(LOG_WARNING, "failed setegid");

  }

#endif

}