/*

 * Dropbear - a SSH2 server

 * 

 * Copyright (c) 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. */

#include "includes.h"

#include "session.h"

#include "dbutil.h"

#include "packet.h"

#include "algo.h"

#include "buffer.h"

#include "dss.h"

#include "ssh.h"

#include "dbrandom.h"

#include "kex.h"

#include "channel.h"

#include "runopts.h"

#include "netio.h"

static void checktimeouts(void);

static long select_timeout(void);

static int ident_readln(int fd, char* buf, int count);

static void read_session_identification(void);

struct sshsession ses; /* GLOBAL */

/* called only at the start of a session, set up initial state */

void common_session_init(int sock_in, int sock_out) {

  time_t now;

#if DEBUG_TRACE

  debug_start_net();

#endif

  TRACE(("enter session_init"))

  ses.sock_in = sock_in;

  ses.sock_out = sock_out;

  ses.maxfd = MAX(sock_in, sock_out);

  if (sock_in >= 0) {

    setnonblocking(sock_in);

  }

  if (sock_out >= 0) {

    setnonblocking(sock_out);

  }

  ses.socket_prio = DROPBEAR_PRIO_NORMAL;

  /* Sets it to lowdelay */

  update_channel_prio();

#if !DROPBEAR_SVR_MULTIUSER

  /* A sanity check to prevent an accidental configuration option

     leaving multiuser systems exposed */

  {

    int ret;

    errno = 0;

    ret = getgroups(0, NULL);

    if (!(ret == -1 && errno == ENOSYS)) {

      dropbear_exit("Non-multiuser Dropbear requires a non-multiuser kernel");

    }

  }

#endif

  now = monotonic_now();

  ses.connect_time = now;

  ses.last_packet_time_keepalive_recv = now;

  ses.last_packet_time_idle = now;

  ses.last_packet_time_any_sent = 0;

  ses.last_packet_time_keepalive_sent = 0;

#if DROPBEAR_FUZZ

  if (!fuzz.fuzzing)

#endif

  {

  if (pipe(ses.signal_pipe) < 0) {

    dropbear_exit("Signal pipe failed");

  }

  setnonblocking(ses.signal_pipe[0]);

  setnonblocking(ses.signal_pipe[1]);

  ses.maxfd = MAX(ses.maxfd, ses.signal_pipe[0]);

  ses.maxfd = MAX(ses.maxfd, ses.signal_pipe[1]);

  }

  ses.writepayload = buf_new(TRANS_MAX_PAYLOAD_LEN);

  ses.transseq = 0;

  ses.readbuf = NULL;

  ses.payload = NULL;

  ses.recvseq = 0;

  initqueue(&ses.writequeue);

  ses.requirenext = SSH_MSG_KEXINIT;

  ses.dataallowed = 1; /* we can send data until we actually 

              send the SSH_MSG_KEXINIT */

  ses.ignorenext = 0;

  ses.lastpacket = 0;

  ses.reply_queue_head = NULL;

  ses.reply_queue_tail = NULL;

  ses.reply_queue_len = 0;

  /* set all the algos to none */

  ses.keys = (struct key_context*)m_malloc(sizeof(struct key_context));

  ses.newkeys = NULL;

  ses.keys->recv.algo_crypt = &dropbear_nocipher;

  ses.keys->trans.algo_crypt = &dropbear_nocipher;

  ses.keys->recv.crypt_mode = &dropbear_mode_none;

  ses.keys->trans.crypt_mode = &dropbear_mode_none;

  ses.keys->recv.algo_mac = &dropbear_nohash;

  ses.keys->trans.algo_mac = &dropbear_nohash;

  ses.keys->algo_kex = NULL;

  ses.keys->algo_hostkey = -1;

  ses.keys->recv.algo_comp = DROPBEAR_COMP_NONE;

  ses.keys->trans.algo_comp = DROPBEAR_COMP_NONE;

#ifndef DISABLE_ZLIB

  ses.keys->recv.zstream = NULL;

  ses.keys->trans.zstream = NULL;

#endif

  /* key exchange buffers */

  ses.session_id = NULL;

  ses.kexhashbuf = NULL;

  ses.transkexinit = NULL;

  ses.dh_K = NULL;

  ses.remoteident = NULL;

  ses.chantypes = NULL;

  ses.allowprivport = 0;

#if DROPBEAR_PLUGIN

        ses.plugin_session = NULL;

#endif

  TRACE(("leave session_init"))

}

void session_loop(void(*loophandler)(void)) {

  fd_set readfd, writefd;

  struct timeval timeout;

  int val;

  /* main loop, select()s for all sockets in use */

  for(;;) {

    const int writequeue_has_space = (ses.writequeue_len <= 2*TRANS_MAX_PAYLOAD_LEN);

    timeout.tv_sec = select_timeout();

    timeout.tv_usec = 0;

    DROPBEAR_FD_ZERO(&writefd);

    DROPBEAR_FD_ZERO(&readfd);

    dropbear_assert(ses.payload == NULL);

    /* We get woken up when signal handlers write to this pipe.

       SIGCHLD in svr-chansession is the only one currently. */

#if DROPBEAR_FUZZ

    if (!fuzz.fuzzing) 

#endif

    {

    dropbear_fd_set(ses.signal_pipe[0], &readfd);

    }

    /* set up for channels which can be read/written */

    setchannelfds(&readfd, &writefd, writequeue_has_space);

    /* Pending connections to test */

    set_connect_fds(&writefd);

    /* We delay reading from the input socket during initial setup until

    after we have written out our initial KEXINIT packet (empty writequeue). 

    This means our initial packet can be in-flight while we're doing a blocking

    read for the remote ident.

    We also avoid reading from the socket if the writequeue is full, that avoids

    replies backing up */

    if (ses.sock_in != -1 

      && (ses.remoteident || isempty(&ses.writequeue)) 

      && writequeue_has_space) {

      dropbear_fd_set(ses.sock_in, &readfd);

    }

    /* Ordering is important, this test must occur after any other function

    might have queued packets (such as connection handlers) */

    if (ses.sock_out != -1 && !isempty(&ses.writequeue)) {

      dropbear_fd_set(ses.sock_out, &writefd);

    }

    val = select(ses.maxfd+1, &readfd, &writefd, NULL, &timeout);

    if (ses.exitflag) {

      dropbear_exit("Terminated by signal");

    }

    if (val < 0 && errno != EINTR) {

      dropbear_exit("Error in select");

    }

    if (val <= 0) {

      /* If we were interrupted or the select timed out, we still

       * want to iterate over channels etc for reading, to handle

       * server processes exiting etc. 

       * We don't want to read/write FDs. */

      DROPBEAR_FD_ZERO(&writefd);

      DROPBEAR_FD_ZERO(&readfd);

    }

    /* We'll just empty out the pipe if required. We don't do

    any thing with the data, since the pipe's purpose is purely to

    wake up the select() above. */

    ses.channel_signal_pending = 0;

    if (FD_ISSET(ses.signal_pipe[0], &readfd)) {

      char x;

      TRACE(("signal pipe set"))

      while (read(ses.signal_pipe[0], &x, 1) > 0) {}

      ses.channel_signal_pending = 1;

    }

    /* check for auth timeout, rekeying required etc */

    checktimeouts();

    /* process session socket's incoming data */

    if (ses.sock_in != -1) {

      if (FD_ISSET(ses.sock_in, &readfd)) {

        if (!ses.remoteident) {

          /* blocking read of the version string */

          read_session_identification();

        } else {

          read_packet();

        }

      }

      /* Process the decrypted packet. After this, the read buffer

       * will be ready for a new packet */

      if (ses.payload != NULL) {

        process_packet();

      }

    }

    /* if required, flush out any queued reply packets that

    were being held up during a KEX */

    maybe_flush_reply_queue();

    handle_connect_fds(&writefd);

    /* loop handler prior to channelio, in case the server loophandler closes

    channels on process exit */

    loophandler();

    /* process pipes etc for the channels, ses.dataallowed == 0

     * during rekeying ) */

    channelio(&readfd, &writefd);

    /* process session socket's outgoing data */

    if (ses.sock_out != -1) {

      if (!isempty(&ses.writequeue)) {

        write_packet();

      }

    }

  } /* for(;;) */

  /* Not reached */

}

static void cleanup_buf(buffer **buf) {

  if (!*buf) {

    return;

  }

  buf_burn_free(*buf);

  *buf = NULL;

}

/* clean up a session on exit */

void session_cleanup() {

  TRACE(("enter session_cleanup"))

  /* we can't cleanup if we don't know the session state */

  if (!ses.init_done) {

    TRACE(("leave session_cleanup: !ses.init_done"))

    return;

  }

  /* BEWARE of changing order of functions here. */

  /* Must be before extra_session_cleanup() */

  chancleanup();

  if (ses.extra_session_cleanup) {

    ses.extra_session_cleanup();

  }

  /* After these are freed most functions will fail */

#if DROPBEAR_CLEANUP

  /* listeners call cleanup functions, this should occur before

  other session state is freed. */

  remove_all_listeners();

  remove_connect_pending();

  while (!isempty(&ses.writequeue)) {

    buf_free(dequeue(&ses.writequeue));

  }

  m_free(ses.newkeys);

#ifndef DISABLE_ZLIB

  if (ses.keys->recv.zstream != NULL) {

    if (inflateEnd(ses.keys->recv.zstream) == Z_STREAM_ERROR) {

      dropbear_exit("Crypto error");

    }

    m_free(ses.keys->recv.zstream);

  }

  if (ses.keys->trans.zstream != NULL) {

    if (deflateEnd(ses.keys->trans.zstream) == Z_STREAM_ERROR) {

      dropbear_exit("Crypto error");

    }

    m_free(ses.keys->trans.zstream);

  }

#endif

  m_free(ses.remoteident);

  m_free(ses.authstate.pw_dir);

  m_free(ses.authstate.pw_name);

  m_free(ses.authstate.pw_shell);

  m_free(ses.authstate.pw_passwd);

  m_free(ses.authstate.username);

#endif

  cleanup_buf(&ses.session_id);

  cleanup_buf(&ses.hash);

  cleanup_buf(&ses.payload);

  cleanup_buf(&ses.readbuf);

  cleanup_buf(&ses.writepayload);

  cleanup_buf(&ses.kexhashbuf);

  cleanup_buf(&ses.transkexinit);

  if (ses.dh_K) {

    mp_clear(ses.dh_K);

  }

  m_free(ses.dh_K);

  if (ses.dh_K_bytes) {

    buf_burn_free(ses.dh_K_bytes);

  }

  m_burn(ses.keys, sizeof(struct key_context));

  m_free(ses.keys);

  TRACE(("leave session_cleanup"))

}

void send_session_identification() {

  buffer *writebuf = buf_new(strlen(LOCAL_IDENT "\r\n") + 1);

  buf_putbytes(writebuf, (const unsigned char *) LOCAL_IDENT "\r\n", strlen(LOCAL_IDENT "\r\n"));

  writebuf_enqueue(writebuf);

}

static void read_session_identification() {

  /* max length of 255 chars */

  char linebuf[256];

  int len = 0;

  char done = 0;

  int i;

  /* Servers may send other lines of data before sending the

   * version string, client must be able to process such lines.

   * If they send more than 50 lines, something is wrong */

  for (i = IS_DROPBEAR_CLIENT ? 50 : 1; i > 0; i--) {

    len = ident_readln(ses.sock_in, linebuf, sizeof(linebuf));

    if (len < 0 && errno != EINTR) {

      /* It failed */

      break;

    }

    if (len >= 4 && memcmp(linebuf, "SSH-", 4) == 0) {

      /* start of line matches */

      done = 1;

      break;

    }

  }

  if (!done) {

    TRACE(("error reading remote ident: %s\n", strerror(errno)))

    ses.remoteclosed();

  } else {

    /* linebuf is already null terminated */

    ses.remoteident = m_malloc(len);

    memcpy(ses.remoteident, linebuf, len);

  }

  /* Shall assume that 2.x will be backwards compatible. */

  if (strncmp(ses.remoteident, "SSH-2.", 6) != 0

      && strncmp(ses.remoteident, "SSH-1.99-", 9) != 0) {

    dropbear_exit("Incompatible remote version '%s'", ses.remoteident);

  }

  DEBUG1(("remoteident: %s", ses.remoteident))

}

/* returns the length including null-terminating zero on success,

 * or -1 on failure */

static int ident_readln(int fd, char* buf, int count) {

  char in;

  int pos = 0;

  int num = 0;

  fd_set fds;

  struct timeval timeout;

  TRACE(("enter ident_readln"))

  if (count < 1) {

    return -1;

  }

  DROPBEAR_FD_ZERO(&fds);

  /* select since it's a non-blocking fd */

  /* leave space to null-terminate */

  while (pos < count-1) {

    dropbear_fd_set(fd, &fds);

    timeout.tv_sec = 1;

    timeout.tv_usec = 0;

    if (select(fd+1, &fds, NULL, NULL, &timeout) < 0) {

      if (errno == EINTR) {

        continue;

      }

      TRACE(("leave ident_readln: select error"))

      return -1;

    }

    checktimeouts();

    /* Have to go one byte at a time, since we don't want to read past

     * the end, and have to somehow shove bytes back into the normal

     * packet reader */

    if (FD_ISSET(fd, &fds)) {

      num = read(fd, &in, 1);

      /* a "\n" is a newline, "\r" we want to read in and keep going

       * so that it won't be read as part of the next line */

      if (num < 0) {

        /* error */

        if (errno == EINTR) {

          continue; /* not a real error */

        }

        TRACE(("leave ident_readln: read error"))

        return -1;

      }

      if (num == 0) {

        /* EOF */

        TRACE(("leave ident_readln: EOF"))

        return -1;

      }

#if DROPBEAR_FUZZ

      fuzz_dump(&in, 1);

#endif

      if (in == '\n') {

        /* end of ident string */

        break;

      }

      /* we don't want to include '\r's */

      if (in != '\r') {

        buf[pos] = in;

        pos++;

      }

    }

  }

  buf[pos] = '\0';

  TRACE(("leave ident_readln: return %d", pos+1))

  return pos+1;

}

void ignore_recv_response() {

  /* Do nothing */

  TRACE(("Ignored msg_request_response"))

}

static void send_msg_keepalive(void) {

  time_t old_time_idle = ses.last_packet_time_idle;

  struct Channel *chan = get_any_ready_channel();

  CHECKCLEARTOWRITE();

  if (chan) {

    /* Channel requests are preferable, more implementations

    handle them than SSH_MSG_GLOBAL_REQUEST */

    TRACE(("keepalive channel request %d", chan->index))

    start_send_channel_request(chan, DROPBEAR_KEEPALIVE_STRING);

  } else {

    TRACE(("keepalive global request"))

    /* Some peers will reply with SSH_MSG_REQUEST_FAILURE, 

    some will reply with SSH_MSG_UNIMPLEMENTED, some will exit. */

    buf_putbyte(ses.writepayload, SSH_MSG_GLOBAL_REQUEST); 

    buf_putstring(ses.writepayload, DROPBEAR_KEEPALIVE_STRING,

      strlen(DROPBEAR_KEEPALIVE_STRING));

  }

  buf_putbyte(ses.writepayload, 1); /* want_reply */

  encrypt_packet();

  ses.last_packet_time_keepalive_sent = monotonic_now();

  /* keepalives shouldn't update idle timeout, reset it back */

  ses.last_packet_time_idle = old_time_idle;

}

/* Returns the difference in seconds, clamped to LONG_MAX */

static long elapsed(time_t now, time_t prev) {

  time_t del = now - prev;

  if (del > LONG_MAX) {

    return LONG_MAX;

  }

  return (long)del;

}

/* Check all timeouts which are required. Currently these are the time for

 * user authentication, and the automatic rekeying. */

static void checktimeouts() {

  time_t now;

  now = monotonic_now();

  if (IS_DROPBEAR_SERVER && ses.authstate.authdone != 1

    && elapsed(now, ses.connect_time) >= AUTH_TIMEOUT) {

      dropbear_close("Timeout before auth");

  }

  /* we can't rekey if we haven't done remote ident exchange yet */

  if (ses.remoteident == NULL) {

    return;

  }

  if (!ses.kexstate.sentkexinit

      && (elapsed(now, ses.kexstate.lastkextime) >= KEX_REKEY_TIMEOUT

      || ses.kexstate.datarecv+ses.kexstate.datatrans >= KEX_REKEY_DATA

      || ses.kexstate.needrekey)) {

    TRACE(("rekeying after timeout or max data reached"))

    ses.kexstate.needrekey = 0;

    send_msg_kexinit();

  }

  if (opts.keepalive_secs > 0 && ses.authstate.authdone) {

    /* Avoid sending keepalives prior to auth - those are

    not valid pre-auth packet types */

    /* Send keepalives if we've been idle */

    if (elapsed(now, ses.last_packet_time_any_sent) >= opts.keepalive_secs) {

      send_msg_keepalive();

    }

    /* Also send an explicit keepalive message to trigger a response

    if the remote end hasn't sent us anything */

    if (elapsed(now, ses.last_packet_time_keepalive_recv) >= opts.keepalive_secs

      && elapsed(now, ses.last_packet_time_keepalive_sent) >= opts.keepalive_secs) {

      send_msg_keepalive();

    }

    if (elapsed(now, ses.last_packet_time_keepalive_recv)

      >= opts.keepalive_secs * DEFAULT_KEEPALIVE_LIMIT) {

      dropbear_exit("Keepalive timeout");

    }

  }

  if (opts.idle_timeout_secs > 0

      && elapsed(now, ses.last_packet_time_idle) >= opts.idle_timeout_secs) {

    dropbear_close("Idle timeout");

  }

  if (opts.max_duration_secs > 0

      && elapsed(now, ses.connect_time) >= opts.max_duration_secs) {

    dropbear_close("Max duration reached");

  }

}

static void update_timeout(long limit, time_t now, time_t last_event, long * timeout) {

  TRACE2(("update_timeout limit %ld, now %llu, last %llu, timeout %ld",

    limit,

    (unsigned long long)now,

    (unsigned long long)last_event, *timeout))

  if (last_event > 0 && limit > 0) {

    *timeout = MIN(*timeout, MAX(0, limit - elapsed(now, last_event)));

    TRACE2(("new timeout %ld", *timeout))

  }

}

static long select_timeout() {

  /* determine the minimum timeout that might be required, so

  as to avoid waking when unneccessary */

  long timeout = KEX_REKEY_TIMEOUT;

  time_t now = monotonic_now();

  if (!ses.kexstate.sentkexinit) {

    update_timeout(KEX_REKEY_TIMEOUT, now, ses.kexstate.lastkextime, &timeout);

  }

  if (ses.kexstate.needrekey) {

    timeout = 0;

  }

  if (ses.authstate.authdone != 1 && IS_DROPBEAR_SERVER) {

    /* AUTH_TIMEOUT is only relevant before authdone */

    update_timeout(AUTH_TIMEOUT, now, ses.connect_time, &timeout);

  }

  if (ses.authstate.authdone) {

    update_timeout(opts.keepalive_secs, now,

      MAX(ses.last_packet_time_keepalive_recv, ses.last_packet_time_keepalive_sent),

      &timeout);

  }

  update_timeout(opts.idle_timeout_secs, now, ses.last_packet_time_idle,

    &timeout);

  update_timeout(opts.max_duration_secs, now, ses.connect_time,

    &timeout);

  /* clamp negative timeouts to zero - event has already triggered */

  return MAX(timeout, 0);

}

const char* get_user_shell() {

  /* an empty shell should be interpreted as "/bin/sh" */

  if (ses.authstate.pw_shell[0] == '\0') {

    return "/bin/sh";

  } else {

    return ses.authstate.pw_shell;

  }

}

void fill_passwd(const char* username) {

  struct passwd *pw = NULL;

  if (ses.authstate.pw_name)

    m_free(ses.authstate.pw_name);

  if (ses.authstate.pw_dir)

    m_free(ses.authstate.pw_dir);

  if (ses.authstate.pw_shell)

    m_free(ses.authstate.pw_shell);

  if (ses.authstate.pw_passwd)

    m_free(ses.authstate.pw_passwd);

  pw = getpwnam(username);

  if (!pw) {

    return;

  }

  ses.authstate.pw_uid = pw->pw_uid;

  ses.authstate.pw_gid = pw->pw_gid;

  ses.authstate.pw_name = m_strdup(pw->pw_name);

  ses.authstate.pw_dir = m_strdup(pw->pw_dir);

  ses.authstate.pw_shell = m_strdup(pw->pw_shell);

  {

    char *passwd_crypt = pw->pw_passwd;

#ifdef HAVE_SHADOW_H

    /* "x" for the passwd crypt indicates shadow should be used */

    if (pw->pw_passwd && strcmp(pw->pw_passwd, "x") == 0) {

      /* get the shadow password */

      struct spwd *spasswd = getspnam(ses.authstate.pw_name);

      if (spasswd && spasswd->sp_pwdp) {

        passwd_crypt = spasswd->sp_pwdp;

      } else {

        /* Fail if missing in /etc/shadow */

        passwd_crypt = "!!";

      }

    }

#endif

    if (!passwd_crypt) {

      /* android supposedly returns NULL */

      passwd_crypt = "!!";

    }

    ses.authstate.pw_passwd = m_strdup(passwd_crypt);

  }

}

/* Called when channels are modified */

void update_channel_prio() {

  enum dropbear_prio new_prio;

  int any = 0;

  unsigned int i;

  TRACE(("update_channel_prio"))

  if (ses.sock_out < 0) {

    TRACE(("leave update_channel_prio: no socket"))

    return;

  }

  new_prio = DROPBEAR_PRIO_NORMAL;

  for (i = 0; i < ses.chansize; i++) {

    struct Channel *channel = ses.channels[i];

    if (!channel) {

      continue;

    }

    any = 1;

    if (channel->prio == DROPBEAR_PRIO_LOWDELAY) {

      new_prio = DROPBEAR_PRIO_LOWDELAY;

      break;

    }

  }

  if (any == 0) {

    /* lowdelay during setup */

    TRACE(("update_channel_prio: not any"))

    new_prio = DROPBEAR_PRIO_LOWDELAY;

  }

  if (new_prio != ses.socket_prio) {

    TRACE(("Dropbear priority transitioning %d -> %d", ses.socket_prio, new_prio))

    set_sock_priority(ses.sock_out, new_prio);

    ses.socket_prio = new_prio;

  }

}