/*

 * Dropbear - a SSH2 server

 * 

 * Copyright (c) 2002-2004 Matt Johnston

 * Copyright (c) 2004 by Mihnea Stoenescu

 * 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 "algo.h"

#include "buffer.h"

#include "session.h"

#include "kex.h"

#include "ssh.h"

#include "packet.h"

#include "bignum.h"

#include "dbrandom.h"

#include "runopts.h"

#include "signkey.h"

#include "ecc.h"

static void checkhostkey(const unsigned char* keyblob, unsigned int keybloblen);

#define MAX_KNOWNHOSTS_LINE 4500

void send_msg_kexdh_init() {

  TRACE(("send_msg_kexdh_init()"))  

  CHECKCLEARTOWRITE();

#if DROPBEAR_FUZZ

  if (fuzz.fuzzing && fuzz.skip_kexmaths) {

    return;

  }

#endif

  buf_putbyte(ses.writepayload, SSH_MSG_KEXDH_INIT);

  switch (ses.newkeys->algo_kex->mode) {

#if DROPBEAR_NORMAL_DH

    case DROPBEAR_KEX_NORMAL_DH:

      if (ses.newkeys->algo_kex != cli_ses.param_kex_algo

        || !cli_ses.dh_param) {

        if (cli_ses.dh_param) {

          free_kexdh_param(cli_ses.dh_param);

        }

        cli_ses.dh_param = gen_kexdh_param();

      }

      buf_putmpint(ses.writepayload, &cli_ses.dh_param->pub);

      break;

#endif

#if DROPBEAR_ECDH

    case DROPBEAR_KEX_ECDH:

      if (ses.newkeys->algo_kex != cli_ses.param_kex_algo

        || !cli_ses.ecdh_param) {

        if (cli_ses.ecdh_param) {

          free_kexecdh_param(cli_ses.ecdh_param);

        }

        cli_ses.ecdh_param = gen_kexecdh_param();

      }

      buf_put_ecc_raw_pubkey_string(ses.writepayload, &cli_ses.ecdh_param->key);

      break;

#endif

#if DROPBEAR_CURVE25519

    case DROPBEAR_KEX_CURVE25519:

      if (ses.newkeys->algo_kex != cli_ses.param_kex_algo

        || !cli_ses.curve25519_param) {

        if (cli_ses.curve25519_param) {

          free_kexcurve25519_param(cli_ses.curve25519_param);

        }

        cli_ses.curve25519_param = gen_kexcurve25519_param();

      }

      buf_putstring(ses.writepayload, cli_ses.curve25519_param->pub, CURVE25519_LEN);

      break;

#endif

  }

  cli_ses.param_kex_algo = ses.newkeys->algo_kex;

  encrypt_packet();

}

/* Handle a diffie-hellman key exchange reply. */

void recv_msg_kexdh_reply() {

  sign_key *hostkey = NULL;

  unsigned int keytype, keybloblen;

  unsigned char* keyblob = NULL;

  TRACE(("enter recv_msg_kexdh_reply"))

#if DROPBEAR_FUZZ

  if (fuzz.fuzzing && fuzz.skip_kexmaths) {

    return;

  }

#endif

  if (cli_ses.kex_state != KEXDH_INIT_SENT) {

    dropbear_exit("Received out-of-order kexdhreply");

  }

  keytype = ses.newkeys->algo_hostkey;

  TRACE(("keytype is %d", keytype))

  hostkey = new_sign_key();

  keybloblen = buf_getint(ses.payload);

  keyblob = buf_getptr(ses.payload, keybloblen);

  if (!ses.kexstate.donefirstkex) {

    /* Only makes sense the first time */

    checkhostkey(keyblob, keybloblen);

  }

  if (buf_get_pub_key(ses.payload, hostkey, &keytype) != DROPBEAR_SUCCESS) {

    TRACE(("failed getting pubkey"))

    dropbear_exit("Bad KEX packet");

  }

  switch (ses.newkeys->algo_kex->mode) {

#if DROPBEAR_NORMAL_DH

    case DROPBEAR_KEX_NORMAL_DH:

      {

      DEF_MP_INT(dh_f);

      m_mp_init(&dh_f);

      if (buf_getmpint(ses.payload, &dh_f) != DROPBEAR_SUCCESS) {

        TRACE(("failed getting mpint"))

        dropbear_exit("Bad KEX packet");

      }

      kexdh_comb_key(cli_ses.dh_param, &dh_f, hostkey);

      mp_clear(&dh_f);

      }

      break;

#endif

#if DROPBEAR_ECDH

    case DROPBEAR_KEX_ECDH:

      {

      buffer *ecdh_qs = buf_getstringbuf(ses.payload);

      kexecdh_comb_key(cli_ses.ecdh_param, ecdh_qs, hostkey);

      buf_free(ecdh_qs);

      }

      break;

#endif

#if DROPBEAR_CURVE25519

    case DROPBEAR_KEX_CURVE25519:

      {

      buffer *ecdh_qs = buf_getstringbuf(ses.payload);

      kexcurve25519_comb_key(cli_ses.curve25519_param, ecdh_qs, hostkey);

      buf_free(ecdh_qs);

      }

      break;

#endif

  }

#if DROPBEAR_NORMAL_DH

  if (cli_ses.dh_param) {

    free_kexdh_param(cli_ses.dh_param);

    cli_ses.dh_param = NULL;

  }

#endif

#if DROPBEAR_ECDH

  if (cli_ses.ecdh_param) {

    free_kexecdh_param(cli_ses.ecdh_param);

    cli_ses.ecdh_param = NULL;

  }

#endif

#if DROPBEAR_CURVE25519

  if (cli_ses.curve25519_param) {

    free_kexcurve25519_param(cli_ses.curve25519_param);

    cli_ses.curve25519_param = NULL;

  }

#endif

  cli_ses.param_kex_algo = NULL;

  if (buf_verify(ses.payload, hostkey, ses.newkeys->algo_signature, 

      ses.hash) != DROPBEAR_SUCCESS) {

    dropbear_exit("Bad hostkey signature");

  }

  sign_key_free(hostkey);

  hostkey = NULL;

  send_msg_newkeys();

  ses.requirenext = SSH_MSG_NEWKEYS;

  TRACE(("leave recv_msg_kexdh_init"))

}

static void ask_to_confirm(const unsigned char* keyblob, unsigned int keybloblen,

  const char* algoname) {

  char* fp = NULL;

  FILE *tty = NULL;

  int response = 'z';

  fp = sign_key_fingerprint(keyblob, keybloblen);

  if (cli_opts.always_accept_key) {

    dropbear_log(LOG_INFO, "\nHost '%s' key accepted unconditionally.\n(%s fingerprint %s)\n",

        cli_opts.remotehost,

        algoname,

        fp);

    m_free(fp);

    return;

  }

  fprintf(stderr, "\nHost '%s' is not in the trusted hosts file.\n(%s fingerprint %s)\nDo you want to continue connecting? (y/n) ", 

      cli_opts.remotehost, 

      algoname,

      fp);

  m_free(fp);

  tty = fopen(_PATH_TTY, "r");

  if (tty) {

    response = getc(tty);

    fclose(tty);

  } else {

    response = getc(stdin);

    /* flush stdin buffer */

    while ((getchar()) != '\n');

  }

  if (response == 'y') {

    return;

  }

  dropbear_exit("Didn't validate host key");

}

static FILE* open_known_hosts_file(int * readonly)

{

  FILE * hostsfile = NULL;

  char * filename = NULL;

  char * homedir = NULL;

  homedir = getenv("HOME");

  if (!homedir) {

    struct passwd * pw = NULL;

    pw = getpwuid(getuid());

    if (pw) {

      homedir = pw->pw_dir;

    }

  }

  if (homedir) {

    unsigned int len;

    len = strlen(homedir);

    filename = m_malloc(len + 18); /* "/.ssh/known_hosts" and null-terminator*/

    snprintf(filename, len+18, "%s/.ssh", homedir);

    /* Check that ~/.ssh exists - easiest way is just to mkdir */

    if (mkdir(filename, S_IRWXU) != 0) {

      if (errno != EEXIST) {

        dropbear_log(LOG_INFO, "Warning: failed creating %s/.ssh: %s",

            homedir, strerror(errno));

        TRACE(("mkdir didn't work: %s", strerror(errno)))

        goto out;

      }

    }

    snprintf(filename, len+18, "%s/.ssh/known_hosts", homedir);

    hostsfile = fopen(filename, "a+");

    if (hostsfile != NULL) {

      *readonly = 0;

      fseek(hostsfile, 0, SEEK_SET);

    } else {

      /* We mightn't have been able to open it if it was read-only */

      if (errno == EACCES || errno == EROFS) {

          TRACE(("trying readonly: %s", strerror(errno)))

          *readonly = 1;

          hostsfile = fopen(filename, "r");

      }

    }

  }

  if (hostsfile == NULL) {

    TRACE(("hostsfile didn't open: %s", strerror(errno)))

    dropbear_log(LOG_WARNING, "Failed to open %s/.ssh/known_hosts",

        homedir);

    goto out;

  }  

out:

  m_free(filename);

  return hostsfile;

}

static void checkhostkey(const unsigned char* keyblob, unsigned int keybloblen) {

  FILE *hostsfile = NULL;

  int readonly = 0;

  unsigned int hostlen, algolen;

  unsigned long len;

  const char *algoname = NULL;

  char * fingerprint = NULL;

  buffer * line = NULL;

  int ret;

  if (cli_opts.no_hostkey_check) {

    dropbear_log(LOG_INFO, "Caution, skipping hostkey check for %s\n", cli_opts.remotehost);

    return;

  }

  algoname = signkey_name_from_type(ses.newkeys->algo_hostkey, &algolen);

  hostsfile = open_known_hosts_file(&readonly);

  if (!hostsfile) {

    ask_to_confirm(keyblob, keybloblen, algoname);

    /* ask_to_confirm will exit upon failure */

    return;

  }

  line = buf_new(MAX_KNOWNHOSTS_LINE);

  hostlen = strlen(cli_opts.remotehost);

  do {

    if (buf_getline(line, hostsfile) == DROPBEAR_FAILURE) {

      TRACE(("failed reading line: prob EOF"))

      break;

    }

    /* The line is too short to be sensible */

    /* "30" is 'enough to hold ssh-dss plus the spaces, ie so we don't

     * buf_getfoo() past the end and die horribly - the base64 parsing

     * code is what tiptoes up to the end nicely */

    if (line->len < (hostlen+30) ) {

      TRACE(("line is too short to be sensible"))

      continue;

    }

    /* Compare hostnames */

    if (strncmp(cli_opts.remotehost, (const char *) buf_getptr(line, hostlen),

          hostlen) != 0) {

      continue;

    }

    buf_incrpos(line, hostlen);

    if (buf_getbyte(line) != ' ') {

      /* there wasn't a space after the hostname, something dodgy */

      TRACE(("missing space afte matching hostname"))

      continue;

    }

    if (strncmp((const char *) buf_getptr(line, algolen), algoname, algolen) != 0) {

      TRACE(("algo doesn't match"))

      continue;

    }

    buf_incrpos(line, algolen);

    if (buf_getbyte(line) != ' ') {

      TRACE(("missing space after algo"))

      continue;

    }

    /* Now we're at the interesting hostkey */

    ret = cmp_base64_key(keyblob, keybloblen, (const unsigned char *) algoname, algolen,

            line, &fingerprint);

    if (ret == DROPBEAR_SUCCESS) {

      /* Good matching key */

      DEBUG1(("server match %s", fingerprint))

      goto out;

    }

    /* The keys didn't match. eep. Note that we're "leaking"

       the fingerprint strings here, but we're exiting anyway */

    dropbear_exit("\n\n%s host key mismatch for %s !\n"

          "Fingerprint is %s\n"

          "Expected %s\n"

          "If you know that the host key is correct you can\nremove the bad entry from ~/.ssh/known_hosts", 

          algoname,

          cli_opts.remotehost,

          sign_key_fingerprint(keyblob, keybloblen),

          fingerprint ? fingerprint : "UNKNOWN");

  } while (1); /* keep going 'til something happens */

  /* Key doesn't exist yet */

  ask_to_confirm(keyblob, keybloblen, algoname);

  /* If we get here, they said yes */

  if (readonly) {

    TRACE(("readonly"))

    goto out;

  }

  if (!cli_opts.always_accept_key) {

    /* put the new entry in the file */

    fseek(hostsfile, 0, SEEK_END); /* In case it wasn't opened append */

    buf_setpos(line, 0);

    buf_setlen(line, 0);

    buf_putbytes(line, (const unsigned char *) cli_opts.remotehost, hostlen);

    buf_putbyte(line, ' ');

    buf_putbytes(line, (const unsigned char *) algoname, algolen);

    buf_putbyte(line, ' ');

    len = line->size - line->pos;

    /* The only failure with base64 is buffer_overflow, but buf_getwriteptr

     * will die horribly in the case anyway */

    base64_encode(keyblob, keybloblen, buf_getwriteptr(line, len), &len);

    buf_incrwritepos(line, len);

    buf_putbyte(line, '\n');

    buf_setpos(line, 0);

    fwrite(buf_getptr(line, line->len), line->len, 1, hostsfile);

    /* We ignore errors, since there's not much we can do about them */

  }

out:

  if (hostsfile != NULL) {

    fclose(hostsfile);

  }

  if (line != NULL) {

    buf_free(line);

  }

  m_free(fingerprint);

}

void recv_msg_ext_info(void) {

  /* This message is not client-specific in the protocol but Dropbear only handles

  a server-sent message at present. */

  unsigned int num_ext;

  unsigned int i;

  TRACE(("enter recv_msg_ext_info"))

  /* Must be after the first SSH_MSG_NEWKEYS */

  TRACE(("last %d, donefirst %d, donescond %d", ses.lastpacket, ses.kexstate.donefirstkex, ses.kexstate.donesecondkex))

  if (!(ses.lastpacket == SSH_MSG_NEWKEYS && !ses.kexstate.donesecondkex)) {

    TRACE(("leave recv_msg_ext_info: ignoring packet received at the wrong time"))

    return;

  }

  num_ext = buf_getint(ses.payload);

  TRACE(("received SSH_MSG_EXT_INFO with %d items", num_ext))

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

    unsigned int name_len;

    char *ext_name = buf_getstring(ses.payload, &name_len);

    TRACE(("extension %d name '%s'", i, ext_name))

    if (cli_ses.server_sig_algs == NULL

        && name_len == strlen(SSH_SERVER_SIG_ALGS)

        && strcmp(ext_name, SSH_SERVER_SIG_ALGS) == 0) {

      cli_ses.server_sig_algs = buf_getbuf(ses.payload);

    } else {

      /* valid extension values could be >MAX_STRING_LEN */

      buf_eatstring(ses.payload);

    }

    m_free(ext_name);

  }

  TRACE(("leave recv_msg_ext_info"))

}