/src/libssh/src/session.c

Source
/*
 * session.c - non-networking functions
 *
 * This file is part of the SSH Library
 *
 * Copyright (c) 2005-2013 by Aris Adamantiadis
 *
 * The SSH Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The SSH Library 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 Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the SSH Library; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#include "config.h"

#include <string.h>
#include <stdlib.h>

#ifdef _WIN32
#include <winsock2.h>
#endif

#include "libssh/priv.h"
#include "libssh/libssh.h"
#include "libssh/crypto.h"
#include "libssh/server.h"
#include "libssh/socket.h"
#include "libssh/ssh2.h"
#include "libssh/agent.h"
#include "libssh/packet.h"
#include "libssh/kex.h"
#include "libssh/session.h"
#include "libssh/misc.h"
#include "libssh/buffer.h"
#include "libssh/poll.h"
#include "libssh/pki.h"
#include "libssh/gssapi.h"

#define FIRST_CHANNEL 42 // why not ? it helps to find bugs.

/**
 * @defgroup libssh_session The SSH session functions
 * @ingroup libssh
 *
 * Functions that manage a session.
 *
 * @{
 */

/**
 * @brief Create a new ssh session.
 *
 * @returns             A new ssh_session pointer, NULL on error.
 */
ssh_session ssh_new(void)
{
    ssh_session session = NULL;
    char *id = NULL;
    int rc;

    session = calloc(1, sizeof (struct ssh_session_struct));
    if (session == NULL) {
        return NULL;
    }

    session->next_crypto = crypto_new();
    if (session->next_crypto == NULL) {
        goto err;
    }

    session->socket = ssh_socket_new(session);
    if (session->socket == NULL) {
        goto err;
    }

    session->out_buffer = ssh_buffer_new();
    if (session->out_buffer == NULL) {
        goto err;
    }

    session->in_buffer = ssh_buffer_new();
    if (session->in_buffer == NULL) {
        goto err;
    }

    session->out_queue = ssh_list_new();
    if (session->out_queue == NULL) {
        goto err;
    }

    session->alive = 0;
    session->auth.supported_methods = 0;
    ssh_set_blocking(session, 1);
    session->maxchannel = FIRST_CHANNEL;
    session->proxy_root = true;

    session->agent = ssh_agent_new(session);
    if (session->agent == NULL) {
        goto err;
    }

    /* Initialise a default PKI context */
    session->pki_context = ssh_pki_ctx_new();
    if (session->pki_context == NULL) {
        goto err;
    }

    /* OPTIONS */
    session->opts.StrictHostKeyChecking = SSH_STRICT_HOSTKEY_ASK;
    session->opts.port = 22;
    session->opts.fd = -1;
    session->opts.compressionlevel = 7;
    session->opts.nodelay = 0;
    session->opts.identities_only = false;
    session->opts.server_alive_interval = 0;
    session->opts.server_alive_count_max = 3;
    session->opts.batch_mode = false;
    session->opts.gateway_ports = false;
    session->opts.control_master = SSH_CONTROL_MASTER_NO;

    session->opts.flags = SSH_OPT_FLAG_PASSWORD_AUTH |
                          SSH_OPT_FLAG_PUBKEY_AUTH |
                          SSH_OPT_FLAG_KBDINT_AUTH |
                          SSH_OPT_FLAG_GSSAPI_AUTH;
    session->opts.pubkey_auth = SSH_PUBKEY_AUTH_ALL;

    session->opts.exp_flags = 0;

#ifdef WITH_GSSAPI
    session->opts.gssapi_key_exchange_algs =
        strdup(GSSAPI_KEY_EXCHANGE_SUPPORTED);
    if (session->opts.gssapi_key_exchange_algs == NULL) {
        goto err;
    }
#endif /* WITH_GSSAPI */

    /* Lazy allocation for identity_non_exp before populating the defaults */
    if (session->opts.identity_non_exp == NULL) {
        session->opts.identity_non_exp = ssh_list_new();
        if (session->opts.identity_non_exp == NULL) {
            goto err;
        }
    }

    id = strdup("%d/.ssh/id_ed25519");
    if (id == NULL) {
        goto err;
    }

    rc = ssh_list_append(session->opts.identity_non_exp, id);
    if (rc == SSH_ERROR) {
        goto err;
    }

#ifdef HAVE_ECC
    id = strdup("%d/.ssh/id_ecdsa");
    if (id == NULL) {
        goto err;
    }
    rc = ssh_list_append(session->opts.identity_non_exp, id);
    if (rc == SSH_ERROR) {
        goto err;
    }
#endif

    id = strdup("%d/.ssh/id_rsa");
    if (id == NULL) {
        goto err;
    }
    rc = ssh_list_append(session->opts.identity_non_exp, id);
    if (rc == SSH_ERROR) {
        goto err;
    }

#ifdef WITH_FIDO2
    /* Add security key identities */
    id = strdup("%d/.ssh/id_ed25519_sk");
    if (id == NULL) {
        goto err;
    }
    rc = ssh_list_append(session->opts.identity_non_exp, id);
    if (rc == SSH_ERROR) {
        goto err;
    }

#ifdef HAVE_ECC
    id = strdup("%d/.ssh/id_ecdsa_sk");
    if (id == NULL) {
        goto err;
    }
    rc = ssh_list_append(session->opts.identity_non_exp, id);
    if (rc == SSH_ERROR) {
        goto err;
    }
#endif /* HAVE_ECC */
#endif /* WITH_FIDO2 */

    /* Explicitly initialize states */
    session->session_state = SSH_SESSION_STATE_NONE;
    session->pending_call_state = SSH_PENDING_CALL_NONE;
    session->packet_state = PACKET_STATE_INIT;
    session->dh_handshake_state = DH_STATE_INIT;
    session->global_req_state = SSH_CHANNEL_REQ_STATE_NONE;

    session->auth.state = SSH_AUTH_STATE_NONE;
    session->auth.service_state = SSH_AUTH_SERVICE_NONE;

    return session;

err:
    free(id);
    ssh_free(session);
    return NULL;
}

/**
 * @brief Deallocate a SSH session handle.
 *
 * @param[in] session   The SSH session to free.
 *
 * @see ssh_disconnect()
 * @see ssh_new()
 */
void ssh_free(ssh_session session)
{
  int i;
  struct ssh_iterator *it = NULL;
  struct ssh_buffer_struct *b = NULL;

  if (session == NULL) {
    return;
  }

  /*
   * Delete all channels
   *
   * This needs the first thing we clean up cause if there is still an open
   * channel we call ssh_channel_close() first. So we need a working socket
   * and poll context for it.
   */
  for (it = ssh_list_get_iterator(session->channels);
       it != NULL;
       it = ssh_list_get_iterator(session->channels)) {
      ssh_channel_do_free(ssh_iterator_value(ssh_channel,it));
      ssh_list_remove(session->channels, it);
  }
  ssh_list_free(session->channels);
  session->channels = NULL;

#ifdef WITH_PCAP
  if (session->pcap_ctx) {
      ssh_pcap_context_free(session->pcap_ctx);
      session->pcap_ctx = NULL;
  }
#endif

  ssh_socket_free(session->socket);
  session->socket = NULL;

  if (session->default_poll_ctx) {
      ssh_poll_ctx_free(session->default_poll_ctx);
  }

  SSH_BUFFER_FREE(session->in_buffer);
  SSH_BUFFER_FREE(session->out_buffer);
  session->in_buffer = session->out_buffer = NULL;

  if (session->in_hashbuf != NULL) {
      SSH_BUFFER_FREE(session->in_hashbuf);
  }
  if (session->out_hashbuf != NULL) {
      SSH_BUFFER_FREE(session->out_hashbuf);
  }

  crypto_free(session->current_crypto);
  crypto_free(session->next_crypto);

  ssh_agent_free(session->agent);

  SSH_PKI_CTX_FREE(session->pki_context);

  ssh_key_free(session->srv.rsa_key);
  session->srv.rsa_key = NULL;
  ssh_key_free(session->srv.ecdsa_key);
  session->srv.ecdsa_key = NULL;
  ssh_key_free(session->srv.ed25519_key);
  session->srv.ed25519_key = NULL;

  if (session->ssh_message_list) {
      ssh_message msg;

      for (msg = ssh_list_pop_head(ssh_message, session->ssh_message_list);
           msg != NULL;
           msg = ssh_list_pop_head(ssh_message, session->ssh_message_list)) {
          ssh_message_free(msg);
      }
      ssh_list_free(session->ssh_message_list);
  }

  if (session->kbdint != NULL) {
    ssh_kbdint_free(session->kbdint);
  }

  if (session->packet_callbacks) {
    ssh_list_free(session->packet_callbacks);
  }

#ifdef WITH_GSSAPI
    ssh_gssapi_free(session);
    SAFE_FREE(session->opts.gssapi_key_exchange_algs);
#endif

  /* options */
  if (session->opts.identity) {
      char *id = NULL;

      for (id = ssh_list_pop_head(char *, session->opts.identity);
           id != NULL;
           id = ssh_list_pop_head(char *, session->opts.identity)) {
          SAFE_FREE(id);
      }
      ssh_list_free(session->opts.identity);
  }

  if (session->opts.identity_non_exp) {
      char *id = NULL;

      for (id = ssh_list_pop_head(char *, session->opts.identity_non_exp);
           id != NULL;
           id = ssh_list_pop_head(char *, session->opts.identity_non_exp)) {
          SAFE_FREE(id);
      }
      ssh_list_free(session->opts.identity_non_exp);
  }

    if (session->opts.certificate) {
        char *cert = NULL;

        for (cert = ssh_list_pop_head(char *, session->opts.certificate);
             cert != NULL;
             cert = ssh_list_pop_head(char *, session->opts.certificate)) {
            SAFE_FREE(cert);
        }
        ssh_list_free(session->opts.certificate);
    }

    if (session->opts.certificate_non_exp) {
        char *cert = NULL;

        for (cert = ssh_list_pop_head(char *, session->opts.certificate_non_exp);
             cert != NULL;
             cert = ssh_list_pop_head(char *, session->opts.certificate_non_exp)) {
            SAFE_FREE(cert);
        }
        ssh_list_free(session->opts.certificate_non_exp);
    }

    ssh_proxyjumps_free(session->opts.proxy_jumps);
    SSH_LIST_FREE(session->opts.proxy_jumps);
    SSH_LIST_FREE(session->opts.proxy_jumps_user_cb);
    SAFE_FREE(session->opts.proxy_jumps_str);

    if (session->opts.send_env) {
        char *pattern = NULL;

        for (pattern = ssh_list_pop_head(char *, session->opts.send_env);
             pattern != NULL;
             pattern = ssh_list_pop_head(char *, session->opts.send_env)) {
            SAFE_FREE(pattern);
        }
        ssh_list_free(session->opts.send_env);
    }

    while ((b = ssh_list_pop_head(struct ssh_buffer_struct *,
                                  session->out_queue)) != NULL) {
        SSH_BUFFER_FREE(b);
    }
    ssh_list_free(session->out_queue);

  ssh_agent_state_free(session->agent_state);
  session->agent_state = NULL;

  SAFE_FREE(session->auth.auto_state);
  SAFE_FREE(session->serverbanner);
  SAFE_FREE(session->clientbanner);
  SAFE_FREE(session->banner);
  SAFE_FREE(session->disconnect_message);
  SAFE_FREE(session->peer_discon_msg);

  SAFE_FREE(session->opts.agent_socket);
  SAFE_FREE(session->opts.bindaddr);
  SAFE_FREE(session->opts.username);
  SAFE_FREE(session->opts.host);
  SAFE_FREE(session->opts.originalhost);
  SAFE_FREE(session->opts.config_hostname);
  SAFE_FREE(session->opts.tag);
  SAFE_FREE(session->opts.homedir);
  SAFE_FREE(session->opts.sshdir);
  SAFE_FREE(session->opts.knownhosts);
  SAFE_FREE(session->opts.global_knownhosts);
  SAFE_FREE(session->opts.ProxyCommand);
  SAFE_FREE(session->opts.gss_server_identity);
  SAFE_FREE(session->opts.gss_client_identity);
  SAFE_FREE(session->opts.pubkey_accepted_types);
  SAFE_FREE(session->opts.control_path);
  SAFE_FREE(session->opts.preferred_authentications);
  SAFE_FREE(session->opts.forward_agent_sock_path);

  if (session->opts.local_forward) {
      char *entry = NULL;

      for (entry = ssh_list_pop_head(char *, session->opts.local_forward);
           entry != NULL;
           entry = ssh_list_pop_head(char *, session->opts.local_forward)) {
          SAFE_FREE(entry);
      }
      ssh_list_free(session->opts.local_forward);
  }

  if (session->opts.remote_forward) {
      char *entry = NULL;

      for (entry = ssh_list_pop_head(char *, session->opts.remote_forward);
           entry != NULL;
           entry = ssh_list_pop_head(char *, session->opts.remote_forward)) {
          SAFE_FREE(entry);
      }
      ssh_list_free(session->opts.remote_forward);
  }

  for (i = 0; i < SSH_KEX_METHODS; i++) {
      if (session->opts.wanted_methods[i]) {
          SAFE_FREE(session->opts.wanted_methods[i]);
      }
  }

  SAFE_FREE(session->server_opts.custombanner);
  SAFE_FREE(session->server_opts.moduli_file);

  _ssh_remove_legacy_log_cb();

  /* burn connection, it could contain sensitive data */
  ssh_burn(session, sizeof(struct ssh_session_struct));
  SAFE_FREE(session);
}

/**
 * @brief get the client banner
 *
 * @param[in] session   The SSH session
 *
 * @return Returns the client banner string or NULL.
 */
const char* ssh_get_clientbanner(ssh_session session) {
    if (session == NULL) {
        return NULL;
    }

    return session->clientbanner;
}

/**
 * @brief get the server banner
 *
 * @param[in] session   The SSH session
 *
 * @return Returns the server banner string or NULL.
 */
const char* ssh_get_serverbanner(ssh_session session) {
    if (!session) {
        return NULL;
    }
    return session->serverbanner;
}

/**
 * @brief get the name of the current key exchange algorithm.
 *
 * @param[in] session   The SSH session
 *
 * @return Returns the key exchange algorithm string or NULL.
 */
const char* ssh_get_kex_algo(ssh_session session) {
    if ((session == NULL) ||
        (session->current_crypto == NULL)) {
        return NULL;
    }

    switch (session->current_crypto->kex_type) {
    case SSH_KEX_DH_GROUP1_SHA1:
        return "diffie-hellman-group1-sha1";
    case SSH_KEX_DH_GROUP14_SHA1:
        return "diffie-hellman-group14-sha1";
    case SSH_KEX_DH_GROUP14_SHA256:
        return "diffie-hellman-group14-sha256";
    case SSH_GSS_KEX_DH_GROUP14_SHA256:
        return "gss-group14-sha256-";
    case SSH_KEX_DH_GROUP16_SHA512:
        return "diffie-hellman-group16-sha512";
    case SSH_GSS_KEX_DH_GROUP16_SHA512:
        return "gss-group16-sha512-";
    case SSH_KEX_DH_GROUP18_SHA512:
        return "diffie-hellman-group18-sha512";
    case SSH_KEX_ECDH_SHA2_NISTP256:
        return "ecdh-sha2-nistp256";
    case SSH_GSS_KEX_ECDH_NISTP256_SHA256:
        return "gss-nistp256-sha256-";
    case SSH_KEX_ECDH_SHA2_NISTP384:
        return "ecdh-sha2-nistp384";
    case SSH_KEX_ECDH_SHA2_NISTP521:
        return "ecdh-sha2-nistp521";
    case SSH_KEX_CURVE25519_SHA256:
        return "curve25519-sha256";
    case SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG:
        return "curve25519-sha256@libssh.org";
    case SSH_GSS_KEX_CURVE25519_SHA256:
        return "gss-curve25519-sha256-";
    case SSH_KEX_SNTRUP761X25519_SHA512_OPENSSH_COM:
        return "sntrup761x25519-sha512@openssh.com";
    case SSH_KEX_SNTRUP761X25519_SHA512:
        return "sntrup761x25519-sha512";
    case SSH_KEX_MLKEM768X25519_SHA256:
        return "mlkem768x25519-sha256";
    case SSH_KEX_MLKEM768NISTP256_SHA256:
        return "mlkem768nistp256-sha256";
#ifdef HAVE_MLKEM1024
    case SSH_KEX_MLKEM1024NISTP384_SHA384:
        return "mlkem1024nistp384-sha384";
#endif /* HAVE_MLKEM1024 */
#ifdef WITH_GEX
    case SSH_KEX_DH_GEX_SHA1:
        return "diffie-hellman-group-exchange-sha1";
    case SSH_KEX_DH_GEX_SHA256:
        return "diffie-hellman-group-exchange-sha256";
#endif /* WITH_GEX */
    }
    return NULL;
}

/**
 * @brief Check if current session keys were exchanged using
 *        a GSSAPI key exchange method.
 *
 * @param[in] session The SSH session.
 *
 * @return True if GSSAPI key exchange took place, false otherwise
 *         (other or no key exchange took place).
 */
bool ssh_session_kex_is_gss(ssh_session session)
{
    if (session == NULL || session->current_crypto == NULL) {
        return false;
    }
    return ssh_kex_is_gss(session->current_crypto);
}
/**
 * @brief get the name of the input cipher for the given session.
 *
 * @param[in] session The SSH session.
 *
 * @return Returns cipher name or NULL.
 */
const char* ssh_get_cipher_in(ssh_session session) {
    if ((session != NULL) &&
        (session->current_crypto != NULL) &&
        (session->current_crypto->in_cipher != NULL)) {
        return session->current_crypto->in_cipher->name;
    }
    return NULL;
}

/**
 * @brief get the name of the output cipher for the given session.
 *
 * @param[in] session The SSH session.
 *
 * @return Returns cipher name or NULL.
 */
const char* ssh_get_cipher_out(ssh_session session) {
    if ((session != NULL) &&
        (session->current_crypto != NULL) &&
        (session->current_crypto->out_cipher != NULL)) {
        return session->current_crypto->out_cipher->name;
    }
    return NULL;
}

/**
 * @brief get the name of the input HMAC algorithm for the given session.
 *
 * @param[in] session The SSH session.
 *
 * @return Returns HMAC algorithm name or NULL if unknown.
 */
const char* ssh_get_hmac_in(ssh_session session) {
    if ((session != NULL) &&
        (session->current_crypto != NULL)) {
        return ssh_hmac_type_to_string(session->current_crypto->in_hmac, session->current_crypto->in_hmac_etm);
    }
    return NULL;
}

/**
 * @brief get the name of the output HMAC algorithm for the given session.
 *
 * @param[in] session The SSH session.
 *
 * @return Returns HMAC algorithm name or NULL if unknown.
 */
const char* ssh_get_hmac_out(ssh_session session) {
    if ((session != NULL) &&
        (session->current_crypto != NULL)) {
        return ssh_hmac_type_to_string(session->current_crypto->out_hmac, session->current_crypto->out_hmac_etm);
    }
    return NULL;
}

/**
 * @internal
 * @brief Close the connection socket if it is a socket created by us.
 * Does not close the sockets provided by the user through options API.
 */
void
ssh_session_socket_close(ssh_session session)
{
    if (session->opts.fd == SSH_INVALID_SOCKET) {
        ssh_socket_close(session->socket);
    }
    session->alive = 0;
    session->session_state = SSH_SESSION_STATE_ERROR;
}

/**
 * @brief Disconnect impolitely from a remote host by closing the socket.
 *
 * Suitable if you forked and want to destroy this session.
 *
 * @param[in]  session  The SSH session to disconnect.
 */
void
ssh_silent_disconnect(ssh_session session)
{
    if (session == NULL) {
        return;
    }

    ssh_session_socket_close(session);
    ssh_disconnect(session);
}

/**
 * @brief Set the session in blocking/nonblocking mode.
 *
 * @param[in]  session  The ssh session to change.
 *
 * @param[in]  blocking Zero for nonblocking mode.
 */
void ssh_set_blocking(ssh_session session, int blocking)
{
    if (session == NULL) {
        return;
    }
    session->flags &= ~SSH_SESSION_FLAG_BLOCKING;
    session->flags |= blocking ? SSH_SESSION_FLAG_BLOCKING : 0;
}

/**
 * @brief Return the blocking mode of libssh
 * @param[in] session The SSH session
 * @returns 0 if the session is nonblocking,
 * @returns 1 if the functions may block.
 */
int ssh_is_blocking(ssh_session session)
{
    return (session->flags & SSH_SESSION_FLAG_BLOCKING) ? 1 : 0;
}

/* Waits until the output socket is empty */
static int ssh_flush_termination(void *c){
  ssh_session session = c;
  if (ssh_socket_buffered_write_bytes(session->socket) == 0 ||
      session->session_state == SSH_SESSION_STATE_ERROR)
    return 1;
  else
    return 0;
}

/**
 * @brief Blocking flush of the outgoing buffer
 * @param[in] session The SSH session
 * @param[in] timeout Set an upper limit on the time for which this function
 *                    will block, in milliseconds. Specifying -1
 *                    means an infinite timeout. This parameter is passed to
 *                    the poll() function.
 * @returns           `SSH_OK` on success, `SSH_AGAIN` if timeout occurred,
 *                    `SSH_ERROR` otherwise.
 */
int ssh_blocking_flush(ssh_session session, int timeout){
    int rc;
    if (session == NULL) {
        return SSH_ERROR;
    }

    rc = ssh_handle_packets_termination(session, timeout,
            ssh_flush_termination, session);
    if (rc == SSH_ERROR) {
        return rc;
    }
    if (!ssh_flush_termination(session)) {
        rc = SSH_AGAIN;
    }

    return rc;
}

/**
 * @brief Check if we are connected.
 *
 * @param[in]  session  The session to check if it is connected.
 *
 * @return              1 if we are connected, 0 if not.
 */
int ssh_is_connected(ssh_session session) {
    if (session == NULL) {
        return 0;
    }

    return session->alive;
}

/**
 * @brief Get the fd of a connection.
 *
 * In case you'd need the file descriptor of the connection to the server/client.
 *
 * @param[in] session   The ssh session to use.
 *
 * @return              The file descriptor of the connection, or -1 if it is
 *                      not connected
 */
socket_t ssh_get_fd(ssh_session session) {
  if (session == NULL) {
    return -1;
  }

  return ssh_socket_get_fd(session->socket);
}

/**
 * @brief Tell the session it has data to read on the file descriptor without
 * blocking.
 *
 * @param[in] session   The ssh session to use.
 */
void ssh_set_fd_toread(ssh_session session) {
  if (session == NULL) {
    return;
  }

  ssh_socket_set_read_wontblock(session->socket);
}

/**
 * @brief Tell the session it may write to the file descriptor without blocking.
 *
 * @param[in] session   The ssh session to use.
 */
void ssh_set_fd_towrite(ssh_session session) {
  if (session == NULL) {
    return;
  }

  ssh_socket_set_write_wontblock(session->socket);
}

/**
 * @brief Tell the session it has an exception to catch on the file descriptor.
 *
 * @param[in] session   The ssh session to use.
 */
void ssh_set_fd_except(ssh_session session) {
  if (session == NULL) {
    return;
  }

  ssh_socket_set_except(session->socket);
}

/**
 * @internal
 *
 * @brief Poll the current session for an event and call the appropriate
 * callbacks. This function will not loop until the @p timeout is expired.
 *
 * This will block until one event happens.
 *
 * @param[in] session   The session handle to use.
 *
 * @param[in] timeout   Set an upper limit on the time for which this function
 *                      will block, in milliseconds. Specifying
 *                      `SSH_TIMEOUT_INFINITE`
 *                      (-1) means an infinite timeout.
 *                      Specifying `SSH_TIMEOUT_USER` means to use the timeout
 *                      specified in options. 0 means poll will return
 *                      immediately.
 *                      This parameter is passed to the poll() function.
 *
 * @return              `SSH_OK` on success, `SSH_ERROR` otherwise.
 */
int ssh_handle_packets(ssh_session session, int timeout)
{
    ssh_poll_handle spoll = NULL;
    ssh_poll_ctx ctx = NULL;
    int tm = timeout;
    int rc;

    if (session == NULL || session->socket == NULL) {
        return SSH_ERROR;
    }

    spoll = ssh_socket_get_poll_handle(session->socket);
    if (spoll == NULL) {
        ssh_set_error_oom(session);
        return SSH_ERROR;
    }
    ssh_poll_add_events(spoll, POLLIN);
    ctx = ssh_poll_get_ctx(spoll);

    if (ctx == NULL) {
        ctx = ssh_poll_get_default_ctx(session);
        if (ctx == NULL) {
            ssh_set_error_oom(session);
            return SSH_ERROR;
        }
        rc = ssh_poll_ctx_add(ctx, spoll);
        if (rc != SSH_OK) {
            return SSH_ERROR;
        }
    }

    if (timeout == SSH_TIMEOUT_USER) {
        if (ssh_is_blocking(session)) {
            tm = ssh_make_milliseconds(session->opts.timeout,
                                       session->opts.timeout_usec);
        } else {
            tm = 0;
        }
    }
    rc = ssh_poll_ctx_dopoll(ctx, tm);
    if (rc == SSH_ERROR) {
        session->session_state = SSH_SESSION_STATE_ERROR;
    }

    return rc;
}

/**
 * @internal
 *
 * @brief Poll the current session for an event and call the appropriate
 * callbacks.
 *
 * This will block until termination function returns true, or @p timeout
 * expired.
 *
 * @param[in] session   The session handle to use.
 *
 * @param[in] timeout   Set an upper limit on the time for which this function
 *                      will block, in milliseconds. Specifying
 *                      `SSH_TIMEOUT_INFINITE` (-1) means an infinite timeout.
 *                      Specifying SSH_TIMEOUT_USER means using the timeout
 *                      specified in options. 0 means poll will return
 *                      immediately.
 *                      SSH_TIMEOUT_DEFAULT uses the session timeout if set or
 *                      uses blocking parameters of the session.
 *                      This parameter is passed to the poll() function.
 *
 * @param[in] fct       Termination function to be used to determine if it is
 *                      possible to stop polling.
 * @param[in] user      User parameter to be passed to fct termination function.
 * @returns             `SSH_OK` on success, `SSH_AGAIN` if timeout occurred,
 *                      `SSH_ERROR` otherwise.
 */
int ssh_handle_packets_termination(ssh_session session,
                                   int timeout,
                                   ssh_termination_function fct,
                                   void *user)
{
    struct ssh_timestamp ts;
    int timeout_ms = SSH_TIMEOUT_INFINITE;
    int tm;
    int ret = SSH_OK;

    /* If a timeout has been provided, use it */
    if (timeout >= 0) {
        timeout_ms = timeout;
    } else {
        if (ssh_is_blocking(session)) {
            if (timeout == SSH_TIMEOUT_USER || timeout == SSH_TIMEOUT_DEFAULT) {
                if (session->opts.timeout > 0 ||
                    session->opts.timeout_usec > 0) {
                    timeout_ms =
                        ssh_make_milliseconds(session->opts.timeout,
                                              session->opts.timeout_usec);
                }
            }
        } else {
            timeout_ms = SSH_TIMEOUT_NONBLOCKING;
        }
    }

    /* avoid unnecessary syscall for the SSH_TIMEOUT_NONBLOCKING case */
    if (timeout_ms != SSH_TIMEOUT_NONBLOCKING) {
        ssh_timestamp_init(&ts);
    }

    tm = timeout_ms;
    while(!fct(user)) {
        ret = ssh_handle_packets(session, tm);
        if (ret == SSH_ERROR) {
            break;
        }
        if (ssh_timeout_elapsed(&ts, timeout_ms)) {
            ret = fct(user) ? SSH_OK : SSH_AGAIN;
            break;
        }

        tm = ssh_timeout_update(&ts, timeout_ms);
    }

    return ret;
}

/**
 * @brief Get session status
 *
 * @param session       The ssh session to use.
 *
 * @returns A bitmask including `SSH_CLOSED`, `SSH_READ_PENDING`,
 *          `SSH_WRITE_PENDING` or `SSH_CLOSED_ERROR` which
 *          respectively means the session is closed, has data to
 *          read on the connection socket and session was closed
 *          due to an error.
 */
int ssh_get_status(ssh_session session) {
  int socketstate;
  int r = 0;

  if (session == NULL) {
    return 0;
  }

  socketstate = ssh_socket_get_status(session->socket);

  if (session->session_state == SSH_SESSION_STATE_DISCONNECTED) {
    r |= SSH_CLOSED;
  }
  if (socketstate & SSH_READ_PENDING) {
    r |= SSH_READ_PENDING;
  }
  if (socketstate & SSH_WRITE_PENDING) {
      r |= SSH_WRITE_PENDING;
  }
  if ((session->session_state == SSH_SESSION_STATE_DISCONNECTED &&
       (socketstate & SSH_CLOSED_ERROR)) ||
      session->session_state == SSH_SESSION_STATE_ERROR) {
    r |= SSH_CLOSED_ERROR;
  }

  return r;
}

/**
 * @brief Get poll flags for an external mainloop
 *
 * @param session       The ssh session to use.
 *
 * @returns A bitmask including `SSH_READ_PENDING` or `SSH_WRITE_PENDING`.
 *          For `SSH_READ_PENDING`, your invocation of poll() should include
 *          POLLIN.  For `SSH_WRITE_PENDING`, your invocation of poll() should
 *          include POLLOUT.
 */
int ssh_get_poll_flags(ssh_session session)
{
  if (session == NULL) {
    return 0;
  }

  return ssh_socket_get_poll_flags (session->socket);
}

/**
 * @brief Get the disconnect message from the server.
 *
 * @param[in] session   The ssh session to use.
 *
 * @return              The message sent by the server along with the
 *                      disconnect, or NULL in which case the reason of the
 *                      disconnect may be found with ssh_get_error.
 *
 * @see ssh_get_error()
 */
const char *ssh_get_disconnect_message(ssh_session session) {
  if (session == NULL) {
    return NULL;
  }

  if (session->session_state != SSH_SESSION_STATE_DISCONNECTED) {
    ssh_set_error(session, SSH_REQUEST_DENIED,
        "Connection not closed yet");
  } else if(!session->peer_discon_msg) {
    ssh_set_error(session, SSH_FATAL,
        "Connection correctly closed but no disconnect message");
  } else {
    return session->peer_discon_msg;
  }

  return NULL;
}

/**
 * @brief Get the protocol version of the session.
 *
 * @param session       The ssh session to use.
 *
 * @return The SSH version as integer, < 0 on error.
 */
int ssh_get_version(ssh_session session) {
    if (session == NULL) {
        return -1;
    }

    return 2;
}

/**
 * @internal
 * @brief Callback to be called when the socket received an exception code.
 * @param code        The exception code from the socket layer.
 * @param errno_code  The errno value associated with the exception.
 * @param user        Pointer to the SSH session.
 */
void ssh_socket_exception_callback(int code, int errno_code, void *user){
    ssh_session session = (ssh_session)user;

    SSH_LOG(SSH_LOG_RARE,
            "Socket exception callback: %d (%d)",
            code,
            errno_code);
    session->session_state = SSH_SESSION_STATE_ERROR;
    if (errno_code == 0 && code == SSH_SOCKET_EXCEPTION_EOF) {
        ssh_set_error(session, SSH_FATAL, "Socket error: disconnected");
#ifdef _WIN32
    } else if (errno_code == WSAENETDOWN) {
        ssh_set_error(session, SSH_FATAL, "Socket error: network down");
    } else if (errno_code == WSAENETUNREACH) {
        ssh_set_error(session, SSH_FATAL, "Socket error: network unreachable");
    } else if (errno_code == WSAENETRESET) {
        ssh_set_error(session, SSH_FATAL, "Socket error: network reset");
    } else if (errno_code == WSAECONNABORTED) {
        ssh_set_error(session, SSH_FATAL, "Socket error: connection aborted");
    } else if (errno_code == WSAECONNRESET) {
        ssh_set_error(session,
                      SSH_FATAL,
                      "Socket error: connection reset by peer");
    } else if (errno_code == WSAETIMEDOUT) {
        ssh_set_error(session, SSH_FATAL, "Socket error: connection timed out");
    } else if (errno_code == WSAECONNREFUSED) {
        ssh_set_error(session, SSH_FATAL, "Socket error: connection refused");
    } else if (errno_code == WSAEHOSTUNREACH) {
        ssh_set_error(session, SSH_FATAL, "Socket error: host unreachable");
#endif
    } else {
        char err_msg[SSH_ERRNO_MSG_MAX] = {0};
        ssh_set_error(session,
                      SSH_FATAL,
                      "Socket error: %s",
                      ssh_strerror(errno_code, err_msg, SSH_ERRNO_MSG_MAX));
    }

    session->ssh_connection_callback(session);
}

/**
 * @brief Send a message that should be ignored
 *
 * @param[in] session   The SSH session
 * @param[in] data      Data to be sent
 *
 * @return              `SSH_OK` on success, `SSH_ERROR` otherwise.
 */
int ssh_send_ignore (ssh_session session, const char *data) {
    const int type = SSH2_MSG_IGNORE;
    int rc;

    if (ssh_socket_is_open(session->socket)) {
        rc = ssh_buffer_pack(session->out_buffer,
                             "bs",
                             type,
                             data);
        if (rc != SSH_OK){
            ssh_set_error_oom(session);
            goto error;
        }
        ssh_packet_send(session);
        ssh_handle_packets(session, 0);
    }

    return SSH_OK;

error:
    ssh_buffer_reinit(session->out_buffer);
    return SSH_ERROR;
}

/**
 * @brief Send a debug message
 *
 * @param[in] session          The SSH session
 * @param[in] message          Data to be sent
 * @param[in] always_display   Message SHOULD be displayed by the server. It
 *                             SHOULD NOT be displayed unless debugging
 *                             information has been explicitly requested.
 *
 * @return                     `SSH_OK` on success, `SSH_ERROR` otherwise.
 */
int ssh_send_debug (ssh_session session, const char *message, int always_display) {
    int rc;

    if (ssh_socket_is_open(session->socket)) {
        rc = ssh_buffer_pack(session->out_buffer,
                             "bbsd",
                             SSH2_MSG_DEBUG,
                             always_display != 0 ? 1 : 0,
                             message,
                             0); /* empty language tag */
        if (rc != SSH_OK) {
            ssh_set_error_oom(session);
            goto error;
        }
        ssh_packet_send(session);
        ssh_handle_packets(session, 0);
    }

    return SSH_OK;

error:
    ssh_buffer_reinit(session->out_buffer);
    return SSH_ERROR;
}

 /**
 * @brief Set the session data counters.
 *
 * This function sets the counter structures to be used to calculate data
 * which comes in and goes out through the session at different levels.
 *
 * @code
 * struct ssh_counter_struct scounter = {
 *     .in_bytes = 0,
 *     .out_bytes = 0,
 *     .in_packets = 0,
 *     .out_packets = 0
 * };
 *
 * struct ssh_counter_struct rcounter = {
 *     .in_bytes = 0,
 *     .out_bytes = 0,
 *     .in_packets = 0,
 *     .out_packets = 0
 * };
 *
 * ssh_set_counters(session, &scounter, &rcounter);
 * @endcode
 *
 * @param[in] session   The SSH session.
 *
 * @param[in] scounter  Counter for byte data handled by the session sockets.
 *
 * @param[in] rcounter  Counter for byte and packet data handled by the session,
 *                      prior compression and SSH overhead.
 */
void ssh_set_counters(ssh_session session, ssh_counter scounter,
                              ssh_counter rcounter) {
    if (session != NULL) {
        session->socket_counter = scounter;
        session->raw_counter = rcounter;
    }
}

/**
 * @deprecated Use ssh_get_publickey_hash()
 */
int ssh_get_pubkey_hash(ssh_session session, unsigned char **hash)
{
    ssh_key pubkey = NULL;
    ssh_string pubkey_blob = NULL;
    MD5CTX ctx = NULL;
    unsigned char *h = NULL;
    int rc;

    if (session == NULL || hash == NULL) {
        return SSH_ERROR;
    }

    /* In FIPS mode, we cannot use MD5 */
    if (ssh_fips_mode()) {
        ssh_set_error(session,
                      SSH_FATAL,
                      "In FIPS mode MD5 is not allowed."
                      "Try ssh_get_publickey_hash() with"
                      "SSH_PUBLICKEY_HASH_SHA256");
        return SSH_ERROR;
    }

    *hash = NULL;
    if (session->current_crypto == NULL ||
        session->current_crypto->server_pubkey == NULL) {
        ssh_set_error(session, SSH_FATAL, "No current cryptographic context");
        return SSH_ERROR;
    }

    rc = ssh_get_server_publickey(session, &pubkey);
    if (rc != SSH_OK) {
        return SSH_ERROR;
    }

    rc = ssh_pki_export_pubkey_blob(pubkey, &pubkey_blob);
    ssh_key_free(pubkey);
    if (rc != SSH_OK) {
        return SSH_ERROR;
    }

    h = calloc(MD5_DIGEST_LEN, sizeof(unsigned char));
    if (h == NULL) {
        SSH_STRING_FREE(pubkey_blob);
        return SSH_ERROR;
    }

    ctx = md5_init();
    if (ctx == NULL) {
        SSH_STRING_FREE(pubkey_blob);
        SAFE_FREE(h);
        return SSH_ERROR;
    }

    rc = md5_update(ctx,
                    ssh_string_data(pubkey_blob),
                    ssh_string_len(pubkey_blob));
    if (rc != SSH_OK) {
        SSH_STRING_FREE(pubkey_blob);
        md5_ctx_free(ctx);
        SAFE_FREE(h);
        return rc;
    }
    SSH_STRING_FREE(pubkey_blob);
    rc = md5_final(h, ctx);
    if (rc != SSH_OK) {
        SAFE_FREE(h);
        return rc;
    }

    *hash = h;

    return MD5_DIGEST_LEN;
}

/**
 * @brief Deallocate the hash obtained by ssh_get_pubkey_hash.
 *
 * This is required under Microsoft platform as this library might use a
 * different C library than your software, hence a different heap.
 *
 * @param[in] hash      The buffer to deallocate.
 *
 * @see ssh_get_pubkey_hash()
 */
void ssh_clean_pubkey_hash(unsigned char **hash)
{
    SAFE_FREE(*hash);
}

/**
 * @brief Get the server public key from a session.
 *
 * @param[in]  session  The session to get the key from.
 *
 * @param[out] key      A pointer to store the allocated key. You need to free
 *                      the key using ssh_key_free().
 *
 * @return              `SSH_OK` on success, `SSH_ERROR` on error.
 *
 * @see ssh_key_free()
 */
int ssh_get_server_publickey(ssh_session session, ssh_key *key)
{
    ssh_key pubkey = NULL;

    if (session == NULL ||
        session->current_crypto == NULL ||
        session->current_crypto->server_pubkey == NULL) {
        return SSH_ERROR;
    }

    pubkey = ssh_key_dup(session->current_crypto->server_pubkey);
    if (pubkey == NULL) {
        return SSH_ERROR;
    }

    *key = pubkey;
    return SSH_OK;
}

/**
 * @deprecated Use ssh_get_server_publickey()
 */
int ssh_get_publickey(ssh_session session, ssh_key *key)
{
    return ssh_get_server_publickey(session, key);
}

/**
 * @brief Allocates a buffer with the hash of the public key.
 *
 * This function allows you to get a @p hash of the public @p key. You can then
 * print this hash in a human-readable form to the user so that he is able to
 * verify it. Use ssh_get_hexa() or ssh_print_hash() to display it.
 *
 * @param[in]  key      The public key to create the hash for.
 *
 * @param[in]  type     The type of the hash you want.
 *
 * @param[out]  hash    A pointer to store the allocated buffer. It can be
 *                      freed using ssh_clean_pubkey_hash().
 *
 * @param[in]  hlen     The length of the hash.
 *
 * @return SSH_OK on success, SSH_ERROR if an error occurred.
 *
 * @warning It is very important that you verify at some moment that the hash
 *          matches a known server. If you don't do it, cryptography won't help
 *          you at making things secure.
 *          OpenSSH uses SHA256 to print public key digests.
 *
 * @see ssh_session_update_known_hosts()
 * @see ssh_get_hexa()
 * @see ssh_print_hash()
 * @see ssh_clean_pubkey_hash()
 */
int ssh_get_publickey_hash(const ssh_key key,
                           enum ssh_publickey_hash_type type,
                           unsigned char **hash,
                           size_t *hlen)
{
    ssh_string blob = NULL;
    unsigned char *h = NULL;
    int (*digest)(const unsigned char *, size_t, unsigned char *) = NULL;
    int rc, ret = SSH_ERROR;

    rc = ssh_pki_export_pubkey_blob(key, &blob);
    if (rc < 0) {
        goto out;
    }

    switch (type) {
    case SSH_PUBLICKEY_HASH_SHA1:
        digest = sha1;
        *hlen = SHA_DIGEST_LEN;
        break;
    case SSH_PUBLICKEY_HASH_SHA256:
        digest = sha256;
        *hlen = SHA256_DIGEST_LEN;
        break;
    case SSH_PUBLICKEY_HASH_MD5:
#if defined(HAVE_LIBCRYPTO) && OPENSSL_VERSION_NUMBER < 0x30000000L
        /* In FIPS mode without OpenSSL providers, we cannot use MD5 */
        if (ssh_fips_mode()) {
            SSH_LOG(SSH_LOG_TRACE,
                    "In FIPS mode MD5 is not allowed."
                    "Try using SSH_PUBLICKEY_HASH_SHA256");
            goto out;
        }
#endif
        digest = md5;
        *hlen = MD5_DIGEST_LEN;
        break;
    default:
        goto out;
    }

    h = calloc(1, *hlen);
    if (h == NULL) {
        goto out;
    }

    rc = digest(ssh_string_data(blob), ssh_string_len(blob), h);
    if (rc != SSH_OK) {
        free(h);
        goto out;
    }

    *hash = h;
    ret = SSH_OK;

out:
    SSH_STRING_FREE(blob);
    return ret;
}

/** @} */

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Created: 2026-10-22 06:47