Commit message: security: fix for vulnerability CVE-2014-0017

When accepting a new connection, a forking server based on libssh forks
and the child process handles the request. The RAND_bytes() function of
openssl doesn't reset its state after the fork, but simply adds the
current process id (getpid) to the PRNG state, which is not guaranteed
to be unique.
This can cause several children to end up with same PRNG state which is
a security issue.
CVE: CVE-2014-0017
CWE: CWE-310
Vulnerability description: The RAND_bytes function in libssh before 0.6.3, when forking is enabled, does not properly reset the state of the OpenSSL pseudo-random number generator (PRNG), which causes the state to be shared between children processes and allows local users to obtain sensitive information by leveraging a pid collision.

Project: libssh

int ssh_bind_accept_fd(ssh_bind sshbind, ssh_session session, socket_t fd){
    int i, rc;

    if (session == NULL){
        ssh_set_error(sshbind, SSH_FATAL,"session is null");
        return SSH_ERROR;
    }

    session->server = 1;
    session->version = 2;

    /* copy options */
    for (i = 0; i < 10; ++i) {
      if (sshbind->wanted_methods[i]) {
        session->opts.wanted_methods[i] = strdup(sshbind->wanted_methods[i]);
        if (session->opts.wanted_methods[i] == NULL) {
          return SSH_ERROR;
        }
      }
    }

    if (sshbind->bindaddr == NULL)
      session->opts.bindaddr = NULL;
    else {
      SAFE_FREE(session->opts.bindaddr);
      session->opts.bindaddr = strdup(sshbind->bindaddr);
      if (session->opts.bindaddr == NULL) {
        return SSH_ERROR;
      }
    }

    session->common.log_verbosity = sshbind->common.log_verbosity;
    if(sshbind->banner != NULL)
    	session->opts.custombanner = strdup(sshbind->banner);
    ssh_socket_free(session->socket);
    session->socket = ssh_socket_new(session);
    if (session->socket == NULL) {
      /* perhaps it may be better to copy the error from session to sshbind */
      ssh_set_error_oom(sshbind);
      return SSH_ERROR;
    }
    ssh_socket_set_fd(session->socket, fd);
    ssh_socket_get_poll_handle_out(session->socket);

    /* We must try to import any keys that could be imported in case
     * we are not using ssh_bind_listen (which is the other place
     * where keys can be imported) on this ssh_bind and are instead
     * only using ssh_bind_accept_fd to manage sockets ourselves.
     */
    rc = ssh_bind_import_keys(sshbind);
    if (rc != SSH_OK) {
      return SSH_ERROR;
    }

#ifdef HAVE_ECC
    if (sshbind->ecdsa) {
        session->srv.ecdsa_key = ssh_key_dup(sshbind->ecdsa);
        if (session->srv.ecdsa_key == NULL) {
          ssh_set_error_oom(sshbind);
          return SSH_ERROR;
        }
    }
#endif
    if (sshbind->dsa) {
        session->srv.dsa_key = ssh_key_dup(sshbind->dsa);
        if (session->srv.dsa_key == NULL) {
          ssh_set_error_oom(sshbind);
          return SSH_ERROR;
        }
    }
    if (sshbind->rsa) {
        session->srv.rsa_key = ssh_key_dup(sshbind->rsa);
        if (session->srv.rsa_key == NULL) {
          ssh_set_error_oom(sshbind);
          return SSH_ERROR;
        }
    }
    return SSH_OK;
}