noble (3) nbd_opt_starttls.3.gz

Provided by: libnbd-dev_1.20.0-1_amd64 bug

NAME
       nbd_opt_starttls - request the server to initiate TLS


SYNOPSIS
        #include <libnbd.h>

        int nbd_opt_starttls (
              struct nbd_handle *h
            );


DESCRIPTION
       Request that the server initiate a secure TLS connection, by sending "NBD_OPT_STARTTLS".  This can only
       be used if nbd_set_opt_mode(3) enabled option mode; furthermore, if you use nbd_set_tls(3) to request
       anything other than the default of "LIBNBD_TLS_DISABLE", then libnbd will have already attempted a TLS
       connection prior to allowing you control over option negotiation.  This command is disabled if
       nbd_supports_tls(3) reports false.

       This function is mainly useful for integration testing of corner cases in server handling; in particular,
       misuse of this function when coupled with a server that is not careful about resetting stateful commands
       such as nbd_opt_structured_reply(3) could result in a security hole (see CVE-2021-3716 against nbdkit,
       for example).  Thus, when security is a concern, you should instead prefer to use nbd_set_tls(3) with
       "LIBNBD_TLS_REQUIRE" and let libnbd negotiate TLS automatically.

       This function returns true if the server replies with success, false if the server replies with an error,
       and fails only if the server does not reply (such as for a loss of connection, which can include when the
       server rejects credentials supplied during the TLS handshake).  Note that the NBD protocol documents that
       requesting TLS after it is already enabled is a client error; most servers will gracefully fail a second
       request, but that does not downgrade a TLS session that has already been established, as reported by
       nbd_get_tls_negotiated(3).


RETURN VALUE
       This call returns a boolean value.


ERRORS
       On error -1 is returned.

       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

       The following parameters must not be NULL: "h".  For more information see "Non-NULL parameters" in
       libnbd(3).


HANDLE STATE
       nbd_opt_starttls can be called when the handle is in the following state:

        ┌─────────────────────────────────────┬─────────────────────────┐
        │ Handle created, before connecting   │ ❌ error                │
        │ Connecting                          │ ❌ error                │
        │ Connecting & handshaking (opt_mode) │ ✅ allowed              │
        │ Connected to the server             │ ❌ error                │
        │ Connection shut down                │ ❌ error                │
        │ Handle dead                         │ ❌ error                │
        └─────────────────────────────────────┴─────────────────────────┘


VERSION
       This function first appeared in libnbd 1.16.

       If you need to test if this function is available at compile time check if the following macro is
       defined:

        #define LIBNBD_HAVE_NBD_OPT_STARTTLS 1


SEE ALSO
       nbd_aio_opt_starttls(3), nbd_create(3), nbd_get_tls_negotiated(3), nbd_opt_structured_reply(3),
       nbd_set_opt_mode(3), nbd_set_tls(3), nbd_supports_tls(3), libnbd(3).


AUTHORS
       Eric Blake

       Richard W.M. Jones


       Copyright Red Hat


LICENSE
       This 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 of the License, or
       (at your option) any later version.

       This 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 this library; if not,
       write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA