nbdkit-tls-fallback-filter - nbdkit TLS protection filter

       Eric Blake

       Copyright Red Hat

       "nbdkit-tls-fallback-filter" is designed to be used when offering a connection that allows but does not
       require TLS from clients, in order to offer safe alternative content to plaintext clients, only exposing
       the underlying plugin to authenticated users.  This may provide a nicer failure mode for plaintext
       clients than the harsher "nbdkit --tls=require".

       When this filter detects a plaintext connection, it ignores the client's export name, and provides a
       single read-only export with 512 bytes of data and content that defaults to the message "This NBD server
       requires TLS authentication before it will serve useful data."

       When using this filter, it is recommended to place this filter first in the command line, to reduce the
       chance that any work done by ".open" in earlier filters can be exploited by plaintext connections as a
       denial of service attack to starve further authenticated connections.  Note that this filter will fail to
       load if the plugin requests the "SERIALIZE_CONNECTIONS" thread model, as a plaintext client holding its
       connection open indefinitely would be such a starvation.

$filterdir/nbdkit-tls-fallback-filter.so
           The filter.

           Use "nbdkit --dump-config" to find the location of $filterdir.

       Redistribution and use in source and binary forms, with or without modification, are  permitted  provided
       that the following conditions are met:

       •   Redistributions  of  source  code must retain the above copyright notice, this list of conditions and
           the following disclaimer.

       •   Redistributions in binary form must reproduce the above copyright notice, this list of conditions and
           the following disclaimer in the documentation and/or other materials provided with the distribution.

       •   Neither the name of Red Hat nor the names of its contributors may  be  used  to  endorse  or  promote
           products derived from this software without specific prior written permission.

       THIS  SOFTWARE  IS  PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
       INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND  FITNESS  FOR  A  PARTICULAR
       PURPOSE  ARE  DISCLAIMED.  IN  NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
       INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,  PROCUREMENT  OF
       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
       ON  ANY  THEORY  OF  LIABILITY,  WHETHER  IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
       DAMAGE.

nbdkit-1.42.2                                      2025-04-02                      nbdkit-tls-fallback-filter(1)

       nbdkit-tls-fallback-filter - nbdkit TLS protection filter

tlsreadme=MESSAGE
           This  optional  parameter can be used to use "MESSAGE" as the contents of the dummy export exposed to
           plaintext clients, using trailing NUL bytes to round the size up to 512 bytes.

nbdkit(1), nbdkit-tls(1), nbdkit-filter(3).

        nbdkit --tls=on --filter=tls-fallback plugin [plugin-args...]
               [tlsreadme=MESSAGE]

       "nbdkit-tls-fallback-filter" first appeared in nbdkit 1.22.