nbdkit-tls-fallback-filter(1)

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

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

DESCRIPTION
"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.

PARAMETERS

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.

FILES

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

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

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

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

AUTHORS
Eric Blake

COPYRIGHT
Copyright (C) 2020 Red Hat Inc.

LICENSE
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.