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.

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           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.

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