nbdkit --tls=on --filter=tls-fallback plugin [plugin-args...] [tlsreadme=MESSAGE]
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
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.
This optional parameter can be used to use
MESSAGEas the contents of the dummy export exposed to plaintext clients, using trailing NUL bytes to round the size up to 512 bytes.
nbdkit --dump-configto find the location of
nbdkit-tls-fallback-filter first appeared in nbdkit 1.22.
nbdkit(1), nbdkit-tls(1), nbdkit-filter(3).
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nbdkit(1), nbdkit-filter(3), nbdkit-plugin(3), nbdkit-release-notes-1.22(1), nbdkit-tls(1).