NAME

       nbdkit-protect-filter - write-protect parts of a plugin

SYNOPSIS

        nbdkit --filter=protect plugin protect=START-END [protect=...]

DESCRIPTION

       "nbdkit-protect-filter" is a filter for nbdkit(1) that lets you write-protect parts of the
       underlying plugin.  This prevents clients from modifying ranges of the plugin, while still
       allowing the NBD connection to be writable in general.

       One use for this is to prevent clients from adding a phony header to the data to make it
       look like a non-raw disk format (like adding a qcow2 header), since that can be used in
       some exploits.

       To make the whole plugin readonly, use the nbdkit -r option on the command line.  To give
       selective access to the server, use nbdkit-ip-filter(1).  To serve only a subset of the
       plugin use nbdkit-offset-filter(1) or nbdkit-partition-filter(1).

EXAMPLES

   Protect the boot sector
       Protect the first part of the boot sector from writes, but allow the MBR partition table
       to be updated:

        nbdkit --filter=protect file disk.img protect=0-0x1bd

   Protect everything except a single partition
       Allow clients to write to a single partition on the disk, but prevent modifications to the
       partition table, boot sector, other partitions, or any other metadata outside the
       partition:

        $ fdisk -l disk.img
        Device    Boot  Start       End  Sectors Size Id Type
        disk.img1 *      2048  12580863 12578816   6G 83 Linux
        $ start=$((2048*512))
        $ end=$((12580863*512+511))
        $ nbdkit --filter=protect file disk.img protect=~$start-$end

       Notes:

       •   Data in other partitions and parts of the disk is still readable.

       •   The '~' character complements the range protected.  You might need to escape it from
           the shell using quotes or backslash.

       •   This is different from nbdkit-partition-filter(1) — that filter exposes the partition
           as a whole device.

PARAMETERS

       protect=START-END
           Protect the bytes starting at offset "START" through to offset "END" (inclusive).
           Reads are permitted.  Writes to the protected range are only permitted if they do not
           change the content.  If an attempt is made to change the content, then the error
           "NBD_EPERM" (Operation not permitted) is returned to the client.

           "START" and "END" can be expressed in decimal, octal ("0NN") or hexadecimal ("0xNN").
           If omitted then they default to the start and end of the underlying plugin
           respectively.

           This parameter can be given multiple times to protect several ranges.

       protect=~START-END
           This protects the complement of the range "START" to "END".

FILES

       $filterdir/nbdkit-protect-filter.so
           The filter.

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

VERSION

       "nbdkit-offset-filter" first appeared in nbdkit 1.30.

SEE ALSO

       nbdkit(1), nbdkit-file-plugin(1), nbdkit-ip-filter(1), nbdkit-offset-filter(1),
       nbdkit-partition-filter(1), nbdkit-filter(3).

AUTHORS

       Richard W.M. Jones

COPYRIGHT

       Copyright (C) 2021 Red Hat Inc.

LICENSE

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