nbdkit-protect-filter(1)

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
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.

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