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.IX Title "nbdkit-protect-filter 1"
.TH nbdkit-protect-filter 1 2026-04-25 nbdkit-1.47.8 NBDKIT
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH NAME
nbdkit\-protect\-filter \- write\-protect parts of a plugin
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit \-\-filter=protect plugin protect=START\-END [protect=...]
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-protect\-filter\*(C'\fR is a filter for \fBnbdkit\fR\|(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.
.PP
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.
.PP
To make the whole plugin readonly, use the nbdkit \fI\-r\fR option on the
command line, or \fBnbdkit\-readonly\-filter\fR\|(1).  To give selective
access to the server, use \fBnbdkit\-ip\-filter\fR\|(1).  To serve only a
subset of the plugin use \fBnbdkit\-offset\-filter\fR\|(1) or
\&\fBnbdkit\-partition\-filter\fR\|(1).
.SH EXAMPLES
.IX Header "EXAMPLES"
.SS "Protect the boot sector"
.IX Subsection "Protect the boot sector"
Protect the first part of the boot sector from writes, but allow the
MBR partition table to be updated:
.PP
.Vb 1
\& nbdkit \-\-filter=protect file disk.img protect=0\-0x1bd
.Ve
.SS "Protect everything except a single partition"
.IX Subsection "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:
.PP
.Vb 6
\& $ 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
.Ve
.PP
Notes:
.IP \(bu 4
Data in other partitions and parts of the disk is still readable.
.IP \(bu 4
The \f(CW\*(Aq~\*(Aq\fR character complements the range protected.  You might need
to escape it from the shell using quotes or backslash.
.IP \(bu 4
This is different from \fBnbdkit\-partition\-filter\fR\|(1) — that filter
exposes the partition as a whole device.
.SH PARAMETERS
.IX Header "PARAMETERS"
.IP \fBprotect=\fRSTART\fB\-\fREND 4
.IX Item "protect=START-END"
Protect the bytes starting at offset \f(CW\*(C`START\*(C'\fR through to offset \f(CW\*(C`END\*(C'\fR
(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 \f(CW\*(C`NBD_EPERM\*(C'\fR (Operation not
permitted) is returned to the client.
.Sp
\&\f(CW\*(C`START\*(C'\fR and \f(CW\*(C`END\*(C'\fR can be expressed in decimal, octal (\f(CW\*(C`0NN\*(C'\fR) or
hexadecimal (\f(CW\*(C`0xNN\*(C'\fR).  If omitted then they default to the start and
end of the underlying plugin respectively.
.Sp
This parameter can be given multiple times to protect several ranges.
.IP \fBprotect=~\fRSTART\fB\-\fREND 4
.IX Item "protect=~START-END"
This protects the complement of the range \f(CW\*(C`START\*(C'\fR to \f(CW\*(C`END\*(C'\fR.
.SH FILES
.IX Header "FILES"
.ie n .IP \fR\fI$filterdir\fR\fI/nbdkit\-protect\-filter.so\fR 4
.el .IP \fR\f(CI$filterdir\fR\fI/nbdkit\-protect\-filter.so\fR 4
.IX Item "$filterdir/nbdkit-protect-filter.so"
The filter.
.Sp
Use \f(CW\*(C`nbdkit \-\-dump\-config\*(C'\fR to find the location of \f(CW$filterdir\fR.
.SH VERSION
.IX Header "VERSION"
\&\f(CW\*(C`nbdkit\-protect\-filter\*(C'\fR first appeared in nbdkit 1.30.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-file\-plugin\fR\|(1),
\&\fBnbdkit\-ip\-filter\fR\|(1),
\&\fBnbdkit\-map\-filter\fR\|(1),
\&\fBnbdkit\-offset\-filter\fR\|(1),
\&\fBnbdkit\-partition\-filter\fR\|(1),
\&\fBnbdkit\-readonly\-filter\fR\|(1),
\&\fBnbdkit\-filter\fR\|(3).
.SH AUTHORS
.IX Header "AUTHORS"
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP \(bu 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP \(bu 4
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.
.IP \(bu 4
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.
.PP
THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS \*(Aq\*(AqAS IS\*(Aq\*(Aq 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.
