newgidmap.1.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
   SPDX-FileCopyrightText: 2013 Eric W. Biederman
   SPDX-License-Identifier: BSD-3-Clause
-->
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  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<refentry id='newgidmap.1'>
  <refentryinfo>
    <author>
      <firstname>Eric</firstname>
      <surname>Biederman</surname>
      <contrib>Creation, 2013</contrib>
    </author>
  </refentryinfo>
  <refmeta>
    <refentrytitle>newgidmap</refentrytitle>
    <manvolnum>1</manvolnum>
    <refmiscinfo class="sectdesc">User Commands</refmiscinfo>
    <refmiscinfo class="source">shadow-utils</refmiscinfo>
    <refmiscinfo class="version">&SHADOW_UTILS_VERSION;</refmiscinfo>
  </refmeta>
  <refnamediv id='name'>
    <refname>newgidmap</refname>
    <refpurpose>set the gid mapping of a user namespace</refpurpose>
  </refnamediv>

  <refsynopsisdiv id='synopsis'>
    <cmdsynopsis>
      <command>newgidmap</command>
      <arg choice='plain'>
	<replaceable>pid</replaceable>
      </arg>
      <arg choice='plain'>
	<replaceable>gid</replaceable>
      </arg>
      <arg choice='plain'>
	<replaceable>lowergid</replaceable>
      </arg>
      <arg choice='plain'>
	<replaceable>count</replaceable>
      </arg>
      <arg choice='opt'>
	<arg choice='plain'>
	  <replaceable>gid</replaceable>
	</arg>
	<arg choice='plain'>
	  <replaceable>lowergid</replaceable>
	</arg>
	<arg choice='plain'>
	  <replaceable>count</replaceable>
	</arg>
	<arg choice='opt'>
	  <replaceable>...</replaceable>
	</arg>
      </arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1 id='description'>
    <title>DESCRIPTION</title>
    <para>
      The <command>newgidmap</command> sets <filename>/proc/[pid]/gid_map</filename>
      based on its command line arguments and the gids allowed. Subgid
      delegation can either be managed via <filename>/etc/subgid</filename>
      or through the configured NSS subid module. These options are mutually
      exclusive.
    </para>

    <para>
      Note that the root group is not exempted from the requirement for a valid
      <filename>/etc/subgid</filename> entry.
    </para>

    <para>
      After the pid argument, <command>newgidmap</command> expects sets of 3 integers:
      <variablelist>
	<varlistentry>
	  <term>gid</term>
	  <listitem>
	    <para>
	      Beginning of the range of GIDs inside the user namespace.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term>lowergid</term>
	  <listitem>
	    <para>
	      Beginning of the range of GIDs outside the user namespace.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term>count</term>
	  <listitem>
	    <para>
	      Length of the ranges (both inside and outside the user namespace).
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </para>

    <para>
      <command>newgidmap</command> verifies that the caller is the owner
      of the process indicated by <option>pid</option> and that for each
      of the above sets, each of the GIDs in the range [lowergid,
      lowergid+count) is allowed to the caller according to
      <filename>/etc/subgid</filename> before setting
      <filename>/proc/[pid]/gid_map</filename>.
    </para>
    <para>
      Note that newgidmap may be used only once for a given process.
    </para>
    <para>
      Instead of an integer process id, the first argument may be
      specified as <replaceable>fd:N</replaceable>, where the integer N
      is the file descriptor number for the calling process's opened
      file for <filename>/proc/[pid[</filename>.  In this case,
      <command>newgidmap</command> will use
      <refentrytitle>openat</refentrytitle><manvolnum>2</manvolnum>
      to open the <filename>gid_map</filename> file under that
      directory, avoiding a TOCTTOU in case the process exits and
      the pid is immediately reused.
    </para>

  </refsect1>

  <refsect1 id='options'>
    <title>OPTIONS</title>
    <para>
      There currently are no options to the <command>newgidmap</command> command.
    </para>
    <variablelist remap='IP'>
    </variablelist>
  </refsect1>

  <refsect1 id='files'>
    <title>FILES</title>
    <variablelist>
      <varlistentry>
	<term><filename>/etc/subgid</filename></term>
	<listitem>
	  <para>List of user's subordinate group IDs.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><filename>/proc/[pid]/gid_map</filename></term>
	<listitem>
	  <para>Mapping of gids from one between user namespaces.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1 id='see_also'>
    <title>SEE ALSO</title>
    <para>
      <citerefentry>
	<refentrytitle>login.defs</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>newusers</refentrytitle><manvolnum>8</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>subgid</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>useradd</refentrytitle><manvolnum>8</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>userdel</refentrytitle><manvolnum>8</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>usermod</refentrytitle><manvolnum>8</manvolnum>
      </citerefentry>.
    </para>
  </refsect1>
</refentry>