File: restricted-sh.html

package info (click to toggle)
abs-guide 10-4
links: PTS, VCS
area: main
in suites: bookworm, bullseye, forky, sid, trixie
size: 6,952 kB
sloc: sh: 14,129; makefile: 81
file content (351 lines) | stat: -rw-r--r-- 5,567 bytes
parent folder | download | duplicates (6)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML
><HEAD
><TITLE
>Restricted Shells</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
"><LINK
REL="HOME"
TITLE="Advanced Bash-Scripting Guide"
HREF="index.html"><LINK
REL="UP"
TITLE="Advanced Topics"
HREF="part5.html"><LINK
REL="PREVIOUS"
TITLE="Subshells"
HREF="subshells.html"><LINK
REL="NEXT"
TITLE="Process Substitution"
HREF="process-sub.html"><META
HTTP-EQUIV="Content-Style-Type"
CONTENT="text/css"><LINK
REL="stylesheet"
HREF="common/kde-common.css"
TYPE="text/css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=iso-8859-1"><META
HTTP-EQUIV="Content-Language"
CONTENT="en"><LINK
REL="stylesheet"
HREF="common/kde-localised.css"
TYPE="text/css"
TITLE="KDE-English"><LINK
REL="stylesheet"
HREF="common/kde-default.css"
TYPE="text/css"
TITLE="KDE-Default"></HEAD
><BODY
CLASS="CHAPTER"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#AA0000"
VLINK="#AA0055"
ALINK="#AA0000"
STYLE="font-family: sans-serif;"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="subshells.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="process-sub.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="CHAPTER"
><H1
><A
NAME="RESTRICTED-SH"
></A
>Chapter 22. Restricted Shells</H1
><P
><A
NAME="RESTRICTEDSHREF"
></A
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="DISABLEDCOMMREF"
></A
>Disabled commands in restricted
	  shells</B
></P
><DL
><DT
></DT
><DD
><DIV
CLASS="FORMALPARA"
><P
><B
> . </B
>Running a script or portion of a script in
        <I
CLASS="FIRSTTERM"
>restricted mode</I
> disables certain commands
        that would otherwise be available. This is a security measure
        intended to limit the privileges of the script user and to
        minimize possible damage from running the script.</P
></DIV
></DD
></DL
></DIV
><P
>The following commands and actions are disabled:</P
><UL
><LI
><P
>Using <TT
CLASS="REPLACEABLE"
><I
>cd</I
></TT
> to change the working
	  directory.</P
></LI
><LI
><P
>Changing the values of the
	  <TT
CLASS="REPLACEABLE"
><I
>$PATH</I
></TT
>,
	  <TT
CLASS="REPLACEABLE"
><I
>$SHELL</I
></TT
>,
	  <TT
CLASS="REPLACEABLE"
><I
>$BASH_ENV</I
></TT
>,
	  or <TT
CLASS="REPLACEABLE"
><I
>$ENV</I
></TT
> <A
HREF="othertypesv.html#ENVREF"
>environmental variables</A
>.</P
></LI
><LI
><P
>Reading or changing the <TT
CLASS="REPLACEABLE"
><I
>$SHELLOPTS</I
></TT
>,
	  shell environmental options.</P
></LI
><LI
><P
>Output redirection.</P
></LI
><LI
><P
>Invoking commands containing one or more
	  <SPAN
CLASS="TOKEN"
>/</SPAN
>'s.</P
></LI
><LI
><P
>Invoking <A
HREF="internal.html#EXECREF"
>exec</A
> to substitute
	  a different process for the shell.</P
></LI
><LI
><P
>Various other commands that would enable monkeying
	  with or attempting to subvert the script for an unintended
	  purpose.</P
></LI
><LI
><P
>Getting out of restricted mode within the script.</P
></LI
></UL
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="RESTRICTED"
></A
><P
><B
>Example 22-1. Running a script in restricted mode</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;#  Starting the script with "#!/bin/bash -r"
   4&nbsp;#+ runs entire script in restricted mode.
   5&nbsp;
   6&nbsp;echo
   7&nbsp;
   8&nbsp;echo "Changing directory."
   9&nbsp;cd /usr/local
  10&nbsp;echo "Now in `pwd`"
  11&nbsp;echo "Coming back home."
  12&nbsp;cd
  13&nbsp;echo "Now in `pwd`"
  14&nbsp;echo
  15&nbsp;
  16&nbsp;# Everything up to here in normal, unrestricted mode.
  17&nbsp;
  18&nbsp;set -r
  19&nbsp;# set --restricted    has same effect.
  20&nbsp;echo "==&#62; Now in restricted mode. &#60;=="
  21&nbsp;
  22&nbsp;echo
  23&nbsp;echo
  24&nbsp;
  25&nbsp;echo "Attempting directory change in restricted mode."
  26&nbsp;cd ..
  27&nbsp;echo "Still in `pwd`"
  28&nbsp;
  29&nbsp;echo
  30&nbsp;echo
  31&nbsp;
  32&nbsp;echo "\$SHELL = $SHELL"
  33&nbsp;echo "Attempting to change shell in restricted mode."
  34&nbsp;SHELL="/bin/ash"
  35&nbsp;echo
  36&nbsp;echo "\$SHELL= $SHELL"
  37&nbsp;
  38&nbsp;echo
  39&nbsp;echo
  40&nbsp;
  41&nbsp;echo "Attempting to redirect output in restricted mode."
  42&nbsp;ls -l /usr/bin &#62; bin.files
  43&nbsp;ls -l bin.files    # Try to list attempted file creation effort.
  44&nbsp;
  45&nbsp;echo
  46&nbsp;
  47&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="subshells.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="process-sub.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Subshells</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="part5.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Process Substitution</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>