289 lines
5.2 KiB
HTML
289 lines
5.2 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Language-Specific Issues</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Secure Programming for Linux and Unix HOWTO"
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REL="NEXT"
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TITLE="C/C++"
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HREF="c-cpp.html"></HEAD
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COLSPAN="3"
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ALIGN="center"
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>Secure Programming for Linux and Unix HOWTO</TH
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></TR
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WIDTH="10%"
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ALIGN="left"
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>Prev</A
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><DIV
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CLASS="CHAPTER"
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><H1
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><A
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NAME="LANGUAGE-SPECIFIC"
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></A
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>Chapter 10. Language-Specific Issues</H1
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><TABLE
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BORDER="0"
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WIDTH="45%"
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ALIGN="LEFT"
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VALIGN="TOP"
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><I
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><P
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><I
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>Undoubtedly there are all sorts of languages in the world,
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yet none of them is without meaning.</I
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></P
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></I
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></TD
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></TR
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><I
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><SPAN
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CLASS="ATTRIBUTION"
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>1 Corinthians 14:10 (NIV)</SPAN
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></I
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></TD
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></TABLE
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><DIV
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CLASS="TOC"
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><DL
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><DT
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><B
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>Table of Contents</B
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></DT
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><DT
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>10.1. <A
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HREF="c-cpp.html"
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>C/C++</A
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></DT
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><DT
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>10.2. <A
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HREF="perl.html"
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>Perl</A
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></DT
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><DT
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>10.3. <A
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HREF="python.html"
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>Python</A
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></DT
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><DT
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>10.4. <A
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HREF="shell.html"
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>Shell Scripting Languages (sh and csh Derivatives)</A
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></DT
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><DT
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>10.5. <A
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HREF="ada.html"
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>Ada</A
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></DT
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><DT
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>10.6. <A
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HREF="java.html"
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>Java</A
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></DT
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><DT
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>10.7. <A
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HREF="tcl.html"
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>Tcl</A
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></DT
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><DT
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>10.8. <A
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HREF="php.html"
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>PHP</A
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></DT
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></DL
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></DIV
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><P
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>There are many language-specific security issues.
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Many of them can be summarized as follows:
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<P
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></P
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><UL
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><LI
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><P
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>Turn on all relevant warnings and protection mechanisms available to you
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where practical.
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For compiled languages, this includes
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both compile-time mechanisms and run-time mechanisms.
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In general, security-relevant programs should compile cleanly with
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all warnings turned on.</P
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></LI
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><LI
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><P
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>If you can use a ``safe mode'' (e.g., a mode that limits the activities
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of the executable), do so.
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Many interpreted languages include such a mode.
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In general, don't depend on the safe mode to provide absolute protection;
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most language's safe modes have not been sufficiently analyzed for their
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security, and when they are, people usually discover many ways to exploit it.
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However, by writing your code so that it's secure out of safe mode, and
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then adding the safe mode, you end up with defense-in-depth (since in
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many cases, an attacker has to break both
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your application code and the safe mode).</P
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></LI
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><LI
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><P
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>Avoid dangerous and deprecated operations in the language.
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By ``dangerous'', I mean operations which are difficult to use correctly.
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For example, many languages include
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some mechanisms or functions that are ``magical'', that
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is, they try to infer the ``right'' thing to do using a heuristic -
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generally you should avoid them, because an attacker may be able to
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exploit the heuristic and do something dangerous instead of what was intended.
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A common error is an ``off-by-one'' error, in which the bound is
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off by one, and sometimes these result in exploitable errors.
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In general, write code in a way that minimizes the likelihood of
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off-by-one errors.
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If there are standard conventions in the language (e.g., for writing loops),
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use them.</P
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></LI
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><LI
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><P
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>Ensure that the languages'
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infrastructure (e.g., run-time library) is available and secured.</P
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></LI
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><LI
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><P
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>Languages that automatically garbage-collect strings should be
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especially careful to immediately erase secret data
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(in particular secret keys and passwords).</P
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></LI
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><LI
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><P
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>Know precisely the semantics of the operations that you are using.
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Look up each operation's semantics in its documentation.
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Do not ignore return values unless you're sure they cannot be relevant.
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Don't ignore the difference between ``signed'' and ``unsigned'' values.
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This is particularly difficult in languages which don't support exceptions,
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like C, but that's the way it goes.</P
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></LI
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></UL
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></P
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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>Prev</A
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>Prevent Include/Configuration File Access</TD
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>C/C++</TD
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