# HG changeset patch
# User Christian Urban <christian dot urban at kcl dot ac dot uk>
# Date 1413675711 -3600
# Node ID 51fa0549fc8f34b9ac716f871c22eb2aa21b210c
# Parent  95e14b2dbc94e6380268aed9aa34f52d2328eefb
updated

diff -r 95e14b2dbc94 -r 51fa0549fc8f handouts/ho04.pdf
Binary file handouts/ho04.pdf has changed
diff -r 95e14b2dbc94 -r 51fa0549fc8f handouts/ho04.tex
--- a/handouts/ho04.tex	Sat Oct 18 23:07:50 2014 +0100
+++ b/handouts/ho04.tex	Sun Oct 19 00:41:51 2014 +0100
@@ -86,17 +86,35 @@
 \end{itemize}
 
 \noindent This will typically involve quite a lot of
-programs on a Unix system. I counted 87 programs with the
+programs on a Unix system. I counted 95 programs with the
 setuid attribute set on my bog-standard MacOSX system
 (including the program \pcode{/usr/bin/login}).
 The problem is that if there is a security problem with
 one of them, then malicious users (or outside attackers)
 can gain root access.
 
+The main rule for files that have the setuid attribute set is
+that when running such files they will run not with the
+callers access rights, but with the owner of the files rights.
+So \pcode{/usr/bin/login} will always be running with root
+access rights, no matter who invokes this program.
+
 \subsubsection*{Secrecy and Integrity}
 
 
 
+\subsubsection*{Further Information}
+
+If you want to know more about the intricacies of the
+``simple'' Unix access control system you might find the
+relatively readable paper about ``Setuid Demystified'' 
+useful.
+
+\begin{center}\small
+\url{http://www.cs.umd.edu/~jkatz/TEACHING/comp_sec_F04/downloads/setuid.pdf}
+\end{center}
+
+
 \end{document}
 
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