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1 \documentclass{article} |
1 \documentclass{article} |
2 \usepackage{../style} |
2 \usepackage{../style} |
3 \usepackage{../langs} |
3 \usepackage{../langs} |
4 |
4 |
5 \begin{document} |
5 \begin{document} |
|
6 \fnote{\copyright{} Christian Urban, 2014} |
6 |
7 |
7 \section*{Handout 4 (Access Control)} |
8 \section*{Handout 4 (Access Control)} |
8 |
9 |
9 Access control is essentially about deciding whether to grant |
10 Access control is essentially about deciding whether to grant |
10 access to a resource or deny it. Sounds easy, no? Well it |
11 access to a resource or deny it. Sounds easy, no? Well it |
26 attributes} of a file. There are typically three modes for |
27 attributes} of a file. There are typically three modes for |
27 access: \underline{\textbf{r}}ead, \underline{\textbf{w}}rite |
28 access: \underline{\textbf{r}}ead, \underline{\textbf{w}}rite |
28 and e\underline{\textbf{x}}ecute. Moreover there are three |
29 and e\underline{\textbf{x}}ecute. Moreover there are three |
29 user groups to which the modes apply: the owner of the file, |
30 user groups to which the modes apply: the owner of the file, |
30 the group the file is associated with and everybody else. |
31 the group the file is associated with and everybody else. |
31 A typical permission of a file owned by \texttt{bob} might look as |
32 A typical permission of a file owned by \texttt{bob} |
|
33 being in the group \texttt{staff} might look as |
32 follows: |
34 follows: |
33 |
35 |
34 \begin{center} |
36 \begin{center} |
35 ${\underbrace{\LARGE\texttt{-}}_{\text{\makebox[0mm]{directory}}}} |
37 ${\underbrace{\LARGE\texttt{-}}_{\text{\makebox[0mm]{directory}}}} |
36 \;{\underbrace{\LARGE\texttt{r{}-{}-}}_{\text{user}}}\, |
38 \;{\underbrace{\LARGE\texttt{r{}-{}-}}_{\text{user}}}\, |
39 \LARGE\texttt{bob}\;\;\;\texttt{staff}$ |
41 \LARGE\texttt{bob}\;\;\;\texttt{staff}$ |
40 \end{center} |
42 \end{center} |
41 |
43 |
42 \noindent For the moment let us ignore the directory bit. The |
44 \noindent For the moment let us ignore the directory bit. The |
43 Unix access rules imply that Bob will only have read access to |
45 Unix access rules imply that Bob will only have read access to |
44 this file, even if he is in the group \texttt{staff} and the |
46 this file, even if he is in the group \texttt{staff} and this |
45 group access permissions allow read and write. Similarly every |
47 group's access permissions allow read and write. Similarly every |
46 member in the \texttt{staff} group who is not \texttt{bob}, |
48 member in the \texttt{staff} group who is not \texttt{bob}, |
47 will only have read-write access permissions, not |
49 will only have read-write access permissions, not |
48 read-write-execute. |
50 read-write-execute. |
49 |
51 |
50 This |
52 This |