代做CSI4109 Assignment #2代写数据结构语言

CSI4109 Assignment #2

Due: Mar 28th 12:59pm

Mandatory Access Control (MAC)

In this homework assignment, you will implement the read-down, write-up mandatory access control policy discussed in class. Specifically, you will write a command-line tool called  mac , which, together with  setuid / setgid  functionalities in Linux, is used as a mechanism to implement this policy.

•  This command line tool  mac  will be owned by the user  root  and the group  root , and be given the permissions:  6755 , where the  setuid ,  setgid , and executable bit are set as follows.

-rwsr-sr-x 1 root root 18K Mar 14 21:04 mac

• Objects: There are four documents (a document for each security classification level) that are pro-

tected by the mandatory access control policy:  top_secret.data ,  secret.data ,  confidential.data , and  unclassified.data . These four files are classified as TOP_SECRET ,  SECRET ,  CONFIDENTIAL ,

and  UNCLASSIFIED , respectively.  These four files will be (i) pre-created, (ii) owned by the user root  and the group  root , and (iii) given the permissions:  0640  as follows.

-rw-r----- 1 root  root 20 Mar 14  16:01  secret.data -rw-r----- 1 root  root 24 Mar 14  21:15  top_secret.data -rw-r----- 1 root  root 26 Mar 14  21:15  unclassified.data -rw-r----- 1 root  root 26 Mar 14  21:15  confidential.data

Note that the owners and permissions of these files must stay the same at all times.

• Subjects: All non-root users in the system are considered as subjects.  Security clearance levels of subjects are specified in a file called  mac.policy , which is owned by the user  root  and the group  root , and given the permissions:  0640  as follows.

-rw-r----- 1 root root 23 Mar 14  21:17 mac.policy

mac.policy will be pre-created and written in the following format:

: clearance level> : clearance level>

Remember that subjects whose access is controlled by our policy are non-root users; that is, the command line tool  mac  will be executed by a non-root user whose primary group is the same as the name of that user.  (e.g., the user  david  and the group  david ) This effectively prevents subjects from reading or manipulating the data files directly; this requires accesses to the data files be always mediated by the program  mac .

• Dropping the root privilege: During the execution of  mac , drop the   root  privilege when you do not need it anymore, by changing the effective  uid  and  gid  of the process.  (Hint: Use the following functions:  seteuid ,  getuid ,  setegid , and  getgid .)

• Logging: After dropping your root privilege, append the command line arguments followed by a newline character to the per-user log file named  .log . Do not log, however, what has been writen.

$ ./mac read secret.data $ cat david.log read secret.data $ ./mac write  secret.data  TEST_INPUT $ cat david.log read secret.data write secret.data

If the log file doesn’t exist for the given user, it must be created before appending. Once created, this file must at all times be owned by the executing non- root  user and group, and be given the permissions:  0640 . You can assume that the user has the permission to create a file in its current working directory. (Hint: Use the following functions:   getpwuid  and  umask .)

Interface. All variable inputs to the program (e.g.,   ) will be  [a-zA-Z0-9_\-\.]  (i.e., alphanumeric, underscore, dash, and period). All matching is case-sensitive.

You must implement the following command-line interface:

./mac read file>

reads and prints the content of the document file (e.g.,  top_secret.data ) followed by a newline character on standard output, if and only if (i) the security clearance level for the executing user is specified in  mac.policy , and (ii) our read-down confidentiality policy allows it. Otherwise, print  ACCESS  DENIED , followed by a newline character.  You can assume that    is always valid (one of the four files specified above).

./mac write  a>

appends    followed by a newline character to the file   , if and only    if the executing user has a security clearance level, and the policy allows it.  Otherwise, print     ACCESS  DENIED , followed by a newilne character. You can assume that a given   (one of the four given above) is always valid.

Example. With  david:SECRET  written in the  mac.policy  file:

$ whoami david $  sudo  cat  mac.policy david:SECRET

Running the program as follows:

./mac read secret.data

• will produce the following output on standard output:

THIS IS SECRET DATA

./david.log looks like:

read secret.data

And running the program again as follows:

./mac read confidential.data

• will produce the following output on standard output:

THIS IS CONFIDENTIAL DATA

./david.log now looks like:

read secret.data read confidential.data

And running the program again as follows:

./mac read top_secret.data

• will produce the following output on standard output:

ACCESS DENIED

./david.log now looks like:

read secret.data read confidential.data read top_secret.data

Implementation.

• Your program must work on Ubuntu 22.04 64-bit with the default packages installed. In addition to the default packages, the following packages for languages are also installed:

– C ( gcc )

– Rust and Cargo ( rustc  and  cargo ) with selection of crates pre-installed for you in the grading environment. If you are using Rust, provided  Cargo.toml  should not be modified.

Again, you’re probably better off if you setup a virtual machine to work on the course assignments early on.  You can use VirtualBox, a free and open-source VM monitor software.  Or, if you are using MS Windows, you may want to use WSL (WSL version 2 is recommended.) (Ubuntu 22.04 on Microsoft Store).

Submission Instructions. Submit on LearnUs (ys.learnus.org) your source code, along with a  Makefile  and  README .  When the command  make  is run, the  Makefile  must create your exe- cutable, called  mac , on the same directory as your  Makefile   and  README .  These files must not be included in any subdirectory. Note that we may invoke  make  multiple times, and it needs to work every single time.  After creating  mac , we will change its owner and owning group, as well as permissions, as specified above. We will also create the data files as well as the policy file, and change their owner and owning group and permissions as specified above. Your  README  file must be plain text and should contain your name, student ID, and a description of how your program works.  Your submission can be zipped, if required; your submission will be unzipped once before grading.  However, the directory structure described above still apply.

Grading Rubric

• All required files exist, and  make  successfully creates an executable file  mac . (2 pts)

•  Produces a log file in a correct format. (1 pt)

•  The log file’s owner/group owner/permissions are correct at all times. (2 pts)

•  Read accesses are correctly controlled. (3 pts)

•  Write accesses are correctly controlled. (2 pts)

Note: It is your responsibility to comply with the specification as well as our grading environment. You can request regrading for minor problems (e.g., issues caused by using different environments),but they will result in deductions of 1 or more points.

Late policy: 1 pt deduction for every 3 hours that is late. This means that late submission up to 3 hours get one point deduction, 6 hours two point deduction, and so on.