若您有关于此作业的任何需求，本人主页, 可添加vx：codingtutor 或者qq：122929048
Changes since version 0.1: • Link to rubric • Allow markdown • Change 1(d) from “show” to “indicate” • Clarify structure of a “scores” field line • Clarify that lseek is also an option for file searching • Fix privilege-dropping requirement • Permit aborting execution in lieu of error propagation • Clarify that valid names and scores must fit the field • Remove “printed” for error message • Add detail on marks breakdown You can see a list of all changes made to the project spec by viewing its commit history on GitHub, here. Introduction • This project contributes 30% towards your final mark this semester, and is to be completed as individual work. • The project is marked out of 140. • The deadline for this assignment is listed on the assessments page of the CITS3007 at https://cits3007.github.io/assessment/, and is 5:00 pm Thursay 20 October. • You are expected to have read and understood the University Guidelines on Academic Conduct. In accordance with this policy, you may discuss with other students the general principles required to understand this project, but the work you submit must be the result of your own effort. • You must submit your project before the submission deadline above. There are significant Penalties for Late Submission (click the link for details). Marks breakdown/rubric document A marks breakdown/rubric document for the project is available from the CITS3007 website at https://cits3007.github.io/assessment/#project which describes (among other details) the standards a submission should meet to get more than minimal marks.
Help3007 forum. Items to submit You will need to submit:
- a PDF report, report.pdf
- a text file containing the answer to a question (answers.txt), and 3. a C file, adjust_score.c Do not submit a .zip or .tar file or other archive. PDF report Your PDF report should use A4 size pages. The font for body text should be between 9 and 12 points. The report should contain numbered headings, with useful heading titles. Each question should be answered on a new page. Any diagrams, charts or tables used must be legible and large enough to read when viewed on-screen at 100% magnification. All pages (except the cover, if you have one) should be numbered. If you give scholarly or other references, you may use any standard citation style you wish, as long as it is consistent. Cover sheets, diagrams, charts, tables, bibliographies and reference lists do not count towards any page-count maximums. As an alternative to submitting a PDF, you may submit your report in neatly formatted (max. 72 characters per line) Markdown, and we will either read it directly or generate a report from it. In that case: • Your project file should be called report.md • It should either adhere to the CommonMark spec or be Pandoc-compliant Markdown • It should be easily readable as plain text, and contain no diagrams, charts or raw LaTeX • If present, a bibliography should appear as a plain bulleted list at the end of the report (do not use citation keys (@), BibTex, or similar features). “AMS short alpha-numeric” would be a good citation style (AMS style guide, sec 10.3). text file The format for the text file is given in Part 1. C files Your code is expected to be clearly written, well-formatted, and easy for others to understand. It should follow sound programming practices, including: • the use of meaningful comments • well chosen identifier names • appropriate choice of basic data-structures, data-types, and functions • appropriate choice of control-flow constructs • proper error-checking of any library functions called, and • cleaning up/closing any files or resources used. It should compile without errors or warnings with gcc, using the compilation flags “-std=c11 -pedantic -Wall -Wextra”.
complete part of this project, you should document any reasonable assumptions you had to make in order to answer a question or write a method. In that case, make sure your report has as one of its first sections a section entitled “Assumptions”, in which you list these, giving each one a number and explaining why you think it’s a reasonable assumption. Then in your code or later in your report, you can briefly refer to these assumptions (e.g. “This test case assumes that Assumption 1 holds, so that we can . . . ”). Part 1: CVE-2019-17498 (70 marks) For this part of the project, you will need to investigate CVE-2019-17498. In your report, you should include a section on this CVE, addressing the following questions. a. What product or software package does CVE-2019-17498 affect? What type of vulnerability or vulnerabilities does the CVE represent? (10 marks) b. How severe is the impact of the CVE? What factors go into assessing this impact? (10 marks) c. Describe how the CVE could be exploited, and what the consequences of a successful exploit could be. (20 marks) d. Indicate the C source code that gives rise to the vulnerability described by this CVE. On the first line of your “answers.txt” file, provide a URL for the vulnerable version of the C file, then a space, then a range of line numbers (two numbers separated by a dash). (You may also include these in your report if you wish.) (10 marks) e. Explain what changes were made in the affected product to address the vulnerability described by the CVE, and how they work. (20 marks) For each question you should cite your sources. (These may be traditionally published works, but are more likely to be webpages.) (Maximum length: 5 pages)
Part 2: setuid program (70 marks) You are employed by a games publisher which develops the popular game Curdle, in which players are provided with images of various fermented or coagulated milk–based products – cheeses and yoghurts – and are required to guess the particular product. Although available for multiple platforms, the most popular one on which Curdle is available is Linux (specifically, Ubuntu 20.04, running on the x86-64 platform). On Linux, the files used by the game (for instance, a file storing scores achieved by different players) are owned by the user curdle. Your task is to write a small portion of the game executable which modifies a scores file used by the game. Running ls -l on the scores file produces the following listing:
Every line in the scores file is 20 characters long (excluding the newline character) and consists of two “fields”: 10 characters for a player name of maximum length 9, ending in a NUL, and 10 characters for a score. For player names shorter than 9 characters or scores shorter than 10 characters, you may assume the field is padded with NUL characters to ensure it’s 10 characters in length total. Write a file adjust_score.c containing a single function, adjust_score(), with the following signature 1 2
int adjust_score(uid_t uid, const char * player_name, int score_to_add, char **message)
• uid contains the user ID of the curdle user • player_name is the name of the current player • score_to_add is the player’s score for this game • the caller should pass in the address of a pointer-to-char to message, in which adjust_score can write an error message (if needed). You should assume the program will be run as a setuid program owned by the user curdle, and that the first thing the main function for the game does is to call seteuid() to set the effective UID to the real UID (i.e., to drop privileges), and then call setegid() to do the same for the group ID. The adjust_score function should do the following: • Open the scores file (using appropriate privileges) • Read through the scores file for a line starting with player_name. • If such a line is found, your program should read the int, derive a new score by adding the value in score_to_add, then replace the original line with a new line containing the new score. (Hint: you will want to use fseek() or lseek().) • If such a line is not found, add a new, valid score line to the end of the file containing the player name and score (which is simply score_to_add). The function should drop any special privileges used after they are no longer required. If the score was changed successfully, the function should return 1; if not, it should return 0, and: • allocate memory for an error message using malloc() • write an error message to that memory, and • set *message to the newly allocated memory. (As an alternative: your implementation of the function may return 1 on success, and abort execution of the program on any failure. But some marks will be available for programs that do handle errors and provide an error message, as outlined above.) If a score or player name cannot be represented or stored in the characters available for them in a line, that counts as an error – the situation should be checked for and an appropriate error message written. You may use helper functions if desired which are called by the adjust_score function. 4 Your code will be awarded 40 marks for correct operation, 10 marks for use of appropriate secure coding techniques, and 20 marks for code concision and clarity. It should avoid introducing any security vulnerabilities.