Department of Electrical Engineering and Computer ScienceMASSACHUSETTS INSTITUTE OF TECHNOLOGY6.033 Computer Systems Engineering: Spring 2007Quiz IIIThere are 19 questions and 17 pages in this quiz booklet. Answer each question according to theinstructions given. You have 90 minutes to answer the questions.Most questions are multiple-choice questions. Next to each choice, circle the word True or False,as appropriate. A correct choice will earn positive points, a wrong choice may earn negativepoints, and not picking a choice will score 0. The exact number of positive and negative pointsfor each choice in a question depends on the question and choice. The maximum score for eachquestion is given near each question; the minimum for each question is 0. Some questions areharder than others and some questions earn more points than others—you may want to skim allquestions before starting.If you find a question ambiguous, be sure to write down any assumptions you make. Be neat andlegible. If we can’t understand your answer, we can’t give you credit!Write your name in the space below AND at the bottom of each page of this booklet.THIS IS AN OPEN BOOK, OPEN NOTES QUIZ.NO PHONES, NO COMPUTERS, NO LAPTOPS, NO PDAS, ETC.CIRCLE your recitation section number:10:00 1. Madden/Komal11:00 2. Madden/Zhang 3. Katabi/Komal 10. Yip/Chachulski12:00 4. Yip/Zhang 5. Katabi/Chachulski1:00 6. Ward/Shih 7. Girod/Schultz2:00 8. Ward/Schultz 9. Girod/ShihDo not write in the boxes below1-5 (xx/21) 6-10 (xx/34) 11-15 (xx/25) 16-19 (xx/20) Total (xx/100)Name:6.033 Spring 2007, Quiz 3 Page 2 of 17I Short Reading QuestionsI.1 Buffer overruns1. [4 points]:For each of the following approaches, indicate whether it will completely eliminatebuffer-overrun vulnerabilities in a user’s program:(Circle True or False for each choice.)(a) True / False Have the operating system mark stack memory pages as non-executable.(b) True / False Have the operating system mark heap memory pages as non-executable.(c) True / False Save an extra copy of a function call’s return address (e.g., on a separate call andreturn stack) and make sure the two copies match before jumping.(d) True / False Re-write all programs (including libraries) in Java (or another type safe languagewith array bounds checking).I.2 SubversionAlice and Bob are collaborating on the Java code that implements their DP2 design. Using SVN (Subver-sion), they maintain the following set of files that compile into a working implementation of DP2.trunk/Makefiletree.javaserver.javapeer.javatracker.java2. [4 points]: Which of the following statements are true?(Circle True or False for each choice.)(a) True / False If Alice and Bob concurrently edit different methods which are on different linesof tree.java on their respective up-to-date repositories (i.e., they ran SVN up before eitherof them started editing), then neither Alice nor Bob will be able to commit directly, withoutencountering an error message.(b) True / False If Alice and Bob concurrently edit different methods of tree.java on theirrespective up-to-date repositories (i.e., they ran SVN up before either of them started editing),neither Alice or Bob will need to manually resolve a conflict.(c) True / False If Alice and Bob concurrently attempt to edit tree.java on their respective up-to-date repositories, SVN will prevent Alice and Bob from concurrently editing tree.java.(d) True / False Alice edits peer.java and Bob edits server.java. Both Alice and Bobverify that the project builds correctly after their edits, and they commit without error. Whentheir sleeping teammate Charles wakes up from a nap and updates, his repository is certain tobuild without error.Name:6.033 Spring 2007, Quiz 3 Page 3 of 17I.3 WormsBen decides to start an ISP. He buys a /8 address space (i.e., 224addresses) that has never been used before.A few days after he buys this address space, a worm is launched. The worm targets a buffer overflow in theFOO server, which listens on UDP port 5044. Ben monitors all traffic sent to his address space on that portand plots the number of packets versus time in Figure 1 below.t i m e1 0 , 0 0 0p a c k e t s / s e c01 0 0p a c k e t s / s e cFigure 1: Packets per second from the point that the worm starts.Assume the worm spreads by probing random IP addresses, and that its pseudo-random number generatoris bug-free and generates a complete permutation of the integers before revisiting any integer. Ben learnsfrom a security analyst that each infected machine sent 100 packets/second.3. [4 points]: Give an estimate of the total number of machines that run the FOO server?(Circle the BEST answer)(a) 100 machines(b) 7.2 × 1018machines(c) 25,600 machines(d) 8,000 machinesName:6.033 Spring 2007, Quiz 3 Page 4 of 174. [5 points]:Ben thinks that the worm used a hit list of vulnerable addresses (i.e., addresses of FOOservers). Do you agree? If you do, what is the best estimate for the number machines contained in thehit list?(Circle the BEST answer)(a) no hit list(b) 100 machines(c) 256 machines(d) 25600 machines(e) 80 machinesI.4 Privacy5. [4 points]:The 4th Amendment of the Constitution, as interpreted in the Olmstead vs. U.S. rulingin 1928, established that the boundary of a person’s property defines the area in which he or she canexpect privacy protection (“a man’s house is his castle”). According to Daniel Weitzner’s lecture,which of the following technologies have led to changes in the definition and boundaries of privacyprotection in the United States legislative and legal systems?(Circle True or False for each choice.)(a) True / False telephone booth(b) True / False email(c) True / False community websites like www.facebook.com(d) True / False public waste management systemsName:6.033 Spring 2007, Quiz 3 Page 5 of 17II The BitdiddlerBen Bitdiddle is designing a file system for a new handheld computer, the Bitdiddler, which is designed tobe especially simple, for, as he likes to say, “people who are just average, like me.”In keeping with his theme of simplicity and ease of use for average people, Ben decides to design a filesystem without directories. The disk is physically partitioned into three regions: an inode list, a free list, anda collection of 4K data blocks, as in the Unix file system. Unlike in the Unix file system, each inode containsthe name of the file it corresponds to, as well as a bit indicating whether or not the inode is in use. LikeUnix, it also contains a list of
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