The names all the functions the bomb calls
Step 1: Get Your Bomb
Each group of students will attempt to defuse their own personalized bomb. Each bomb is a Linux binary executable file that has been compiled from a C program. To obtain your group’s bomb, one (and only one) of the group members should point your Web browser to the bomb request daemon at
• bomb: The executable binary bomb.
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Your job is to defuse the bomb.
You can use many tools to help you with this; please look at the hints section for some tips and ideas. The best way is to use your favorite debugger to step through the disassembled binary.
linux> ./bomb psol.txt
then it will read the input lines from psol.txt until it reaches EOF (end of file), and then switch over to stdin. In a moment of weakness, Dr. Evil added this feature so you don’t have to keep retyping the solutions to phases you have already defused.
You should do the assignment on Linux ugrad machines (lin**.ugrad.cs.ubc.ca where ** ranges from 00 to 25). In fact, there is a rumor that Dr. Evil really is evil, and the bomb will always blow up if run elsewhere. There are several other tamper-proofing devices built into the bomb as well, or so they say.
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Hints (Please read this!)
There are many ways of defusing your bomb. You can examine it in great detail without ever running the program, and figure out exactly what it does. This is a useful technique, but it not always easy to do. You can also run it under a debugger, watch what it does step by step, and use this information to defuse it. This is probably the fastest way of defusing it.
There are many tools which are designed to help you figure out both how programs work, and what is wrong when they don’t work. Here is a list of some of the tools you may find useful in analyzing your bomb, and hints on how to use them.
• gdb
The GNU debugger, this is a command line debugger tool available on virtually every platform. You can trace through a program line by line, examine memory and registers, look at both the source code and assembly code (we are not giving you the source code for most of your bomb), set breakpoints, set memory watch points, and write scripts. Here are some tips for using gdb.
• objdump -t
This will print out the bomb’s symbol table. The symbol table includes the names of all functions and global variables in the bomb, the names of all the functions the bomb calls, and their addresses. You may learn something by looking at the function names!• objdump -d
Use this to disassemble all of the code in the bomb. You can also just look at individual functions. Reading the assembler code can tell you how the bomb works.
• strings
This utility will display the printable strings in your bomb.
Looking for a particular tool? How about documentation? Don’t forget, the commands apropos and man are your friends. In particular, man ascii might come in useful. Also, the web may also be a treasure trove of information. If you get stumped, feel free to ask your TA for help.