Lecture 23 - Graphics Wrap-up, Buffer Overflows, System Calls

Question 1

GTK+

Answer 1

• GIMP toolkit
• multi-platform tools for creating graphical user interfaces (GUIs)

Question 2

security

Answer 2

• the way that you write your software can make a difference in how secure it is
• ex. we’ve used strcpy() when copying data into a buffer array of limited size
• not doing so could cause your program to be vulnerable to buffer overflows
• if your software is trusted by the system, others can use buffer overflows to break in

Question 3

Address Space Layout Randomization

Answer 3

• ASLR changes the addresses of many things every time a program executes
• harder to exploit certain vulnerabilities

Question 4

kernel invocation/what causes the switch to kernel mode?

Answer 4

• system calls
• page faults
• signals
• hardware

Question 5

system calls

Answer 5

• system calls are the interface between processes and the OS kernel

Question 6

Stack layout

Answer 6

• *envp/argv
• argc, argv, envp
• return address
• main’s frame pointer
• main’s automatic variables
• func1’s arguments
• return address
• func1’s frame pointer
• func1’s automatic variables

Question 7

system call types

Answer 7

• process management (create, terminate, execute, wait, etc.)
• file management (create file, delete, open, close, read write, getattr, setattr, etc.)
• device management (ioctl, read, write, etc.)
• information management (getpid, alarm, sleep, etc.)
• communication - between processes (pipe, shmget, mmap, etc.)

Question 8

open() system call

Answer 8

• in open (const char *pathname, int flags[, mode_t mode])
• flags include
• access mode (O_RDONLY), O_WRONLY, O_RDRWR) - required
• file creation flags (O_CLOEXEC, O_CREAT, O_TRUNC, etc) - optional
• file status flags (O_APPEND, O_SYNC, O_NONBLOCK, etc)
• mode is your usual file creation mode

Question 9

close() system class

Answer 9

• int close (int fd)
• decrements the reference count for the appropriate open file object
• object is reclaimed (if reference count == 0)
• returns -1 on error and sets error
• failing to close() fds results in a file descriptor leak
• arguably worse than a memory leak

Question 10

using assembly language in C