网络安全基础COMP3301/COMP7308课程作业补习

辅导案例-COMP3301/COMP7308课程中，将向学生介绍组织面临的现实世界的网络安全挑战，并学习应用通过其他计算机科学课程获得的知识和技能来应对这些挑战。挑战将从攻击者的角度(如何利用系统)和防御者的角度(如何保护系统或应对威胁)的角度进行审查。将探讨针对软件，Web应用程序，网络，操作系统，密码系统和人员的常见攻击和防御策略。该课程还将介绍网络安全管理概念，包括安全运营，风险管理，安全工程和安全体系结构，并针对专门从事网络安全的不同职业道路提供指导。

COMP3301/COMP7308 2024 Assignment 2 (DRAFT)

• DRAFT

• Revision : 232

1 Process Accounting Pseudo Device Driver

This assignment asks you to write a device driver for the OpenBSD kernel that implements a replacement

for the current process accounting facility.

Process accounting is a facility that allows administrators to audit the system resource utilisation of

commands run by users.

Process accounting in OpenBSD is currently implemented via the acct(2) system call that enables or

disables of logging of commands to a file, the accton(8) utility for calling the syscall, and the sa(8) and

lastcom(8) utilities for processing said file. The format of the file is described in the acct(5) manual

page.

A pseudo device driver is an actual driver, but not one that implements support for physical hardware. It

provides a virtual, software only, service for user programs to use.

Device special file are entries in a filesystem that refer to a set of functions in the kernel that implement

file behaviour such as open, read, write, and close.

Examples of pseudo device drivers that provide device special files are zero(4), null(4), tun(4), and

tap(4).

This is an individual assignment. You should feel free to discuss aspects of C programming and the

assignment specification with fellow students. You should not actively help (or seek help from) other

students with the actual coding of your assignment solution. It is cheating to look at another student’s

code and it is cheating to allow your code to be seen or shared in printed or electronic form. You should

note that all submitted code may be subject to automated checks for plagiarism and collusion. If we detect

plagiarism or collusion, formal misconduct proceedings will be initiated against you. If you're having

trouble, seek help from a member of the teaching staff. Don't be tempted to copy another student's code.

You should read and understand the statements on student misconduct in the course profile and on the

school web-site: https://www.itee.uq.edu.au/itee-student-misconduct-including-plagiarism

2 Specifications

This assigment specifies the replacement of the acct(2) system call with a pseudo device driver that

provides a device special file that produces messages analogous to the entries written to the accounting

file.

The acct(4) driver will provide a superset of the functionality that is provided by the current system

call. The system call only records information about the process when it exits, but the driver will also

report information about process forks and execs.

2.1 Code Style

Your code is to be written according to OpenBSD's style guide, as per the style(9) man page.

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2.2 Compilation

Your code is to be built as part of the kernel on an amd64 OpenBSD 6.5 or -current system.

The changes to the kernel necessary to configure an acct(4) driver so it can be compiled will be supplied

as a diff available from Blackboard. The diff can be applied by running the following:

dlg@r630 ~$ cd /usr/src/ sys

dlg@r630 sys$ patch

Hmm... Looks like a unified diff to me...

The driver must be implemented in a single file, and placed in sys/dev/acct .c next to the sys/dev/acct.h

provided by the diff described above.

2.3 Messages

The messages that a program reads from the device driver are represented as a set of structs. The kernel

driver populates the structs when the relevant events occur in the kernel, and makes them available for a

program to read.

The structure of the messages the driver should produce is provided in sys/dev/acct.h.

2.3.1 Common Fields

All messages from the driver start with a common set of fields that are contained in struct acct_common.

The other messages all contain struct acct_common as their first field.

The first three fields of the common structure refer to the message itself, rather than the process the

message is about. The ac_type field contains a number representing the type of the current message, eg, a

value of 0 or ACCT_MSG_FORK states that the message is about a process forking and should be interpreted

as the associated message structure.

The ac_len field contains the number of bytes used for this message, including the ac_type and ac_len

fields.

ac_seq is a simple wrapping counter that increments for every message that the driver generates. If the

driver receives notification from the rest of the kernel that an event has occurred (eg, acct_fork() is

called when a process forks), but is unable to generate a message about it, the sequence number should

still be incremented so that the userland consumer of the messages will know that an event has been lost.

The counter should be reset to 0 when the acct(4) device is opened.

The remaining common fields should be set for the process the message is about.

2.3.2 exit message

The exit message corresponds with struct acct_exit. The information in this message corresponds with

the information described in acct(5). acct(2) may be used as a reference when filling in the information

in this message.

2.3.3 fork event

The fork message corresponds with struct acct_fork, and is generated when a process forks a new child.

The information in the message should be based on the parent of the new process, apart from ac_cpid

which contains the process ID of the new child. Note that acct_fork is given a pointer to the child, not

the parent.

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2.3.4 exec event

The exec message corresponds with struct acct_exec, and is geneated when a process calls exec(). It

exists to record the new name of the binary the program is executing.

2.4 Driver entry points

acct.c must provide the following functions to support the integration into the kernel, and to provide

the required interface for userland to access the driver.

2.4.1 Kernel entry points

The kernel is patched to call 3 functions when a process forks, execs, or exits. Those functions are

acct_fork(), acct_exec(), and acct_exit() respectively. All these functions take a struct process

* as their only argument, and do not return anything to the caller.

2.4.2 Userland entry points

acctattach( ) is called when the kernel starts running for the driver to configure any state needed for it

to operate.

acctopen() is called when a program attempts to open a device file with the corresponding major number

to this driver. It should allow only the 0th minor to be opened, opened exclusively, and only opened for

reading. Read/write or write only opens of the device should fail with EPERM. The sequence number for

generated messages should be reset to 0 on every open.

acctclose() should clean up any state associated with the open driver.

acctioctl() should support FIONREAD, and FIONBIO as per the ioctl(2) manpage. FIONASYNC should

not be implemented.

acctread() dequeues aa single message, and copies as much of that one message as possible to userland.

It should support non-blocking reads.

acctwrite() should return EOPNOTSUPP as the driver does not support being written to by a userland

process.

The driver should support non-blocking I/O (well, just O) by implementing acctpoll() and

acctkqfilter().

3 Submission

You are required to implement the acct(4) driver by writing your code in a single file, sys/ dev/acct.c.

This file in the OpenBSD source tree will be committed to your SVN repo as ass2/acct.c.

Submission must be made electronically by committing to your Subversion repository on

source.eait.uq.edu.au. In order to mark your assignment the markers will check out ass2/acct.c

from your repository. Code checked in to any other part of your repository will not be marked.

As per the source.eait.uq.edu.au usage guidelines, you should only commit source code and Makefiles.

The due date for the code submission is the beggining of your prac session, either 10am on Wednesday

the 19th, or 2pm on Thursday the 20th of September 2024. Note that no submissions can be made more

than 120 hours past the deadline under any circumstances.

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3.1 Recommendations

The following kernel functionality may or may not be useful in the implementation of this assigment:

• malloc(9) - kernel memory allocator

• pool(9) - resource pool manager

• TAILQ_INIT(3) - doubly-linked list macros

• KASSERT(9) - kernel assert routines

• uiomove(9) - move (copy) data described by a struct uio

• mutex(9) - kernel mutex implementation

• rwlock(9) - kernel read/write lock implementation

• tsleep(9), and wakeup(9) - process context sleep and wakeup

The majority of the OpenBSD kernel still runs under a Big Giant lock, known as the kernel lock, which

can be used to provide implicit serialisation of code in this driver . The kernel lock is taken and released

with KERNEL_LOCK() and KERNEL_UNLOCK() respectively, or if it is assumed to be held, may be asserted

with KERNEL_ASSERT_LOCKED().

4 Testing

A tool will be provided that reads from the special file and parses the messages as per sys/dev/acct.h.

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