COMP3301代写、代做C/C++语言编程

日期：2024-08-07 08:56

COMP3301 Semester 1 2024 Assignment 1

COMP3301 Assignment 11

OpenBSD Zones “Episode 3: Return of the Sys(call)”2

Due: 3pm Monday in Week 5(19th of August)3

Submission: BlackBoard (reflection) and Git.4

Demo and git are marked in your lab session in week 55

Last Updated: July 30, 20246

1 Academic Integrity7

All assessments are individual. You should feel free to discuss aspects of C programming and8

assessment specifications with fellow students and discuss the related APIs in general terms.9

You should not actively help (or seek help from) other students with the actual10

coding of your assessment. It is cheating to look at another student’s code, and it is11

cheating to allow your code to be seen or shared in printed or electronic form. You should note12

that all submitted code will be subject to automated checks for plagiarism and collusion. If we13

detect plagiarism or collusion (outside of the base code given to everyone), formal misconduct14

proceedings will be initiated against you.15

If you’re having trouble, seek help from a teaching staff member. Do not be tempted to copy16

another student’s code. You should read and understand the statements on student misconduct17

in the course profile and on the school website: https://eecs.uq.edu.au/current-students/18

guidelines-and-policies-students/student-conduct.19

1.1 Use of AI Tools20

All assessment tasks evaluate students’ abilities, skills and knowledge without the aid of gen-21

erative Artificial Intelligence (AI) or Machine Translation (MT). Students are advised that the22

use of AI technologies to develop responses (e.g. code generation) is strictly prohibited and23

may constitute student misconduct under the Student Code of Conduct.24

2 Introduction25

This assignment will extend a basic implementation of “zones” in the OpenBSD kernel. The26

main area of improvement will be separating group and user permissions on zone operations.27

You will be provided with a diff that adds the basic zones functionality to OpenBSD. You will28

need to make changes and improvements on top of this diff.29

The purpose of this assignment is for you to demonstrate an understanding of the role of an30

operating system kernel and how it supports processes making system calls, as well as your31

skills in reading, understanding, and modifying existing code.32

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COMP3301 Semester 1 2024 Assignment 1

2.1 Background33

Zones extend the isolation of processes beyond what is traditionally provided by UNIX and34

UNIX-like systems, including OpenBSD. Traditionally, all processes running on an OpenBSD35

are visible to all other processes. This can be demonstrated by running commands like top(1),36

ps(1), and pgrep(1)/pkill(1), which can show all processes running in a system:37

$ ps -ax

PID TT STAT TIME COMMAND

While all processes are visible to each other, they are restricted from interacting with each38

other based on the user that each process is running as. A non-root user can only signal their39

own processes. Attempts to signal processes running as another user fails:40

$ whoami

dlg

$ ps -U _sndio

PID TT STAT TIME COMMAND

47188 ?? I$ kill 47188

ksh: kill: 47188: Operation not permitted

$

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COMP3301 Semester 1 2024 Assignment 1

However, the root user is allowed to signal any process:41

$ doas kill 47188

doas (dlg@comp3301.eait.uq.edu.au) password:

$ ps -U _sndio

PID TT STAT TIME COMMAND

$

3 Zones Implementation42

Zones are implemented for this assignment to add further isolation of processes. Processes43

running within a zone can only see and interact with processes running within the same zone,44

regardless of which user within the zone is running the commands. This implementation is45

loosely modelled on the design of Solaris Zones as described in PSARC/2002/174.46

The exception to this enhanced isolation is for processes running in the ”global” zone, which is47

the default zone that is created and exists on boot. Processes running in the global zone can48

see all other processes in the system, including those running in other (non-global) zones, and49

the root user in the global zone can signal any of these processes too. However, non-root users50

in the global zone cannot signal processes in other zones, even if they are running as the same51

user.52

The provided diff implements changes to the kernel and several userland utilities and adds a53

zone(8) command and man page. The zone(8) command provides several sub-commands that54

expose the functionality of the kernel zone subsystem.55

3.1 Provided Zone Syscalls56

zone_create()57

zoneid_t zone_create(const char *zonename);

zone_create() creates a new zone id for use in the system, with a unique name specified by58

zonename.59

zone_destroy()60

int zone_destroy(zoneid_t z);

zone_destroy() deletes the specified zone instance. The zone must have no running processes61

inside it for the request to succeed.62

zone_enter()63

int zone_enter(zoneid_t z);

zone_enter() moves the current process into the specified zone.64

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COMP3301 Semester 1 2024 Assignment 1

zone_list()65

int zone_list(zoneid_t *zs, size_t *nzs);

In the global zone zone_list() provides the list of zones in the running system as an array of66

zoneid ts. If run in a non-global zone, the list will only contain the current zone.67

zone_name()68

int zone_name(zoneid_t z, char *name , size_t namelen);

The zone_name() syscall provides the name of the zone identified by the z argument. If run69

in a non-global zone the z id must be the identifier for the current zone. In the global zone it70

can be any zone identifier.71

zone_id()72

1zoneid_t zone_id(const char *name);

zone_id() provides the id associated with the name zone. If run in a non-global zone, only the73

current zone name may be specified. If name is a NULL pointer the zone id calling process is74

running in is returned.75

zone_stats()76

1int zone_stats(zoneid_t z, struct zstats *zstats);

zone_stats() provides an assortment of operating system statistics resulting from processes77

in the zone associated with the id z.78

3.2 zone(8)79

1usage: zone create zonename

2zone destroy zonename

3zone exec zonename command ...

4zone list

5zone id [zonename]

6zone name [zid]

7zone stats [-H] [-o property [ ,...] zone [...]

The zone(8) program uses the zone syscalls to allow systems administrators or operators to80

use the zone subsystem in the kernel.81

zone create82

zone create uses the zone_create() syscall to create a zone with the specified name.83

zone destroy84

zone destroy uses the zone_destroy() syscall to create a zone with the specified name. If a85

zone with the specified name does not exist, zone(8) will attempt to interpret the argument86

as a numeric zone identifier.87

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COMP3301 Semester 1 2024 Assignment 1

zone exec88

zone exec uses the zone_enter() syscall to move itself into the specified zone, and then89

executes the program. If a zone with the specified name does not exist, zone(8) will attempt90

to interpret the argument as a numeric zone identifier.91

zone list92

zone list uses the zone_list() syscall to fetch a list of ids for the currently running zones,93

and iterates over it calling the zone_name() syscall to print out the list of zone ids and names.94

zone name / zone id95

zone name and zone id use their associated syscalls zone_name() and zone_id() to return96

the name of a zone given its id, or the id of a zone given its name.97

zone stats98

zone stats uses the zone_stat() syscall to obtain and print out to the user a series of statis-99

tics from processes running in the current zone. See the manual page in zone(8) for more100

information.101

3.3 Your Tasks102

You will be adding additional functionality to a series of zone(8) sub-commands, adding three103

new zone(8) sub-commands, and implementing any necessary changes to the kernel zones104

system to support them.105

Your additional functionality centers around zone permissions. Files have an associated “user”106

and “group”, and this user or group may have permission to operate on the file. Your task is to107

associate zones with a particular owner and group, and allow the owner of the zone and users108

who are in that group to perform operations on the zone (regardless of whether they are the109

owner of the zone).110

In short, where zones are now only controllable by root, your changes will allow the owner of111

a zone and a different group of users to control a zone.112

The additional sub-commands you will be implementing are: zone rename, which will change113

the name of a zone; zone chown, which will change the owner of a zone in a manner similar114

to the existing chown(8); and zone chgrp, which will change the group of a zone in a manner115

similar to the exist chgrp(8).116

4 Instructions117

To complete the assignment, you will need to do the following.118

4.1 Apply the diff119

1- Fetch https://stluc.manta.uqcloud.net/comp3301/public /2024/a1 -zones -base.

patch

2- Create an a1 branch

3- ‘git checkout -b a1 ‘

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COMP3301 Semester 1 2024 Assignment 1

4- Apply the base patch to the a1 branch

5- ‘git am /path/to/a1 -zones -base.patch ‘ in /usr/src

6- Build the kernel

7- ‘cd /usr/src/sys/arch/amd64/compile/GENERIC.MP ‘

8- ‘make obj ‘

9- ‘make config ‘

10- ‘make -j 5‘

11- ‘doas make install ‘

12- Reboot into the kernel

13- ‘doas reboot ‘

14- ‘make obj ‘ in /usr/src

15- ‘doas make includes ‘ in /usr/src/include

16- Verify the zones syscalls are in /usr/include/sys/syscall.h

17- Verify /usr/include/sys/zones.h exists

18- Make and install libc

19- ‘cd /usr/src/lib/libc ‘

20- ‘make -j 5‘

21- ‘doas make install ‘

22- Optional: make ps , and pkill/pgrep

23- make zone (8)

24- ‘cd /usr/src/usr.sbin/zone ‘

25- ‘make ‘

26- ‘doas make install ‘

27- Verify ‘zone (8)‘ and the zones subsystem works:

28$ zone list

29ID NAME

300 global

31$ zone create

32usage: zone create zonename

33$ zone create test

34zone: create: Operation not permitted

35$ doas zone create test

36doas (dlg@comp3301.eait.uq.edu.au) password:

37$ zone list

38ID NAME

390 global

4042101 test

41$ zone id

420

43$ zone id test

4442101

45$ zone exec test ps -aux

46zone: enter: Operation not permitted

47$ doas zone exec test ps -aux

48USER PID %CPU %MEM VSZ RSS TT STAT STARTED TIME COMMAND

49root 41705 0.0 0.1 628 580 p0 R+pU/0 3:37PM 0:00.14 ps -aux

50$ doas zone exec test zone id

5142101

52$ doas zone exec test zone id global

53zone: id: No such process

54$

As you add the functionality specified in the next sections, some of these steps will be repeated.120

eg, changing the kernel means rebuilding and installing the kernel. Adding a syscall means121

making the syscall stub as a function visible in the headers (make includes), and callable122

through libc.123

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COMP3301 Semester 1 2024 Assignment 1

A note on errors124

We have over-specified the errors you should return from your syscalls - if you do not require an125

error code (for example, never returning ENOMEM on memory failures because you never allocate126

any memory) then you do not have to use it. The reverse is also true - if you find an error case127

that is not listed, choose an appropriate error from errno(2). We will not explicitly test all128

errors, but during your code interview, we will expect you to be able to explain the suitability129

of the error codes you use.130

4.2 Zone Rename131

The zone(8) commands should be extended to enable renaming of zones. Zones should only132

be able to be renamed by the owner, root, or members of the zone’s group. Additionally, the133

global zone cannot be renamed, and zone names must be unique.134

1$ zone

2usage: zone create zonename

3zone destroy zonename

4zone exec zonename command ...

5zone list

6zone name [id]

7zone id [zonename]

8zone rename id name

9$ doas zone create foo

10$ zone list

11ID NAME

120 global

13289 foo

14$ doas zone rename 298 bar

15$ zone list

16ID NAME

170 global

18289 bar

19$ doas zone rename 0 something

20zone: name: Permission denied

21$ doas zone rename 289 global

22zone: name: File exists

4.3 Modifications to Existing Syscalls135

zone_create() syscall136

The zone_create() syscall should now ensure that the created zone is associated with the137

group of the user that created it, as well as the user themself. Additionally, this will mean138

ensuring that non-root users can create zones.139

All other syscalls140

The full suite of zone_* syscalls should permit users with matching credentials to perform zone141

operations on them, not only the owner and the root user.142

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COMP3301 Semester 1 2024 Assignment 1

4.4 Zone name and zone list143

zone_name() syscall144

The zone_name() syscall should be renamed to zone_info(). Subsequently, it should return145

not only the name and namelen, but a struct, containing the id of the user and the id of the146

group that has permission to control the zone. The zone(8) userland sub-command for zone147

name should also be modified in line with these changes - the name should be changed to zone148

info and the additional information should be provided to the user.149

zone list150

The zone list subcommand should now take flags: -o and -g. If either of these flags are151

provided, the owner and the group that have control over the zones should also be printed, in152

table format.153

4.5 Zone chown and chgrp154

The zone(8) commands and the kernel zones system should be extended to enable changing155

the owner and group of a zone. Zone owners and groups should only be able to be changed by156

the owner, root, or members of the zone’s group. Additionally, the owner of the global zone157

cannot be changed.158

1$ zone

2usage: zone create zonename

3zone destroy zonename

4zone exec zonename command ...

5zone list

6zone name [id]

7zone id [zonename]

8zone chown [id]

9zone chgrp [id]

To support these subcommands, you will need to implement the following system calls:159

zone_chown() syscall160

int zone_chown(zoneid_t z, uid_t user);

The zone_chown() syscall alters the owner of the zone identified by the z argument. The new161

owner should be the owner identified by the user argument. If called from a non-global zone162

then the z id must be the identifier for the current zone, but in the global zone it can be any163

zone identifier.164

Potential Errors:165

EPERM - the user does not have permission to alter the zone z166

ESRCH - the zone identified by z does not exist167

ENOMEM - the system was not able to allocate memory168

EINVAL - the zone to alter was the global zone169

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COMP3301 Semester 1 2024 Assignment 1

zone_chgrp() syscall170

int zone_chgrp(zoneid_t z, gid_t group);

The zone_chgrp() syscall alters the owner of the zone identified by the z argument. The new171

owner should be the group identified by the group argument. If called from a non-global zone172

then the z id must be the identifier for the current zone, but in the global zone it can be any173

zone identifier.174

Potential Errors:175

EPERM - the user does not have permission to alter the zone z176

ESRCH - the zone identified by z does not exist177

ENOMEM - the system was not able to allocate memory178

EINVAL - the zone to alter was the global zone179

5 Other Requirements & Suggestions180

5.1 Code Style181

Your code is to be written according to OpenBSD’s style guide, as per the ‘style(9)‘ man page.182

An automatic tool for checking for style violations is available at uqcloud.net/comp3301/public/2022/cstyle.pl>. This tool will be used to calculate your184

style marks for this assignment.185

5.2 Compilation186

Your code for this assignment is to be built on an amd64 OpenBSD 7.5 system identical to your187

course-provided VM.188

189

The following steps must succeed:190

make obj; make config; make in src/sys/arch/amd64/compile/GENERIC.MP191

make obj; make includes in src192

make obj; make; make install in src/lib/libc193

make obj; make; make install in src/usr.sbin/zone194

The existing Makefiles in the provided code are functional as-is, but may need modification195

as part of your work for this assignment. Note that the existing Makefile ensures the -Wall196

flag is passed to the compiler, as well as a few other warning and error-related flags.197

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COMP3301 Semester 1 2024 Assignment 1

5.3 Provided code198

The provided code which forms the basis for this assignment can be downloaded as a single199

patch file at:200

https://stluc.manta.uqcloud.net/comp3301/public/2024/a1-zones-base.patch201

202

You should create a new a1 branch in your repository based on the openbsd-7.5 tag using git203

checkout, and then apply this base patch using the git am command:204

1$ git checkout -b a1 openbsd -7.5

2$ ftp https://stluc.manta.uqcloud.net/comp3301/public /2024/a1 -zones -base.

patch

3$ git am < a1 -zones -base.patch

4$ git push origin a1

5.4 Recommendations205

The following order will likely be the most reasonable way to complete this assignment:206

1. Download, build, and install the zones patch.207

2. Add the zone rename subcommand to zone(8).208

3. Minimally modify zone_create() to store credentials.209

4. Rewrite zone_name() to zone_info().210

This ensures you have a way to view the credentials of a zone.211

5. Add the zone_chown() and zone_chgrp() syscalls.212

6. Add the corresponding zone chown and zone chgrp commands to zone(8).213

7. Fix up any tiny bugs and ensure it’s all working. But you did that as you were going... right?214

Additionally, it is strongly recommended (and in some cases, required) that the following APIs215

be considered for use as part of your changes:216

? ucred(9) - provides necessary handlers for dealing with user and group credentials217

? copyin(9)/copyout(9) - provides the ability to copy data across the userspace boundary218

? user_from_uid(3) - conversions from group/user name to id and back219

? strtonum(3) - BSD style safe string to int conversions220

? Finally, you may wish to look at the header file sys/proc.h to see how user and group221

credentials are currently stored by threads.222

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COMP3301 Semester 1 2024 Assignment 1

6 Reflection223

Provide a reflection on your implementation by briefly answering the following questions:224

1. Describe the steps you took or draw a flowchart.225

2. Describe an error that you encountered.226

3. Describe how the error was debugged.227

4. Describe how the bug was solved.228

Upload both pdf and your answers it as a pdf to the Blackboard a1 reflection submission. Page229

length is a maximum 2 pages or less. Pdf name must be your STUDENT NUMBER -230

a1.pdf. Note this is your XXXXXXXX ID number and not sXXXXXXX login.231

7 Submission232

Submission must be made electronically by committing to your Git repository on ‘source.eait.uq.edu.au‘.233

In order to mark your assignment the markers will check out the ‘a1‘ branch from your reposi-234

tory. Code checked into any other branch in your repository will not be marked.235

236

As per the ‘source.eait.uq.edu.au‘ usage guidelines, you should only commit source code and237

Makefiles.238

239

Your ‘a1‘ branch should consist of:240

? The openbsd-7.5 base commit241

? The A1 base patch commit242

? Commit(s) for adding the required functionality243

7.1 Marking244

Your submission will be marked by course tutors and staff, during an in-person demo with you,245

at your lab session during the due week. You must attend your session, in-person, otherwise246

your submission will not be marked. Online attendence, e.g. zoom, is not permitted.247

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