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    Sudo Mastery: IT Mastery, #13
    Sudo Mastery: IT Mastery, #13
    Sudo Mastery: IT Mastery, #13
    Ebook306 pages3 hours

    Sudo Mastery: IT Mastery, #13

    By Michael W Lucas

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    About this ebook

    Sudo: You're Doing It Wrong

    Unix-like operating systems use a rudimentary access control system: the root account can do anything, while other users are peasants with only minimal access. This worked fine in UNIX's youth, but now that sysadmin responsibilities are spread among many people and applications, many people need a tiny slice of root's power.

    Sudo lets you divide root's monolithic power between the people who need it with accountability and auditability.

    Sudo Mastery will teach you to:

    • design a secure sudo policy
    • simplify policies with lists and aliases
    • manage shell environments
    • verify system integrity via intrusion detection
    • deploy a single sudo policy across your enterprise
    • manage sudo policies via LDAP
    • log and debug sudo
    • record and replay full sudo sessions
    • use authentication systems other than passwords

    Master sudo with Sudo Mastery!

    LanguageEnglish
    PublisherTilted Windmill Press
    Release dateAug 20, 2019
    ISBN9781393557845
    Sudo Mastery: IT Mastery, #13
    Author

    Michael W Lucas

    Michael W Lucas lives in Detroit, Michigan. He is the author of several critically-acclaimed nonfiction books and assorted short stories. His interests include martial arts and Michigan history.

    Read more from Michael W Lucas

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      Book preview

      Sudo Mastery - Michael W Lucas

      Sudo Mastery

      2nd Edition

      by Michael W Lucas

      Table of Contents

      Title Page

      Acknowledgements

      Chapter 0: Introduction

      What Is Sudo?

      What’s Wrong with Sudo?

      What Does Sudo Protect You From?

      Sudo Terms and Support

      Prerequisites

      Who Should Read This Book?

      Learning Sudo

      Avoiding Sudo

      What Groups Am I In?

      Programs versus Groups

      Eliminating Root

      Book Overview

      Chapter 1: Sudo Essentials

      sudo 101

      Sudo Features

      Running Commands as Another User

      Running Commands as Another Group

      Changing Usernames but Keeping Your Groups

      Viewing Your Sudo Privileges

      Reading Sudoers

      Multiple Entries

      Permitting Commands as Other Users

      Special Characters

      Reading the Policy

      Chapter 2: Managing Sudoers

      Creating Sudoers

      Visudo Editors

      Testing and Verifying Sudoers

      User Access Testing

      Testing for Automation and Distribution

      Including Files in Sudoers

      Including Individual Files

      Including Directories

      Chapter 3: Lists and Aliases

      Wildcards

      Matching Individual Numbers and Characters

      Matching Directories

      Matching Everything

      Wildcard Dangers

      Blocking Everything

      Aliases

      User Lists and Aliases

      Operating System Groups

      User ID

      Group ID

      Netgroup

      Non-Unix Group

      Non-Unix Group ID

      User Aliases

      Hosts, Host Lists and Aliases

      IP Addresses

      Netgroups

      Host Aliases

      RunAs Lists and Aliases

      RunAs Lists

      RunAs Aliases

      Command Lists and Aliases

      Command Aliases

      Command Tags

      Excess Rules

      The Command Alias ALL Is Dangerous

      Allowing All Legitimate Commands

      Negation in Lists

      Aliases in sudo(8)

      Chapter 4: Options and Defaults

      Defaults

      Option Types

      Boolean Options

      Integer Options

      Integers Usable in a Boolean Context

      String Options

      Setting Options for Specific Contexts

      Per-User Defaults

      Per-Host Defaults

      Per-Command Defaults

      Per RunAs Defaults

      Conflicting Defaults

      Options and Lists

      Chapter 5: Shell Escapes, Editing, and Policies

      Forbidding Commands from Executing Commands

      Editing Files

      Configuring Sudoedit

      Using Sudoedit

      Symlinks and Directory Ownership

      Policies and Commands

      Chapter 7: Configuring Sudo

      Sudo’s Default Configuration

      sudo.conf

      Sudo Core Dumps

      Plugins

      Plugin Path

      Installing Plugins

      Configuring the Sudoers Policy

      Chapter 8: Environments

      Sudo-Specific Environment Variables

      Dangerous Environment Variables

      Execution Environment

      Environment Variable Filtering

      Preserving Environment Variables

      Sanitizing Environment Variables

      Sudo’s Standard Shell Environment

      Keep Nothing

      Setting the Environment for One Rule

      Retaining the User Environment

      Discarding Environment Variables

      Environment Option Priority

      Allowing User Overrides

      Target User Environment

      Environment Customization

      Adding Environment Variables

      Managing PATH

      Managing HOME

      Managing Pagers

      Running Shells with Sudo

      Terminals and Graphic Interfaces

      No Terminal

      Requiring a Terminal

      Backgrounding Commands

      Timeouts

      Timeouts as Soft Policy Enforcement

      User Timeouts

      Chapter 9: Intrusion Detection

      Digest Algorithm

      Generating Digests

      Digests in Sudoers

      Multiple Operating Systems

      Automating Checksum-Aware Sudoers

      Creating Command Aliases with Checksums

      Creating a Master Alias

      Custom Aliases

      Putting It All Together

      Chapter 10: Policy Distribution

      Global Policy Hints

      Hostnames and Sudoers

      DNS and Sudoers

      IP Addresses

      One Network, One Sudoers

      Transforming and Filtering Sudoers

      A Sample Policy

      cvtsudoers Output Format

      Filtering by Host, User, or Group

      Expanding Aliases

      The cvtsudoers Config File

      Chapter 11: Security Policies in LDAP

      Prerequisites

      The Sudo Schema

      Adding Sudo to Traditional OpenLDAP

      OpenLDAP with Online Configuration

      Adding Sudo to Active Directory

      The Policy Container

      LDAP Sudo Policies versus Sudoers

      Transforming Sudoers to LDIF

      Sudo Rules in LDIF

      Sudo Rules and Roles

      sudoUser

      sudoHost

      sudoCommand

      sudoOption

      sudoRunAsUser

      sudoRunAsGroup

      sudoOrder

      Activating LDAP in sudo(8)

      Finding the LDAP Policy

      Tell sudo To Use LDAP

      Disabling Sudoers

      Migrations and Learning SudoRoles

      LDAP Caching

      Chapter 12: Logging, Mail, and Debugging

      Syslog

      Customizing Sudo Syslog

      Syslog Security

      Email

      Sending Mail

      Setting Email Conditions

      Mail Tags

      Debugging Sudo and Sudoers

      Subsystems and Levels

      Configuring Debug Logging

      Debug Usefulness

      Complete Session Logging

      I/O Log Directory

      Enabling I/O Logging

      Listing I/O Logs

      Viewing Individual Sessions

      Altering Playback

      Real Time Monitoring

      Searching I/O Logs

      I/O Log Rotation

      Chapter 13: Authentication

      Password Management and Failure

      Password Attempts and Timeouts

      Alternate Passwords

      Failure Responses

      Customizing the Password Prompt

      Custom Prompts via Policy

      User Prompt Customization

      Effective and Expiration Dates

      Selectively Disabling Authentication

      Authentication Caching and Timeouts

      Configuring Timeouts

      Erasing Timeouts

      Multi-Session Authentication

      Authentication, Updates, and Queries

      Lecturing Users

      PAM and Sudo

      Prerequisites

      Configuring PAM

      authorized_keys Location

      Afterword

      Patronizers

      Sponsors

      Print Sponsors

      Ebook Sponsors

      About the Author

      Copyright Information

      Acknowledgements

      The first edition isn’t pining, it’s passed on! The edition is no more! It has ceased usefulness! It’s gone to meet the recycler! It’s remaindered! Bereft of readers, it rests in peace! THIS… is an ex-book!

      There are many reasons to do a second edition of Sudo Mastery: the replacement of sudo2ldif with cvtsudoers, new options, changes in the technology environment, and my own deeper understanding of sudo. Honesty compels me to confess that sudo’s addition of Monty Python insults, giving me an opportunity to start each chapter with a mangled Python quote, probably weighed more heavily in this decision than it should have. The person who helped me come up with the quotes, there are some who call him… Tim.

      Before publication, this book was reviewed for technical accuracy by Ron Collinson, Trix Farrar, Thomas Harrison, Dwayne Hart, Ed Neville, Daniele Palumbo, Carsten Strotmann, and Grant Taylor. While I appreciate my technical reviewers, all errors in this book are mine. Reviewers who want blame for errors should go make their own.

      Thanks also to Todd Miller, who has the Sisyphean task of maintaining sudo across dozens of platforms.

      XKCD fans should note that the author does not particularly enjoy sandwiches. Miod Vallat, currently comfortably ensconced in France, would really like a sandwich with nice fresh bread, really good mustard, and low-carb ground glass and rusty nails. It’s unlikely that I’ll get to France any time this decade, so if you could help him out I’d appreciate it.

      I apologize for the fault in the book design. Those responsible have been sacked. The chapters have been numbered in an entirely different style at great expense and at the last minute.

      For Liz.

      Chapter 0: Introduction

      He's not root, he's a very naughty boy.

      Resolved: controlling a user’s access to a computer’s privileged programs and files is a right pain. The few systems that could more or less cope with mapping real-world privileges onto digital schemes didn’t survive. The best access control systems in popular operating systems merely inflict less torment than the others.

      The most widespread operating system these days is Unix, which controls programs and file access through users and groups. Each individual user has a unique username, and usernames are arranged into uniquely named groups. Specific users and groups get permission to access specific files and programs. This scheme was developed decades ago, when a large university might have a couple of UNIX servers. Hundreds of users logged onto each server for mail, Usenet, and other computation-heavy applications. Students went in one group, grad students in another, then professors, staff, and so on. Individual classes and departments might have their own groups.

      Among all those accounts, root is special. The root account has ultimate control of the system. To protect the host, Unix restricts some programs so that only root can run them. Only root can reconfigure the network, mount filesystems, and restart programs that attach to privileged network ports. Only root can add new users. This made sense when a whole university campus might have only one or two computers—reconfiguring the network or adding storage is a serious task in that environment. Management of multimillion-dollar systems that thousands of people rely on should remain in trusted, skilled hands.

      Today, instead of a single UNIX™ we have untold Unixes, several BSDs, innumerable Linuxes, and similar-but-not-quite-Unixy variants. For ease of reference I’ll call the whole family Unix, even though that’s not strictly accurate. Anyone reading this introduction probably has a few Unixes in their home and one on their belt. Teams of people might share sysadmin tasks, or one person might completely control each system, or anything in between. Our security requirements are completely different from twentieth-century universities.

      Large organizations with many servers often divide sysadmin responsibilities between skilled individuals. One person might be responsible for the care and feeding of the operating system, while a second person handles the server’s primary application. The server supports the application, and the application is the reason the server exists. Both people must perform tasks that require root-level privileges.

      The problem is, root access is all-or-nothing. Unix doesn’t differentiate between access to change the kernel and "access to install and upgrade applications in /opt." An application administrator with root access can change the kernel and adjust filesystems.

      Many small teams rely on gentleman’s agreements to only touch the parts of the system each person is responsible for. Such agreements decay exponentially with the number of people involved. Two people can just about keep things straight. Once you have a sysadmin team and a DBA team, such agreements start off with finger-pointing and devolve into bloodbaths. Sometimes the resulting debacles are not the fault of anyone in the organization; I’ve seen more than one disaster trace back to a vendor-provided script that committed unspeakable acts upon a helpless server.

      Organizations need finer-grained access control than root provides.

      The all-or-nothing model breaks down even more when everyone has a Unix system. Setting aside the innumerable phones and tablets specifically engineered for user-friendliness, many of us run Unix on a desktop or laptop. Every time you access a USB drive or use a coffee shop wireless network, something on the system needs root-level privileges. Becoming root isn’t terribly onerous on your own system—log in as yourself, use su(1) to switch users, enter the root password, run your privileged commands, and exit the root account. Performing this ritual every time you put in a USB drive, bounce the network, restart or reconfigure software, or install new packages gets annoying. Add-on tools like automounters and network managers help, but configuring them requires—wait for it—root privileges.

      The computer industry is full of really smart people who have expanded the classic Unix access control model. One method is through setuid and setgid programs. While programs normally work with the privileges of the user who runs them, setuid and setgid set their effective user and group ID to some other user. Many setuid programs run as root. Changing your password requires editing secure files in /etc, so passwd(1) is setuid root. Intruders really like setuid and setgid programs, and gleefully exploit any flaws in them to achieve illicit root access. Most programmers don’t have the level of skill needed to truly lock down setuid and setgid programs, and on some platforms such security is nearly impossible. Additionally, most operating systems don’t let you make shell scripts setuid.

      We also have several varieties of access control list (ACL) that more broadly expand the user-group-others ownership model. ACLs allow you to set highly customized file and command ownership. This person owns the file, but these people and these groups—except for these folks, unless they’re specifically given permission earlier—can modify it, and these other people and groups—with their own exclusions—can execute it, while read access is restricted to these people and groups… And of course, all these different ACL implementations are ever so slightly incompatible. NFSv4 ACLs were designed to be interoperable with Microsoft’s NTFS ACLs. The specification is over 107,000 words long—and they still didn’t manage complete compatibility. At this point the sysadmin starts contemplating a career cleaning up real sewage instead of the metaphorical kind. Very few people can implement ACLs on a single platform, and deep expertise in one ACL system isn’t completely applicable to other platforms. ACLs have a place in systems administration, and they’re invaluable if you really need them. But most of us try really, really hard not to need them.

      Sadly, access control lists are about as good as it gets.

      That’s why the world has settled on sudo.

      What Is Sudo?

      Sudo is a program that allows conditional escalation of user privilege. The system owner creates a list of commands that each user can run. When the user wants to run a command that requires root, he asks sudo(8) to run the command for him. Sudo consults its permissions list. If the list grants the user permission to run that command, sudo runs the command as root. If the user does not have permission to run the command, sudo informs him. Running sudo does not require the root password, but rather the user’s own authentication credentials. (SUSE Linux uses a special configuration to require the root password for sudo, but they’re the exception.)

      Sudo lets the sysadmin delegate root privileges to specific people for very specific tasks. She can tell sudo to require authentication for some users or commands and not for others, or only on certain machines, all with one configuration file.

      Many enterprise software suites, like PostgreSQL, require running commands under a specific dedicated account. Users must switch to this account before managing certain core functions. You can configure sudo to permit users access to this account, or to only permit them to run certain specific commands as this user. Maybe your junior DBA needs access to dump the database, while the lead DBA needs a full-on shell prompt as the database account. Sudo lets you do that.

      Finally, sudo logs everything everybody asks it to do. It can even record the contents of individual sudo sessions, showing you exactly who broke what.

      What’s Wrong with Sudo?

      If sudo is so great, why doesn’t everybody use it?

      Sudo adds another layer of system administration. That layer demands time, energy, and attention. It requires learning yet another danged program when you already have too much to do. If you’re responsible for running an organization with several groups of administrators, investing in learning and deploying sudo will dramatically reduce your workload and inter-group problems.

      Some

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