App Account Mapping to Linux Users

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Del curso dictado por Vanderbilt University

Engineering Maintainable Android Apps

95 calificaciones

Vanderbilt University

Engineering Maintainable Android Apps

95 calificaciones

Curso 4 de 5 en SpecializationAndroid App Development

Engineering Maintainable Android Apps, which is a 4 week MOOC that shows by example various methods for engineering maintainable Android apps, including test-driven development methods and how to develop/run unit tests using JUnit and Robotium (or equivalent automated testing frameworks for Android), as well as how to successfully apply common Java/Android software patterns to improve the extensibility and clarity of Android apps. Students will work on the appropriate automated unit quizzes, based on the material covered in the lecture videos. These lessons will demonstrate the benefits of good software engineering practices that are targeted at creating maintainable code for mobile apps. There will be roughly 3-4 hours of student engagement time per week, including video lectures, and quizzes. The ordering of the modules within the course is designed to be flexible. In particular, students can watch the videos in whatever order suits their experience and needs, e.g., they may want to watch the unit testing videos prior to the software pattern videos if they prefer to learn about unit testing first.

De la lección

Security & Sustainability II

This module provides an introduction to Unit Testing using the Junit 4.0 Framework in Android, as well as an introduction to Testing Frameworks using the Robotium open-source test framework for writing graybox testing cases to automate the testing of multi-Activity Android apps.

Traditional App Accounts3:15

Traditional vs. Mobile App Accounts5:28

App Account Mapping to Linux Users4:45

Apps Lie & Steal4:23

How Android Protects Apps13:52

What Android Does Not Protect14:20

The Challenges of Secure Coding2:48

Security Vulnerability Walkthrough7:30

The iRemember App Example3:38

Privilege Escalation I5:40

Privilege Escalation II4:07

Privilege Escalation III6:22

Course Wrap-up13:59

Conoce a los instructores

Dr. Douglas C. Schmidt
Professor of Computer Science and Associate Chair of the Computer Science and Engineering Program
Electrical Engineering and Computer Science
Michael Walker
Instructor - Graduate Student pursuing PhD in Computer Science
EECS
Dr. C. Jules White
Assistant Professor of Computer Science
Electrical Engineering and Computer Science

When your app gets installed, that's when the system creates the identity, or

the account, that's going to be associated with your app.

So, let's dive a little deeper into what that actually means on app or Android when

you install an app, and what happens under the hood to create that user account.

Well, when you create an Android app,

one of things you have to specify is an Android manifest.xml file.

And this is a file that all of you should be very well familiar with

if you've been building Android apps.

And what this does is it tells Android

things that it needs to know about your app in order to install it on the system,

in order to understand what each different components are.

And very importantly from a security perspective,

it tells it which capabilities of the hardware platform

on the Android device or the capabilities provided by other apps,

like the Contacts app, that you want to have access to in your app.

So you declare a series of uses permissions.

And these are things that your app wants to

have access to on the underlying platform.

And each of these user permissions corresponds to some type

of underlying capability of the device.

Something like access to the Internet maybe, or access to the camera.

And your app declares all of these things up front so

that when the user installs your app on their device,

Android can go and scan all of these user permissions,

figure out what they map to in terms of capabilities in your device,

and then present a menu to the user saying do you want to allow

this app to have access to x, y and z things.

So the user gets to decide is this okay?

And if they say that it's okay, what Android does is it takes all

these user permissions and it goes and creates an account on the underlying

Linux operating system that's part of Android for your app.

So, Android is a modified version of Linux that runs on mobile devices.

And when you create, install an app, and then create a user account for

it, what's actually happening is that the underlying Linux operating system

is creating a user for that app.

So, this and this, basically

create the Linux user for your app.

This is what's going to define the capabilities of this linux user.

It's the things that you ask for in your manifest file.

Underneath the hood, each of the things you ask for like Internet or

camera, each of those has a separate Linux group that's associated with it.

For example, you may have the camera group.

And this is a user group that is set up

to define the set of users that have access to the camera.

And this is already on the device when you install the app.

And so, what Android does is it creates your Linux user and

then based on each of the uses permissions it figures out which

of the different user groups your account should be associated with.

So it associates this app for a photo editor, let's say,

with its own Linux user.

And then it associates that Linux user with the underlying camera group.

And so now, when your app is running, if your app goes and

tries to access the camera, Android and it's underlying Linux kernel

can look at the user account associated with your app, and then can check

if it's part of this Linux user group that should have access to the camera.

So underneath the hood, all of these permissions that we see in our apps and

that are manifested as uses permissions in the Android manifest XML files,

actually get mapped down to Linux user groups.

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